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Effects of

Marketing Research Report No.599

U. S. DEPT. OF AGRICULTURE
NATIONA! Acre roa) "TBRARY

MAY 1 6 1963

Temperature: :«:.:..:;
and Humidity

on Cheese
Mites,

®With Review of Literature

U. S. DEPARTMENT OF AGRICULTURE
Agricultural Marketing Service
Market Quality Research Division,

in cooperation with

UNIVERSITY OF WISCONSIN
Agricultural Experiment Station

PREFACE

In attempts to develop methods by which food products can be marketed free from
contamination by insects, the Stored-Product Insects Branch of the Market Quality
Research Division, Agricultural Marketing Service, has established several labora-
tories where insect preventive and control studies are conducted on many commodities,
The mite studies on cheese are carried out at the Madison, Wis., field station. Much
of the research conducted to date has involved the use of insecticides, including fumi-
gants, However, there is an ever-increasing demand by the general public for the safer
use--or even the elimination--of insecticides on or near food. The purpose of this
study was to investigate in the laboratory the effects of some nonchemical treatments
on mites infesting cheese.

The studies show that the two environmental factors of temperature and humidity
can be regulated so as to be effective against mites. However, these same conditions
that kill the mites also hinder proper flavor development or aging, and may cause
cracking and loss of weight in cheddar cheese, For these reasons, controlled tempera-
ture and relative humidity may not be practical in storage warehouses or curing rooms,
but they may be useful in other areas in processing and marketing channels. Followup
studies need to be conducted on a larger scale before any recommendations can be made,

CONTENTS

Page

SUMIMALY «6 ede Seay SSS CE Skee. Rotman ei is wean ch scesteeoern ee SOC MeINs eis feeb is (cl om 3
Introduction 21% Wc c Xs sere, 1s sie pero ke Gis sooner ot elles 6. oe. he, 1s <i tohlel OCR MMC oNs coma aen a ioneme 4
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Confinement- cylinders: s37...c cucnsstetel eine 0... ©. Ss ee\ el auger ol or chou eeireiial ones) =) Sones 6
SPECIES OL MTNITES Way a tel cereesges slacken monet enias 1 4:(016.cs To! alvo dela te MetteMemel Molle <o)tsi"e lal ifels 6
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Experiments on control, with lowered humidity ... . «o's. «© ejsiese we) s.0, 0 oucrokss ra
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Review ofcliteratures<\5 ils. umes Metemenet ec: 6. (eres su sas) Chis ene neem meMslioieleston Selisaelie 37
iterature: Cited. 4 vaWess + Aico Gite alte neicucieedi © ol isl alse ee uins CM Om Me OMT te seb sinks 42

Washington, D, C. May 1963

EFFECTS OF TEMPERATURE AND HUMIDITY ON CHEESE MITES

With Review of Literature ”

2

Oey Os
_ by William L.“Hilsenhoff and Robert J. Dicke>

SUMMARY

Life history studies with Acarus siro L. and Tyrophagus putrescentiae (Schr.) on
cheese showed that no eggs of either species of cheese mites hatched at 32°F., regard-
less of the relative humidity (r.h.). At 38° F., eggs that were incubated ata r.h, of 84,
92, or 100 percent hatched and developed to maturity. The average development time
at 38° F, and 100 percent r.h. was 137 days for A. siro and 169 days for T. putrescentiae.
Some eggs hatched at r.h, of 68 and 76 percent, but the larvae failed to develop to
maturity.

Tests at 44°, 50°, and 56° F. showed that, as the temperature was raised, the
length of time required for a mite to complete its life cycle was reduced. At 56°F. and
100 percent r.h,, A. siro required only 26 days and T. putrescentiae 38 days. As the
relative humidity at each temperature was decreased, the length of the life cycle of the
mites was increased, Although a few eggs sometimes hatched ata r.h. as low as 48

percent, the resulting larvae seldom reached adulthood at a r.h, of less than 61 percent,

The rate of development of different individuals under the same conditions varied
considerably. Mold growth also seemed to influence the rate of development to some
extent. Typical approximate percentages of time spent in each stage of development
were: Egg, 37 percent; larva, 16; resting larva, 7; protonymph, 12; resting proto-
nymph, 7; deutonymph, 14; and resting deutonymph, 8 percent. A hypopus stage in the
species studied was never encountered in any of the low-temperature tests and probably
is very rare.

Survival tests with A, siro and T. putrescentiae on wood, wax, and cheese showed
that, as the temperature was increased or the relative humidity decreased, the survival
time was shortened. Relative humidities of 61 percent or less were definitely detri-
mental to cheese mite survival on wood or wax, even at the lower temperatures. On
cheese, however, ar.h, of 43 percent or lower was necessary to cause complete mor-
tality. T. putrescentiae was better able to survive under adverse conditions than was
A. siro,

The egg-hatching tests showed that a decrease in temperature or in relative humidity
reduced the viability and delayed the hatching of the eggs of A. siro. The same was true
with T, putrescentiae, except that a r.h, of 84 percent, instead of 100 percent, was
optimum for this species.

A final test conducted in large chambers in the laboratory to investigate the practica-
bility of cheese mite control by lowering the relative humidity showed thata r.h, of 61
percent or lower was effective in killing exposed mites within 4 weeks. At these humidi-
ties, the mites could survive only in cracks beneath the waxed surface. Weight loss by
the cheese at the lowest humidities was less than 1/2 of 1 percent in 4 weeks, indicating
that moisture loss during this short period of storage would not be a serious problem in
well-waxed cheese kept at these lower humidities.

1 Dr. Hilsenhoff was formerly with the Dairy-Product Insects Laboratory, Madison, Wis., a station of the Stored-Product
Insects Branch, Market Quality Research Division, Agricultural Marketing Service, U.S. Department of Agriculture, operated in
cooperation with the University of Wisconsin. He is now an assistant professor, and Dr. Dicke is a professor, both with the Depart-
ment of Entomology, University of Wisconsin, at Madison.

3

Since storage at low temperatures impairs flavor development of some cheese, and
low humidities may cause cracking and some loss in weight, control of mites in ware-
houses by regulating these two environmental factors should not be attempted without
further research, This does not preclude the possibility of their use as control meas-
ures under some circumstances, however, as they may be of some benefit in other
areas in the processing and marketing channels,

INTRODUCTION

Cheese mites are the most important arthropod pests of stored cheese. Most of
the important species are in the families Acaridae, Glycyphagidae, and Carpoglyphidae.
These mites attack all types of cheese that require aging or curing, Although the mites
are very tiny, the tremendous numbers that are often present under conditions favorable
to them can consume a considerable quantity of cheese. Infested cheese becomes un-
sightly and unsalable, and is subject to condemnation and confiscation by government
inspectors, Control of cheese mites is essential to prevent such losses.

Prevention of mite infestation should be the first step in any mite control program,
This is not easy, because cheese mites live not only on cheese, but on many other ma-
terials, Many species are important pests of stored grain, They have been found in the
soil, in grain fields, in stable litter, in bird nests, on rodents, birds, and insects, and
in almost any place that is moist enough to prevent their desiccation. They are carried
into cheese warehouses on cheese, old cheese boxes, human clothing, and even other
insects. Their entry would be difficult to detect because of their almost microscopic
size. Some may even migrate unaided into the warehouse from a nearby grain field,
bird nest, or rodent nest,

Sanitation is essential to any effective control program. Elimination of conditions
under which mites might breed rapidly, and precautions to prevent mites from entering
the warehouse will help keep down the mite population.

Cheese mites may be controlled in several ways, but so far no entirely satisfactory
method has been found, The use of waxes or films on cheese in storage is standard, but
it does not protect completely. Wax is the most commonly used covering, but it cracks
easily, and this permits mites to enter and become established. Even a perfectly waxed
cheese is not completely safe. Mites feed on the mold that grows on the surface of the
wax. Given enough time, they can chew their way through the wax to the cheese.

Fumigation with methyl bromide is the only effective method of mite control
presently used, An experienced fumigator can eliminate mites by this method, but often
a warehouse is quickly reinfested and the fumigation must be repeated after only a few
weeks, The main objection to fumigation is the sizable expense,

Insecticides provide many possibilities for control, but they have several drawbacks,
An insecticide applied to shelves, floors, and walls of a warehouse could give effective,
long-lasting, and inexpensive control. A rapidly detoxified insecticide applied to the
waxed cheese could be very effective and inexpensive to apply. Perhaps an insecticide
incorporated into the wax could be used. However, any insecticide used in mite control
must give virtually 100-percent control, leave no toxic residues in the cheese, and im-
part no odors, off-flavors, or off-colors to the product. Considerable research is
needed on this problem.

Environmental control has been considered as another possibility. At present,
low-temperature storage of cheese is being used to give some measure of mite control,
but no attempt is being made to control mites by lowering the relative humidity. The
purpose of this study was to investigate the effects of temperature and relative humidity
on cheese and cheese mites.

In this study, only Acarus siro L. and Tyrophagus putrescentiae (Schr.), the two
most important cheese pest species in Wisconsin, were used. Only cheddar cheese was
used in the experiments, because it is by far the most widely produced, and it is the type
on which mite infestations are most common,

MATERIALS AND METHODS

Temperature Control

The temperature-control equipment consisted mostly of refrigerators. The main
unit was a walk-in refrigerator, about 250 cubic feet in capacity. Any desired tempera-
ture below 60° F. could be maintained in this unit. A regular fluctuation every 50 minutes
of + 19°F, was caused by the cooling cycle, but the mean temperature remained nearly
constant, The temperature fluctuation in the tightly closed humidity chambers was less
than + 1/2° F, from the mean, due to the rapidity of the temperature fluctuation in the
circulating air outside the chambers,

A refrigerated fumigation chamber about 100 cubic feet in capacity also was used.
This chamber had a fluctuation of + 2° F., caused by a 15-minute cooling cycle. Because
of the very rapid cycle, the temperature within the humidity chambers probably remained
almost constant. To supplement the larger units, three ordinary household refrigerators
were used, These held a fairly constant temperature, but were not as reliable as the
larger units.

For experiments involving temperatures near or above room temperature, an elec-
tric oven was placed in the refrigerated fumigation chamber, This oven maintained a
temperature within t1/2° F. of the desired mean.

Humidity Control

Dilutions of sulfuric acid with water were used to control humidity, This method of
humidity control is described quite thoroughly by Wilson (45)*, Buxton (3), Buxton and
Mellanby (4), Stokes and Robinson (43), and Solomon (40), Humidity chambers were con-
structed from 1/2-gallon ice cream cartons, 115 mm, in diameter. The top half of each
carton was sawed off to leave a carton 115 mm. in height. This carton was then thoroughly
waxed with paraffin, A crystallizing dish, 50 mm. high and 90 mm. in diameter, was
embedded in wax in the bottom of each carton. This dish was filled with about 100 ml. of
sulfuric acid solution calculated to give the desired relative humidity. The dish was cov-
ered with a piece of 1/4-inch mesh wire screen, on which the experimental material was
placed, The top for the humidity chamber consisted of a clear plastic dish that fitted
very tightly over the top of the carton, This plastic cover permitted observation of the
experimental material without opening the humidity chamber.

Much larger humidity chambers were similarly constructed from 2-1/2-gallon ice
cream cartons, waxed with paraffin. A larger crystallizing dish, 75 mm. high and 150mm,
in diameter, was embedded in wax in the bottom along one edge of each carton, Instead of
a wire screen to support the experimental material, each large chamber had two pieces
of 1/4-inch plywood. A piece 204 mm. long and 51 mm. wide was placed over the side
of the crystallizing dish opposite the point that was in contact with the side of the cartan,
Another strip of plywood 140 mm, long and 32 mm. wide ran from the center of the first
piece to the point where the dish contacted the side of the carton, The waxed lid of the
carton served as the top for this larger humidity chamber.

2 Underlined numbers in parentheses refer to items in Literature Cited, p. 42.

Confinement Cylinders

To confine the mites to a test surface and yet allow air to reach the surface, small
glass cylinders 19 mm. in height were used. These cylinders were cut from pyrex glass
tubing of an inside diameter of 12 mm. The inner surface of each cylinder was ground
with emery cloth until it was opaque and completely covered with very tiny particles of
glass. The confinement cylinder was secured to the test surface with wax. Mites attempt-
ing to crawl out of such a cylinder would slip on the tiny glass particles and fall back onto
the test surface. After use, each cylinder was thoroughly cleaned and reground before
being used again, These cylinders were ground with an electric motor turning a shaft
covered with very coarse emery cloth, 3

Species of Mites

Cultures of A. siro and T. putrescentiae were maintained on small cubes of cheddar
cheese in the walk-in refrigerator. The high humidity in this refrigerator was ideal for
mite rearing. All cultures were confined in ice cream cartons, the upper, inner edges of
which were liberally coated with ''Tangle foot''* to prevent escape of the mites. Flat
1/2-gallon cartons were used because of the ease with which blocks of cheese containing
mites could be removed. To prevent mites from escaping through the bottom, the cartons
were heavily waxed with cheese wax.

EXPERIMENTS ON LIFE HISTORY

The effects of temperature and relative humidity on the life history of A. siro and
T. putrescentiae were studied over a wide range of the temperatures and humidities that
could occur in cheese warehouses.

Procedure

A series of humidity chambers ranging from 22 to 100 percent r.h. was prepared and
placed in refrigeration units of the desired temperatures. At least 2 days were allowed
for the humidity in these chambers to come to equilibrium before any experimental ma-
terial was placed in them,

Pieces of cheddar cheese, 83 mm. long, 51 mm. wide, and 25 mm, thick, were
coated with cheese wax at 230-240° F. Eight circles of wax, 2 mm. in diameter, were
cut from the top surface of each block of cheese. The wax was scored with a very small
cork borer, and the wax within the circle was removed with a scalpel. Great care was
taken not to cut the surface of the cheese, as this would cause cracks to develop in the
cheese later on in the experiment. A confinement cylinder was attached around each
circle of exposed cheese by heating one end of the cylinder for a few seconds, setting it
in its proper place, and allowing it to cool. The wax was melted by the heat of the cylin-
der, and when it hardened again, it held the cylinder very securely.

For convenience, the circles of exposed cheese were arranged in two rows of four,
In one row, 20 adult female A. siro were placed in each cylinder, and in the other, 20
adult female T, putrescentiae. This work was done in the walk-in refrigerator to prevent
"oiling" of the cheese. Oiling occurs when natural oils exude from the cheese at tempera-
tures in excess of about 60° F, Mites from a culture were picked up individually on the
point of an insect pin and transferred to the cylinders, Care was taken not to transfer

3 This method was developed by Hamilton Laudani, H. T. Vanderford, and C. D, Wooten at the Stored-Product Insects
Laboratory in Savannah, Ga,

4 Use of trade names is for identification purposes only and does not constitute endorsement by the U.S, Department of
Agriculture,

eggs along with the mites. The mites were then held in the cylinders for 24 hours at
56° F. and 92 percent r.h, and allowed to lay eggs. After the egg-laying period, all
mites were removed from the cylinders, Each block of cheese containing eggs was
placed in a humidity chamber and incubated at the desired temperature and humidity.
All cylinders were observed daily, and the number of mites in each life stage was re-
corded, Observations were continued until all mites had reached the adult stage or
died.

Results

The effects of temperature and relative humidity on the life history of A. siro and
T. putrescentiae were pronounced. Lowering of either the temperature or the relative
humidity tended to slow down or stop development in both species tested. No eggs of
either species hatched at any humidity at 32°F, (data not shown in table), Eggs were
incubated at this temperature for 180 days; when they were removed to a warmer tem-
perature, they proved to be no longer viable. Ata r.h. of about 45 percent or less and
temperatures of 56° and 50° F., no eggs of either species hatched, At ar.h. of about
65 percent or less, the eggs of neither species hatched at temperatures of 44° and 38° F,
When eggs did hatch at the lower humidities, the mites often did not survive, but died in
the larval, larval resting, or protonymphal stage.

The results of the life history studies of A. siro and T, putrescentiae are sum -
marized in tables 1 and 2 in the appendix, pages 15 to 18. Data for the 10 percent of
the mite population that developed most slowly were excluded because abnormal mites
often would fall into this group.

Individual mites varied considerably in rate of development. Sometimes there was a
noticeable difference in development time from one replicate to another. In tables 1 and
2, the average length of time spent in each stage was calculated for the mites that de-
veloped most rapidly at each combination of temperature and humidity. Among the active
feeding stages, the larval stage was usually longest and the protonymphal stage the short-
est. The resting stages all required less time than any of the active feeding stages, and
all appeared to last about the same length of time.

In calculations of average development time, the results from the four replicates

at each combination of temperature and humidity were totaled to give the number of mites
in each stage of development each day from the time the first egg hatched until all had
become adults, The percent of mites in each stage, with respect to the total mites in

all stages, was calculated for each day of development, The first day on which 90 percent
of the mites reached a given stage of development was recorded for each life stage. This
was also recorded for each 5-percent interval down to 5 percent, The amount of time
spent in a given stage was found by subtracting the first day a given percentage of that
stage was reached from the day the same percentage of the next succeeding stage was
reached. The average development period for the first 90 percent of the mites is an
. average of the development periods at each 5-percent level up to and including the 90-
percent level,

An example is the calculation of the average length of time the first 50 percent of
A. siro spent in the deutonymph stage at 56°F. and 92 percent r.h, Table 3, on page 19,
gives the percent of mites in each life stage on each day; this table shows that the first
day on which 5 percent of the mites had reached the deutonymph stage was the 23rd day.
Ten percent, as well as 15, 20, 25, and 30 percent, had reached this stage by the 24th
day. On the 26th day, 5 percent of the mites had reached or passed the resting deuto-
nymph stage, since, in these calculations, the percent of mites in any succeeding stage
was added to the percent in the stage being determined, Thus, after 27 days, 10 percent
were resting deutonymphs, and after 28 days, 15 and 20 percent had reached or passed
the resting deutonymph stage. The same data presented under other circumstances are

shown in table 4 on page 19. The average for the first 10 percent would be the average of
the 5- and 10-percent levels, or 3 days, The average for the first 50 percent would be
the average of all the levels up to and including the 50-percent level, or 4.2 days.

The average amount of time spent in each life stage also was calculated for the first
50 percent and for the first 10 percent of the mites reaching each stage, The 50-percent
level is probably the best indication of the proportionate amount of time spent in each
stage. The 10-percent level is a measure of the potential speed of development at each
combination of temperature and relative humidity.

A special procedure was used to calculate the length of time in the egg stage. Gen-
erally, between 25 and 75 eggs were laid in each cylinder, but many of these became
hidden with mold, especially at the three higher relative humidities. Consequently, it
was impossible to determine the total number of eggs or how many failed to hatch in
each cylinder, The number of larvae present was recorded daily, and when there was
no longer an increase in this number, all of the viable eggs were assumed to be hatched.
The number of larvae present at this time was determined to be equal to the number of
eggs that hatched, The number of eggs yet to hatch could then be calculated for each pre-
ceding day by subtracting the number of larvae present at that time from the number of
eggs that eventually hatched.

Other corrections were necessary in the calculation of the time spent in the egg
stage. Since the eggs were laid over a 24-hour period, they differed as much as 1 day
in their age. The first 50 percent of the eggs that hatched were said to have been laid on
day 0, andthe latter 50 percent were said to have been laid on day 1,

Another correction for the length of time spent in the egg stage had to be made at
combinations of temperature and relative humidity other than 56° F. and 92 percent r.h,
Since all eggs were laid over a 24-hour period at this temperature and humidity, some of
the eggs were incubated for up to 1 day before they were placed in the test temperature
and relative humidity. The correction was often insignificant, and it was applied only
when it amounted to more than half a day. To calculate this correction, the following
formulas were used:

correction = X - b

a ebay = eo

where X = corrected period of development for the egg at the test temperature and
humidity

a = average development time for the egg at 56°F. and 92 percent r.h,

b = most rapid observed development time for the egg at the test temperature
and humidity

This correction applied completely only to those eggs that had developed for 1 day at
56° F, and 92 percent r.h, It applied to a varying extent to all eggs except those that had
just been laid at the end of the oviposition period. If the correction were 3 days, 20 per-
cent of the eggs would be said to have been laid on day -3, 20 percent on day -2, 20 per-
cent on day -l, 20 percent on day 0, and 20 percent on day 1.

In the development cycle, the greatest percentage of time was spent in the egg stage.
After incubation of the eggs, the tiny hexapod larvae emerged through a longitudinal slit.
These larvae fed actively. As they increased in size, they became more and more rounded
in appearance, and their backs became increasingly more strongly arched, Then feeding
ceased and the larvae went into the quiescent larval resting stage. In this stage, these
very much rounded forms were often found lying on their backs or sides, making abso-
lutely no movement, and with the legs somewhat contracted. Upon ecdysis, a flattened,

8

octopod protonymph appeared and immediately began active feeding. Upon feeding, this
form also became more and more arched until it, too, went into a resting stage. Ecdysis
of this stage produced a deutonymph. No hypopial stages were ever encountered in any of
these experiments, and only one A. siro hypopus was ever found in the cultures. The
development of the deutonymph closely paralleled that of the protonymph,

Small deutonymphs could be distinguished from large protonymphs at this early stage
of development only because the deutonymphs were still somewhat more flattened than
the large protonymphs, which had become quite arched,

Adults, emerging from resting deutonymphs upon the final molt, could be easily dis-
tinguished from the other stages by the presence of genital organs. At all temperatures
studied, copulation was noted in both species within 24 hours after the final molt,

EXPERIMENTS ON SURVIVAL

These tests were to determine the ability of mites to survive under a wide range of
combinations of temperature and relative humidity.

Procedure

Experiments were set up on three different substrates--wood, wax, and cheese,
These were conducted at 17 relative humidities, ranging from 6 to 100, at temperature
intervals of 6° F. from 32°F, to 98°F, Because oiling takes place on cheese at about
60° F, and above, survival of mites on wax and cheese could be tested only at tempera-
tures of 56°F, and lower. A. siro and T. putrescentiae were checked simultaneously in
these experiments, Four confinement cylinders, each containing five mites, were used
for each species at each temperature and humidity combination. Only adults and a few
deutonymphs were used in these tests, The number of mites surviving was recorded
daily for 12 days and after 2, 3, 4, and 5 weeks. A mite was considered dead only when
incapable of any movement,

In the tests for survival on cheese, the blocks of cheese were exactly like those in
the life history studies, except that a larger circle of wax, 4mm. indiameter, was re-
moved before attaching the confinement cylinder.

Cheese blocks for tests of survival on wax also were prepared exactly like those
used in the life history studies, with one exception. No circle of wax was removed; the
cylinders were attached to the unbroken waxed surface, In this test, no cheese was avail-
able to the mites as food.

Attaching confinement cylinders to wood needed a different technique. In tests at
62° F, and above, two rows of four cylinders were placed ona block of white pine wood,
76mm. long, 51 mm. wide, and 19 mm, thick. A second block, of similar size and
covered with felt, was placed on top of the cylinders, sandwiching them between the two
blocks, This cylinder sandwich was held together by a rubber band, The bottom or test
block was dipped briefly in paraffin at about 200° F., so that all the wood and just the
bottom of the cylinders became coated with wax. After the wax had hardened for a few
seconds, the rubber band was removed and the test block was ready for use. If wax
seeped into any of the cylinders, the test block was rejected.

At temperatures of 56° F. and lower, the survival studies on wood were run at the
same time and in the same humidity chambers as the survival studies on wax. Two small
blocks, 60 mm. long, 19 mm. wide, and 25 mm. thick, were used instead of a larger
block, The confinement cylinders were attached by the same method as they were to the
larger blocks of wood, but only four cylinders were attached to each of the small blocks,

A small block with attached cylinders was then placed on each side of the waxed cheese
block in the humidity chamber.

Results

The results of these tests are contained in tables 5 through 11, on pages 20to 34.
An increase in temperature or a decrease in relative humidity decreased the survival of
the cheese mites. The mites withstood lower humidities when in direct contact with the
cheese than when placed on either wood or wax. Relative humidities of 61 percent or
less, at cheese storage temperatures, were definitely detrimental to survival of cheese
mites on wood or wax. Humidities of 43 percent or less caused complete mortality of
mites in contact with the cheese, T. putrescentiae survived adverse conditions better
than A. siro did,

EXPERIMENTS ON EGG VIABILITY

To determine the effects of temperature and relative humidity on the viability of
mite eggs, tests were set up at those combinations of temperature and relative humidity
at which egg hatching was recorded in the life history studies,

Procedure

Forty eggs of each species were incubated at each combination of temperature and
relative humidity. Blocks of cheese of the same size as those used in the life history
studies were waxed with black wax, which was prepared by adding finely divided carbon
to regular cheese wax, Eggs deposited were readily visible against the black background.
Two rows of four cylinders each were attached to the wax. In one row, 10 adult female
A. siro were placed in each cylinder, and in the other, 10 adult female T. putrescentiae.
These mites were allowed to lay eggs for 24 hours at 56° F. and 92 percent r.h, After
this egg-laying period, all adult mites and all eggs except 10 were removed from each
cylinder. The eggs on each cheese block were then incubated at the temperature and rela-
tive humidity to be tested. The cylinders were checked daily and the number of unhatched
eggs recorded,

Results

The results of this test are contained in table 12, page 35. Unfortunately, when this
experiment was set up, tests could not be run simultaneously at 50°F. and 56°F, Tests
at 38°, 44°, and 56°F, were set up at the same time, and the one at 50° F. was set up
about a month later. The results of the tests set up at the same time showed that a de-
crease in temperature caused a decrease in egg viability and a delay in hatching, A de-
crease in relative humidity caused a delay in hatching and a decrease in viability in the
eggs of A, siro., Relative humidities of 84 and 76 percent seemed to be optimum for T.
putrescentiae,

As in the life history studies, a correction factor was calculated to compensate for
partial incubation of the eggs at the oviposition temperature and humidity. In these ex-
periments, the correction was calculated to be the average increase in incubation time.
The formula used in the life history studies was altered to read:

correction = X-b

(b-1/2) (2a

2S Qa

where X = the corrected average incubation period for the test temperature and
humidity

10

a = the average incubation period for the oviposition temperature and
humidity

b = the observed average incubation period for the test temperature and
humidity

The correction factor has not been applied to the figures in table 12, but is listed for each
combination of temperature and relative humidity.

EXPERIMENTS ON CONTROL WITH LOWERED HUMIDITY

This test was set up to determine whether cheese mites could be controlled by low-
ering the humidity.

Procedure

In this test, small cheddars weighing about 500 grams each were cut from a larger
cheddar, using a sharpened tin can, These small cheddars fit snugly, after waxing, ina
pint ice cream carton, The small cheddars were waxed with black wax and double dipped
at 230° to 240° F. Any cracks or holes in the wax coat were repaired with a small drop
of wax and a spatula. The weight of each cheddar was recorded. One-half of the cheddars
were placed in pint ice cream cartons, used to simulate cheese boxes. Twenty-six holes,
made with a dissecting needle, were distributed evenly over the surface of each carton,
The holes permitted some air circulation and also allowed mites to enter the carton as
they could a cheese box, The rest of the cheddars were not put into the simulated cheese
boxes.

The large humidity chambers were used in this experiment, About 500 ml. of sul-
furic acid solution, calculated to give the desired humidity, was given 2 days to come to
equilibrium with the air in the chamber. Relative humidities of 38 to 100 percent were
tested at 56° F, A small unboxed cheddar was placed on one arm of the T made by the
two strips of wood resting on the crystallizing dish, and a boxed cheddar on the other
arm. A small cube of cheese on which were several thousand A, siro was placed at the
base of the T, along with a similar cube on which were several thousand T, putrescentiae.
After 4 weeks, the cheddars were removed, weighed, and checked for mite infestation,

Results

The results of this test are shown in table 13, page 36. Relative humidities of 84
percent or more were highly favorable for the development of both species of cheese mites
tested, At r.h, of 61 percent or less, mites survived only in cracks under the wax.
Weight loss by the cheese, due to moisture loss, was negligible during the 4-week test
period, even at the lower humidities. No correlation was apparent between weight loss
and whether or not the cheese was in a carton during the experiment,

DISCUSSION

In the life history studies of T. putrescentiae, the development times at the various
humidities were almost the same at 44° F, and 50° F. A comparison with the development
times of A, siro at various temperatures indicates that the development times for T.
_putrescentiae at 50° F. are somewhat longer than would be expected. This effect could
not be caused, however, by incorrectly measured temperature or by an abnormal cheese
substrate, since the tests with T. putrescentiae were run at the same time and on the
same block of cheese as were those with A. siro, which behaved as anticipated, It is
difficult to determine just what factor could have caused the results obtained. Perhaps a
different strain of T. putrescentiae was used in the tests at 50°F, Another possibility

Vt

is that an adverse strain of mold was present in the tests at 50°F. A contributing factor
to ERE situation was undoubtedly the fact that the tests involving T. putrescentiae at

50° F. were conducted in two parts. The egg-to-deutonymph development was checked at
the same time as A, siro, but the deutonymph-to-adult development was checked ina
different test. The substrate onto which these deutonymphs emerged was apparently not
exactly to their liking, since the deutonymph part of the development cycle was abnor-
mally long. This, however, would account for only part of the apparent discrepancy.

It is possible that no discrepancy exists, but that T. putrescentiae reacts similarly to
both 44° and 50°F, 7

Mold appears to affect the rate of development of mites. It was evident that the mites
did eat mold when it was present, but that they could get along without it. At 68 percent
r.h,, no mold growth occurred, yet mites were able to complete their development cycle.
Just the right amount of mold seemed to enhance the development of mites. Too much
mold retarded the development of mites, probably because it prevented them from reach-
ing the cheese, their main food source.

Another condition of the substrate that apparently affected the rate of development of
mites was that caused by mites' previously having fed on it. A cheese surface that had
been fed on before seemed more desirable than a freshly cut cheese surface. Perhaps
for the same reason, several mites feeding in a given area tended to develop more
rapidly than one or two isolated mites.

A comparison of results of the life history studies with those of other workers will
not be attempted because of insufficient data on temperature and relative humidity in the
literature, Another factor that makes comparison difficult is that most tests conducted
by others were at higher temperatures and on grain or flour and not on cheese, It is
generally agreed, however, that the lowering of temperature or relative humidity is un-
favorable to mites and slows their rate of development.

Although mites of A. siro and T. putrescentiae were subjected to a wide range of
combinations of temperature 1re and humidity in the life history studies, not one hypopus
was observed. Thousands of mites, perhaps even millions, were observed in the general
cultures, yet only one hypopus was ever found in these cultures. This was a hypopus of
A, siro. This form was extremely active and was constantly moving about through the
other mites in the colony.

The literature on hypopus formation and the reasons for their formation is quite
contradictory. Some species of mites are much more prone to hypopus formation than
others, A. siro and T putrescentiae are not noted for abundant hypopus formation,
Polezhaev (24) subjected A. siro to many combinations of humidity and temperature and
was unable to produce any hypopi. A. siro hypopi, as well as the hypopi of other species,
seem to be generally associated with high temperatures and humidities, Cheese cannot
be stored at high temperatures, and this probably accounts for the absence of hypopi on

cheese,

The results of the egg- -hatching tests conducted with T, putrescentiae showd that no
eggs hatched at 44° or 38°F. Eggs of this species, at these temperatures, hatched at
the four highest humidities tested in the life history studies. Eggs of both species hatched
at some lower humidities in the life history studies than in the egg hatching studies, In
the life history studies, a few of the eggs were deposited and incubated directly on cheese,
while in the egg hatching tests all eggs were on wax. The higher humidity of the micro-
climate at the surface of the cheese could cause eggs deposited there to hatch when the
general humidity in the chamber was lower. To explain why no eggs of T, putrescentiae
hatched at 44° or 38° F. is rather difficult. Perhaps the black waxed cheese used in the
egg hatching tests had some slight detrimental effect on the eggs, This, when combined
with lowered temperatures or humidities, could have prevented the eggs from hatching.
This would help to explain why the percentage of eggs hatching was lower than the 93 to
94 percent reported by Ihde (12), The fact that most of the eggs in the egg-hatching tests

12

were moved with an insect pin, while those in the life history studies were not touched,
might also contribute to the differences in hatchability. The use of more than one strain
of T. putrescentiae, or the physiological condition of the culture used, might help to
explain the differences.

The egg-hatching tests show that the highest rate of hatching in A. siro takes place
at 100 percent r.h., and decreases as the humidity is lowered. In T. putrescentiae, the
greatest egg hatch occurred at 84 percent r.h, The lowest r.h, at which the eggs of
either species hatched was 61 percent, These results closely parallel the findings of

Kozulina (15).

The survival studies show that a r.h, of 68 percent or less is not conducive to mite
survival, The reason for this is probably moisture loss through the integument, All of
these mites respire through their integument, and drying of the integument would inter-
fere with normal gas exchange and cause suffocation and death, As the temperature in-
creases, so does the vapor pressure of water, This would cause more rapid dessication
at higher temperatures, accounting for the fact that mites are better able to survive low
humidity at lower temperatures. As the temperature decreases, the rate of metabolism
in these cold-blooded creatures decreases, and this would explain the longer survival at
lower temperatures, even at optimum humidities. In the survival tests, mites were
better able to survive low humidities on cheese than on wax or wood, This was probably
the result of a higher humidity in the microclimate above the cheese, or a result of addi-
tional moisture that was picked up from cheese eaten, There was undoubtedly no starva-
tion effect, since the mites on wood or wax were able to survive a considerable period
of time under optimum environmental conditions,

In the survival studies, only adult mites and a few deutonymphs were used, Except
for the egg stage, these forms appeared to be the most hardy. The smaller forms were
less resistant to adverse conditions. Resting stages seemed even more susceptible to
adversity than were the active forms, but it was difficult to be certain of this since it
was impossible to tell by observation just when a resting form was actually dead.

The results of these studies may have some interesting practical applications, It is
thought that cheese warehouses may become mite infested through used cheese boxes that
still contain mites. The results of the survival studies show this would be very unlikely
if these empty boxes had been stored for even a short time at a low humidity. Almost
any heated building in the winter time would have a relative humidity low enough to kill
all of the mites in a few days. Daytime summer humidities also would be generally low
enough to kill any exposed mites. Only where used cheese boxes had been stored in a
humid enough place could mites from that source become a problem. The survival studies
showed that cheese mites were well able to survive on wood in the absence of food for a
fairly long time, providing the temperature and relative humidity were favorable.

The results of the experiments show that two environmental factors, low temperature
and low humidity, might be useful in controlling mites in cheddar cheese, but both have
undesirable features that might outweigh their ability to control mites. Also, since these
methods have not been given a positive trial under actual cheese storage conditions, they
might not be as effective as in the laboratory, so recommendations cannot be made at
this time.

As the temperature is lowered, the rate of cheese mite development becomes slower
and slower, Thus, the lower the temperature at which cheese is stored, the longer the
period before the number of mites will make fumigation necessary. Life history studies
show that at some temperatures between 38° and 32° F., none of the mite eggs hatch.

A temperature of 32° F., therefore, would prevent any increase in mite population and
should offer excellent control, but might affect the quality of the cheese. Only mites
brought in from outside would be present in such a warehouse. They would survive a long
time, but would produce no larvae as long as the cheese was held at 32° F. Fumigation
probably would not be needed.

13

On the other hand, storage at low temperature impairs flavor development of the
cheese. Practically no flavor development or aging takes place in cheddar cheese stored
at 32°F. Also, at such low temperatures, evaporationis so slow that itis almostnegligible.
Thus, cheese stored at 32° F. would remain moist after a long period of storage. Main-
taining a cheese warehouse at 32° F. would be more expensive than maintaining it at
some higher temperature, especially during the heat of summer. This would be partly
offset by the lower cost of maintaining a 32° F. temperature during the winter. Such
costs would be more than compensated for if the need for fumigation were eliminated.

As relative humidity is lowered, the rate of development of the mites is decreased,
This was indicated by the results of the survival studies and the life history studies. To
further support these studies, the test with the very small cheddars showed that low hu-
midities could kill mites. In this test, tremendous numbers of mites were placed next to
the test cheese, but after 4 weeks, the only mites present on cheese at 61 percent r.h,
or less were in cracks. Normal cheddars, especially younger ones, would not be nearly
so likely to crack as the unbandaged small cheddars were, A warehouse or curing room
maintained at a r.h. of 60 percent or less would probably remain free from significant
mite infestations,

During the winter, a r.h, of 60 percent is normal in shelf-curing rooms maintained
at 56° F. Relative humidities between 70 and 80 percent were most common in storage
warehouses where the temperature ranged from 40° to 45° F. During the summer, the
r.h, in the curing rooms and warehouses was generally between 80 and 90 percent.

Low humidity might cause an undesirable checking of the cheese. The question is,
would a r.h, of 60 percent be so low as to cause serious checking, especially if the
cheese had been well waxed? The test with the small cheddars showed that moisture loss
was negligible during 4 weeks at humidities even less than 60 percent, and these ched-
dars had a much greater surface-to-volume ratio than a normal-sized cheddar.

Before control by low humidity can be recommended, one must consider whether the
possibility of damage to the cheese, plus the cost of buying and operating equipment to
maintain low humidity to control mites, would be offset by the elimination of fumigation
costs, In a shelf-curing room, humidity would probably not be hard to control, butina
cheese warehouse, where cheeses are packed close together and stacked to the ceiling,
it might be difficult to lower the humidity among the piles of cheese.

To test the assumption that mite control is possible in a cheese curing room by
maintaining a r.h. of 60 percent, observations of mite populations and r,h,. readings
were made in cheese warehouses at 4-month intervals, Mite populations on cheddars
being shelf-cured at 56° F. had reached a point in mid-November where fumigation was
necessary. In mid-March, 4 months after fumigation, no mites were found on cheese
in this curing room. The r.h. was about 60 percent. By mid-July, a very large mite
population was again present, making fumigation necessary. The r.h,. was about 80 per-
cent, This seasonal fluctuation in humidity was as might be expected, since during the
winter the absolute humidity of the outside air is much lower than in the summer,

If the disadvantages can be overcome, two possibilities for effective control of mites
are indicated--a temperature of 32°F. or ar.h. of 60 percent or less. Control with
temperature would apply only to cheese warehouses. It is possible that mite control with
low humidities could be used in both warehouses and shelf-curing rooms, but would prob-
ably be most effective in the latter. Studies on a larger scale must be conducted before
recommendations can be made.

14

APPENDIX

Tables

Acarus

TABLE 1.--Average number of days spent in each stage of development by the first 10, 50, and 90 percent of

siro that showed the maximum growth rate

Avere”~- aumber of days in each stage

Mites

Maximum

number

humidity | of mites

4
g

Total

Resting

deutonymph

Deuto-
nymph

Resting
protonymph

Proto-
nymph

I Resting
= ES

4.5

a given

stage of
deve lopment

observed

Relative

Days

Days

Days

Percent

Number

Number

Percent

2.0 1.5 3.5 1.0

1.5

54 30 10 11.0

100

114

114

92

33

57

84

27

87

76

36

54

19

61

died ---

19.0

10

54

48 and below - no eggs hatched --

50° F.

67

73

100

84

85

92

55

58

33

77

76

46

66

68

61

18

54

48

43 and below - no eggs hatched --

15

TABLE 1.--Average number of days spent in each stage of development by the first 10, 50, and 90 percent of Acarus
siro that showed the maximum growth rate--Continued

Maximum aes Average number of days in each stage
Relative | number b A Pe ng
humidity | of mites CCT | paecoe
Ehaonval stage of Resting ie Resting eee aes Total
development larva protonymph eee aes 2
Percent Number Number Percent Days Days Days Days Days Days Days
44° F,
100 78 56 10 25.0 10.5 4.5 6.5 3.0 6.5 5.0 61.0
50 25.0 12.0 4.4 6.4 Siow) 6.0 Dial 63.2
90 26.4 12.2 4.9 6.6 3.2 6.9 \7/ 65.9
92 72 70 10 29.5 12.5 4.5 Bye) 4.0 6.5 6.5 69.0
50 31.8 V5 4.9 5.9 3.5 8.3 INS) TLs5
90 34.2 10.8 4.6 a7 4.1 9.0 Diatt: 74.1
84 160 159 10 29.0 13.0 4.0 6.5 Sine) 6.5 6.0 68.5
50 30.7 125 4.2 6.2 353 7.8 5.8 70.5
90 32.6 11.6 4.4 yal 3.9 8.6 Goi: TEIGS)
76 88 50 10 26.5 16.0 7/0) 9.0 4.5 15.0 6.0 84.0
50 27.8 18.3 6.4 9.0 6.6 14.3 6.1 88.6
90 28.8 9 6.1 10.3 7.2 14.8 ¢/oe} 95.4
68 6 O 10 33:50 died --- --- --- --- --- ---
50 34.3 died --- --- --- --- --- ---
90 35.2 died --- --- --- --- --- ---
61 and below - no eggs hatched -- --- --- --- --- tees --- --- ---
38° F
100 48 2 (40) 10 58.5 21.5 8.0 10.0 4.0 W7S5. 11.0 130.5
+ (40) 50 59.1 230: 8.0 9.8 5.6 20.9 10.4 136.9
90 61.5 24.6 8.6 9.9 D2 23.6 a val 144.5
92 58 2 (43) 10 62.0 21.0 8.5 12.0 DED 1925 a ESS} 140.0
+ (40) 34 50 65.2 Pll 9.6 10.8 ot 22.9 10.3 147.2
90 65.4 23.6 10.8 alas / 59 24.8 10.2 152.4
84 79 2 (64) 10 70.0 Ae) 9.0 ala A(o) 7.5 36.0 7.3 158.5
+ (40) 24 50 70.3 18.6 8.9 13.3 6.5 41.1 9.8 168.5
90 71.6 PSY 10.3 14.1 6.5 46.0 8.7 178.9
76 34 0 10 72.0 died --- --- --- --- --- ---
50 Pls died --- --- --- --- --- ---
90 70.4 died --- --- --- --- --- ---
68 3 O 10 79.0 died --- --- --- --- --- ---
50 77.8 died --- --- --- --- --- ---
90 7174 died --- --- --- --- --- ---

61 and below - no eggs hatched -- --- --- --- --- --- --- --- ---

1 The lengths of the deutonymph and resting deutonymph stages were determined separately. The figure in parentheses
represents the number of resting protonymphs used for this determination.
2 Represents the number of mites reaching the deutonymph stage.

16

TABLE 2.--Average number of days spent in each stage of development by the first 10, 50, and 90 percent of
Tyrophagus putrescentiae that showed the maximum growth rate

Maximum ie apt Average number of days in each stage
Relative | number ae
humidity] of mites stage of = : .
observed ‘ K Resting] Proto- Resting Deuto- Resting Total
evelopmen larva | nymph |protonymph | nymph | deutonymph

Percent Number Number Percent Days Days Days Days Days Days Days Days

56; Wi
100 28 15 10 12.5 6.0 2.5 4.0 2.5 6.0 3.0 36.5
50 13.4 7.6 2.2 5.4 1.6 5.8 2.3 38.3
90 13.3 9.9 1.8 5.3 ZL 7.8 Bent 42.9
92 74 46 10 12.5 6.0 2.0 4.0 1.5 6.0 325 35.5
50 1375 i 6.6 2.1 4.7 2.3 7.3 2.6 38.7
90 13.6 Tel 2.1 5.8 2.4 7.6 Zo) 41.1
84 117 60 10 13.5 7.0 2.0 5.0 2:5 7.0 3.0 40.0
50 13.9 7.6 2.6 Sol 265 7.5 32 42.4
90 14.2 8.6 2.9 5.8 2.9 8.2 2.9 45.5
76 104 29 10 13.0 8.0 4.0 335 2.0 5.0 2.5 38.0
50 13.7 10.2 3.2 3.7 2.2 5.3 Bal 41.0
90 13.7 12.2 3.5 3.9 2.0 5-13 2.9 43.5
68 53 18 10 13.0 10.5 2.5 5.0 135 6.0 3.0 41.5
50 13.5 12.1 207 4.8 1.9 5.4 332 43.6
90 13.7 14.0 2.6 461 2a 5.6 3.3 45.4
61 81 14 10 1345 9.5 2.5 4.0 2.0 4.5 2-5 38.5
50 14.1 11.2 3.8 3.4 2.0 4.8 2.8 42.1
90 14.3 13.4 4.8 Sab 2.0 4.7 2.9 45.2
54 30 O 10 15.5 18.5 4.0 died --- --- --- ---
50 16.5 17.5 4.0 died --- --- --- ---
90 Ae / i al ta 2.2 died --- --- --- ---
48 10 ) 10 16.0 12.0 died --- --- --- --- ---
| 50 16.4 15.7 died --- --- --- --- ---
| 90 17.1 16.3 died --- --- --- --- ---
43 and below - no eggs hatched -- --- --- --- --- an --- --- ---

| 50° F.

|
| 100 47 2 (39) 10 27.5 15.0 7.0 10.5 6.5 17.0 8.0 91.5
+..(38) 22 50 2139: 6.7 6.3 11.4 54 19.1 8.0 94.8
90 28.4 17.8 6.2 12.1 4.6 22.2 8.9 100.2
| 92 72 2 (25) 10 28.0 15.5 6.5 12.0 5.0 17D 6.5 91.0
| + (39) 24 50 28.9 16.1 7.9 10.8 4.4 19.0 6.6 93.7
90 29.7 17.4 eve) 10.7 4.5 21.69, Dish 97.8
| 84 81 2 (10) 10 26.0: 15.5 8.0 a5 4.0 17.0 11.0 95.0
+ (41) a bah 50 28.4 18.0 9.5 12.4 5.8 18.7 es: LO5.1
90 29.2 21.4 9.0 11.8 6.4 22.4 12a 112.3:
76 90 Zils) 10 29.5 14.0 6.5 9.5 6.5 15.0 20 88.0
+ (40) 10 50 30.2 15.3 9.4 8.6 5A 17.0 12.6 98.5
90 30.5 20.1 8.9 6.6 Dee 24.6 11.3 107.2
68 73 2 (17) 10 31.0 14.5 6.0 10.0 4.5 16.0 11.0 93.0
1 (40) 9 50 31.8 16.7 TED 10.0 6.4 20.0 12.2 104.6
90 32.1 18.7 7.6 9.9 7.4 28.0 9.9 113.6
61 27 6) 10 31.0 28.0 died --- --- --- --- ---
50 3159 (2687 died --- --- --- --- ---
90 3250 2753 died --- --- --- --- ---
54 31 ¢) 10 30.0 22.0 died --- --- --- --- ---
50 30.55 . 23.3 died --- --- --- --+ ---
90 30.7 25.6 died --- --- --- --- ---
48 49 0 10 30.0 13.0 died --- --- --- --- ---
50 30.2 18.6 died --- --- --- --- ---
90 30.4 died --- --- --- --- --- ---
43 and below - no eggs hatched -- --- --- --- --- --- --- --- ---
17

TABLE 2.--Average number of days spent in each stage of development by the first 10, 50, and 90 percent of
Tyrophagus putrescentiae that showed the maximum growth rate--Continued

Mites
completing

Maximum Average number of days in each stage

Relative | number E

humidity | of mites = erven : :

Speed stage of Resting | Proto- Resting | Deuto- Resting Total
development protonymph | nymph | deutonymph e
Percent Number Number Percent Days Days Days Days Days Days Days Days
44° F.
100 14 8 10 25.0 19.0 9.0 11.0 5.0 12.0 3.5 84.5
50 30.2 19.3 6.3 13.9 py alo 5.6 91.6
90 30.9 22.2 6.4 13.3 4.7 13.4 5.4 96.3
92 14 10 10 33.0 13.0 6.0 8.5 4.5 9.0 7.0 83.0
50 33.6 15.3 59 Ted 5.8 12.3 7.8 88.2
90 33'sD 17.6 4.8 12.0 4.9 13/30 7.8 93.6
84 10 4 10 33.0 17.0 3.0 12.0 5.0 14.0 6.0 90.0
50 33.1 18.5 2.2 13.0 del: 13.8 6.9 92.6
90 34.2 19.8 3.4 13.0 Dal: 10.9 7.4 94.4
76 10 3 10 33.0 21.0 9.0 14.0 7.0 13).0 7.0 104.0
50 32.9 22.0 13.5 9.0 5.8 21.4 6.6 134.2
90 34.2 25.4 39 13.9 6.9 18.0 W/d/ 120.0
68 and below - no eggs hatched -- --- --- --- --- --- --- --- ---
38° F.

100 35 2 (26) 10 63.0 28.5 7.0 15D 7.0 26.0 nly ee) 164.5
1 (40) 18 50 63.7 28.9 8.9 1533 5.8 29.2 16.9 168.7
90 63.8 30.7 8.7 14.8 7.6 saben 16.3 173.0
92 59 Ai.(7.) 10 72.0 30.0 8.0 14.5 B.D 42.0 17.0 187.0
(38) 16 50 72.6 33.4 9.8 20.5 9.5 36.5 16.6 198.9
90 Tel 36.3 9.4 23.6 8.4 36.8 16.2 204.4
84 52 2 (30) 10 76.5 PALES: WES) 15.0 11.0 46.0 14.0 197.5
+.-(41) 4 50 76.7 29.9 9.2 18.7 8.8 46.1 aks jaa 202.5
90 78.1 31.6 8.8 20.4 8.6 46.2 12.6 206.3
76 4 6) 10 79.0 died --- --- --- --- --- ---
50 77.8 died --- --- --- --- --- ---
90 77.4 died --- --- --- --- --- ---

68 and below - no eggs hatched -- -=- = —— rim =s= ooo === ===

+ The lengths of the deutonymph and resting deutonymph stages were determined separately. The figure in parentheses
represents the number of resting protonymphs used for this determination.
* Represents the number of mites reaching the deutonymph stage.

18

TABLE 3.--Proportion of Acarus siro in each of several life

stages on a given number of days after hatching

Percentage in life stage

Days

Resting

deutonymph Boe

Deutonymph

Percent Percent Percent

TABLE 4.--Time taken for given percentages of Acarus siro to reach the deutonymphal and
resting deutonymphal stages, and time spent in the deutonymphal stage

Time taken--
Mites ‘

To reach In deutonymphal To reach resting

deutonymphal stage stage deutonymphal stage
Percent Days Days Days
5 23 3 26
10 24 3 21
LS 24 4 28
20 24 4 28
25 24 5 29
30 24 > 29
35 25 4 29
40 25 5 30
45 25 5 30
50 26 4 30

19

TABLE 5.--Mortality of Acarus siro on wood exposed to various combinations of temperature
and relative humidity

Mortality at temperature of--

Relative
humidity | 32°F.|38°F.| 44°F.| 50°F.| 56°F.| 62°F.| 68°F.| 74°F. | 80°F. | 86°F.| 92°F. | 98°F.

After 1 day

Pet Pet. Pet. Pet. Pet. Pet Pet. Pet. Pet.) Ret. Pet. Pct. Pct.
100 O 0) 0 5 0 10 0 0 0 O 60 100
22 9 O e) O 0 2 0 20 10 35 95 100

84 O O 5 O O 22 10 80 65 100 100 100

76 O O O O 10 42 9) 100 61 100 100 100

68 O 0 O 16 2) 83 100 100 100 100 100 100

61 0 O 0) 0 80 68 100 100 100 100 100 100

54 0 O O O 35 76 100 100 100 100 100 100

48 0 0 10 14 10 90 100 100 100 100 100 100
43 0 0 O e) 10 92 100 100 100 100 100 100
38 5 O 10 20 24 96 100 100 100 100 100 100
Be 5 0 2 15 fae) <P) 100 100 100 100 100 100

mh 2 O 2 29 rail 100 100 100 100 100 100 100

22 0 0 10 O Sth 89 100 100 100 100 100 100

L/ 5 0 10 eS) 26 92 100 100 100 100 100 100

ale 0 0 10 39 24 100 100 100 100 100 100 100

2 0 O 25 45 24 100 100 100 100 100 100 100

6 O 0 20 20 29 100 100 100 100 100 100 100

20

TABLE 5.--Mortality of Acarus siro on wood exposed to various combinations of temperature
and relative humidity--Continued

Mortality at temperature of--

Relative] 32°p,|3g°r.| 44°F. |50°F. |56°F. | 62°F. | 68°F. | 74°F. | 80°F. | 86°r.| 92°F.| 98°F.
humidity

After 5 days
Pets | Pet. Pet, Pet. Pet. Pot. Pet... Pot. Pot. Pot. Pet... Pet. Pet.
100 10 50 0) 5 S 10 O 15 26 25 100 100
92 14 69 O 5 17 9 0 25 48 60 100 100
84 5 55 24 70 2k 58 10 85 95 100 100 100
76 30 74 100 65 48 96 95 100 100 100 100 100
68 62 95 100 100 95 100 100 LOO 100 100 100 100
61 60 90 100 100 100 100 100 100 100 100 100 100
54 65 100 100 100 100 100 100 100 100 100 100 100
48 67 100 100 100 100 100 100 100 100 100 100 100
43 85 100 100 100 100 100 100 100 100 100 100 100
38 70 100 100 100 100 100 LOO 100 100 100 100 100
32 90 100 100 100 100 100 100 100 100 100 100 100
27 67 100 100 100 100 100 100 100 100 100 100 100
22 95 100 100 100 100 100 100 100 100 100 100 100
a7, 100 100 100 100 100 100 100 100 100 100 100 100
13 100 100 100 100 100 100 100 100 100 100 100 100
9 100 100 100 100 100 100 100 100 100 100 100 100
6 100 100 100 100 100 100 100 100 100 100 100 100
After 7 days

21

TABLE 5.--Mortality of Acarus siro on wood exposed to various combinations of temperature
and relative humidity--Continued

Mortality at temperature of--

humidity

After 14 days

Pet. | Pct. Pct. Pot. Pot. Pet. Pct, Pet. Poet. Pot. Pet. Pet. Pot.
100 5 90 5 15 40 60 85 100 100 100 100 100
92 18 100 22 30 33 86 100 100 100 100 100 100
84 10 85 44 70 63 87 85 100 100 100 100 100
76 78 100 100 65 86 100 100 100 100 100 100 100
68 100 100 100 100 100 100 100 100 100 100 100 100
61 100 100 100 100 100 100 100 100 100 100 100 100
54, 100 100 100 100 100 100 100 100 100 100 100 100
48 100 100 100 100 100 100 100 100 100 100 100 100
43 100 100 100 100 100 100 100 100 100 100 100 100
38 100 100 100 100 100 100 100 100 100 100 100 100
32 100 100 100 100 100 100 100 100 100 100 100 100
27 100 100 100 100 100 100 100 100 100 100 100 100
22. 100 100 100 100 100 100 100 100 100 100 100 100
ally, 100 100 100 100 100 100 100 100 100 100 100 100
13 100 100 100 100 100 100 100 100 100 100 100 100
9 100 100 100 100 100 100 100 100 100 100 100 100

6 100 100 100 100 100 100 100 100 100 100 100 100

After 35 days

90 =100 100 100 100 ‘LOO 100 100 100
100 #8100 100 100 100 100 100 100 100

90) © 200 100 100 100 100 100 100 100
85* 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
LOO 100 100 100 100 100 100 100 100
100 > -100 100 100 100 100 100 100 100
LOO (2.00 100 100 100 100 100 100 100
100 #100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100

22

TABLE 6.--Mortality of Acarus siro on waxed cheese exposed to various combinations of

Relative
humidity

temperature and relative humidity

Mortality at temperature of--

c+

0)
O
5
5
e)
O
e)
5
0
)
5
5)
0
5
5
0
O

'U
fe)

‘J
fe)

| oe
Ww OoOOOWNO ae hee

‘J
Q
cot

oOO0O00 eee

OOONO

WH

After 1 day

23

Relative
humidity

Mortality at temperature of--

After 5 days
Pet. Pet.
0 O
6 5
5 30
40 47
80 68
95 78
100 95
95 100
74 100
100 100
95 100
95 100
100 100
100 100
100 100
100 100
100 100
After 7 days
0) 0
18 10
5 30
40 68
90 100
100 87
100 100
100 100
100 100
100 100
100 100
100 100
100 100
100 100
100 100
100 100
100 100

100
100
100

100

100
100

56°F.

TABLE 6.--Mortality of Acarus siro on waxed cheese exposed to various combinations of
temperature and relative humidity--Continued

Mortality at temperature of-- Mortality at temperature of--

Relative = ° O O° 0 Relative O ° fo)
humidity | 32 F. | 38°F. 56°F «|| humidity 38-F. WeA4eF. |s5008.

After 14 days After 35 days

24

TABLE '7.--Mortality of Acarus siro on unwaxed cheese exposed to various combinations of
temperature and relative humidity

Mortality at temperature of-- Mortality at temperature of--

Relative oO O fe) O fe) Relative O fe) (e) fe)
humidity BOO PR ESSe Fe! 'ly 24° RN £500 Be 56c Be. humid ty 32°R? | 36°R. 1:44°RS | 50°RS| 56°Rr.
After 1 day After 5 days
Pet Pet. Pet. Pet. Pct. Pet. Pet. Pet. Pet Pet. Pet. Pet.
100 0 0 0 0 0 100 0 0 5 6 5
92 0 0 0 0 0 92 5 @) 0 0 5
84, 0 0 0 0 @ 84, 9 0 5 @ 0
76 0 0 5 O 0 76 0 0 5 10 10
68 0 0 0 O 0 68 0 5 AT 45 14
61 0 0 5 @) 0 61 25 10 85 10 24
54, 0 0 5 @) 0 54 28 45 90 100 10
48 0 0 37 @ 0 48 13 38 100 100 38
43 @) @) @) 5 0 43 (*) 77 90 100 95
38 0 0 5 O 0 38 30 79 100 100 100
32 0 0 10 0 6 32 60 75 100 100 100
27, 5 0 16 0 0 27 27 7d, 100 100 100
22 0 0 15 5 5 oy 60 75 100 100 100
ay 0 0 7 5 0 17 87 70 100 100 100
13 @) 0 25 0 @) 13 73 75 100 100 100
9 @) 0 30 5 @) 9 (+) 100 100 100 100
6 9) 5 46 5 0 6 50 80 100 100 100
After 3 days After 7 days
100 0 0 O 6 5 100 0 0 10 6 10
92 5 0 0 0 0 92 5 5 5 4 10
84, 9 0 @) 0 0 84, 9 0 5 5 6
76 0 © 5 10 5 76 @) @) 5 10 20
68 @) 0 15 35 0 68 5 10 67 50 19
61 10 @ 45 5 5 61 40 45 95 14 29
54, 5 0 60 45 5 54, 43 86 90 100 nl
48 0 58 66 24, 48 33 94, 100 100 43
43 (7) 9 40 90 80 43 4 100 90 100 95
38 20 5 50 70 70 38 90 100 100 100 100
32 40 5 79 100 94, 32 80 100 100 100 100
BF @) 0 68 80 100 27 67 100 100 100 100
22 20 10 55 100 100 22 80 100 100 100 100
7, 20 15 73 93 100 17 100 100 100 100 100
13 20 0 85 100 100 13 100 100 100 100 100
9 0 15 100 1060.. 2100 9 Ce) 100 100 100 100
6 10 15 85 100 95 6 100 100 100 100 100

See footnote at end of table.

25

TABLE '7.--Mortality of Acarus siro on unwaxed cheese exposed to various combinations of
temperature and relative humidity--Continued

Mortality at temperature of-- Mortality at temperature of--
humidity humidity
After 14 days After 35 days

Pet. Pet. Pet. Pet. Pct. Pet. Pet. Peibe.P us Pete sj GPCbe se wPebes _Peite
100 15 @) 26 sky ie (>) 100 25 15 90 83 (3)
92 15 5 15 I, Peace) 92 20 10 75 4.3 (7)

84. 19 10 5 20 al 84 43 32 55 55 (7)

76 0 @) 5 10 25 76 30 ee) 53 35 (=)

68 30 15 80 55 29 68 75 55 93 70 62

61 95 75 100 33 52 61 100 80 100 62 76

54, 100 90 100 100 16 54 100 90 100 100 21

48 100 100 100 100 52 48 100 100 100 100 62

43 (*) 100 100 100 100 43 GG) 100 100 100 100

38 100 100 100 100 100 38 100 100 100 100 100

32 100 100 100 100) »--160 Be 100 100 100 100 100

27 100 100 100 100 100 27 100 100 100 100 100

22 100 100 100 100 100 22 100 100 100 100 100

17 100 100 100 100 100 17 100 100 100 100 100

13 100 100 100 100 100 13 100 100 100 100 100

9 (*) 100 100 100 100 9 (4) 100 100 100 100

6 100 100 100 100 100 6 100 100 100 100 100

+ No data; cracks had developed in cheese in all replicates and observations were dis-
continued.

2 Mites not visible because of heavy mold growth.

3 Large colony of mites.

TABLE 8.--Mortality of Tyrophagus putrescentiae on wood exposed to various combinations of
temperature and relative humidity

Mortality at temperature of--

Relative | 350m | 3g°r,|44°r. | 50°r. |56°r. | 62°r. | 680r.| 74°Fr.| so°r. | ger. | 92°r.| 98°F.
humidity
After 1 day

Pet. | Pet. Pct. Pct. Pet. Pct. Pet. Pet. Pet. Pet. Pet. Pet. Pet.
100 0 0 5 0 0 0 0 19 0 0 0 100
92 5 Z 0 0 0 0 5 38 15 5 55-100
84 Z 0 0 0 0 9 15 55 26 4 65-100
76 0 y 0 0 0 0 55 65 45 65 100 100
68 0 fe) 5 0 0 ay, 59 30 80 40 80 100
Al 0 0 0 0 0 5 90 55 95 85 100 100
54 0 0 5 0 0 50 85 55 52 85 100 100
48 0 0 5 0 5 55 95 85 40 95 100 100
43 0 0. i 0 0 1g 80 90 38 100 100 #100
38 0 0 0 5 4 9 90 100 45 90 100 100
92 5 0 0 0 5 48 30 95 55 100 100 #100
27 5 0 15 0 0 23 90 95 62 100 100 °&# 100
22 fe) 5 5 0 0 55 95 80 79 100 100 #100
17 0 5 5 0 0 48 100 95 73 100 100 #100
13 0 5 5 5 0 86 85 95 95 100 100 #100
9 5 0 0 0 0 29° WO0ee - TOO 43 100 100 #100

6 0 0 5 0 0 50 100 100 76 100 100 #100

27

TABLE 8.--Mortality of Tyrophagus putrescentiae on wood exposed to various combinations of
temperature and relative humidity--Continued ;

Mortality at temperature of--

Relative Oo O O° O° O° O ° Oo Oo O° ° re)
humidity 50° Fa| 5645) 625F5) 682F al '74°R2 | SOLE. 86°F. } 92 Fe 98°F.

After 5 days

Pet. | Pet. (Pot. Pet, Pot.) Pet. Petes Pet. | Pete Beta eret. apeeets were.
100 10 19 10 O O 23 3) 29 O @) O 100
92 5 46 25 O 6 AL} 5) Dili 30 ale) 70 100
84 12 9 10 30 2) 19 30 95 79 WD 100 100
76 O 48 14 25 27 91 95 100 100 100 100 100
68 5 30 35 40 30 100 100 100 100 100 100 100
61 16 19 15 80 81 100 100 100 100 100 100 100
54 2) 2) 48 50 65 100 100 100 100 100 100 100
48 30 40 55 86 90 100 100 100 100 100 100 100
43 “19 48 40 60 Al 100 100 100 100 100 100 100
38 10 20 10 85 92 100 100 100 100 100 100 100
32 9 67 15 85 100 100 100 100 100 100 100 100
27 9 Cals 60 9572 A100 100 100 100 100 100 100 100
22 > py) 35 85 89 100 100 100 100 100 100 100
/ 9 60 60 95 95 100 100 100 100 100 100 100
13 24 60 BD 95 95 100 100 100 100 100 100 100
9 10 52 40 90 95 100 100 100 100 LOO 100 100

6 19 15) 50 95 79 100 100 100 100 100 100 100

28

TABLE 8.--Mortality of Tyrophagus putrescentiae on wood exposed to various combinations of
temperature and relative humidity--Continued

Mortality at temperature of--

humidity

After 14 days

100 2D Vial 10 5 25 50 15 48 43 67 vee) 100
92 9 92 30 5 7 5D) 5) 71 65 50 85 100
84 12 48 15 30 15 33 50 90 95 85 100 100
76 10 95 76 30 5D 100 95 100 100 100 100 100
68 24 95 95 65 40 100 100 100 100 100 100 100
61 63 85 95 95 100 100 100 100 100 100 100 100
5A 62 95 95 100 87 100 100 100 100 100 100 100
48 90 95 90 100 95 100 100 100 100 100 100 100
43 95 100 95 100 100 100 100 100 100 100 100 100
38 90 90 95 100 100 100 100 100 100 100 100 100
32 95 100 95 100 100 100 100 100 100 100 100 100
aL 95 100 100 100 100 100 100 100 100 100 100 100
22 7D 100 100 100 100 100 100 100 100 100 100 100
ayy: 95 100 100 100 100 100 100 100 100 100 100 100
13 95 100 100 100 100 100 100 100 100 100 100 100

9 90 100 100 100 100 100 100 100 100 100 100 100
6 100 nkele) LOO LOO 100 100 100 100 100 100 100 100

29

TABLE 9.--Mortality of Tyrophagus putrescentiae on waxed cheese exposed to various
combinations of temperature and relative humidity

Mortality at temperature of--

Relative | 320p,| 38°F, | 44°F. | 50°F. | 56°F.
humidity

Mortality at temperature of--

After 1 day After 5 days

Pet. Pe Pet. Pet. Pet. Pet Pet Pct. Pet Pet.
100 O O O O O 6 O O
92 O O O O O O 10 O
84 0 O O O O 30 O 5
76 O e) O O 21 lS) O 5
68 O O O O 1:5 9 10 50
61 O O O 6 SH 10 40 94
54 O O O D 58 45 20 65
48 O O O O 68 31/ 20 76
43 O O O 5 90 25 a) 80
38 O O O 23 78 70 40 92
32 0 O 5 O 90 63 52 65
27 O 5 O 5 95 85 47 Di
22 O 5 O 4 90 yale 20 78
LZ O O O O 82 87 48 90
13 O O O 13 100 85 53 100

9 O 10 O O 100 80 79 86

6 O O O 100 90 71 80

After 7 days

100 6 O O O O 100 ay 5 12 O 12
92 5 O O 10 O 92 5 O O ls O
84 O O 10 0 5 84 O O 50 O 5
76 5 12 10 O O 76 24 33 30 O 15
68 O O 5 5 10 68 35 50 18 25 70
61 10 5) 5 15 12 61 55 90 42 Be: 100
54, 30 8 15 5 10 54 80 100 65 80 85
48 43 9 Pak O 48 48 95 100 58 65 95
43 20 25 5 O ales) 43 90 100 1) 80 100
38 10 39 35 O 54 38 90 100 90 100 100
32 35 21 zl 5 35 32 90 100 95 90 90
27 26 40 30 O 24 Aili 90 100 90 100 100
22 14 38 29 O 43 22 86 100 100 95 100
17 22 15 22 5 45 ake 89 100 96 100 95
13 24 40 27 16 52 13 100 100 96 90 100

9 15 40 45 th 29 9 100 100 90 100 100

6 21 50 20 19 40 6 90 100 100 95 100

30

TABLE 9.--Mortality of Tyrophagus putrescentiae on waxed cheese exposed to various
combinations of temperature and relative humidity--Continued

Mortality at temperature of--

humidity

After 14 days

Mortality at temperature of--

After 35 days

Relative
humidity

Pet. Bets: (Pet. Pet. Pet. Pet. Pet. Pet. Pet. Pet.
100 28 5 35 15 59 30 88 100 100
92 5 0 10 20 +50 35 100 100 89
84 5 19 50 O 35 90 90 95 95
76 62 83 45 10 50 100 95 100 100
68 95 95 45 55 90 100 64 100 95
61 100 100 Tt, 75 100 100-100 §200)-- “100
54 100 100 95 100 100 100 100 100 ~~ 100
48 100 100 100 90 100 100 100 100 ~~ 100
43 100 100 100 100° 100 100 100 100 ~~ 100
38 100 100 100 100 100 100 100 100 #100
32 100 100 100 100 100 100 100 100 ~~ 100
27 100 100 100 100 100 100 100 4100 ~~ °# 4100
22 100 100 100 100 100 100 100 100 °# 100
17 100 100 100 100 100 100 100 100 °# 100
13 100 100 100 100 100 100 100 100 100
9 100 100 100 100 100 100. «100 +100) 100
6 100:1. iO 100 100 100 100 100 100 #100

31

TABLE 10.--Mortality of Tyrophagus putrescentiae on unwaxed cheese exposed to various
combinations of temperature and relative humidity

Mortality at temperature of-- Mortality at temperature of--

Relative fe) fo) fo) fe) Relative fe) Oo fo) fe) Oo
After 1 day After 5 days
Pet. Pet. .' Pet. Pot. / Pet. ict. et Pet, Pet. Ret) Pet
100 5 0 O 0 @) 5 0) 0 6) 0
92 O 0 0 O 0 ) fe) 9) fe) )
84 O 0 5 e) 6 fe) fe) 5 @) Tal
76 O O O 0 0 6) fe) fe) @) 0
68 5 0 0 ) 0) 5 5 7 0 0
61 5 e) ) 0 0) 9 1) 25 0) 6
54, s) 5 9) 0 > 0 5 24 10 5
48 0 0 0 0 0 ) 5 45 27 5
43 e) O 0 0 0 9 20 70 47 5
38 5 e) 0 0 0 13 O 47 45 5
ae 0 0 0) 0 0 0) 4 53 50 0
Call 0 e) 5 0) 0 9 4 85 50 12
22 0 0 O e) 5 7 0) 67 92 23
any 5 e) e) 0 e) 5 0) 100 29 9
a) 0 e) 0 5 0 O @) 100 95 10
9 fe) 9) ) 0 0 G 6 100 85 12
6 0 5 0 0 0 0) 24 100 75 18
After 3 days After 7 days
100 5 @) 0 O fe) 100 5 0 6) ) 0)
92 ) 0 ) 0) ) 92 ) 0 ) 10 4
84 0 0) 5 @) ala 84 0 ) 5 ) ot
76 @) ) 0 o) 6) 76 O ) 5 ) )
68 5 0 0 ) 0 68 5 5 7 fe) @)
61 5 0 5 ) ) 61 9 25 40 5 6
54, 0 5 ) 0 5 54, 4 5 62 30 5
48 0 5 0 0 5 48 G2) 5 90 50 5
43 9 @) 20 18 0 43 20 35 70 88 5
38 fe 0 7 15 0) 38 13 33 100 70 15
32 @) ) 20 10 6) 32 ) 18 93 65 23
27 6 0 15 10 ) 27 18 17 100 90 12
22 0 @) 0 uly 14 22 5 5 100 100 45
17 5 0 20 ) 4 17 10 38 100 64 7
13 @) ) 40 67 5 13 ) 33 100 100 10
9 0) 4 43 40 31 9 Ge) 25 100 95 48
6 e) 14 25 45 ) 6 20 57 100 95 53

See footnote at end of table.

32

TABLE 10.--Mortality of Tyrophagus putrescentiae on unwaxed cheese exposed to various
combinations of temperature and relative humidity--Continued

Mortality at temperature of-- Mortality at temperature of--

umidity

After 14 days After 35 days

1 No data; cracks had developed in cheese in all replicates, and observations were dis-
continued.

2 Mites not visible because of heavy mold growth.

? Large colony of mites.

33

TABLE 11.--Number of days required to produce 100-percent mortality of Acarus siro and Tyrophagus putrescentiae on various surfaces exposed to different

combinations of temperature and relative humidity

p>
p
od
d
[os
Pp
%
fe}
&
~
g
o
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oO
Ay
!
je)
oO
qd
o
Oo
3
ue}
Oo
&
Py
fe)
Pp
2
QA

On cheese at
temperature of--

On waxed cheese at

Relative

On wood at temperature of--

temperature of--

humidity

Acarus siro

Days Days Days Days Days Days Days Days Days Days Days

dl

34

utrescentiae

rophagus

t the end of 35 days.

iving a

ites still 1

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Bd oB€

--jo ‘ytd pue ‘y 90S ‘y’d pues “yg sfeq

deT{UsoSeijnd Snseydorsky OITs snieoy

peyoyey sS3e jo asequeoreg

AYTPTuMY eATpPeTed pue eunjzereduiay Jo sucTpBUTQUOD SNOFIBA 4B peyoyey sdde oeTyUsoserjnd snseydors], puw oxts snzevoy jo ,sesvyueored saTyetTnuMO--*2T AIGVL

35

TABLE 13.--Weight of waxed miniature cheddars and extent of mite infestation after exposure
to large populations of Acarus siro and Tyrophagus putrescentiae at 56° F. and various

relative humidities

Weight of cheese

Relative humidity and Gain or
condition of cheese At start After loss
of test 4 weeks | during

test

Percent

40.17
eZ

100 percent r.h.:
Boxed cheese..
Unboxed cheese.....

92 percent rehis:
Boxed cheese.
Unboxed cheese.....

323
-23

84 percent r.h.:
Boxed cheeSe...eeee
Unboxed cheese.....

76 percent r.h.:
Boxed cheese....-e.
Unboxed cheese...

68 percent r.h.:
Boxed cheeSe....ee-

Unboxed cheese.....

61 percent r.h.:
Boxed cheese.......

54 percent r.h.:
Boxed cheese......-

48 percent r.h.:
Boxed cheese.......

Unboxed cheese.....
43 percent r.h.:

Boxed cheeSe..eceee

38 percent r.h.:
Boxed cheese....eee

36

Extent of mite infestation

cheese.
cheese.

entire
entire

mites
mites

1,000
1, 000

or
or

more
more

over
over

cheese.
cheese.

entire
entire

mites
mites

or
or

more
more

over
over

1,000
1, 000

cheese.
cheese.

entire
entire

mites
mites

1,000
1,000

more
more

or
or

over
over

About
About

200 mites over entire cheese.
200 mites over entire cheese.

About 10 T. putrescentiae mostly along
edges of cheese.

About 100 mites mostly along edges of
cheese.

No live mites.
About 200 mites in crack along edge
of cheese.

No live mites.
About 10 T. putrescentiae in crack on
edge of cheese.

About 20 T. putrescentiae in crack on
edge of cheese.
No live mites.

No live mites.
No live mites.

No live mites.
3 T. putrescentiae in a crack in the
cheese.

Review of Literature

Observations on the life history of mites have been made by many workers in this
field. Most of these studies include some data on temperature and humidity. Various
species names have been used, but to avoid confusion, the names used by Nesbitt (18),
Baker and Wharton (1), and Robertson (30) will be used for the various mite species.

Almost all of the cheese mites belong to the Glycyphagidae, Carpoglyphidae, or
Acaridae families. According to Ewing and Nesbitt (7), Acaridae is the correct name for
the family formerly known as Tyroglyphidae.

The presently accepted names of some of the common cheese mites and their syn-
onyms are as follows:

Presently accepted name Synonyms
Acarus siro L. 1758 Tyroglyphus farinae

Aleurobius farinae

Tyrophagus putrescentiae (Schr. , 1781) Tyrophagus castellanii
T. longior var, castellanii
T. nadinus

T. noxius

Tyrophagus longior (Gervais, 1884) T. dimidiatus

Tt. infestans

Lepidoglyphus destructor Schr. 1781 Glycyphagus destructor

Ge cadaverus”

Acarus destructor

Carpoglyphus lactis L. 1758 A. lactis

Carpoglyphus passulorum
C. anonymous
Caloglyphus rodionovi Zakhv. 1937 Tyroglyphus mycophagus

Glycyphagus domesticus DeGeer 1778 No synonyms.

The life cycle of the mites in the cheese mite group, as we understand it today, was
summarized by Michael in 1884 (17). When the egg hatched, a six-legged larva appeared.
This larva fed for a time and then entered an inert, brief resting stage. After ecdysis,
an octopod, the protonymph, appeared. After feeding and growth, the protonymph also
went into a resting stage. Upon ecdysis, either a deutonymph or a specialized form
called the hypopus appeared. The hypopus stage will be discussed separately later, The
deutonymph very closely resembled the protonymph, but was larger. The deutonymph
fed and grew and finally entered into a resting stage. Ecdysis produced the adult mite,

Reuter (25) described three nymphal stages, the protonymph, the deutonymph, and
the tritonymph. Reuter's deutonymph, an active migratory form corresponding to
Michael's hypopus, was omitted in many life cycles. The tritonymph of Reuter was the
same as the deutonymph described by Michael,

az Glycyphagus cadaverus is a distinct species in Russia.

5)

Eales (6) reported on the life histories of certain cheese mites. These studies
lacked temperature and relative humidity data, and the time spent in each stage of devel-
opment was not definitely ascertained,

Newstead and Duvall (19) published some biological observations on A, siro and
L. destructor, A. sirofemales at 64° to 71°F. each laid 3 to 4 eggs per day and a total
of 20 to 30 eggs during their lifetime. A typical life history at this temperature was as
follows: Egg 3 to 4 days, larva 3 days, resting larva 1 to 2 days, and nymphal stages
6 to 8 days. The life history of L. destructor was almost identical to that of A. siro.
A moisture content of at least 13 percent (r.h. of about 58 percent) was necessary for
the survival of these mites in grain or flour, At temperatures of 60° to 70° F., the mite
populations increased very rapidly, while at 40° to 50° F., they increased slowly.
Newstead and Morris (20) found that when the moisture content in flour was maintained
at 13 percent, the population of A. siro multiplied rapidly, but when the moisture con-
tent was 12.4 percent, it increased very slowly. When the moisture content was 12.2
percent, all mites were dead in 2 to 3 weeks.

Belyaev et al. (2) stated that A. siro and T, longior developed best in grain at 64,4°

to 71.6° F. and 18 to 24 percent moisture content. At this temperature and humidity,
the eggs hatched in 4 to 5 days, but at 46.4° to 50° F., 11 to 12 days were required.

Smaragdova (36) found that grain mites reared at 86° F. were more resistant to
heat and cold than were mites reared at 68°F. In these tests, a dry atmosphere in-
creased the rate of mortality. In 1935, Sokolov (42) reported A. siro to be the most
prevalent mite in stored grain, A moisture content of 16 to 20 percent and a temperature
of 64.4° to 77° F. were optimum for development, but movement, mating, oviposition,
and hatching occurred at temperatures as low as 35,6°F,

Observations of Zakhvatkin (46) that mites were not present in hay or straw unless
the moisture content was above 12 percent substantiate the findings of Newstead and
Morris (20).

Dustan (5) reported on the results of some experiments with A. siro on cheese, At
60° F. the eggs of this mite hatched in 12 to 14 days, and 3 to 4 weeks were required for
development to the adult stage. No humidity data were mentioned, Practically no mite
damage was observed in cheese stored at 32° to 35° F, Even at 35° to 409 F., cheese
could be stored for several months with comparative safety, but at temperatures above
40°F, the mites were quite active and caused noticeable damage. At temperatures of
50° to 60° F., the mites were very active, and the damage to the cheese was quite ex-
tensive. High humidity favored the development of mites, but not to so great an extent
as high temperature. The last of 50 A. siro became dormant at 26.9° F, and the first
became active again at 28.7° F. The largest individuals reacted first. At 37° to 40°F.,
the mites continued to feed and probably breed at a very slow rate,

Rodionov (31) placed mites of various species in a glass tube with a temperature
gradient to determine what temperature was most preferred by different species of
mites. The temperature at which most mites congregated was as follows: A. siro 67° F.;
L. destructor 73.4°F.; T. putrescentiae 16,00 Besland CG, rodionow |93.cour.

Oboussier (21) tested the effect of humidity on C, lactis, G. domesticus, G.
cadaverus, and iTS putrescentiae. The development of all forms was favored by mois-
ture. T. putrescentiae bred rapidly at 98 percent r.h,, were less active at 75 percent,
and were mostly dead after 24 hours at 54 percent. Oboussier also observed that infes-
tation of new material was due mostly to wandering nymphs, The development time

varied a great deal among individuals.

38

Kozulina (15) exposed eggs of A. siro and T, putrescentiae to r.h. of 30 to 100 per-
cent and temperatures of 68° to 71.6°F. The largest percentage of eggs of A. siro
hatched at 100 percent r.h, The lowest humidity at which any eggs hatched was 60 per-
cent, The largest percentage of eggs of T. putrescentiae hatched at 70 percent, and 55
percent was the lowest r.h, at which eggs of this species hatched, A temperature of 32° F.
for 24 hours killed 70 to 92.5 percent of the 3- to 4-day-old eggs of A. siro. Polezhaev
(24) found the optimum conditions for the development of A. siro to be a temperature of
62.6° to 77°F. anda r.h. of 60 to 100 percent.

Gilyarov (8) noted that A, siro and T. putrescentiae fed on mold growing on seeds
of kok-saghuiz. The mites could not penetrate the hard seed coat, but their feeding on
the mold prevented lumping of the seed and increased its germination. A colony of mites

could clean mold-covered seed in 3 to 4 days.

Zakhvatkin (47) stated that the lowest r.h, at which A, siro survived was 60 percent,
and the optimum was 75 to 80. The lowest r.h, at which T. putrescentiae survived was
70 and the optimum 90 percent. Temperature affected mites less than humidity did.

A. siro did not develop at temperatures below 46.4° F. nor T, putrescentiae below 48.2° F.
The best temperatures for development were 68°F. to 71.6° F. for A. siro and 77°F. for
T. putrescentiae,

Hughes (11) showed that at 68° F., ar.h,. higher than 58. 3 to 65 percent was essen-
tial for the survival of A, siro, At 80 and 90 percent r.h,, breeding began in 5 days,
but at 74 percent r.h,, breeding did not begin until after 9 days. All mites were dead in
1 day at 20 percent r.h,, in 2 days at 45.5 percent, and in 4 days at 58. 3 percent. After
9 days atar.h, of 65.6 percent, mites were still living butnot breeding.

Studying T. putrescentiae on dried fruit, Lombardini (16) found that this mite devel-
oped most rapidly at 77° F. It spent 7 days in the egg stage, 5 days as a larva, 3 days
asa Brown yn e: and 2 days as a deutonymph, At 42. 8° F., eggs hatched after 13 days,
but at 89.6° F., no eggs hatched at all. Humidity was reported to have no apparent effect
on the hatching time,

Solomon (37, 38, and 39) reported that humidity played a dominant role in the life
of A, siro. An increase in relative humidity increased the rate of multiplication, These
mites were unable to live in grain or flour with a moisture content of less than 12 percent
(55 to 60 percent r,h.), The optimum temperature for growth and survival was 64,4 to
TTR. Temperatures of 104° F. caused complete mortality, but the mites were very
resistant to low temperatures, Like A. siro, mites of the genus Glycyphagus were un-
able to live in grain or flour with less than 12-percent moisture content. Mites of the
genus Acarus did best in media with a moisture content of more than 14 percent, while
Glycyphagus preferred a moisture content of 13 to 16 percent,

Robertson (27) showed that different species of mites were prevalent in cheese
stored at different temperatures. T. longior and Tyrolichus casei were most prevalent
at curing room temperatures, At 40° to 50° F., Tyrophagus was rare, and A, siro,

G. domesticus, and L. destructor were common, In another article (28), she reports
that cheese mite adults can live at least 7 months at 50°F,

Gray (9) reported A, siro as the most important mite pest of grain. A moisture con-
tent of 14 percent was necessary for infestation of grain by this species. Temperature
was less important; mites bred at temperatures as low as 40°F. The optimum was con-
sidered to be at 65°F

A study of population dynamics by Solomon (41) showed warm temperatures and high
humidities to be conducive to the rapid development of A, siro.

In a thesis, Ihde (12) discussed the biology of cheese mites and the effect of tem-
perature and humidity on their development, In one experiment, the life histories of
five species were compared at 55° F, and 100 percent r.h,

39

The longevity of adult male and female mites at 55° F. and 100 percent r.h. was
studied in four species, The females lived slightly longer than the males, but the dif-
ference between species was very small,

In a series of experiments on the effect of temperature and relative humidity on the
biology of A. siro, temperatures of 42° F, and 55°F. were combined with r.h. of 35,
55, 70, and 100 percent. The first experiment determined the effect on development. As
the temperature or relative humidity was lowered, the development time increased for
each life stage from the egg through the deutonymph.

A second experiment showed that lowering the relative humidity and increasing the
temperature shortened the lives of A. siro.

A third experiment showed the effect of different temperature and humidity combina-
tions on the longevity of A. siro confined without food, The results were similar to those
obtained when the mites were confined on cheese,

The fourth experiment showed that no eggs were laid at either of the two lower
humidities.

A final experiment showed the adverse effect of low relative humidity on the via-
bility of A. siro eggs.

Robertson (29) reported that a temperature of 53.6° to 57.2°F. andar.h. of 90 to
95 percent were ideal for the buildup of a population of cheese mites. A temperature of
41° to 42,8° F. anda r.h. of 80 to 85 percent were not so good, Dutch cheeses stored
under conditions ideal for mite buildup were not troubled with mites because of the
process of oiling this type of cheese before storage.

With cultures on mold at 77° F., Rivard (26) studied the effects of r.h. of 70, 80,
90, and 100 percent on the rates of development and mortality of the immature stages of
T. putrescentiae, At 60 percent r,h., no eggs were laid by the mites, Eggs laid at 70
percent r.h, and incubated at 60 percent all failed to hatch, Mortality in the egg stage
ranged from 33 to 44 percent at the other humidities tested. Mortality in the other stages
ranged from about 15 percent at 80 and 90 percent r. h. to 20 and 25 percent at 70 and
100 percent r.h., respectively. Average total development time was 12.6 days at 100
percent r,h., 12.2 days at 90 percent, 13.9 days at 80 percent, and 18.9 days at 70 per-
cent. The males developed slightly faster than the females. Additional experiments in
1959 showed that at 70 percent r.h., mites survived longer than at higher humidities,
and most of the males lived longer than the females. The preoviposition period averaged
2 days at 80, 90, and 100 percent r.h, and 3 days at 70 percent r,h,, while the oviposi-
tion period ranged from an average of 36 days at 70 percent r.h, to 23 days at 100 per-
cent, The rate of oviposition at 90 percent r.h. was more than twice as great as that at
70 percent, and intermediate rates of oviposition were observed at 80 and 100 percent
r. he

The hypopus stage of the cheese mites has been the subject of a great deal of discus-
sion. Michael (17) discussed at some length the hypopus question, A summary of the
literature in 1884 showd at least eight different definitions of the hypopus by various
workers, The following definitions had been published:

1, ''Hypopus is a separate family of adult Acarina, '!

2. ''Hypopus is the immature stage of Gamasus,"'

3. ''Hypopus is an itch mite,"

4, ''Hypopus is the adult of some species of Acaridae, ''

5. '"Hypopus is a parasite, first internal and then external, "'
6. ''Hypopus is a 'travelling dress',"'

40

7. ''Hypopus is the female of Acarus,"'

8. ''Hypopus is the cuirassed, heteromorphous, adventitious nymph of Acarids,
etc, , appearing only for the distribution and preservation of the species under
adverse conditions, '"'

Michael discovered that a hypopus was a development stage, sometimes but not
always present in the life cycle of mites. The hypopus formed by ecdysis from the proto-
nymph stage. After another molt, it changed to a deutonymph, The hypopus was flattened
and hardened, It was resistant to drought and heat that would easily destroy the other
development stages of the mites, Michael found that the formation of hypopi was not due
to unfavorable conditions, more hypopi seemingly being produced under ideal conditions,
The hypopus was not parasitic, but attached itself to insects and other animals apparently
for transportation,

Reuter (25) called the hypopus stage a ''deutonymph" and the stage commonly known
as the deutonymph was referredto as the ''tritonymph"’. The 'deutonymph" stage of Reuter
(Hypopus) was described by him as an active migratory form.

Eales (6) reported finding the hypopus form of T, longior, but made no observations
on its biology.

Schulze (32) found a Tenebrio molitor beetle with 700 hypopi of the species C.
rodionovi attached, After further work (33) on A. siro, Schulze reported two types of
hypopi, identified as Hypopus I and Hypopus II. The first was a motile form and the latter
was an inert form. Hypopus I was considered a primary form of Hypopus II, and was
less resistant to drying and cold temperatures than the latter. Oudemans (22) stated
that the Hypopus II stage described by Schulze was the hypopus of Acarus farris and not
A. siro, although it was conceded that the former species might be a degenerate form of
the latter. Schulze (34) refuted Oudeman's view.

Schulze (35) also studied the factors relating to hypopus formation and the changing
of the hypopus to a deutonymph in C, rodionovi. Some of the protonymphs, which were
morphologically distinct from the others, formed hypopi independently of environment.
Of the remaining protonymphs, many could be made to form hypopi by depriving them of
suitable food. Temperature and relative humidity were found to have no effect on hypo-
pus formation, Before a hypopus would molt into the deutonymph stage, environmental
moisture greater than when the hypopus formed was necessary, At a temperature of
80,4° F. or higher, 100 percent of the hypopi changed to deutonymphs within 45 hours,
while at 56. 8° F., only 37.5 percent had become deutonymphs after 20 days.

Belyaev et al. (2) found the hypopi of A, siro and T, longior to be abundant in de-
cayed seed with a 50-percent moisture content. When these hypopi were placed in media
with 18-percent moisture content, adults were present in 4 to 8 days, Sokolov (42) found
-hypopi numerous under similar conditions, He reported that hypopi appeared in numbers
only if the grain was moldy or very dirty.

Hora (10), working with G. domesticus, found that 50 percent of the protonymphs
formed hypopi under ideal conditions of 779 F. and 90 percent r.h, Hora's studies showed
the hypopus to be a resistant form, taking the place of the protonymph resting stage.
Hypopi gave rise to deutonymphs that developed into normal female or male adults.

The cause of hypopus formation was not discovered, but it was' found not to be the result
of abnormal environment or of overcrowding.

Debris collected from a stable by Jary (13) contained numerous mites. As the
samples dried, many mites went into a hypopial stage, and when reared to adults were
found to be A, siro. Jary (14) found frequent hypopus formation in Calaglyphus sp. reared
at 68° to 69, 8° F, In Eberhardia sp., they were less common under the same conditions.

41

Polezhaev (23) experimented with L. destructor to determine the cause of hypopus
formation, Hypopi were less abundant at 80 percent r.h, than at higher or lower humid-
ities. Removal of food for different lengths of time tended to check the appearance of
hypopi and caused increased mortality. Polezhaev disagreed with Hora's view that out-
side conditions do not affect hypopus formation, Further work (24) on hypopus formation
in L. destructor indicated that hypopi were scarce or absent under optimum conditions
for mite development and were more numerous as conditions deviated from the optimum,
Hypopi changed to deutonymphs only at temperatures above 53,6° F, At high temperatures,
ar.h, of 80 percent or higher was necessary for the transformation. Work with A. siro
showed no hypopus formation at any time when the temperature was from 35, 6° to 86° F,
or the r.h. was from 40 to 100 percent,

Zakhvatkin (47) stated that mite species fall into three classes with respect to
hypopus formation, One group of species produces a small but rather constant number
of hypopi. A second group of species always forms the hypopus stage. The third group
of species forms hypopi only under undesirable environmental conditions such as drying,
lack of food, deterioration of quality of food, and abnormal temperatures,

Ushatinskaya (44) studied the effect of temperature and r.h, on the formation of
hypopi in L, destructor, At 32° F., no hypopi occurred, and at 41°F., only a few. A
temperature of 50° F. produced 1.8 percent hypopi in 78 days and 29.1 percent in 200
days. With the exception of a few at 50° F., hypopi did not become deutonymphs unless
the temperature was 53,6° F, or higher. This caused an accumulation of hypopi at the
lower temperatures. At temperatures of 77° and 86° F., not more than 0.5 percent
hypopi appeared. A moisture content in the grain of 13,2 to 17.2 percent (57-84 percent
rh.) was necessary for hypopus formation, Hypopus formation occurred most often at
temperatures of 59° to 71. 6° F. and a moisture content of 16 to 16.3 percent (80 percent
T7hks) i

LITERATURE CITED

(1) Baker, E. W., and Wharton, G. W.
1952. An Introduction to Acarology. 465 pp., illus. New York.

(2) Belyaev, I. M., Shesterikova, M. N., and Popov, P. V.
1932. Materialen zur Forschung der Oelsamen Schadlinge bei Aufbewahren.
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(3) Buxton) PP.’ A.
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(4) Buxton, P. A., and Mellanby, K.
1934. The Measurement and Control of Humidity. Bul. Ent. Res. 25:171-175.

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1938. The Effects of Temperature and Certain Chemicals on Cheese Mites.
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(6)e Eales..iN..B.

1917. The Life History and Economy of the Cheese Mites. Ann. Appl. Biol.
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42

(7) Ewing, H..E., and Nesbitt, H. H. S.
1942, Some Notes on the Taxonomy of Grain Mites. Proc. Biol. Soc. Wash,
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(8) Gilyarov, M. S,
1941, The Feeding of the Granary Mites Tyroglyphus farinae L. and
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(11) Hughes, T. E.
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(19) Newstead, R., and Duvall, H. M.
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43

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HH;
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Vici Gre

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Weve

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46

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