/\^(S^\5- W(D;i
Bulletin 402
Cc
' I
September, 1937
A<S^
no.^a.
A Study of the Bulb Mite
(Rhizoglyphus hyacinthi Banks)
PHILIP GARMAN
Figiire 86. Section of infested bulb, and a mite greatly enlarged.
CONNECTICUT AGRICULTURAL EXPERIMENT STATION
BOARD OF CONTROL
His Excellency, Governor Wilbur L. Cross, ex-officio. President
Elijali Rogers, Vice-President Southington
Edward C. Schneider, Secretary Middletown
William L. Slate, Treasurer New Haven
Joseph W. Alsop Avon
Charles G. Morris Newtown
Albert B. Plant Branford
Olcott F. King South Windsor
Administration
STAFF
William L. Slate, B.Sc, Director.
Miss L. M. Bbautlbcht, Chief Clerk and Librarian.
Miss Katherine M. Palmer, B.Litt., Editor.
G. E. Graham, In Charge of Buildings and Grounds.
Analytical
Chemistry
E. M. Bailey, Ph.D., Chemist in Charge.
C. E. Shepard
Owen L. Nolan
Harry J. Fisher, Ph.D. \ Assistant Chemists
W. T. Mathis
David G. Waldbn, B.S.
Miss R. B. Hubbell, Ph.D., Biochemist.
Miss Janetha Shepard, 1 ^ , a ■ j j
V P Ryan f General Assistants,
Chas. W. Soderberg, Laboratory Assistant.
V. L. Churchill, Sampling Agent.
Mrs. a. B. Vosburgh, Secretary.
Biochemistry
H. B. Vickery, Ph.D., Biochemist in charge.
George W. Pucher, Ph.D., Assistant Biochemist.
L. S. Nolan, 1 „ , a ■ , j
T P Stickney / ^snerai Assistants.
J. Datillo, Laboratory Assistant
Botany
E. M. Stoddard, B.S., Pomologist, {Acting Botanist in Charge).
Miss Florence A. McCormick, Ph.D., Pathologist.
A. A. DuNLAP, Ph.D., Assistant Mycologist.
A. D. McDonnell, General Assistant.
Entomology
W. E. Brixton, Ph.D., D.Sc, Entomologist in Charge, State Entomologist,
B. H. Walden, B.Agr. \
M. P. Zappe, B.S.
Philip Garman, Ph.D. > Assistant Entomologists.
Roger B. Friend, Ph.D.
Neely Turner, M.A. J
John T. Ashworth, Deputy in Charge of Gypsy Moth Control,
R. C. Botsford, Deputy in Charge of Mosquito Elimination.
J. P. Johnson, B.S., Deputy in Charge of Japanese Beetle Control.
Miss Helen A. Hulsb
Miss Betty Scoville
Secretaries.
Forestry
Walter O. Filley, Forester in Charge.
H. W. Hicock, M.F., Assistant Forester.
J. E. Riley, Jr., M.F., In Charge of Blister Rust Control,*
Miss Pauline A. Merchant, Secretary,
Plant Breeding
Donald F. Jones, Sc.D., Geneticist in Charge.
W. Ralph Singleton, Sc.D.\ ^ . . , _ ....
Lawrence Curtis, B.S., f Assistant Geneticists.
Miss Elizabeth Williams, B.S., Research Assistant.
Mrs. M. C. Preston, Secretary.
Soils
M. F. Morgan, Ph.D., Agronomist in Charge.
H. G. M. Jacobson, M.S., 1 .... , - ,
Herbert A. Lunt, Ph.D., f Assistant Agronomists.
Dwight B. Downs, General Assistant.
Miss Geraldine Everett, Secretary.
Tobacco Substation
at Windsor
Paul J. Anderson, Ph.D., Pathologist in Charge,
T. R. SwANBACK, M.S., Agronomist.
O. E. Street, Ph.D., Plant Physiologist,
C, E. SwANSON, Laboratory Technician,
Miss Dorothy Lenard, Secretary.
* In cooperation with the U. S. D. A.
Printing by The Peiper Press, Inc., Wallingford, Conn.
CONTENTS
Introduction 889
Distribution of the Species 889
The Name of the Bulb Mite 890
General Description 891
Host Plants Infested and Resulting Injury 894
Life History 894
The dimorphic male 896
The hypopus 896
Migration 898
Tabular history 898
Other Mites Associated with the Bulb Mite 899
Enemies 900
Control Measures 900
Summary 902
Bibliography 903
Figure 87. The bulb mite {Rhizoglyphus hyacinthi Banks). 1. Proto-
nymph, enlarged about 80 times. 2. Larva, enlarged about 80 times.
3. Larva, sense organ of the ventral surface of the cephalo-thorax. 4.
Front tibia and tarsus of the female. 5. Fourth tibia and tarsus of male.
6. Egg, enlarged about 80 times. 7. Fourth tibia and tarsus of the female.
8. Front tibia and tarsus of the male. 9. Tritonymph, enlarged about 80 times.
10. Fourth tibia and tarsus of dimorphic male. 11. Deutonymphor hypopus,
enlarged about 80 times.
A STUDY OF THE BULB MITE*
{Rhizoglyphus hyacinthi Banks)
PHILIP GARMAN
Inspection of over a million bulbs in Connecticut during 1919 brought
to light the significant fact that nearly all shipments contained the bulb
mite, R. hyacinthi Banks. In many instances only a few infested bulbs
were found, but in others as high as 15 to 20 percent were apparently
destroyed. Shipments were, however, frequently delayed in transit, accord-
ing to reports, a state of affairs doubtless responsible for the poor condition
of many bulbs when they arrived at their destination. Botten bulbs, too,
are not always the result of mite infestation alone, there being several
other causes of rot and disease ; but the fact that mites are almost uni-
versally found in decayed bulbs has led to the present study of the life
history, habits and control of the pest.
Woods (38) claims that the Bermuda lily disease, caused in part by
mite infestation, is responsible for a yearly loss of 20 to 60 percent of the
entire crop where the plants are forced. Destruction of bulbs has also
been noted by many other American and European workers.
Hodson (17, 1928-29) studied the development of the bulb mite under
greenhouse conditions and concluded that it is not a primary pest of nar-
cissus, infesting injured or rotting bulbs rather than healthy ones. There
are still, however, conflicting views with regard to the importance of the
bulb mite, but it is well known that Tyroglyphidae in general are feeders
on decaying vegetable matter and fungi of various kinds. It seems prob-
able that the bulb mite is most serious in storage or in semi-tropical
countries where breeding conditions are more favorable than in this
locahty. Ogilvie (25. 1935) concluded that the bulb mite frequently gets
a foothold in decayed or injured tissue and may then extend its activity
to healthy tissues alongside. The ability to penetrate into the stem of
growing Bermuda lilies indicates that it may, under certain conditions,
affect the growing plant. The work of Hodson, however, does indicate
that healthy plants ordinarily have little to fear from the bulb mite alone.
Where mites become abundant in storage, there seems to be agreement
that they hasten decay and are, therefore, undesirable. Fortunately,
proper storage facilities, as well as treatments for such pests as bulb flies
and nematodes or eelworms, destroy the mite satisfactorily or prevent
its development.
Some injurious effects of the species in Connecticut were described in
the report of the State Entomologist for 1915 (2, PI. XIV) when 3,000
Easter lilies were destroyed.
DISTRIBUTION OF THE SPECIES
The bulb mite has been reported in shipments to various states and to
Canada. Foreign shipments of bulbs to Connecticut come mostly from
France, Belgium and Holland, but what is apparently the same species
was found in one shipment received from Japan. It has also been reported
in bulbs received from the Bermuda Islands and thus seems to have a
fairly wide distribution.
* Revision of Conn. Agr. Expt. Sta. Bui. 225.
890 Connecticut Experiment Station Bulletin 402
THE NAME OF THE BULB MITE
Banks (1), in 1906, listed under the name of Rhizoglyphus hyacinthi
Boisduval a species of mite which he found in bulbs. Since that time
Americans have followed the name hyacinthi in preference to the name
echinopus of European authors. Michael (23), however, places hyacinthi
as a synonym of echinopus, with the remark that hyacinthi of Boisduval
is a nomum nudum being listed without description. Michael is correct in
this statement, since the original description given by Boisduval is very
meager and is not sufficient for purposes of identification. However, the
description of echinopus given by Fumxouze and Robin (10) shows that
the latter may also have considered a different species; for the species
in hand differs from it (and also Michael's description) in important
particulars.
The most striking of these characters are the chitinous thickenings on
the fourth pair of legs, which occur both in normal and heteromorphic
males. Michael states that the only species bearing this character is R.
crassipes Haller, which was originally described as an American species
(16), but crassipes differs in other particulars from our species, and we
are forced to conclude that either the chitinous thickenings have been
overlooked or the species may be different from all others described. In-
asmuch as Michael (1. c, p. 83) says emphatically that "there are not
any suckers on the leg of the male of any species except R. crassipes
Haller" we are able to conclude that he must have examined the species
which he described, for this particular character. Examination of material
from the U. S. National Museum shows chitinous thickenings on the
fourth pair of legs in R. hyacinthi and R. rhizophagus. The rather frequent
presence of the dimorphic male excludes the species in hand from rhizo-
phagus and refers it to hyacinthi. As already intimated, a search through
Boisduval's works has revealed no adequate description of this species
and either his name, hyacinthi, must be disregarded, or the authority
changed from Boisduval to Banks. The latter course is to be preferred
and the name Rhizoglyphus hyacinthi Banks instead of Rhizoglyphus hya-
cinthi Boisduval should be used, since Boisduval's name cannot be con-
nected with any known species.^
For convenience, the description given by Boisduval is quoted here-
with. Bank's description of the species is found in Bur. Ent., Tech. Ser.
Bui. 13, p. 21, 1906 (pi. V, fig. 49).
Description by Boisduval
Entomologie Horticole p. 86: 1867
"Nous ne trouvons mentionne nulle part Vacarus de la Jacinthe; nous
ne Savons pas s'il n'a pas deja ete observe par quelque naturaliste. Nous
lui donnons le nom provisoire d'acarus des Jacinthes Acarus hyacinthi.'"
1 In spite of the information presented, it is quite possible that the common species in Europe and
America are identical. Until proven that the two are the same, the author prefers to retain the name
hyacinthi. For practical purposes, however, they may be considered the same.
General Description 891
GENERAL DESCRIPTION
Egg (Fig. 87, No. 6): The egg is ellipsoidal, white and semitransparent; .12 by
.07 ram. in size.
Larva (Fig. 87, No. 2): Small, white, somewhat ovoid in shape; genital suckers
absent. Cephalo-thorax with two long setae on the frontal margin above, and two
near the caudo-lateral angle; no minute bristles between the latter as in the adult;
venter of the thorax with a clavate sense organ (Fig. 87, No. 3) between the bases of the
first and second coxae on each side and small setae mesad of these; front tarsi with
strong spines as in the adult, but the clavate hair much longer than the spine imme-
diately beyond it; tip of the tarsus with three slender setae; front tibiae with the usual
long setae on the dorsum, the patella (third segment from end beginning with tarsus)
each with two shorter setae on the dorsum as in the adult. Abdomen with one pair of
legs, the tarsi of each of which bears a long, heavy spine and longer setae on the dorsal
surface and three spines on the ventral; tarsal claw very stout; tibiae each bearing
a single long seta on the dorsal surface ; lateral margins of the abdomen with four setae
on each side and a pair near the anal opening.
Size shortly after emergence from the egg, .15-.2 by .1 mm.; full grown, .25 by .15 mm.
Protonymph (Fig. 87, No. 1) : Similar to the larva in size and shape but larger and
provided with four pairs of legs instead of three; rostrum as in adult; cephalo-thorax
as in adult ; with two long setae on the frontal margin of the dorsum and two near the
caudo-lateral angle; no minute setae between the latter; the front tarsi have, in com-
mon with the adult, a minute clavate hair at the base and to one side of the large clavate
hair; and between the larger clavate hair and the spine (immediately beyond) is a
smaller spine about one-fifth the length of the latter; tip of front tarsi with three slen-
der setae each. The fourth pair of legs has only one seta at the tip of the tarsus and
there is no dorsal spine on that segment; however, there is a strong lateral spine and a
ventral spine. Judging from the spines and setae on the tarsi of leg three in the larva
and the protonymph, the fourth pair of legs of the protonymph must grow in behind
the third pair of the larva.
This stage is most easily distinguished from the tritonymph, which it resembles
more closely than other stages, by the appearance of the genital suckers. In the proto-
nymph only two make their appearance, while in the tritonymph there are three or
four (see Fig. 87, No. 5). There is also some difference in the tarsi of the fourth pair of
legs, the latter possessing no dorsal spine in this stage.
Length full grown, about .4 mm.; width about .2 mm.
Deutonymph or hypopus (Fig. 87, No. 11): Oval in shape, dorsum convex; venter
flat; color brown, the body heavily reinforced throughout with chitin. Rostrum
apparently reduced to a small cylindrical projection entirely covered by the cephalo-
thorax; distal end of rostrum with two long setae, and a smaller one at the base of
each. Mouth parts wanting; cephalo-thorax with two long setae on the front margin
placed closely together, and about the same length as the long setae of the rostruin;
legs for the most part without the heavy spines of the adult, the latter replaced in
most cases by setae; tarsal claws long, curved rather sharply; tarsi of first pair of legs
with four slender setae at tip and two near middle of ventral surface. There is
also a heavy spine on the ventral surface; a large clavate hair nearly half as long as the
segment, and a smaller clavate hair and smaU seta on caudal surface near the larger one.
In front of the larger clavate hair there is also a long seta; front tibia with a long seta
on dorsum and a single spine on each side; patella with a single seta at tip instead of
two, as in all other stages. Abdomen with conspicuous expulsory vesicles on either
side; margin composed of thick, heavy chitin, which shows prominent stria tions under
magnification; venter with conspicuous suckers as in Fig. 87, No. 11, one on each side
of the anal opening, two caudad of this, then a row of fom-, and finally two more. Sur-
roimding the eight caudeJ suckers is a squarish ring which is thickened at each of its
four corners, making it appear as if four additional suckers were present; conspicuous
lines of chitin on the venter, extending cephalo-mesad from the anal opening and each
coxa of legs III and IV; third and fourth pairs of legs short and usually hidden by the
overhanging body wall when viewed from above; tarsi with four setae and two heavy
spines at tip; tibiae with a long seta near tip, on dorsum; margin of abdomen with
four, minute marginal setae.
Length, .2-.3 mm. Width, .13-.18 mm.
892 Connecticut Experiment Station Bulletin 402
Tritonymph (Fig. 87, No 9) : Color white, translucent or semi-opaque, legs brown
or tinged with pink.
Rostrum and cephalo-thorax agreeing in nearly all particulars with the adult female.
Abdomen as in the adult as regards setae; but the genitalia undeveloped; the genital
suckers consist of four indistinct suckers closely approximated (Fig. 87, No. 9).
Length .5-.6 mm., width .3-3.5 mm.
Adult (Fig. 88, Nos. 12-15; Fig. 87, Nos. 4, 5, 7 and 8): Color white, body some-
what transparent; legs, epiinera and rostrum brown, sometimes with a pinkish hue.
Rostrum with large mandibles, which are chelate, maxillary palpi with two distinct
segments closely joined to the rostrum and a very small projection at the tip, which
may represent a third segment. Each of the longer segments with a minute seta, and a
longer seta on each maxilla; cephalo-thorax narrowed rapidly in front, the sides gently
curved, the front margin with two long setae extending beyond the rostrum and placed
closely together; near the caudo-lateraJ angles of the dorsum are also two long setae
between which are two usually minute hairs; venter of cephalo-thorax with conspicu-
ous epimera, the front epimera being united on the mesal line; between the first and
second epimera on each side there is usually a small seta ; first two pairs of legs thicker
than the last two, 5-segmented, the tarsi of the first pair provided with spines and
setae as follows: A large clavate sense organ, near the proximal margin on the dorsum,
and a large heavy spine just distad of this; a much smaller clavate hair at one side of
the larger sense organ, about half its length; between the larger clavate sense organ
first mentioned and the spine, distad of it, is a smaller spine about one- third its length;
at the tip of the tarsus above there is also a large spine with three setae surrounding
it, one of which is much smaller than the rest; ventrad of the tarsal claw there are
usually three or four heavy spines, grouped together, and another proximad of these;
there is a long seta near the proximal spine and a very inconspicuous one on the opposite
surface of the tarsus; tarsal claw not sharply curved; tibia with a long seta on the
dorsum near the distal end which is often as long or longer than the tarsal segment;
there is a single stout spine on the caudal and ventral surface of this segment; the
patella has two closely placed setae near the distal margin of the dorsum and the femur
has a single long seta on the ventral surface; the second tarsus is essentially the same
as the first, except that the smaller clavate hair or sense organ, and the small spine
(between the larger hair and the spine immediately distad) are wanting; one seta is
also lacking from the tip; the third and fourth pairs of legs lack the clavate sense organs
and are different in the two sexes. In the female and normal male the third pairs of
legs are similar; there is a long thick spine at the tip of the tarsus, above and below
which is a long slender seta; on the caudal surface of this segment there is also one seta
and there is a spine on the opposite surface; the ventral surface has a spine shortly
distad of the middle, and a group of about four ventrad of the tarsal claw; the latter is
sharply hooked. The third pair of legs of the dimorphic male is much thicker than the
third pair of the female or normal male. There are four long setae at the tip, and the
tarsal claw seems to be fused with the tarsal segment (Fig. 87, No. 10); the fourth pairs
of legs differ in the two sexes but are the same in dimorphic and normal males. In the
female there is a distal spine on the tarsal segment just above the claw and one lateral
(caudal surface) and one ventral spine in addition, besides a group of three just be-
neath the claw. There are usually three setae, one above and another below the distal
spine, and one lateral seta; in the male the distal dorsal spine is wanting, being re-
placed by a chitinous thickening sometimes called a sucker; proximad of this is still
another thickening and between the two a single seta; the segment possesses the usual
number of spines below the claw on lateral and ventral surfaces (Fig. 87, No. 7).
In the female the lateral surfaces of the abdomen are provided with about five
setae on each side; the ventral surface with three minute setae on each side of the
genital opening and one between the third and fourth coxae, a small one in front of
and to one side of the third coxae, and a long one on each side of the anal opening;
the genital opening forms an inverted V-shaped figure with two genital suckers on
each side (Fig. 88, No. 14) ; the dorsum has five setae on each side, of which the caudal
pair is the longest.
In the male there are the usual five setae on lateral and caudo-lateral surfaces of
the abdomen and one minute seta between the third and fourth pairs of legs on the
ventral surface, and a smaller one in front of and to one side of the third coxae; genital
opening as in Fig. 88, No 12, with two genital suckers on each side. Rehind the genital
opening are found two larger disc-like suckers, with a minute seta, caudad and ceph-
alad, and usually a row of four longer ones beyond the suckers; setae of the dorsum
as in the female.
General Description
893
Figure 88. Adult bulb mite (Rhizoglyphus hyacinthi Banks), enlarged
80 times. 12. Male, ventral view. 13. Female, dorsal view. 14. Female,
ventral view. 15. Male, dorsal view.
894 Connecticut Experiment Station Bulletin 402
Variations: There seems to be some variation both in the length of the setae
of the legs and body and also in the thickness of the tarsal segments. Of seventeen
individuals, however, measured with the micrometer, the ratio of width to length of
tarsus IV ranged from 1-1.6 to 1-2.5, both sexes being examined. There is also a great
variation in the depth of the depressions on the dorsum of the adult, they being almost
obliterated in some individuals.
Length, female .47-.95 mm.; male .5-.6 mm. Width, female .3-.4 mm.; male .25-
.3 nun.
HOST PLANTS INFESTED AND THE RESULTING INJURY
Bulbs of narcissus (Plate II, a, b), hyacinth, tulip, crocus, gladiolus,
amaryllis, Easter lily and other plants are infested by the bulb mite.
In the laboratory the mite has been reared on onions and potatoes, and is
probably capable of subsisting on almost any tuber or bulb. Its common
occurrence in narcissus and lily bulbs may be due to the fact that these
olTer least resistance to attack since the scales are loose and the mites
find it easy to penetrate to the interior. Tulips are least injured, owing to
their outer skin and tight-fitting scales which leave no place for the mites
to enter. Hyacinths seem to be less easV to penetrate than narcissus, while
onions, artificially infested with mites, were not injured unless they were
partly rotten or bruised in the beginning.
That the mites are able to feed on healthy tissue would seem to be
evident both from numerous references to this particular ability by vari-
ous writers and from the experience of those connected with this office
in the case of the Bermuda lilies already mentioned. A small number of
tests have been conducted by the writer in which mites entered and fed on
growing narcissus bulbs. In these, rotten bulbs containing mites were
placed in pots of soil just below healthy ones and the mites readily left
the rotten and entered the healthy bulbs. Plate I, b shows one of the
infested bulbs.
Welsford (37) claims that the rot of narcissus bulbs is transmitted by
the minute worm or nematode, Tylenchus dipsaci Kuhn, and not at all
by the mite, Rhizoglyphus echinopus. This worm, however, has not been
found in many of the rotten bulbs examined, while in few cases have
mites been absent from diseased examples. Welsford himself admits that
the bulb mite does a great deal of damage, but he does not consider it
equal in importance to the nematode as a carrier of disease.
At the present time, the eelworm does not appear to have the importance
in this country that is attached to it in England. Likewise, as already in-
dicated, the bulb mite is not regarded as a major pest but merely as an
agent hastening decay. That narcissus bulbs are able to grow satisfac-
torily even where the mites are numerous has been demonstrated. It is
believed, however, that losses from mite attacks will be found much
greater in storage than elsewhere, and injured or rotten bulbs in lots to be
stored should be eliminated as a primary means of preventing further loss.
LIFE HISTORY
Few people in America seem to have studied the life history of the
bulb mite. Hodson (17) gives a good account of echinopus in England,
describing the life history at a temperature of 60 ° F. Yagi (39) published
a prehminary note on the life cycle in 1919. In this, he makes known
the following facts: "The mite moults twice and the duration of one
Life History 895
generation is about ten days in August, and twenty in June. Tempera-
ture is the chief factor in this variation and has an important effect on
the embryonic development — the number of eggs laid by one female varied
from 9-59, each being dropped singly on the surface of the bulb. The
larva is sluggish and bores in the tissues of bulbs and grape vines. The
adults mate within two to eight hours after reaching maturity and ovi-
position begins on the day of mating. The hfe of the female is about two
to four weeks in summer while that of the male is shorter."
Michael (23) reports one case in which he reared echinopus from egg to
adult in 33 days. He observes three moults instead of two as noted by
Yagi. Careful studies by the writer indicate that hyacinihi moults three
times instead of twice, thus confirming Michael's statement in this regard.
When hypopi appear, however, four moults occur instead of three. The
life period obtained at room temperature 60 to 75° F. (averaging about
68°) varied from 17 to 27 days; with temperature ranging from 70 to
80° F., 9 to 13 days. The mite becomes torpid at 50 to 55° F. and at
about 95°. The air in which the mites lived during the time they were
observed was kept as near optimum humidity as possible, which condition
was judged largely by daily observance of the amount of moisture con-
tained in the lens paper with which each cell was provided.
The period of incubation (temperature averaging 68° F.) lasts from
four to seven days. A six-legged larva emerges from the egg and the mite
lives in this condition three to eight days. The last day or so of this period,
sometimes two days, is spent in a torpid or quiescent state during which
time the larva swells so that the separating line between the thorax and
abdomen is lost. On moulting, the larva acquires two additional legs,
making eight in all. The next period, which may be known as the proto-
nymph,^ lasts two to four days, after which follows a second quiescent
period of about two days and a second moult takes place. This time there
is no increase in the number of legs or much change in form unless a
hypopus, or resting stage, is produced. If normal in form, the mite, now
known as the tritonymph,^ again goes into the quiescent state which lasts
one to two days, and moults. The adult mite then emerges. If, however,
the hypopial state appears after the second moult, the mite may rest for
one or two weeks or more, afterwards moulting and giving rise to the tri-
tonymph. The latter then moults and the adult mite emerges as before.
Adults mate a day or so after becoming mature and the eggs are soon
laid, beginning with a few daily at first and later increasing in number
up to six or eight. Two females observed laid 10 eggs per day for four
successive days, but this is rather unusual. The number of eggs laid has
been found to vary considerably, some females laying more than 100,
others laying only a few. One individual laid 130 eggs in all, while one
other laid 81, and still another 59. The males usually die shortly after
mating, but if kept separate have been observed at this laboratory to live
for more than two months. Females also live from one to two months or
more if properly fed and cared for.
The following shows the course of the life history:
Cycle in which hypopial stage is skipped
Egg — larva — first nymph — third nymph — adult female.
Egg — larva — first nymph — third nymph — dimorphic male adult,
normal male adult.
' The hypopus is regarded as the deutonymph, and is frequently interpolated between protonymph
and tritonymph.
896 Connecticut Experiment Station Bulletin 402
Cycle with hyjxjpial stage
Egg — larva — first nymph — hypopus — third nymph — adult female.
Egg — larva — first nymph — hypopus — third nymph — dimorphic male adult,
normal male adult.
The Dimorphic or Heteromorphic Male
The dimorphic male with enlarged third pair of legs (Figure 87, No. 10)
has been thought by some to be a distinct species, but it has been defi-
nitely proven by others to be merely a form of more or less infrequent oc-
currence. In one lot of mites examined 36 males were seen without en-
countering a single dimorphic form. In other lots the males with and
without enlarged legs appeared in about equal numbers. The dimorphic
males breed freely and the offspring consists of both females and normal
and heteromorphic males. One specimen was seen with an enlarged third
leg on one side and a leg of normal size on the other. The exact function
of the dimorphic male is not clearly understood, nor do we understand
the causes which bring about such differences.
The Hypopus
Rather complete studies of the hypopus of echinopus have been made
by Michael and other European authorities, and it is now regarded as a
normal period in the life history of the mite. Briefly explained, it is a
form similar to some of its ancestors which is produced from time to time
from no apparent reason other than a strong tendency to revert to type
and "is a provision of nature for the distribution of the species occurring
irrespective of adverse conditions." (22) Hodson (17, p. 190) more re-
cently concludes that slightly unfavorable conditions, except low tem-
perature, may cause development of this sta,ge, but admits a lack of ade-
quate evidence on the subject. Hypopi were more abundant in his cultures
during May and September. Notwithstanding, the fact remains that it
is often impossible to distinguish between favorable and unfavorable con-
ditions, and it seems certain that conditions promoting their development
are not always at hand. The following notes relate to the development
of the hypopus.
First of all, it has appeared that hypopi are much more numerous in
jars where the bulbs are rotted enough to leave them in a wet, sticky
condition. Hypopi are produced in dry as well as moist cells, but more
rapidly and frequently more abundantly in the moist cells. This was
demonstrated by use of a moisture gradient consisting of four hanging
drop slides with small cells, clamped to a larger piece of glass and with a
sheet of lens paper between ; one end of the gradient being placed in moist
sand, and each cell provided with a single pair of mites and the necessary
food. The following shows the results of three tests with the gradient
describsd. Cell No. 1 in each case was in contact with moist sand; 2, 3
and 4 farther away in the order mentioned. These tests were then re-
peated with similar results.
Life
History
Percent
No. of ceU
No. of mites
of hypopi
Food used
1
111
27
Unfermented
dry narcissus.
3
83
7
"
4
90
0
Fermented
2
39
82
hyacinth.
3
14
50
"
4
105
0
Fresh
1
213
25
narcissus.
2
60
10
"
3
21
0
"
4
60
0
*'
897
Date
Begun Examined
May 14 July 7
July 24 Sept. 9
On April first a small, tightly corked bottle was provided with about
an inch of moist sand and a number of slices of potato previously infested
with the bulb mite. These mites did not multiply rapidly but reproduced
fairly well, and 100 individuals were counted on June 8, without encoun-
tering a single hypopus. Little or no fermentation took place in the bottle
until after this date and most of the eggs were laid on the outside of the
potato and were fairly dry. However, where the potatoes were in contact
with the sand, there was considerable moisture surrounding the developing
mites. Only one hypopus was seen in the bottle until July 1. During
the latter part of July mold obtained a foothold on the potato but the
mites continued to breed, many of them being covered with a wet, sticky
film. However, even under such conditions, less than 1 percent of hypopi
developed, as was seen by examination on September 9. In order to test
the natural ability of the strain on potato to produce hypopi, mites
were transferred to glass cells with narcissus or hyacinth at several differ-
ent periods during the course of the experiment. Hypopi were produced
abundantly in practically every case, the percentage varying from 10
to 80 percent. In this bottle and five other similar ones made from it,
hypopi did not begin to appear in numbers until about October 25, making
a period of some six months when they did not develop. It is difficult to
explain the appearance of the hypopus in small cell transfers, but it seems
as if some necessary change in conditions must have taken place.
Hypopi developed in light and dark, when fed on decayed and sound
food, in moist and dry cells and apparently when warm and cold. They
also developed about equally well when the food was covered with small
amounts of sugar, alcohol 2 percent and acetic acid 1 percent.
Michael used many experiments to try to induce certain species of
Tyroglyphids to develop without producing hypopi, but failed; and he
concluded that hypopus is a normal stage in their development. Not-
withstanding, in the case of mites like the bulb mite, in which all indi-
viduals do not pass tlirough the hypopus stage, it seems hazardous to
ascribe such a phenomenon entirely to the inherent atavistic tendency or
natural habit of the individuals. It is well known that in a somewhat
similar life cycle found in aphids, reversion to the sexual forms which are
more commonly skipped are induced largely by changes of weather and
food. Some species of aphids, moreover, may be reared continuously
without reversion, when proper conditions of moisture, temperature, etc.,
898 Connecticut Experiment Station Bulletin 402
are maintained, and it seems as if something similar must be true of the
mites under investigation, caused by factors which we have not yet learned
to recognize.
The length of the hypopus stage under favorable conditions is usually
a bout one to two weeks.
Migration of the Species
The hypopus is much more active than the remaining stages in the life
cycle of the mite, and has a tendency to wander from place to place. It
will also attach itself to any moving object. At the time when hypopi
become numerous, the bulbs are commonly well rotted and infested by
numerous small fly larvae, one of which (Scatopse pulicaria Loew)
(Plate I, a) was found in large numbers. The flies of this species were fre-
quently found to be literally covered with hypopi attached by means of
their ventral suckers. Other hypopi were seen riding peacefully on the
backs of predaceous mites, and still others have been found attached to
lepidopterous larvae. The mite is thus afforded an admirable means of
transportation, of which it is capable of taking fufl advantage because of
its structure and habits.
The tables below show the length of the various stages as determined at
this laboratory.
Tabular Life History of the Bulb Mite
LENGTH OF EGG STAGE
Length of stage days
Number observed
Dates
1919
Temperature 60°
-75°
F.
7
8
Sept. 29-Oct. 6.
63^
3
Oct. 10-Oct. 17.
7
4
Oct. 10-Oct. 17.
6y2
4
Oct. 10-Oct. 17.
1920
Temperature 70°
-80°
F.
4
2
July 15-JuIy 19.
3
2
July 16-July 19.
4
3
July 16-July 20,
4
8
July 16-July 20,
LENGTH OF LARVAL STAGE
Length of stage days
Number observed
Dates
1919
Temperature 60°
-75°
F.
8
1
Oct. 3-Oct. 10.
6
1
Oct. 6-Oct. 11.
7
2
Oct. 6-Oct. 12.
6
2
Oct. 17-Oct. 21.
6
1
Oct. 17-Oct. 22.
6
2
Oct. 17-Oct. 22.
6K
2
Oct. 16-Oct. 21.
1920
Temperature 70°
-80°
F.
2
2
July 19-July 21.
3
8
July 20-July 23.
3
2 ■
July 18-July 21.
4
1
July 19-July 23.
5
3
July 19-July 24.
other Species of Mites 899
LENGTH OF FIRST NYMPHAL STAGE (PROTONYMPH)
Length of stage days Number observed Dates
1919
Temperature
60°-
75° F.
3
1
Nov. 10-Nov. 13
3
1
Nov. 12-Nov. 15
4
1
Nov. 11-Nov. 15
3
1
Nov. 8- Nov. 11
4
1
Nov. 8-Nov. 12
8
1
Nov. 16-Nov. 24
5
1
Nov. 19-Nov. 24
3
1
Nov. 20-Nov. 23
2
1
Nov. 20-Nov. 22
1920
Temperat
ure
70°
-80° F.
2
1
July 21-July 23.
2
1
July 21-July 23.
2
1
July 21-July 23.
1
2
July 21-July 22.
2
2
July 21-July 23.
LENGTH OF HYPOPUS STAGE (DEUTONYMPH)
Length of stage days Number observed Dates
1920
Temperature 65°-75° F.
12
7
5
7
13
March 15-March 27.
March 29-April 5.
April 17-April 22.
April lO-April 17.
April lO-April 23.
LENGTH OF THIRD NYMPHAL STAGE (TRITONYMPH)
Length of stage days Number observed Dates
1919
Temperature 60°-75°
F.
4
1
Nov. 15-Nov. 19
3
1
Nov. 11-Nov. 14
4
1
Nov. 12-Nov. 16
3
1
Nov. 24-Nov. 27
3
1
Nov. 23-Nov. 26
4
1
Nov. 22-Nov. 26
1920
Temperature 70°-80°
F.
3
1
July 23-July 26.
3
1
July 24-July 27.
2
1
July 25-July 27.
3
1
July 24-July 27.
2
1
July 23-July 25.
2
2
July 22-July 24.
2
1
July 23-July 25.
Variations obtained in length of life cycle 9-29 days (with hypopus absent from the
cycle) ; with hypopus included 14-42 days.
OTHER SPECIES OF MITES ASSOCIATED WITH THE BULB MITE
Several predator mites and the Tyroglyphid, Histiostoma rostro-serratuSy
are often associated with the bulb mite. In addition, Rhizoglyphus rhizo-
phagus is sometimes found as well as other closely related species. His-
tiostoma rostro-serratus occurs frequently, but seems to flourish in wet,
rotten bulbs and has not been observed to feed on healthy tissue. The
900 Connecticut Experiment Station Bulletin 402
small hypopus of this species is produced abundantly and attaches itself
to Rhizoglyphus or any moving mite or insect. When observed feeding,
the adult Histiostoma is much more granular or opaque in appearance
than the bulb mite and often quite light in color. The predator mites
commonly encountered belong to the superfamily Parasitoidea, being rep-
resentatives of the Parasitini or Laelaptini. Hodson identified one of the
species occurring in England as Hypoaspis sp., but at least four different
species have been sfeen here.
ENEMIES
All the mite predators observed are brown in color and very active
when temperatures permit. In one box of bulbs containing about one-
fourth bushel, these enemies became very numerous and were seen running
about over the bulbs like ants. Doubtless they had destroyed many bulb
mites. In another case, a Mason jar containing bulb mites was entirely
cleared of them in about a month after the predaceous species was first
noticed.
The small Cecidomyid fly, Lestodiplosis sp.,^ was also found feeding upon
the bulb mite. The larvae is a small, pinkish maggot which crawls about
among the mites and feeds on them. It is about 1 mm. long.
CONTROL MEASURES
Morphological studies show that the mite has no trachael system and
cannot be killed, theoretically, by ordinary fumigants. Ewing (7) demon-
strated that 4.1 ounces of potassium cyanide per 5,470 cubic feet, or 1
ounce per 133 cubic feet of air space was insufficient to kill the bulb mite.
At this laboratory, fumigation with carbon disulfide, 1 ounce to 100 cubic
feet, in an air tight container, required 48 hours to obtain a good kill.
Mites on the interior of the bulbs were not killed even with this length
of exposure. Sorauer (29) recommends for use against the mite, R. echino-
pus, a 48-hour carbon disulfide fumigation or immersion in tobacco extract.
Forty percent nicotine sulfate, 1-400, with the addition of soap, killed
only 7.1 percent in tests conducted here. Fir tree oiP was considerably
more efficient, killing 60 to 90 percent in some instances, while in bulbs
soaked in water heated to 55° F., nearly 100 percent were killed. Woods
(38) treated bulbs with mercuric chloride 1-1,000 and 1-2,000, formalin
1-1,000 and 1-2,000, without success. A good kill, however, was obtained
by the writer with formalin heated to 50° C. (122° F.), the bulbs being
left for a period of 10 minutes. Nicotine sulfate, 1-400, heated to 50° C,
and nicotine oleate heated to 50°, were also very successful acaricides. In
all cases, careful observations were made on the hypopus because of its
greater resistance, and the mites were examined daily for three days
after treatment to be sure of results. Paradichlorobenzene was tried by
Ogilvie (25) with some success when used at the rate of 3 grams per cubic
foot for 36 hours. He reports that the treatment kills mites in the interior
as well as the exterior of the bulbs. Nothing is stated by him regarding
action of this material on the bulbs themselves.
1 Determined by Dr. E. P. Felt.
' No longer available.
Control Measures 901
Since the above experiments were reported, the hot-water treatment
has come into use for bulb pests in generaL Milbrath (24, 1925), however,
reported that early and late treatments of bulbs even at the recommended
(9, 1926) temperatures, 110-111.5°, were sometimes unsatisfactory because
of their effect on flowering. Weigel (35, 1928) confirmed Milbrath's experi-
ments and states that hot-water treatment in early August is better than
treatments September 1, October 1, or later. He reports further that
temperatures above 115° F. reduce the number of flowers in the spikes of
paper-white narcissi. It is evident also from the work of Ramsbottom and
Van Slogteren that difficulties of a similar nature were encountered in
Europe, for Van Slogteren states that the hot-water treatment is not
entirely successful on hyacinth (113-115° for 24 hours), and Ramsbottom
(26) states that treatment at 110-111° for three hours may be injurious if
applied before the flower embryo forms. He considered August and Sep-
tember as safe months for this operation. Van Slogteren (31c, p. 157)
stated in 1923 that "the results of the treatment will vary greatly on the
time of the treatment and the developmient of the bulbs." He recognized
the efi'ects upon the flowers and stated that much depends "on the way
the dry bulbs have been kept before and after treatment". He maintained
that the damage from hot-water treatments can be corrected by holding
the bulbs a longer period of time in a "heated bulb house", where develop-
ment takes place slowly. Apparently realizing the dangers of hot-water
sterilization, growers of Wisconsin, as reported by Chambers (4, 1930), were
able to sterilize thousands of bulbs without harmful eff"ects. These treat-
ments were made the last week in August and the first week in September.
More recently there has developed an interest in cyanide and carbon
disulfide fumigation for various bulb pests. Also, the vapor heat treatm.ent
has been revived (18, 1932) and, from experimental evidence thus far pre-
sented, appears to be more successful than the hot-water treatment be-
cause of less injury to the developing flowers. This method consists of
heating the bulbs in a container, using steam instead of hot water and
regulating it with a thermostat. Our experience with this treatment indi-
cates that mites are readily killed in all stages with temperatures of 111
to 114° F.
The hot-water treatments described have been tried by us with com-
plete success as far as the mortality of the mites is concerned, and the
results of others have been confirmed regarding the periods when injuries
to the bulbs are likely to result from the treatments. Short treatments at
relatively high temperatures were successful in the original experiments,
partly because of the favorable time M'hen the experiments were conducted.
The shorter exposures are not recommended for control of nematodes.
Tests with the lower temperatures and longer immersion periods indicate
that retardation and injury often result even with lower temperatures if
used at unfavorable seasons, or if the bulbs are not handled correctly before
or after treatment. In experiments covering this point during 1936 and
1937, afl paper-white narcissi heated in January to 110° F. for two and one-
half hours, 115° F. for one horn-, and 120° F. for one hour failed to bloom,
whereas 30 to 60 percent of the bulbs treated in September produced
flowers. Conditions in the house after forcing was started were not entirely
satisfactory, but there is enough difl'erence in the figures to show the value
902 Connecticut Experiment Station Bulletin 402
of fall treatments. In this connection, Van Slogteren's observations above
should be carefully noted. For convenience, the different practises for
control of the bulb mite are given below.
Unsuccessful Treatments
1. Hydrocyanic acid gas (HCN), the gas obtained by using 1 ounce potassium cyanide
to 133 cubic feet of air space (7).
2. Vacuum fumigation with HCN.
3. Carbon disulfide, 1 ounce to 100 cubic feet — 24-hour fumigation.
4. Formalin, 1 part to 1,000 parts water, and 1 part to 2,000 parts water — cold.
5. Nicotine sulfate, 1 part to 400 parts water, plus soap, 2 pounds to 50 gallons— cold.
6. Mercuric chloride, 1 part to 1,000 parts water, and 1 part to 2,000 parts water — cold.
7. Naphthalene fumigation in paper bags at temperatures prevailing in common storage.
Partly or Entirely Successful Treatments
1. Paradichlorobenzene, 3 grams per cubic foot — •36-hour treatment.
2. Carbon disulfide, 1 ounce to 100 cubic feet — 48-hour treatment.
3. Nicotine sulfate, 1 part to 400, heated to 50° C. (122° F.) for 10 minutes.
4. Formalin (2 percent) heated to 50° C. for 10 minutes.
5. Hot water, 50° C. — bulbs immersed for 10 minutes.
6. Hot water, 43.5° C. (110° F.)— bulbs immersed for 2.5 hours.
7. Vapor heat. 111 to 115° F., averaging 113° F., for 2 hours. (Reported to be effective
with 30 minutes to 1 hour exposures.) (18, 30)
Practises of Value in Getting Rid of the Mites
1. Proper care and fertilization of growing plants (see 13, 15).
2. Care in handling after the bulbs are dug in order to prevent bruises, broken scales, etc.
3. Selection of bulbs to be planted or stored, all soft and rotten bulbs to be discarded.
4. Cold storage, 33 to 35° F., to prevent multiplication of mites while stored.
SUMMARY
(1) The bulb mite may injure growing bulbs under some conditions.
Ordinarily it is not a serious pest of narcissus.
(2) The life cycle may be completed in less than a month (9 to 29 days)
or may be extended to a month and a half if adverse conditions prevail.
(3) It is spread from place to place chiefly by means of the hypopus,
which clings to small flies emerging from the decayed bulbs.
(4) Methods commonly employed for controlling mites consist of hot
water immersions at 110 to 111.5° F. for two and a half to three hours.
Difficulties lie in the selection of the proper time for treatment, and in
handling the bulbs correctly before and after. A promising alternative
consists of vapor heat treatment with controlled temperatures. The tem-
peratures may apparently be somewhat higher than those used in the hot
water method, without injurious effects. Short exposures at a fairly high
temperature employing water, or water with nicotine sulfate, have proven
successful insofar as controlling bulb mites is concerned.
Bibliography 903
BIBLIOGRAPHY
1. Banks, N. Revision of the TyrogJyphidae. U. S. D. A. Bureau Entomology,
Tech. Series 13: p. 21, PI. IV, Fig. 49. 1906.
2. Britton, W. E. Mites injuring Bermuda lilies. Conn. Agr. Expt. Sta., Rpt.
p. 190. 1915.
3. Broadbent, B. M. Further observations on the life history, habits and control of
the narcissus bulb fly, Merodon eguesiris. Jour. Econ. Ent., 20: 94-113. 1927.
4. Chambers, E. L. Hot water treatment of narcissus bulbs in Wisconsin. Jour.
Econ. Ent., 23: 547-550. 1930.
5. Cole, F. L. Fumigation with calcium cyanide for control of greater and lesser bulb
flies. Jour. Econ. Ent., 22: 236-237. 1929.
6. Doucette, C. F. The effect on narcissus bulb pests of immersion in hot water.
Jour. Econ. Ent., 19: 248-251. 1926.
7. Ewing, H. E. Oregon Agr. Expt. Sta., Bui. 70. 1914.
8. Ewing, H. E. Oregon Agr. Expt. Sta., Bui. 121. 1914.
9. Federal regulations and information. F. H. B., S. R. A. Announcement 87: 36-39.
1926.
10. Foumouze, A. and Robin, C. Jour. Anat. Phys., V: 287. 1868.
11. Fracker, S. B. Narcissus inspection problems. Jour. Econ. Ent., 21: 470-476.
1928.
12. Gambrell, F. L. Gladiolus thrips control studies and observations on bulb mite
infestations. Jour. Econ. Ent., 27: 1159-1166. 1934.
13. Griffiths, David. Commercial Dutch-bulb culture in the United States. U. S.
Dept. Agr., Bui. 797, 50 pp., 32 figs. 1919.
14. Griffiths, David. The production of narcissus bulbs. U. S. Dept. Agr., Bui. 1270,
32 pp. 1924.
15. Griffiths, David. American bulbs imder glass. U. S. Dept. Agr., Dept Bui. 1462,
22 pp., 11 pis. 1926.
16. Haller, G. Archiv Naturgeschichte, 50: 218. 1884.
17. Hodson, W. E. H. The bionomics of the bulb mite, Rhizoglvphus echinopus Fu-
mouze and Robin. Bui. Ent. Research, 19: 187-200. 1928-9.
18. Latta, R. The vapor heat treatment as applied to the control of narcissus pests.
Jour. Econ. Ent., 25: 1020-1026, 1 pi. 1932.
19. Mackie, D. B. Problems in dipping narcissus bulbs. Florists Review, 58: 25-26.
1926.
20. Mackie, D. B. Problems pertaining to treatment for the elimination of bulb
pests. Special Pub. Cal. Dept. Agr., 73: 57-60. 1927.
21. McDaniel, Eugenia I. The principal bulb pests in Michigan. Mich. Agr. Expt.
Sta., Special Bui. 173, 23 pp., 11 figs. 1928.
22. Michael, A. D. The hypopus question, or the life-history of certain Acarina.
Jour. Linn. SocZool., XVII: 389. 1884.
23. Michael, A. D. British Tyroglyphidae, II. 1903.
24. Miibrath, D. G. Monthly Bui. Cal. Dept. Agr., XIV: 178-187. 1925.
25. Ogilvie, L. Report of the Plant Pathologist for year 1925. Bermuda Rpt. Dept.
Agr., pp. 36-63. 1925.
26. Ramsbottom, J. K. The control of the narcissus eelworm. Florists Exchange,
59: 481-483. 1925. Also in Gardener's Chronicle, 77, No. 1988, pp. 76-77;
No. 1989, p. 96. 1925.
27. Russell, T. A. Rpt. Dept. Agr., Bermuda, 1932, pp. 24-30.
28. Scott, C. E. Tylenchus dipsaci on narcissus. Phytopathology, 14: 495-502.
1924.
904 Connecticut Experiment Station Bulletin 402
29. Sorauer, P. Pflanzenkrankheiten, III: 108. 1913.
30. Spruijt, F. J. and Blanton, F. S. Vapor-heat treatment for the control of bulb
pests and its effect on the growth of narcissus bulbs. Jour. Econ. Ent., 26: 613-
620. 1933.
31. Van Slogteren, E. Bloembollenculture. Mar. 23, 28, June 1, 1920.
a. Review in Plantenziekten Dienst. Wagengen Viugsahr, 26: 8 pp. 1921.
b. Review also in Tid. Plant. 25: 118-138, 161-171, 177-188, 4 figs., 3 pis. 1920.
c. Report International Conference Phytopath. and Ent., pp. 150-162. 1923.
32. Van Slogteren, E. Weekblad voor Bloembollencultur. Mar. 23, May 28, June
1, 29, 1920.
33. Weigel, C. A. Insects injurious to ornamental greenhouse plants. U. S. Dept.
Agr., Farmers Bui. 1362: 22-41, Fig. 17. 1922.
34. Weigel, C. A. Hot water bulb sterilizers. Jour. Econ. Ent., 20: 113-125. 1927.
35. Weigel, C. A. Results of forcing hot water treated narcissus bulbs. Jour. Econ.
Ent., 21: 352-353. 1928. (Abstract of article appearing in Florists Review,
Aug. 4 and Sept. 15, 1927.)
36. Weigel, C. A., Young, H. D., and Swenson, R. L. An apparatus for the rapid
volatilization of carbon disulphide. Circ. U. S. Dept. Agr. No. 7, 8 pp., 4 figs.
1927.
37. Welsford, E. J. Investigation of bulb rot of narcissus. Ann. Appl. Biology, 82:
36-46. 1917.
38. Woods, A. F. U. S. Dept. Agr., Div. Veg. Phy. and Path., Bui. 14. 1897.
39. Yagi, N. Ber. Ohara Inst. Landwirtsch. Forschungen, i. No. 3: 349-360, 8 figs.,
1 pi. 1918.
PLATE I.
a. Flies, {Scatopse pulicaria Loew) with hypopi of the
bulb mite clinging to them, enlarged 7 times.
b. Mite infestation just beginning in a growing bulb. Its progress is
indicated by the dark lines between the scales, natural size.
PLATE II.
a. Rotten bulb with base removed showing mites, twice
natm-al size.
b. Bulb completely destroyed and containing a great many
mites, natural size.
PLATE III.
^■jur." ' "' —m—s — ^-^ — ■ ■"■ ■■■■■' ""'n
■ %
%'
■ , , 4
i
* . v' ,^^ X ■•
^'1^ r^- -^;-.., ■-: ---;>;^r-" i
a. Mites from a rotten bulb, enlarged 8 times.
b. Infestation just beginning in a healthy bulb, natural
size.
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