EXPERIMENT STATION LIBRARY

3 MbDD DDbia ^73D

^^^Itt

^ a

I

RICULTURAL
STATION
N. R

20

"N. H. Experiment Station

o

^

c

o

-+j

05

o

(M

o

OS

U.

T— 1

CO

CQ

o

<

c

H

m

'-5

5-1-.

hn

>H

U

Pi
<

S

CD

S

^

"ce

o

c«

-*-^

OJ

^

o

M

S

"1—1

^

o

-13

C/J

O ^ o

u

a

u
O.

B

o
U

c
o

C

C5

rt

O - -

^5

c

a

o
U

3

-J.

^coococcccocccoocooccoc

OJmCO^CrO^^'-OJf^. '^•-«CCC-1-'3- — ocooo

T— 'CCV3CwO^OOOCgOCCU~, COCCCOCC

cr c c c c

Or^-— O — — — — ^^''^^ ^^^"~' — ^^""^^^

CC\C-1-^,-.<^'NC

~ CM vC <^. M O re M Tl- to — C Ol — ■

•3- 1^

oi —

r^KN CM

fo eg

\r;

^ (NO c: c o c: c

.=...^ =

— cc^^crc-^c-iccrc:

-1 C^J ^ ''. ^1

_

■^. ^- LC I

r. ^ r- u~.

„

•a- oc

rr. I—

f. -^ CM

LT, r';

u-.

>>

« O B

C

"C 3 u

r:

_ I- c/:

C rt o

rr

•0 = 5

rt

V

<u

V-

u

>

>

.9^ ?.

c:

o

S o

o

•^■^t—.

U

u: X 1^

c •-

OJ c

Alfalfa

Alsike

Barley

Bhiegra

Bluegra

Biickwh

Canada

Corn

Millet,

Millet,

Millet,

Oats

Rape
Red Ct
Red Tr

^5

Bulletin 247

October, 1929

UNIVERSITY OF NEW HAMPSHIRE
EXPERIMENT STATION

THE WHITE PINE WEEVIL
IN NEW HAMPSHIRE

By C. C. PLUMMER and A. E. PILLSBURY

UNIVERSITY OF NEW HAMPSHIRE

EXPERIMENT STATION

DURHAM, N. H.

FIG. 1— Egg in Situ, X 4.
FIG. 4— Adult, X 14.

FIG. 2— Larva, x 10. FIG. 3— Pupa, x lO.S.

THE WHITE PINE WEEVIL
IN NEW HAMPSHIRE^^

By C. C. Plummer and A. E. Pillsbury

INTRODUCTION

The white pine weevil, Piasodes strobi Peck, is a forest insect of major
importance in New Hampshire, where large areas of white pine, Pmus
strubus, are grown. It is estimated that at least 70 per cent of the white
pines in New Hampshire are attacked at some time, or at various times,
in their growth. Some trees are attacked as many as 20 times befsre
attaining maturit}-. After the tree has been injured several times the
timber is of lower grade and often can be used only for box boards or
other relativeh- cheap lumber. In this way the value of the lumber
may be reduced 30 per cent.

The damage caused bj' this insect has done much to discourage refor-
estation with white pine. It has resulted, in manj- cases, in the substi-
tution of red pine, Finns resinosa, for the better known and better liked
species.

In New Hampshire the weevil is universally present wherever white
pine is found. Isolated and small, scattered areas of white pine, com-
mon in the southern part of the state, are injured as much as extensive
plantations.

The work described in this bulletin has been carried on since the fall
of 1925.

HISTORICAL

The white pine weevil is an indigenous American insect, described in
1817 as Rhyncha^nus strobi, by Professor W. D. Peck, of Harvard Uni-
versitj', in a paper published in the "Massachusetts Agricultural Reposi-
tory and Journal." Incidentallj-, this paper is believed to be the first
in which an American injurious insect was described. (Britton, 1919.)
Thomas Say (1831) first referred to the weevil as Pissodes strobi. Since
that time the white pine weevil has often been mentioned in entomo-
logical literature. Early writers contributed a few facts and many erron-
eous suppositions regarding the life histoiy. No doubt some of these
early workers confused P. strobi with closely related species, for several
of their observations have never been verified. Dr. A. D. Hopkins (1907)
was the first to work out the general life history of the weevil. In re-
cent years contributions on the life hi3tor\' and control, made by Walden
(1914, 1915) and Britton (1919) in Connecticut, Peirson (1922) in Mass-
achusetts, and Graham (1926) in New York and Minnesota, have added
materiallj- to our knowledge of the weevil.

*The writers are indebted to Professor W. C. O'Kane and Assistant Professor
P. R. Lowry for their valuable assistance at all times.

N. H. AGRI. EXPERIMENT STATION [Bulletin 247
DESCRIPTIONS

Egg

The egg (Fig. 1) is pearly white, slightly oblong, and equalh' rounded
at both ends. It varies in length from 0.735 mm. to 0.825 mm., the av-
erage being 0.782 mm. The width varies from 0.405 mm., to 0.480 mm.,
the average being 0.452 mm.

Larva

The larva (Fig. 2) is a yellowish-white to white cylindrical footless
grub. The body is divided by transverse constrictions into three tho-
racic and nine distinct abdominal segments, tlie anal lobes forming the
tenth. The thoracic segments are not larger than the first abdominal
se*gment. The width of the head is about one-half that of the body
and is of a light brown to deep yellow color, the anterior margin and the
mandibles being much darker. A shining dorsal plate and a dis-
tinct sternal plate are found on the first thoracic segment. There is
a distinct spiracle on the first thoracic segment ; none on the second
and third thoracic segments; and again distinct spiracles on the first
to eighth abdominal segments. The spiracles are round. The length
of the full grown lar^•a varies from 6.25 mm. to 9.5 mm., the average

Pupa

The pupa (Fig. 3) is exarate or free and is of a creamy white color.
The eyes at the base of the snout are light brown. As the pupa matures
the snout, head, and legs become brown, this shade gradually extending
as the pupa approaches the adult form and color. The abdomen is
square at the tip and has a sharp, slightly curved spine on either side.
The length of the pupa varies from 5.50 mm. to 6.75 mm., the average
being 5.93 mm.

Adult

The adult (Fig. 4) is an oblong-oval weevil. Its color varies from
dark brown to light brown but usually is dark reddish brown. Both
sexes are marked with irregular small patches of grayish-white and yel-
low scales. The grayish-white hind-spots form an almost continuous
band across the posterior third of the elytra. The thorax is definitely
marked with several small round spots of light-colored scales. Small
patches and scattered white scales are found on the sides of the thorax
and femora, and the ventral aspect of both thorax and abdomen. The
beak is shorter than the thorax in the male while it is equal to it in the
female. The geniculate antennae are inserted on the sides of the beak
near the middle. The thorax is as broad at the base as it is long, the
sides parallel along the basal half, beginning to narrow toward the front.
The disc is densely and finely rugose-punctate. The elytra are slightly
wider than the thorax, the sides parallel to a point beyond the hind-spot
where they start to converge and are compressed to an apex. The stria-

October, 1929] WHITE PIXE WEEML 5

tions are distinctly punctured. The legs are strong, .^ubequal. The tibiae
have an incurred spine at the apex. The tarsi are sliort and broad. The
tarsal claws are simple. The length of the adult varies from 4.0 mm. to
6.9 mm., the average being 5.2 mm.

INJURY

Exudations of small clear drops of i)itch from the punctures made in
the upper part of the leader are the first evidence of injury. The pitch
ma\- later run down the stem or remain in small spots which become
white upon hardening. Often injury- is not noticed until the lar\-8e cause
the 3'oung growth to become discolored and wilted. Later in the sea-
son the appearance of dead tips indicates further development of the
insects in the leader.

The most important injury, readih- observed, is confined to the ter-
minal shoot or leader of the white pine, usually extending only as far
as the first whorl of lateral branches.

After the terminal .portion has been killed bj' the feeding of the larvae
the lateral branches next below tend to grow more upright the follow-
ing 3'ear and to compete for the place of leader. The longest lateral
branch assumes this role. In some cases two laterals will maJie approx-
imately the same growth and both will replace the dead leader, resulting
in the formation of a forked tree. Rareh* three or even more laterals
exhibit this phenomenon.

When a lateral branch replaces a leader the trunk of the tree has a
bowed appearance between the nodes where the replacement has taken
place. The number of times a tree has been attacked can readily be
calculated by the appearance of the internodes and by the remains of
the killed leader, which can often be found projecting from the side of
the trunk, even mam* j-ears later.

The host tree ma}- be injured repeatedly from the time it is about
five years old until it reaches maturity. In general, the most extensive
injury- takes place when the trees are from eight to eighteen j-ears of age, or
from five to fifteen feet high. The weeviling gradualh- declines as the
trees approach maturity. It is surprising to note the number of trees
thirt}- or more feet high showing recent weevil injuries. The height of
the older trees makes the injury less noticeable and has led to the gen-
eral belief that trees over thirty years of age are rarel}^ attacked.

Graham (1926) has shown in the relation of injury to crown class and
rate of growth that the weevil seems to choose the most thrifty and
rapidly growing trees in a stand, not necessaril}^ the tallest trees.

Experiments were carried on to note the preference, if any, for dom-
inant and recessive leaders. A dominant leader of large tip diameter
is a good indication of the relatively vigorous condition of the tree by
which it was produced. A screened cage four feet long, two feet wide,
and eighteen inches high with three-eighths inch holes spaced five inches
apart in the wooden floor was used in the experiments. Twenty-two re-
cessi\-e leaders, one-quarter inch in tip diameter and thirteen inches

6 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

long, were alternated in the holes with dominant leaders, one-half inch
in tip diameter and thirteen inches long. Fifty weevils were liberated
on the floor of the cage.

Two days later, June 27, 1927, thirteen weevils were found on the re-
cessive leaders and twenty on the dominant leaders. June 28 the exper-
iment was repeated with different weevils and fresh leaders. This time
the leaders were arranged alternately as before, but in reverse order.
After two days twelve weevils were taken from the recessive and twenty-
six from the dominant leaders.

The experiments confirm field observations, which show that the weev-
il prefers the large and dominant to the small and recessive leader.

In numerous instances it has been noticed that certain trees, which
from their vigorous growth would appear susceptible to weevil attack,
are not injured, while others in the immediate vicinity, which would ap-
pear less susceptible, are attacked. To a certain extent infestation may
be based on chance.

HOST TREES

The white pine weevil feeds principally on white pine. Although
workers have reported this insect as damaging other species of conifers,
such infestation is not economically important. Nonvay spruce is prob-
ably the next most susceptible host.

Hopkins (1911) listed as hosts jack pine, Piniis Banksiana; pitch pine,
Pinus rigida; and red spruce, Picea rubra. Peirson (1922) observed or
verified Japanese pine, Pinus densiflora; Scotch pine, Pinus sylvestris;
and Norway spruce, Picea abies. Currie (1905) lists deodar or Himalay-
an cedar, Cedrus deodara. Packard (1890) mentions balsam fir, Abies
balsamea; and hemh-.'k, Tsuga canadensis. In the course of this study
in New Hampshire the weevil has occasionally been found on Scotch
. pine, pitch pife. red pine, and Norway spruce.

No doubt some of the earlier writere confused the white pine weevil
with other species in the same genus. Probably Currie (1905) and Pack-
ard (1890) erred in this respect. Further, it is possible to find an acci-
dental specimen on some species of conifer other than white pine, al-
though breeding may not take place on the trees noted.

June 21, 1927, several white pine weevils were noted copulating and
feeding on the leaders of two Norway spruce trees about eight years old,
located in Barrington, N. H. They made a large number of feeding
punctures. On either side of the row in which these two trees stood
were other rows of mixed and pure white pine, red pine, and Scotch pine,
15 to 20 feet high. These trees were from 15 to 100 feet away. In these
rows no weevils were found on any other species than white pine.

At the time of the first observation noted above the weevils on the
two Norway spruces were allowed to remain there in order to determine
the extent of injury. Two months later the leaders exhibited no evidence
■of larval tunnels and no signs of injury other than the feeding punctures

October, 1929] WHITE PINE WEEVIL 7

made by the adults. Norway spruce is apparentl}^ resistant although it
is a host.

In order to determine if the white pine weevil can live and breed on
pitch pine and red pine, four leaders from each were placed on June 30,
1928, in glass vials eight inches long and one inch in diameter. Two pairs
of weevils were liberated in each vial. The vials were inserted in a plas-
ter-of-Paris block to provide moisture.

Jul}' 19, thirteen of the sixteen adults on the four red pine leaders were
alive. Larvae were present. Eleven of the weevils placed on pitch pine
leaders were alive, and larvae were present in ever}^ leader.

Later in the season larva; in two of the red pine leaders had died while
three and four adults respectively emerged from the remaining two lead-
ers about September 6. Five, seven, eight, and seven adults respectively
emerged from the four pitch pine leaders about the same date.

REARING METHODS

Rearing was carried on in a screened insectary cage with a canvas roof.
The floor is of earth. The cage is surrounded by a number of white
pine trees and is partially shaded during the day. The temperature is
slightly below that to which the insect is exposed under natural condi-
tions. Certain phases of the life history work were carried on in a small
greenhouse where the temperature was slightly higher than in the field.

Life historj- data, such as the length of the several developmental
stages, were obtained from material in the insectary cage and greenhouse.
When possible, observations were checked with field conditions.

Rearing in the greenhouse and insectary cage was accomplished bj^ us-
ing several plaster-of-Paris blocks. Each block is two feet long, six inches
wide and four inches high. Twentj'^ or twentj-one holes, one inch
in diameter and one-half inch deep, spaced one inch apart, were drilled
in the broad upper surface of the block. A one inch hole was drilled
from end to end through the central part of the block. A one inch hole
drilled in the broad surface near one end connects with the longitudinal
central canal. Corks inserted in the ends of the longitudinal canal retain
water poured in the connecting hole on the broad surface.

Eight glass vials, eight inches long and one inch in diameter, each con-
taining three or four pairs of adults and a fresh white pine leader, were
inserted in the plaster-of-Paris block everj^ day, the open end of the vial
in the block. Twenty-four hours later the leaders were removed and
fresh ones substituted. The weevils were replaced when necessary. The
leaders removed from the vials were examined for eggs under a binocu-
lar microscope. Part of the leaders containing eggs were placed in vials
inserted in blocks kept in the greenhouse and part in blocks in the insec-
tary cage.

The material was examined daih\ Accurate observations could be
made without disturbing the insects. When the larvae advanced to a
point where the food supply was endangered a fresh section of a leader

8 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

of the same diameter was spliced on and wound with thread to hold it in
position. With few exceptions this technique was entirely satisfactory.
Three or fom- successive splices on one leader often were made. Usually
it was not necessary to furnish water more than once a month.

The insectary cage and greenhouse are located in Durham, N. H. Most
of the field observations were made in Madbury, seven miles north of
Durham. Certain field work was carried on in Durham plantations and
a plot outside of Dover, seven miles northeast of Durham.

SEASONAL LIFE HISTORY AND HABITS

In brief, the life history of the weevil is as follows:

The adults leave hibernation about the last of April or the first of May
and make their way to the leaders of white pine. Here they feed in the
vicinity of the new growth and tender buds before moving down the lead-
er to feed and oviposit. They are found on the leader until the middle of
July, at which time they either die or go to other parts of the tree. The
eggs, inserted in the cambium, hatch in from 6 to 20 days. The larvae
work their way down the leader, feeding on the inner bark and cambium.
After they have fed for three or four weeks each one enters the wood and
constructs a pupal cell where it remains for a varying length of time be-
fore pupating. The larval stage occupies about 36 days. The pupal
stage lasts about two weeks and is followed by the eclosion of the adult.
The adults remain within the leader for two or more weeks. After emerg-
ing the adults are found feeding on the branches of the white pine in in-
creasing numbers from the middle of September until the middle of Oc-
tober. On the advent of cold weather they hibernate in the duff.

Some adults, as discovered in this work, do not die after completing
egg-laying but remain alive until a second season when they again lay
eggs.

APPEARANCE IN THE SPRING

In the latter part of April or the first of May, depending on weather
conditions, the weevils leave hibernation and make their way to leaders.

The following dates were noted in this study:

May 5, 1926, at Durham, an adult was noted cling to the top of a hiber-
nating cage in which several weevils had been confined since November,
1925. Weevils were first noted at Barrington Depot, May 6.

In 1927 weevils were found on leaders April 20.

In 1928 the first observation for the year was made May 6. On that
date numerous weevils, feeding and copulating, were found on leaders
and buds exposed to the sun.

In 1929 weevils were first observed April 24.

The work of Graham (1926) with tanglefoot bands on the lower inter-
nodes of white pine showed that the weevil after leaving hibernation may
either fly or crawl up the trunk in order to reach the leader. We have
obtained similar results.

October. 1929] WHITE PINK ^^T■:EVIL 9

Weevils leaving hibernation in the spring appear considerably darker
than they were on emerging in the fall. Some of their scales have been
lost or discolored.

EARLY ACTIVITIES OF THE ADULT

Aside from the more important damage done by the larvae, the adults
infiict considerable injury to the tree bj' chewing broad cavities in the
new buds of the leader. In a few cases eggs hsLve been found in some of
these feeding cavities.

The weevil chews a small circular hole through the bark and cambium
and sometimes slightly into the wood parenchyma. The feeding punc-
tures ma.v extend a short distance into the bark or may extend through
the bark to include the cambium. The weevils seem especiallj^ fond of
cambium tissue. The canity made b\' the wee\"il is much wider basaily
(Fig. 1) because of its acti\'ity in securing as much cambium as possible
from one feeding puncture. While feeding, the weevil is constantly turn-
ing its head in order to use the natural curve of its beak to obtain the
cambium tissue. The structure of the head makes it possible for the wee-
vil to feed with little movement of the body. An hour or more may be
spent in making one feeding puncture. There is no marked diilerence be-
tween the cavities made by the male and female.

Eggs maj' be found in cavities that enter the bark for only a short dis-
tance. Usually, however, they are placed in the deeper cavities, which
provide ample room for one or more eggs. Earl}^ in the season the punc-
tures are usually found near the terminal buds, but as the season progress-
es the eggs are laid further down in the leader. Xo observation has been
made to ascertain if the female oviposits in cavities made by the male.

The adults seem able to live without food for only a short time. Thus.
20 weevils were placed without food in a muslin covered cage on June 29,
1928. Nineteen were dead July 2. The last one died July 3.

MATING

Mating of the weevils takes place in the spring following emergence
from the infested leader, and not in the fall. Shortly after their appear-
ance in the spring and up until their disappearance in July, the weevils
are constantly found in copula. Few single indi\'iduals are present during
this period.

Apparentlj' the female does not have to be fertilized more than once
in the season in order to continue laj'ing fertile eggs. This was brought
out in the course of an experiment to determine the number of eggs laid
by a single female. In several instances the male of the original pair died
earl}' in the season and the female continued to lay fertile eggs through-
out the remainder of the oviposition period. In two instances the males
died sometime between IMaj- 8, 1928, when thej^ were first introduced, and
June 11, when the leaders were removed in order to count the eggs.

10 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

When new leaders were inserted from time to time it was found that
these females continued to lay fertile eggs until July 17, the end of the
oviposition period in the insectarj^ cage.

Graham (1926) cites an example where a female apparently was fertil-
ized before entering hibernation. This is probably a rare occurrence.
In the light of recent observations the instance was more likely that of a
weevil hibernating a second winter. If insemination should happen to
take place in the fall it is a question whether fertile eggs could be laid in
the spring.

RESPONSES

The death-feigning habit of the white pine weevil is strongly developed.
A shadow or movement close to the weevil will cause it to drop from the
leader. This habit appears stronger on bright warm days when the wee-
vils are active. During cool, windy, or rainy weather they remain in a
sluggish condition at the top of the leader among the buds.

The weevil is negatively geotropic and positively phototropic. The
former response is easily demonstrated by completely covering an 8 inch
vial with black paper. When a leader and eight adults were inserted in
such a vial and placed in a block, the feeding punctures were concen-
trated in the top inch of the leader, the remainder containing but few
punctures.

When a similar vial was completely covered except for a quarter of an
inch around the top, 20 punctures were found in the first inch, 26 in the
next 4% inches, and 8 in the last 2 inches of the leader. When such a
vial was completely covered, except for a band 2 mm. wide at the base,
a more general distribution of the feeding punctures occurred.

The fact that the weevil is positivel.v phototropic is used to advan-
tage in control by silvicultural methods.

PREOVIPOSITION

The preoviiiosition period extends from the time the adults emerge
in the fall until shortly after their appearance on the leaders in the
spring, at which time oviposition begins. Histological studies of the
ovaries of the weevil (Plummer, 1929) before and during hibernation
have proved that the oocytes are only partially developed. The weevil
is unable to oviposit in the fall, previous to hibernation.

OVIPOSITION

The oviposition period extends from the time the females begin laying
eggs in the spring until some time in July, when they disappear from the
leader. Thus, the oviposition period may last two months or more.
July 8, 1926, no adults could be found in the field. In 1927 the ovi-
position period in the field terminated on July 9; in 1928, July 12. Wee-
vils confined in a glass moist chamber continued to lay eggs until Sep-
tember 9, 1927.

October, 1929] WHITE PINE WEEVIL 11

After the cavity is prepared the act of oviposition is quickly accom-
plished, occupying from a few seconds to a minute or more. Usually one
egg is inserted in each egg cavity. However, frequently two, occasionally
three, and rarely four or five eggs are found.

To determine the number of eggs laid by a single female a pair of
weevils was placed on each of forty-seven white pine leaders in glass
vials inserted in plaster-of-Paris blocks. The experiment was begun
May 8-11, 1928. Leaders were removed and replaced with fresh ones on
the dates indicated in Table I for the purpose of counting the eggs, or
larvae if anj- had hatched.

Thirteen females or pairs of weevils were dead at the end of the first
period. These are not included in Table I. The experiment was con-
tinued a week longer than shown in Table I to ensure that all of the
females had finished ovipositing. It is impossible to tell exactly when
egg laying began and when it ceased.

SUMMARY OF THE DATA IN TABLE 1

Average number of eggs per female for first five weeks 35.7

Average per female per week 7.

Average number of eggs per female for the next two weeks 32.8

Average per female per w^eek 16.4

Average number of eggs per female for next three w'eeks 59.2

Average per female per week 18.7

Average total number of eggs laid 129.

Maximum number laid bj' a single female 201.

Minimum number laid by a single female 25.

More eggs are laid near the end of the oviposition period, that is from
June 25-26 to July 17, and not earh- in the season as stated by some
writers.

Under field conditions the female may oviposit on several leaders,
or two or more pairs may work together on the same leader. In this
way it is possible for leaders in the field to contain more eggs than the
maximum number found in the insectary cage.

POSTOVIPOSITION AND LONGEVITY

The oviposition period terminates when the weevils gradually dis-
appear from the leaders in July.

After leaving the leader at least a part of the weevils move to other
parts of the tree, especially to the vicinity of the new growth on lower
lateral branches, which seem particularly attractive to them at this season
of the year. Here the}^ are found in a semi-dormant condition. Their
condition is not such that the term "estivation" can be used, for they feed
to some extent and are slightly active. They do not make their typical
feeding punctures but eat small patches of bark and cambium. These
feeding evidences are not found previously to the disappearance of the

12

N. H. AGRI. EXPERIMENT STATION [Bulletin 247

00

^

r

cc

fe3

pq
<

te

1 ro

1

rr

1 CJ^

1 '^'S

1

o^

1 ^

:-

,-

1 "

to

c

1 ^

^

1 ^^

1 ■*

1 "S

1 CSI

t <^J

t .— 1

1 ■=:

1 t^

I

1"-

1"

|«

cj

cr

CO

e^

1 CO

1 "^

1 o_

[

1 •-"

1 ^

1 °

1

(M

CO

1 00

1 '*

1 *^

1 "^

1 o

1 r^

CO

(TO

1 Q

|cO

"^

o

1 '*

1 "*

1 "5

1 '^

IS^

1 ^^

1 W

cs

cv;

CO

00

! ^

1 "^

1 CO

1 •— <

1

iO

oq

00

CO

t^

1 '"'

'^

1 CO

1 c^

1 ^o

1 ^-*

1 o

1 f--

\^

t^

<N

t^

CO

s

"^

■rp

1 -^

<M

00

Cv|

[ "^

oo

CO

1-H

CO

c^

00

CO

^^

1 o

1 "^

1 '"^

1 '^

1 ■*

,_,

1 to

1 t^

1

CO

1

1-H

CI

c^

n

lo

wm

1 "^

1 '^

1 "5

1 ^

iS^s

1 '—"

1 <— «

b^

1 ^

CO

cq

cs

Is

CD

O

1 t^

1 "^

o^

1

1 t"'

***"

1"

Q

1

"^

CO

Si

1 ^1—.

1 ^^

1 •'^

,— )

,_,

M

U3

t^

(M

Oi

1

oo

1 ^

1 "5

! c^

1 c^

1 CO

r- 1

1 00

1 oo

CO

"^

1—1

CM

i oo

1 ^

1

r*

1 =^S

1 "^

1 o

1 "^

1 „,

CO

1 ^

1 "*

CV|

CO

CO

S

! 00

1 "^

_ 1

I Cq

1 MH

1 i— •

CO

CO

1-

«M

t^

CO

LA

1 ^

1 *^

1 o_

m

1 w

TP

p

■^

! oo

1 *«

1 o~

1

1 oo

I to

1"

1 '^

1

CO

|co

eo

! o^*

1 "^

I "^

1 "^

1 o

1-4

•<*<

1 00

CO

CO

1 °°

iM

00

CO

<M

1 "^

t CO

1 o

»iO

1 c^

1 ^H

"""*

CO

QO

rH

»o

C^

to

CO

»M

1 '-~'

1 '^

I ^

1 "^

1 "^

1 --H

I "^

1 OS

to

^

"^

CO

Oi

1 i^

1 -*

1 <=>_

1

^^

CO

1 °

1

C<J

CO

00

1 <—■

1 "^

1 >=>^

1 •— '

^^

o

CO

1 ^

to

CO

r-

"ti

1 "^

1 c^

to

o

„,

' '

to

-M

TT

1-^

«e

1 v™*

•*

1 o_

1

1 1 1

»^

l«

CO

1 Q

1

to

CO

PO

1 o

1 iC

1 CO

! "^

1 CO

1 *- •

1 CO

1 »— (

' "■

M

1 2

!■-

«^j

1 1— <

1 ^

■o

1 "^

1 o

1 '— '

1 CO

1 *— 1

"^

CO

»-H

C^

oo

1 *^

1 C5

1 »o

! CO

*o

1 '=0

1 <—<

1 oo

t —4

1"

lO

'^

CJ

l>.

h :

1 CO

I "^

1 "^

to

1 •— <

1 '— ' *

\ '^

r>.

C^

CO

t^ '

1 "^

1 "^

1 '^

1 ^

1 o^

•~*

1 "

1 "^

1 ^

1 Oi

1 "^

1 "*

1 •— '

1 '-H

CO

CO

1 "^

CN

CO

b-

lA

C^l

to

CO

r«

1

1 ^

1 to
CO

1 "^

1 iO

o

1 »o

iss

1 •— '

1 to

1..

^

! O

1 t^

(M

ira

<M

COw^

_^

^

...

CO

CM

o

'^

-

CO

"^

uo

s?

(M

§

t^

CO

1

^

r^

s

3

^

•-3

o

o

"*^

CO

t/J

CZ3

<^

(M

CT

>H

1

^

<:

00

■^

Pc^

Q

>>

cc

O)

OQ

43

Oj

o

s

;»

13
"-3

>H

C3
t-3

>-

o

o

z

<

<lt

<

z

z

4

03

1

Q

1

T3

Q

<

«t:

o

n

rt

o

H

H

S

S,

m

o

o

H

U)

o

bS

o

o

H

H

fe

w

-^

w

:^

w

;z:

1

1

go

October, 1929] WHITE PINE WEEVIL 13

weevils from the leaders and are found only on trees infested during the
current season. For over a month before any of the weevils of the new
generation emerge from the leader these feeding areas are present.

What percentage of the weevils enter this semi-dormant condition was
not determined because of the difficulty in collecting them. Usually a
single wee\il was found on a tree, although sometimes two or three
were taken. None was found in copula. In 1928, weevils, few in num-
ber, were continually ob.served on the lower lateral branches until Aug-
ust 12. Searches in the duff under infested and uninfested trees failed
to reveal anj' weevils.

In 1928 adult weevils, surviving the experiment to determine the num-
ber of eggs laid, were foimd ali\e on November 12. In this case, where
the weevils were in cages, several were in copula. They died sometime
in the winter. In general, weevils in cages often exhibited longer pe-
riods of feeding, egg-laying and some other activities than those in the
field.

Other species of American and European weevils in the genus Pissodes,
according to Hopkins (1907), may live and deposit eggs for two or
three years. It had been suggested that the white pine weevil might
live for more than one year, although no worker had secured definite
information to that effect.

Barnes (1928) in a longevity experiment succeeded in carrying adults
through a second winter of liibernation. He states nothing concerning
their performance but ends his observations May 28, 1926, saying that
two leaden colored weevils were found at the base of the tree.

In 1928, at Durham, screened cages, five feet high and three feet
square, were placed over four uninfested white pine trees slightly less
than five feet high. The duff under the trees was not disturbed in any
waj'. Ten adults known to have emerged in 1927 and marked with pur-
ple show-card ink on the elytra were liberated in each cage August 9.
1928. October 12, several adults were observed feeding at the tips of
the lateral branches. Fresh feeding evidences were abundant.

Examination of the trees in the cages April 27, 1929, definitely proved
that the weevil maj^ live more than one year. Seven, four, two, and
five weevils, respectively, were noted on various parts of the trees in
the four cages. The paint markings on the elytra were plainly visible.
Numerous feeding punctures were observed on all of the leaders. Some
females were dissected, and fully developed eggs were found.

A part of the marked w-eevils removed from these cages were kept
alive and were given access to a white pine leader. These weevils laid
eggs in the leader and the eggs hatched.

The cages were removed temporarily for close examination May 18.
Six, three, two and six weevils were found on the trees. Thus nearlj-
50 per cent of these wee\ils lived for more than one year.

The leaders were finally remo\ed from the cages August 27, 1929, and
were examined. At that time the leaders were dead or dying. On ex-
amination two dead larvae were found in one leader, three in another.

14 N. H. AGRI. P:XPERIMEXT STATION [Bulletin 247

and a dead weevil was found in a third leader. The fourth leader con-
tained no stage of the weevil, although many feeding punctures were
present.

The writers have been unable to find any gross or histological details
to distinguish the weevils living for more than one year.

DISPERSION

Knowledge concerning the dispersion of Pissodes strobi is incomplete.
At present it is believed that dispersion does not take place in the fall
)n-cvious to hibernation. Repeated observations before and after hi-
bernation show that the weevils are found on trees or in the duff below
trees that were infested during the current season. Graham (1926)

made similar observations.

Seldom has the weevil been seen in flight in the course of this study.
It was first observed June 12, 1928, on a bright, warm afternoon. A
slight breeze was blowing. The observation from field notes is as fol-
lows: "First it walked to the tip of a needle, parallel with the ground,
near the top of a leader. This tree was about five feet high. The wee-
vil stamped its legs rapidly and then flew to another tree about the
same height 15 feet distant. It alighted on the tip of one of the lateral
branches about two feet from the ground. As soon as it alighted the
weevil walked quickly to the trunk of the tree, paused a short time,
walked about six inches down the trunk and then turned and went to the
top part of the leader."

Graham (1926) had much the same experience for he says, "Only once
in the course of these investigations has it been observed on the wing.
This one occasion was in mid-afternoon of a warm day in the early spring
of 1916. On that day many weevils were flying. They were strong fliers
and when in the air their movements were similar to such bark beetles as
Hylurgops. This unusual occurrence suggests the possibility of a short
period of flight during the early spring whereby the weevils become wide-
ly disseminated, followed by a period when it seldom, if ever, takes
wing."

On bringing P. strobi, collected from the leaders of young white pine,
into the laboratoiy on May 14th, 1926, the weevils, after turning them-
selves about several times, unfolded their wings and flew toward the win-
dow, one by one.

Barnes (1928), in studies of dispersion, used a five foot staff stuck
through a circular disc of cardboard and projecting four inches above the
disc. The edges of the cardboard were smeared with tanglefoot to pre-
vent the weevils from walking in the wrong direction. A string was at-
tached to the disc to tell the direction of the wind. He recorded flight
paths of the weevil by placing several adults on the cardboard disc. The
weevils would crawl to the top of the staff where several splinters of
wood vrere tacked so that they could take wing more easily.

He states, "125 flight paths over young trees showed that the weevil

I

October, 1929] ^^•HITE PIXP: WEEVIL 15

flew about eight feet above or at about the level with the leaders. Over
open spaces they flew nearer the ground at an average of about five feet;
the longest about one hundred yards/'

He observed that most of the flights were made to adjacent trees al-
though a number of weevils flew 25 feet or more above the tips and de-
scended at a point near the center of the pine tree.

The same method used by Barnes was tried at this station on three
different occasions under ideal conditions with little success. Two weevils
flew 15 and 30 feet respectively. The weevils did not fly readily and
were inclined to remain on top of the staff.

In the season of 1928 weevils were collected at least once a week, and
usually twice a week, from several of the plots under observation, in or-
der to secure specimens for experimental purposes. Throughout the sea-
son, up to the first of July, it was always possible to collect approximate-
Ij^ the same number of weevils from a plot. Collections from a plot did
not seem to materially reduce the weevil population. It seemed remark-
able if all of these later collections were made up of weevils previously
overlooked. On the other hand, few white pines of the more susceptible
ages were in the immediate vicinity of these plots. The following ex-
periments suggest that weevils may be overlooked, even when search is
repeated and thorough.

Fifty weevils, their elytra marked with red paint, were liberated June
16. 1928, about one foot from the ground on a five foot white pine tree,
located in the center of the Madbur}- plot. On the same day 50 white-
marked weevils were liberated on a four foot tree, the only white pine
in a large field adjoining the Madbury plot on the east. This tree was
at least 150 yards from the nearest pines located in the above plot.

June 18, twenty-three red-marked weevils were found on the tree on
which they were liberated and 31 white-marked weevils were taken from
their tree. Careful scouting failed to reveal any marked weevils on any
of the other trees in the plot.

When these trees were next examined, June 21, six additional white
and seven red-marked weevils were taken from their respective trees.
June 26 two more white and four red-marked weevils were taken. An-
other red weevil was collected June 28.

Thus a total of 38 red and 39 white-marked weevils of the original 50
liberated on each tree were recovered in a period of 12 days, all from
their respective trees.

EGG STAGE

The period when eggs may be found extends from the time when ovi-
position begins in the spring to about ten days after the weevils finish
ovipositing in July. (Chart 1).

Considerable data were secured on the length of the egg stage by util-
ization of the plaster-of-Paris blocks already described. Observations on
the length of the egg stage, and to a less extent subsequent stages, deter-
mined bv this method, are open to a certain degree of error insofar as

16

N. H. AGRI. EXPERIMENT STATION [Bulletin 247

JUNE

10 15 10 iS

JULY

5 10 15 30 25

1926

AUGUST

^ 'P '?> ^,0 3S

SEPTEMBEIR

5 10 15 20 ;5

OCTOBER

MAY

5 10 15 20 25

JUNE

5 10 IS 20 ;5

JULY

5 10 1 5 20 25

AUGUST

5 10 15 20 25

SEPTEMBER

5 10 15 20 25

OCTOBER

5 10 15 20 25

± n:.

IE

U

L1

^^^^^^^^^^

i

riil

i^^

z

^

_

^

'

ITggI

1^

M

i

III 1 1 1 1

■^■^RV>

\^^^^^l

k

192/

-J

III;

^

^^^^1

IPUPAI

k

Ik

M

1 M M

^^^■adu

^^H

_

_

Ml 1 1 1 1 M 1

MAY

5 10 15 20 25

JUNE

5 10 15 20 26

JULY

5 10 15 20 25

AUGUST

5 10 15 i0Z5

SEPTEMBER

5 10 15 20 25

OCTOBER

■j 10 15 20 Z5

Mill

~"

M 1 111 1 i^^B^^

P"

■™n

^

I444

'

IP'

^■larva^^^^H

^

I9i

> D

..i

^^Lm

.8

|PumW

"^

^

•^

Hi^

c

£^^^^1

111 1 1 1 M 1 1 1 1 1 II J

CHART I. Life history of the white pine weevil.

October, 1929]

WHITE PINE WEEVIL

17

the material under observation was examined only once each day, usu-
alh' in the morning. For instance, eggs may have been laid an hour af-
ter a fresh leader was introduced or an hour before it was removed. Like-
wise the eggs may have hatched only a few hours after they were exam-
ined. After some experience, however, it is possible to determine by
the appearance of the egg, or newly-hatched larva, the approximate ter-
mination of the incubation period. Since a large number of specimens
was used the results probably closely approach the length of the several
stages of development.

Table II.— Length of (he Egg Stage, 1928

IN THE INSECTARY CAGE

IN THE GREENHOUSE

Date of

Number op Days !

Date of

OviPOSITION

Number of Days

OviPOSITION

6

7

8

9

10

11

12

13

14

15

5

6

7

g

9

10

11

12

June 13

2

June 14

3

June 14

2

June 15

3

5

June 15

1

June 16

3

June 16

1

June 26

7

—

June 18

6

June 27

5

June 21

3

June 28

2

June 24

2

June 29

2

1

June 25

2

June 30

4

1

June 26

7

14

July 1

1

3

—

June 27

20

July 2

11

June 28

15

9

July 4

5

June 29

21

July 5

2

June 30

4

9

July 6

1

July 1

11

July 11

3

1

July 2

9

July 12

1

July 4

10

Number of
Specimens

3

2

9

18

10

8

3

11

July 5

6

8

July 6

6

July 7

1

July 8

6

July 9

22

July 10

1

July 11

3

10

July 12

5

1

July 13

10

Number of
Specimens

8

72

32

46

38

14

2

10

4

1

18 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

When several eggs were laid in a single leader within 24 hours, most
of the larvae hatched on the same day. Occasionally the eggs did not
all hatch on the same day and it was necessary to mark the unhatched
eggs by inserting in the leader a labelled pin close to the egg in question.
In some instances larvae hatching on different days were destroyed be-
cause of difficulty in following their subsequent movements in the leader.

In Table II the gradual shortening of the egg stage as the season pro-
gressed is evident. In the insectary cage the maximum number of 15
days was recorded for eggs laid June 15. The maximum in the green-
house was 12 days for 11 eggs laid from June 14 to 16. Near the end
of the oviposition period a minimum number of 6 days was required in
the case of 8 eggs laid July 11 and 12. A minimum of five days was nec-
essary in the greenhouse for three eggs laid July 11. Earlier in the sea-
son, before tne observations were made that are included in Table II, it
was found that eggs laid May 19, 1927. required an incubation period of
20 days. The average length of the egg stage in the cage was 9.32 days;
in the greenhouse, 8.66 days.

The averages for this and other stages have been determined by includ-
ing, first, separately, the data for each day in the cage and in the green-
house rearings. These daih- a^-erages were combined to get final figures.

THE LARVAL STAGE

The lar\-a, after eclosion from the egg, remains for several hours in the
pitch of the cavity. It then moves downward, feeding only on the cam-
bium and innermost bark while still very young. Later it consumes the
entire cortex, except the outer bark. When approaching maturity the
larva may also attack the outer wood parenchyma. The thin outer bark
remains intact forming a loose, brown jacket around the dead leader.

Usually the larvae encircle the leader and work downward together un-
der the outer bark. This concentrated manner of attack is of advantage
to the larvae for the tissues are killed quickly and little resin is exuded.
If a larva feeds alone it seldom is able to survive the copious flow of re-
sin induced in a vigorous tree by feeding activities.

The larvae progress rapidly down the leader. The route of descent can
easily be traced by the brown discoloration of the bark, which is evi-
dent soon after the larvae have fed on the underlying tissue. When
conditions are favorable and larvae are abundant they may work down
as far as the second or third whorl of lateral branches, a distance of three
or more feet. Often, however, they do not go below the first whorl of
lateral branches, a distance of eight to thirty or more inches.

In general, from our observations, the average number of larvae in a
single leader varies from 30 to 40. However, a considerable percentage
of these fail to reach the pupal stage. July 17, 1928, one hundred sixty-
one larvae were noted in a single leader under cage conditions. One hun-
dred fort3'-four of the larvae were together in a band one inch wide
;ii()und the leader near the base. Over 100 have often been found in

October, 1929]

WHITE PINE WEEVIL

19

Table III.— Length of the Larval Stage, 1928
IN THE INSECTARY CAGE

Number of Days

Date Hatched

26

27

28

29

30

31

32

33

34

35

36

37

39

41

42

June 27

4

1

—

3

1
15

7
4

5

1

1
5

9

1

3
1

1

3

1

June 28

1

\ June 30

July 1

July 4
July 6

July 7

July 8

July 9

July 10

1 July 11

4

1

3
1

4

5

8

9
2

2

1

30

2
3

1

17

13

4

22

4
1

21

2

2
9

8

2
5

1

0

1
1

Number of Specimens

1

IN THE GREENHOUSE

June 26

June 27

June 28

July

5

July

7

July

8

July

9

July

10

July

11

July

16

Number of Specimens .

4

5

2

2

2

1

2

1

1

1

1

2
1

1
1

1

2

6

3

2

2

2

2

0

8

3

1

1

3

8

3

6

3

4

1

2

leaders taken from the field. In field and insectary material, evidences
of cannibalism have been observed when the larvae are crowded and
have insufficient food.

Individuals hatching after most of the larvae have moved down the
leader consuming all the available food are in a precarious position. If
they are too far from the food supply thej'' perish; if they succeed in
reaching food the competition is often too great for them.

Each larva when nearly mature drops out of line, chews a tunnel into
the heartwood and forms a pupal cell. The entrance to the pupal cell
is blocked by the chips removed during its construction. Under crowded
conditions the inner heartwood is not sufficient to accommodate all of the

20 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

maturing Ian 33. Consequently, shallow pupal cells are constructed in
the outer wo id parenchyma next to the dead bark. In such a case the
outer surface . of the larva is covered over with an arched mass of chips
removed in making the pupal cell. These peripheral pupal cells cause a
bulging of the bark and can be readily detected without its removal.

In New I Hampshire larvse are first found about the last ten days of
May. Som ; are present, though in greatly diminished numbers, the mid-
dle of Sep^ _;mber. (Chart I). There is a marked tendency for the larval
stage to b considerably longer in the spring and early summer. This
is followed by a period in mid-summer when optimum development takes
place. This in turn gives way to another period of lower mean tem-
peratures during which larvae that failed to complete development dur-
ing the previous period maj' linger for several weeks as larvse or pre-
pupse before transforming to pupse. In that part of the larval stage
known as the prepupal period, varying from one to three weeks in length,
the larva remains in a sluggish condition within the newly constructed
pupal cell before transfgrming to a pupa.

Table III, including studies in the summer of 1928, shows the maximum
length of the larA-al stage for one individual hatching in the cage June 28,
to be 42 days; in the greenhouse the maximum was 41 daj's for two lar-
vae hatching July 16. A minimum length of 26 days was recorded for
four larvse hatching July 7 in the cage. The same minimum was found
in the greenhouse. The average length of the larval stage was 36.1 days
in the cage and 33.4 days in the greenhouse.

PUPAL STAGE

The pupal stage is passed in the pupal cells previously described. In
1928 the first pupa was found in field material July 13. Six more were
taken from leaders examined July IS. Puijce were present m infested
leaders until September 26. The greatest number were found between
August 10 and September 10, before and after which dates comparatively
few were in this stage of development. Twenty days, the maximum pu-
pal length in the cage (Table IV), were required for two larvae pupating
August 9; in the greenhouse 19 days were required for one larva pupating
August 7. In the cage the minimum was 10 days, observed in the case
of several larvae pupating between August 6 and 9. A nine-day mini-
mum was required in the greenliouse for larvse pupating July 30 and
August 26. The average length was 13.9 days in the cage and 12.2 da5's
in the greenhouse.

PERIOD FROM EGG TO ADULT

Table V shows the wide range of time that was necessary for develop-
ment from egg to adult, in 1928, under cage and greenhouse conditions.
The maximum total of 69 days in the cage is shown for an egg laid June
14; in the greenhouse 61 days for an egg laid June 26. The minimum in
the cage was 44 days for an egg laid July 2; in the greenhouse, 46 da3's

October, 1929]

WHITE PINE WEEVIL

21

for two eggs laid June 15 and for one laid June 27. The average total
developmental period was 56 days in the cage and 52.7 days in the green-
house.

Table l\.— Length of the Pupal Stage, 1928
IN THE INSECTARY CAGE

Number of Days

D-iTE Pupated

9

10

11

12

13

14

15

16

17

18

19

20

July 30

1

August 2

5

4

4

1

August 3

2

-August 5

1

August 6

1

1

1

1

3

1

16

1

August 7

2

3

2

3

4

4

August 8

2

2

.August 9

1

1

3

6

8

7

2

1

2

August 10

1

1

1

August 12

3

5

2

3

2

1

August 13

1

.August 14

1

1

August 16

1

1

Number of Specimens

0

4

8

15

22

19

12

25

5

7

1

2

IN THE GREENHOUSE

July 30

1

2

3

1

.\ugU3t 2

2

August 4

2

August 5

1

August 6

2

August 7

1

1

1

-

2

1

1

August 9

1

2

1

.\ugust 11

2

August 12

2

2

.August 13

1

1

August 15

1

1

1

2

<

\

August 26

1

1

Number of Specimens

2

9

7

5

6

6

4

2

0

0

1

0

Table V. — Period from Egg to Adult, 1928
IK THE INSECTARY CAGE

Number op Days

Date of

OviPOSlTION

46

0

48
0

49

1

1

50

1

1

1

3

51

3

1
2

1

7

52

1

2
2

1

2
1

2

1

12

53

4
1

7
3

3
3

21

54

2
4

10

7

23

55

3
1

4
4
1

3

4
9

1

1

31

56

T

2

14

2

3

2
6

1

1
2

3

37

57

1
1

8

2

1

1

1

1

16

58

5

2
1
2

1

4

1

16

59

1

2
2

1
6

60

1

1

1

1

1

2

1
8

61

2

2
1

5

62

1

1

1

2

1
6

63

1

1

1

1
4

64

1

1

2

65

1

2
3

69

June 13

June 14

1

June 15

June 18

June 21

June 24

June 26

June 27

June 28

June 29

June 30

July 1

July 2

July 4

July 5

July 6

July 8

July 9

July 11

July 12

July 13

Number of Specimens. . .

1

IN THE GREENHOUSE

June 14

2
1

3

1

1
2

1

1

2
2

4

2
2

1
2

2
9

1
1

1

1

2
6

3
3

1

1

2

1
2

1
6

1

1
2

3

T

2

6

0

1

1

2

1

3

1
1

0

0

0

0

June 15

June 16

June 26

June 27

June 29

June 30

July 1

July 2

July 4

July 5

July 9

July 11

July 12

Number of Specimens. . .

0

October, 1929] WHITE PIXE WEEVIL 23

NEWLY EMERGED ADULTS

When the weevils emerge from the pupal stage they do not vacate their
pupal cells immediately but remain in this location for two or more
weeks. As late as the middle of September many weevils have emerged
and are within the leader. Xo exit holes in the leaders nor weevils in
the field, were found September 10, 1927, when several plantations were
scouted. In general, we can say that the weevils do not leave the lead-
er much before the middle of September. Emergence from the leader is
continued well into October. For this reason, when interpreting Chart
I, it must be remembered that newly emerged adults may be present in
the leader the last of July, but thej' are not found outside of the leader
for several weeks.

After they leave the leader through circular holes in the loose bark the
weevils immediately go to all parts of the tree and feed. The tips of the
lateral branches, in the region of new growth, seem particularly attrac-
tive. The weevils eat small patches of bark and cambium at this time,
but cause no appreciable damage to the tree.

As shown in the first part of this paper, the adults of this generation
seldom, if ever, mate in the fall. Xo egg laying takes place at this sea-
son. Dispersion is believed to take place in the spring.

The weevils after feeding for a varying length of time hibernate in the
duff below the tree from which the}^ have emerged. Many weevils were
found on infested trees examined October 12, 1928. Usually the weevils
gradually disappear from the tree about the latter part of October and
enter hibernation. Hibernation will take place even if the weather is
warm. They hibernate in the duff close to or on top of the ground but
do not enter the soil. The position of the weevils in the duff varies from
just beneath the surface needles to a point next to the underlying ground,
a distance of three inches. Graham (1926), with a modification of the
Berlese trap, succeeded in securing ^\^eevils from hibernating material
with little effort. The task of attempting to find weevils without using
some special apparatus is difficult, due to their close resemblance to part-
icles of duff.

THE NORTHERN PINE WEEVIL

Pissodes approximatus, Hopkins

In this investigation a weevil, presumably Pissodes opproximatus, Hop-
kins, was found attacking the trunk and roots of white pine. The eggs
are laid in the trunk about a foot from the ground. The larvae upon
hatching work under the bark of the trunk and larger roots, usually kill-
ing the tree.

The life history of P. approximatus appears to be similar to that of
P. slrobi. In 1926 adults in white pine were first found at Madbuiy,
N. H., August 6. Specimens were taken the latter .part of August from
the roots of eight year old red pine located in Keene, N. H. On August
30, 1927, fifteen adults, presumed to be P. approximatus, were taken from

24 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

the trunk and roots of a dead white pine located in the Dover Road
plot. Mature larvae and pupse, and predacious Lonchea larvae, were
found in the same tree. In 1928, one pupa taken from the roots of a dy-
ing white pine transformed July 12.

P. approximatus was first described in 1911 by Dr. A. D. Hopkins in
his monograph of the genus Pissodes. Since that time little has been
written concerning it. Felt (1926) reports this species in company with
Hylobius pales, Hbst., attacking Scotch pine. Britton (1919) mentions
it as attacking red pine and stone pine.

Hopkins (1911) says P. approxi?natus can be distinguished from P. stro-
bi by the average larger size and elongate body. The sides of the elytra,
are more narrowed posteriorly. He figures the stems and forks of the
male genitalia. It has been impossible to determine this species by the
kej' given by Hopkins.

A number of experiments were made to determine if the white pine
weevil is able to breed on the trunk and roots of white pine. Several
P. strobi adults were confined to the trunk of a five foot tree by means
of a cylindrical glass tube. Later the tree was dug up and placed in a
pail in the laboratory. Three larvae pupated in the trunk on July 12
and emerged July 25, 1927.

Wire cages, each containing four pairs of white pine weevils, were fast-
ened to the trunks of several trees near the base. Much feeding was
evidenced by the exudation of pitch. Repeated experiments for two
years failed to show breeding in this part of the tree.

The white pine weevil evidently can breed in the trunk of a weakened
tree, such as the one brouglit into the laboratory.

It is possible that adults passing up the trunk after leaving hibernation
may lay eggs in the lower part of the tree. If eggs are laid, they may
hatch and produce larvae which might survive in a weakened tree.

It may be significant that the type specimen of P. approximalus was
reared from a larva in the bark at the base of a white pine tree defoli-
ated bj' the gipsj' moth {Portheiria dispar L.) and tlierefore presumably
weakened.

Our data raise the question whether P. approximalus may not be iden-
tical with P. strobi, though further observations would be necessary for
a definite statement.

CONTROL

No methods of complete control have been developed, although sever-
al satisfactory^ measures for materially reducing infestation are applicable
in ornamental or commercial plantations of white pine. Manifestly, it
may be economically impossible to apply some of the methods used for
controlling the weevil in ornamental plantings to plantations grown for
timber purposes.

Control methods can be divided into two groups, direct and indirect.
Included in the first group are chemical measures such as sprays, washes
and repellents. Direct mechanical measures include, also, the collection

October, 1929] WHITE PINE WEEVIL 25

of adults and the removal of infested leaders. Indirect methods consist
of silvicultural practices to reduce the infestation and to assist the tree
in recovering from weeviling. This is accomplished by adoption of mixed
stands or densely planted stands. Natural or biological control by in-
sect parasites and predators is important.

DIRECT CONTROL METHODS

Chemical Control

Chemical control methods for the white pine weevil have not been fully
investigated. It is a question whether the cost of such control would be
justified in a commercial plantation.

At present we have no spray material giving full control. Walden
(1915) reported that lime-sulphur (1 to 8) was one of the best repellents
tried. Lime-sulphur cannot be expected to give complete control but
will reduce the infestation if applied early in May. Graham (1916) tried
16 different materials including various common spray chemicals. His
results indicated that creosote, which slightly injures the tree, and car-
bolineum, may be of value. Graham found the above materials more
effective than lime-sulphur or arsenate of lead. Experiments by Gra-
ham (1916) and MacAloney (1926), confirmed by us, show that trees
banded with tanglefoot at the base of the leader show^ a substantial de-
crease in weeviling.

In our investigation oil of pine, oil of pine needles, and pinene, were
tried as attrahents. Small muslin bags containing three ounces of bran
saturated with the above oils were tied to the middle lateral branches of
nine trees scattered throughout a plantation. None of these oils attract-
ed any weevils.

Collection of Weevils.

Frequent collection of weevils from the leaders may be applicable to
small ornamental plantings. In order that this method may be effective
weevils should be removed at least once a week during the season. Felt
(1914) and Walden (1915) used a large net, 15 inches in diameter, to
make collecting more expeditious. The net was held on one side of the
leader and the weevils were knocked into it by a sharp blow with a stick
on the opposite side. In New Hampshire collection of weevils has not
proved to be a iiractical means of control.

Removal of Infested Leaders.

The removal of infested leaders just below the farthest point reached
by the larvse is a common method of control. It is important that this
method be practiced successively for several years in order to be effective.
Weevils living for more than one year may be sufficient to cause infesta-
tion the following year after the leaders are pruned. A marked decrease
maj' not be noticed until the third year.

26

N. H. AGRI. EXPERIMENT STATION [l^ullctin 247

This method of control can be used to advantage in smaller plantations
if practiced regularity during the years when the trees are at the age most
susceptible to attack. Of course if all white pine trees in the vicinity
are thus pruned the measure is more effective. Whether this method is
practical in large plantations is a matter for individual decision, accord-
ing to circumstances. Pruning the infested leaders is not ideal, for like
other methods it does not give absolute control. The trees attacked
are just as crooked as the ones whose leaders are not removed, but of
course fewer leaders are weeviled.

The infested leaders should be removed the latter part of June before
the larvae proceed below the first whorl of lateral branches. Another
cutting the last of July will get those previously missed. Care is neces-
sary to prevent the removal of leaders which are injured from other
causes and which would have a chance to recover.

When removed the leaders should not be left on the ground for the
larvae are able to complete development and emerge, thus offsetting all
the benefit that would be derived from pruning.

Often the leaders are burned to destroy the weevils. This procedure
at the same time destroys beneficial insect parasites and predators, impor-
tant in reducing later attack. A method that will kill the weevils and at
the same time allow the parasites and predators to escape is to place the
collected leaders in a tight box or barrel covered with 12 or 14-mesh wire
screen. If 16-mesh wire is used many of the larger insect enemies are
unable to escape. The box or barrel must be tight to prevent the escape
of the weevils. It should be placed in such a position that water will
not collect and drown the beneficial insects. Leaders should remain a
year in the screened container, to allow time for parasites emerging late
in the season to escape and to make sure all of the weevils are dead. The
same container can be utilized from year to year.

Experiments in New Hampshire in cutting off infested leaders show a
reduction in the percentage of weeviling after two years, (Table VI).

In 1928 the trees in the Madbuiy plot were 11 — 13 years old; in the
Dover plot, 14 — 15 years old. From the figures in Table VI it appears
probable that a marked reduction in the Dover plot will be found in 1929.
It maj' be that the weevils that Vive over a second year are responsible
for the high infestation at Madbury in 1927.

Table VI. — Removal of Infested Leaders

Place

MADBURr

Dover

Year

1926

1927

1928

1927

192S

Total Number Trees

3500

3500

3500

1600

1600

203

208

60

130

78

Percent

5.5

5.6

1,8

8.1

4.8

I

October, 1929]

WHITE PINE WEEVIL

INDIRECT CONTROL METHODS

27

Silvicultural Control

Silvicultural control may be brought about (1) by planting white pine
in mixed stands with hardwoods or other species of conifers; (2) by plant-
ing white pine densely.

In planting white pine in mixed stands the principle involved is to
shade the trees sufficiently to reduce weevil attack and at the same time
not interfere with the growth of the white pine. The fact that the wee-
\il is a sun-loving insect makes some measure of control by this method
possible. The hardwoods or conifers used in the mixture should slightly
overtop the white pine during the most susceptible period to weevil at-
tack, that is, -Qntil the trees are about 20 feet high. If this practice is
followed care must be taken not to let the shade trees overtop the white
pine to such an extent that growth of the latter is retarded and the trees
become dwarfed and weakened from competition. Definite schemes of
white pine and hardwood mixtures cannot be suggested since each plan-
tation will present its own problem.

At best this method is not easily planned, since it is difficult to regu-
late the proper amount of hardwood shade for the pine. In New Hamp-
shire the prevalence of the gipsy moth, Porthetria dispar, L., should also
be considered. Caterpillars of the gipsy moth in the third or later in-
stars will migrate to white pine and feed on it.

Dense planting of pine is perhaps the most satisfactoiy method of
control. When white pine is closely planted the trees attacked by the
weevil are better able to recover from injurj' because the competition
for light and space stimulates them to grow straighter. The actual per-
centage of infestation per tree is reduced. In widely spaced stands the
trees tend to become bushy, forked, and crooked and are known as "pas-
ture" or ''cabbage" pines for this reason. Volunteer seedings of pine,
commonly found in New Hampshire, can be made promising plantations
by planting additional pines so that the density appro.ximates 1800 trees
to the acre. In connection with this method it is advisable to remove
the infested leaders in the manner previously described in order further
to reduce the infestation.

Table VII. — Effects of Spacing

1926

1927

Kind of Stand

Spacing

Rate
Per
Acre

No. IN
Plot

No.
Infested

Per
Cent

No.'
Infested

Pbb

Cent

White Pine

4x4
6x6
8x8

8x8

2,722

1,210

907

907

875
378
288
420

20

29

27

18
\Miite Pine

2.2
7.6
9.5

8.6

48

31

32

33
White Pine

5.4

White Pine

8.2

White Pine

11.1

Mixed Red Pine and \\'hite Pine

15.1

28 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

The figures in Table "\TI, derived from plots at the Yale Forestry
School in Swanze}-, N. H., show the correlation between density and in-
festation. These trees were from 8 to 12 feet high.

These trees had been left open to sunlight for three years. Up to the
time of these observations no advantage had been gained by mixing the
red pine and white pine. It is true that the percentage of total .trees at-
tacked in this stand was much smaller, but as the red pines were practi-
cally immune anyway no advantage to the white pine was obtained.

Peirson (1922) and Graham (1926) concluded that planting white pine
at the rate of 1200 or more to the acre will reasonably control the weevil.
The writers believe that planting 1500 or preferably 1800 trees to the
acre will be advantageous.

The trees should be allowed to remain dense until they are from 25 to
30 feet high. Careful thinning as the stand grows will make it possible
to produce good trees showing little unmerchantable timber.

Biological Control

The part nature plays in reducing the number of weevils is of vital
importance. If the high biotic potential of the weevil were not checked
their numbers would far exceed the population actually present. Be-
cause of various natural checks the number of weevils present year by
year is fairly constant; that is, the factors of control are strong enough
to prevent marked outbreaks of this insect.

Since the white pine weevil is an indigenous insect it is improbable
that these natural checks can be artificially increased to any marked ex-
tent. The rearing and liberating of parasites and predators, as practised
against introduced insects, is probabl}- out of the question.

In addition to insect predators birds play some part in control. In
this study the white-breasted nuthatch, Sitta caroUnensis, was the only
bird observed feeding on the larvae in a white pine leader. There are,
no doubt, more species that attack the weevil, for evidences of their feed-
ing are common.

The insect parasites and predators that have been reported attacking
the weevil in its several stages comprise a considerable list of species.
The list of species mentioned in this paper includes only the more impor-
tant ones found in New Hampshire. In addition to these, there are
numerous insects and other Arthropods that are found inhabiting the wee-
viled leaders. Their co-existence with the weevil is of little importance.
Taylor (1928) has listed 90 species of Arthropods taken from weeviled
leaders, in connection with his study of parasites and predators.

Material collected in the course of this study was submitted to Dr. R.
L. Taylor, then at the Bussey Institution, Harvard Uni\-ersity, and par-
asites and predators found were reported by him. Also records were
available from material sent to him from Concord by Mr. W. F. Hale,
assistant state forester. The list of species found, together with those
secured by collection and breeding, follows:

October, 1929] WHITE PINE WEEML 29

Predators

DIPTERA

Lonchcea corticis Taylor (1929), formerly considered as L. rufitar-
sis Macq.; L. polita Say: and L. laticornis Meig., is the most im-
portant predator and also the most important single factor of con-
trol in New Hampshire. L. corticis is responsible for about 50 per
cent reduction in the number of larvae. It also attacks pupse and,
to a le.ss extent, adults. Emergence records extend from May 27 to
July 2, 1928. The fly, shortly after emerging, lays her elongate eggs
in small masses in the bark of an infested leader. After hatching
the larvae remain close together and are found in the larval tunnels
made by the weevil. L. corticis is capable of devouring a larva in
short order. The larvae hibernate together in the pupal cells and
pupate within the leader in the spring. This predator would be
much more effective were it not for a Chalcid, Pleurotropis sp., a
secondary parasite found in large numbers.

COLEOPTERA

Several predaceous clerid beetles are known to attack the weevil.
During this study thej^ have been repeatedly observed on white
pine. Graham (1926) records Elasynoserm terminatus, Say.

Parasites (Parasitoids)

CHALCIDOIDEA

Eurytoma pissodis Gir. is considered an important ectoparasite
of the weevil. Graham (1926) reports 50 per cent parasitism by
this insect in New York. In New Hampshire the parasitism seems
much less, for emergence i-ecords show a total of only 9 males
emerging from 37 leaders compared with 221 male and 187 female
Lonchcea from the same material. Twenty-three leaders from
Concord contained 11 males and 14 females, compared with 33
male and 10 female Lonchcea. The adults emerge during the first
half of July. One specimen pupating June 13 emerged July 12.
The eggs are deposited in infested leaders. Usually only a single
larva is found. After feeding on the larval, pupal, or possibly the
adult stage of the weevil, they pass the winter as larvae in pupal
cells.

Four specimens of Rhopalicus suspensus Ratz. were taken the
middle of June, 1927, from a cage containing infested leaders. One
R. pulchripennis, Crawford, was collected in W. Swanzey on Sep-
tember 3, 1926. It pupated June 13, 1927, and emerged June 27.

One specimen of Coelopisthia sub orbicularis Prov. was taken from
a cage the latter part of May, 1927.

Pleurotropis n. sp., previously mentioned as a secondary parasite,
may emerge from June 1 to the middle of July. Thirty and 43
emerged, respectively, from 37 Durham and 23 Concord leaders
infested in 1927.

30 N. H. AGRI. EXPERIMENT STATION [Bulletin 247

Eupelmus piiii TaA'lor, a primaiy parasite, has not been found
in New Hampshire.

ICHNEUMONOIDEA

A total of 10 male and 20 female Microbracon pini Mues.
emerged from May 27 to June 14, 1927. Only one female emerged
from Concord material. On the basis of numbers this parasite ap-
pears to be important in Durham and not in Concord.

One female Hemiteles hydrophilus Ash. emerged May 29, 1928,
from Concord material.

One male and one female Coeloides pissodis Ash. emerged June
18 and July 2 from Durham leaders.

On September 3, 1926, two specimens of Calliephialtes comstockii
Cress, were collected at W. Swanzey, N. H. This insect has been
reported as a parasite of Petrova comstockiana Fernald, the larva
of which burrows in the twigs of certain conifers, not including
white pine.

Among the braconid parasites mentioned in the literature are
Habrobraconidea bicoloripes Vier. ; Microbracon vanus Prov.; Bra-
con pissodes Ashm.; Spathius brachyrus Ashm.; and Doryctes sp.

CYNIPIDAE

The cynipid, Eacoila sp. wa.s fairly abundant in Durham mater-
ial. Emergence takes place the first half of July. Barnes (1928)
says it is a secondar}- parasite on Lonchcsa.

SUMMARY

The white pine wee\-il is the most important pest of white pine in New
Hampshire.

It attacks dominant trees of large tip diameter in preference to reces-
sive trees of small tip diameter.

Some other species of conifers are occasionally attacked.

The weevil appears the latter part of April or the first of May and be-
gins ovipositing.

Mating takes place in the spring. The female does not have to cop-
ulate throughout the season in order to jjroduce fertile eggs.

The female may lay from 25 to 201 eggs in one season. The average
in these observations was 129.

The ovipositing period terminates near the middle of July.

At the end of oviposition the weevils move to other parts of the tree,
especially to the tips of the lateral branches in the vicinity of new growth.

Some weevils do not die the first year but hibernate and appear a sec-
ond season.

The weevils have a marked tendency to remain on a single host tree.

Dispersion is believed to take place in the spring.

The egg stage varies from 5 to 20 days, the average in these experi-

October, 1929] WHITE PINK WEEVIL 31

ments being 9.3 days in the insectary cage and S.6 days in the greenhouse.

Lar\-ae may be found from the last of May to the middle of September.

The larval stage varies from 26 to 41 days, the average being 36.1 days
in the cage and 33.4 days in the greenhouse.

The pupal period extends from the middle of July to the last of Sep-
tember.

The pupal stage varies from 9 to 20 daj'S, the average being 13.9 in the
cage and 12.2 in the greenhouse.

Total development reciuired an average of 56 daj'S in the cage and
52.7 days in the greenhouse.

The newly-emerged adults remain in the leader for several weeks.

Newly-emerged adults feed in the region of new growth before hiber-
nating in the duflf.

Observations on Pissodes approximatus Hopkins are given.

Lime-sulphur (1-8) may be of value in control.

Mixed stands of white pine and other conifers or hardwoods when pro-
perly grown will show reduced weeviling.

Dense planting at the rate of 1800 trees to the acre will materially re-
duce the percentage of infestation.

Lonchcea corticis Taylor, a dipteron predator, is the most important
natural control factor in Xew Hampshire.

REFERENCES.

Barnes, T. C. 192S. A biological study of the white pine weevil with special

reference to flight, oviposition, phenology, geotropism, parasites, and injuries

to young trees. Doctorate Thesis. Bussey Institution, Harvard University.
Britton. W. E. 1919. The white pine weevil. 19th Report of State Entomolo-
gist, Conn. Agr. Exp. Sta. Bui. 218, p. 144-155, Figs. 17-19.
Currie, Rolla P. 1905. The white pine weevil. Catalog of exhibit of economic

entomology at the Lewis and Clark Centennial Exposition, Portland, Ore.,

U. S. Bur. Ent. BuL 53, p. 91
Felt. E. P. 1913. The white pine weevil. Twenty-ninth Report of the State

Entomologist of New York, p. 30-33.

1926. P. approximatus Hopk. in the roots of Scotch pine. Insect Pest Sur-
vey. Oct. 1.
Graham, S. A. 1916. Notes on the control of the white pine weevil. Jour.

Econ. Ent. Vol. 9, p. 549-551, Table 1.

1926. Biology and control of the white pine weevil, Pissodes strobi Peck.

Cornell Univ. Agr. Exp. Sta. Bui. 449, p. 1-32, Fig. 14.
Hopkins, A. D. 1907. The white pine weevils. ' U. S. Bur. Ent. Circ. 90, p. 1-8,

Fig. 6.

1911. Contributions toward a monograph of the genus Pissodes, U. S. Bur.

Ent. Tech. Ser. No. 20, p. 1-68, Figs. 1-30
MacAloney, H. J. 1926. The white pine weevil problem in the New England

states. Pprs. Forest Prot. Conf., N. Y. St. Coll. Forestry, Nov. 10-12, p. 31-

43, Fig. 4. Syracuse. N. Y.
Packard, A. S. 1890. The white pine weevil, U. S. Ent. Com. Rept. 5, p. 734-

741, 829-830.
Peck, W. D. 1817. On the insects which destroy the young branches of the pear

tree, and the leading shoot of the Wevmouth pine. Mass. Agr. Repository

and Journal, Vol. 4. No. 3, p. 205-211, pis. 2.
Peirson, H. B. 1922. Control of the white pine weevil by forest management.

Harvard Forest Bui. 5. p. 1-42.
Plummer, C. C. 1929. Oogenesis in the white pine weevil. Unpublished data.
Say. T. 1831. Description of North American Curculionidae and an arrangement

of some of our own species agreeably to the method of Schoenherr, p. 14,

New Harmony. 3rd.
Tavlor. R. L. 1928. A new species of Lonchaea Fallen (Lonchaeidae, Diptera).
' Bui. Brook. Ent. Soc. Vol. 23, p. 191-194.

1928. The Arthroped fauna of coniferous leaders weeviled by Pissodes strobi

(Peck). Psyche. Vol. 35, p. 217-225.
Walden B H. 1914, 1915. Experiments in controlling the white pine weevil.

Rep. Conn. Agr. Exp. Sta. for 1914, p. 173; 1915, p. 134.

^

:;if||i|||||||i|i::

:!iSiiiiiilliiiiiilMi