}
SB 2
818 |
C578
ENT

2 146.
Issued February 12, 1912.

United States Department of Agriculture, — (

BUREAU OF ENTOMOLOGY.

L. O. HOWARD, Entomologist and Chief of Bureau.

THE MOVEMENT OF THE MEXICAN COTTON BOLL
WEEVIL IN 1911.

By W. D. Hunters,
In Charge of Southern Field Crop Insect Investigations.

During the season of 1911 the boll weevil was greatly reduced in
numbers throughout its entire range. This resulted from a com-
bination of climatic influences extending over a period of about
three years. So unfavorable were the conditions that the insect
was exterminated in an area covering about 23,000 square miles in
the northwestern portion of Texas and the western portion of Okla-
homa. Undoubtedly these conditions had an important bearing on
the production of the large crop of 1911.

The unfavorable conditions for the weevil which culminated in
1911 began in 1909. In that year drought occurred in Texas and
Louisiana at such a time as to check the development of the imma-
ture stages. In 1910 equally adverse conditions prevailed, and the
pest was further reduced in numbers. At the end of the season of
1910 conditions arose which gave the insect another very important
setback. This was a killing frost which occurred October 29. The
weevils were deprived of their food in all parts of the infested terri-
tory except along the Gulf Coast and in a few isolated localities else-
where. The freeze destroyed outright enormous numbers of the
weevils which were found in the bolls and squares, but the conditions
immediately following the freeze were even more important in re-
ducing the infestation to a very low point. After the freeze of Octo-
ber 29 the weather became warm, and this induced activity on the part
of the weevils that survived. In fact, temperatures occurred for
several weeks which caused the insects to require food. An active
search for food began, but as the cotton had all been killed the ma-
jority of the weevils which had survived the freeze could _find_no

food eee ae i oa qaunsonian testityy™
—Cir. 9,

FEG17 1019

2 THE MOVEMENT OF THE BOLL WEEVIL IN 1911.

The general effect of the cold of October 29 is shown by a study of
the conditions in certain localities which were exempt from freezing
temperatures. In several counties in the vicinity of Cisco, Tex., for
some unexplained reason, the first killing frost in 1910 did not occur
until November 29. At this time most of the weevils were in hiber-
nating quarters. Asa result, in 1911, 1t was found that in the vicinity
of Brownwood there was an area in which the weevils were numerous
and in which considerable damage was done. This area corresponded
exactly with the area in which the freeze of October 29 was not
experienced.

The great reduction in the number of weevils which succeeded in
passing the winter of 1910-11 is shown by hibernation experiments
which were conducted at Tallulah, La. At this place it is determined
- that one-half of 1 per cent of the weevils which entered hibernation
emerged in the spring of 1911. In favorable seasons as high as 12
per cent have survived in that locality and, in fact, the average sur-
vival during seven different seasons in seven widely separated locali-
ties in Texas and Louisiana has been 7 per cent.

The region in which the boll weevil became exterminated in 1911
is the one in which the conditions of drought were most intense in
1909 and 1910 and in which at the same time the conditions for
hibernation are less favorable than in other parts of the cotton belt.
The territory where the loss occurred consists generally of open
country in which but little timber is to be found.

Notwithstanding the great reduction in the numbers of the boll
weevils in the United States in 1911 considerable advance was made
to the east and north when the dispersion movement began in August.
The explanation of this lies in the outbreak of the cotton caterpillar,
which defoliated practically all of the fields throughout the infested
area at about the time the dispersion movement was beginning. The
weevils started on their dispersion flight, encountered fields which
had been stripped by the leaf worm, and continued their flight indefi-
nitely. If the fields just beyond the border of the previously infested .
territory had not been defoliated the weevils would have stopped and
the total area covered would have been much less.

This extensive dispersion of the insect caused it to regain much of
the territory it had lost in Texas and Oklahoma, and Florida became
invaded for the first time. (See map, fig. 1.)

The reasons for the great scarcity of weevils in 1911 are plain.
The reduction was due to a combination of climatic influences
which can only be expected to recur at very infrequent intervals.
With the return of seasons favorable to it the boll weevil will un-
doubtedly regain all of the lost territory and multiply to the same
extent as it has in the past. It must not be supposed from the situa-

THE MOVEMENT OF THE BOLL WEEVIL IN 1911.

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4 THE MOVEMENT OF THE BOLL WEEVIL IN 1911.

tion in 1911 that there is any hope whatever for a permanent reduc-
tion in the importance of the boll weevil. On the contrary, it is nec-
essary for planters to continue their fight against the pest according
to the plans that have been detailed in the publications of the Depart-
ment of Agriculture.
Approved:
James. WILSON,

vomonn neveces. i. iii

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