KNTOJIOLOGY AND PLANT QUARANTINE 
59 
ill the fall of 1936, which partially accounts for the light boll weevil infesta- 
tions in manv areas at the beginning of the 1937 season. 
In Oktibbeha County, Miss., the leaf worms appeared late in July; and about 
August 20, when the second generation of worms began to strip the plants, two 
tests were conducted to determine the amount of damage caused to the crop 
by the leaf worms. In these tests the average gain from dusting was 288 
pounds of seed cotton per acre, the cost of treatment was $2.18, and the profit 
was $10.39 per acre. The increased production was due in part to the develop- 
ment of heavier bolls on the plants that had not been defoliated. 
THRIPS 
Thrips were reported from practically all cotton-growing States as especially 
injurious to seedling cotton during 1936. The extremely dry season was favor- 
able for the increase of thrips. The most extensive damage to cotton occurred 
in the Southeastern States. 
In Cullman County, Ala., during June a large proportion of the cotton plants 
on several thousand acres were defoliated by thrips. A series of tests with 
cube, nicotine, and pyrethrum as dusts and paris green and nicotine as sprays 
v,-as conducted, but no noticeable control vras obtained with any of them. 
With few boll weevils present and favorable seasonal conditions for cotton 
following the serious thrips outbreak in this region, a good yield of cotton was 
produced even though it was delayed 15 to 20 days by the heavy thrips infesta- 
tion during June. In Washington County, Miss., a study of thrips injury to 
40 commercial varieties of cotton revealed no difference in varietal infestation, 
but it was found that early chopping and allowing a greater number of stalks 
to remain in the hill decreased the percentage of terminal buds damaged. 
Destruction of the terminal buds caused a loss in seed-cotton production in 34 
out of 40 varieties and a loss in staple length on damaged plants of 7 varieties. 
Several species of thrips were involved in injury to cotton. 
HEMIPTEROUS INSECTS 
Further studies on the complex problem of damage to cotton in Arizona by 
hemipterous insects confirmed previous results that the most injurious species 
are three stinkbugs of the family Pentatomidae, viz, Enschistus impictlventris 
Sti^l, ChJorocliroa sayi Stal. and Thyanta custator F. All of these feed on the 
bolls and cause shedding, but the most noticeable injury is the lowering of 
grades caused by staining of the lint by pathogenic organisms which follow 
the puncturing of the bolls. The damage was greatest in Yuma County and 
lightest in Pima Coimty, the average of bolls punctured in Arizona being 24 
percent in 1936 as compared with 27 percent in 1935 and 23 percent in 1934. 
Experiments in control with insecticides made on a field basis with power 
dusting machines gave promising results but were not conclusive as to the 
most effective insecticide combinations and methods of application. Popula- 
tion counts of hemipterous cotton insects were made throughout the season on 
frops and weeds to secure information concerning the host-plant relationships 
of the different insect species in connection with their migrations to the cotton 
fields. 
THURBERIA WEEVIL 
Studies over a 10-year period on the life history and habits of the Thurberia 
weevil when removed from its native host. Thiir'beria, and bred exclusively on 
cotton indicate that this weevil v.ill not maintain itself on cultivated cotton 
under the usual cultural practices followed in southeastern Arizona. Experi- 
ments and observations show that where the stalks are destroyed in the fall 
and the usual irrigation practices applied it can be exterminated in 1 year where 
reinfestation from Thurberia plants does not occur. In the vicinity of natural 
infestation, where the weevil readily transfers from Thiirho'ia to cotton, the 
infestation was greatly reduced by destruction of the Thurbcria plants for a 
distance of 1 mile from the cultivated area. It appears that the greatest 
danger from the Thurboria weevil would be its introduction to sections with 
jnore favorable climatic conditions where the boll weevil occups, as it inter- 
breeds with the latter and might produce a biological race more resistant than 
the boll weevil to hot, dry weather and low temperatures. 
BOLLWORM 
In experiments for controlling the bollworm by insecticides, special attention 
was given to determining if the dusting schedule could be simplified by making 
a definite number of applications at fixed intervals. With the heavy bollworm 
infestations that prevailed in eastern Texas last season the best average in- 
