10 ANNUAL REPORTS OF DEPARTMENT OF AGRICUI/TURE, 1951 
there. Late in June infestations of lepidopterous larvae, principally 
the bollworm and the tobacco budworm, were reported in many areas 
in Mississippi. By the latter part of t lie month 1 i irl 1 1 infestations had 
been reported From most of the cotton-growing States. Reports of 
light infestations of lepidopterous Larvae were received from most 
State- in July. By the third week of Auirii-t infestations requiring 
control were reported from many pan- of Louisiana, Texas, Okla- 
homa, and Arizona. Because of a critical shortage of DDT and 
toxaphene, Losses due to bollworms were serious in some areas in these 
State-, especially in ( )klahoma. 
In experiments near Waco, Tex., toxaphene dusl gave better control 
of the bollworm than toxaphene spray. Dieldrin applied at a dosage 
effective for the boll weevil did not give satisfactory control of boll- 
worms. A mixture of aldrin and DDT applied by ait-plane 
spray, at a rate of 0.375 pound of aldrin and 0.375 pound of DDT an 
acre, controlled a heavy infestation of bollworms in a Large-scale 
experiment in north Texas, where rains were frequent and insects 
plentiful. The control of the bollworm with this small quantity of 
DDT was attributed to the fact t hat the t reatments were started a- the 
infestation developed and were continued at regular intervals 
throughout the infestation period. 
Causes of Seasonal Decline in Effectiveness of Insecticides Studied 
Field cage tests over a 3-yearperiod at ( College Station. Tex., showed 
the effect of the advancing season on the effectiveness of several insecti- 
cides against the boll weevil. Toxaphene, technical benzene hexa- 
chloride, aldrin. and dieldrin were only about one-half a- effective in 
September and October a- in dune and July, and calcium arsenate was 
approximately two-third- as effective. Dp to four time- the normal 
dosage of these insecticides did not increase late-season mortality. 
Extremely high dosages were required to effect in September and 
October a kid equal to that obtained in June and July. In one 
season's tests, EPN did not -how the reduction in effectiveness shown 
by the chlorinated hydrocarbon insecticides and calcium arsenate. 
Phosphorus insecticides evidently differ from the other insecticides in 
the way they affect the boll weevil. 
Biochemical investigations showed that the fat content of the boll 
weevil greatly increased a- the season advanced. ran<_ r inL r from an 
average of L9 percent on a dry-weighi basis in overwintered weevils 
in June t<> ■_'•_'. ( .> percent in field-collected weevils in October. When 
correlated with toxicity data, these results indicate a highly significant 
negative relationship between the fat content of tin 4 boll weevil and 
the effectiveness of certain chlorinated hydrocarbon insecticides, a 
relat ion-hip not evident with EPN, 
This research was conducted with funds authorized under the 
Eft search and Market ing Act. 
Bureau Sponsors Conference <>n Cotton Insects 
The yearly conference to pool the results of experiments on the con- 
trol of cotton insects wbs of wider scope than in previous years. 
Participating in the fourth conference, held at Memphis. Tenm. in 
December I960, were 7<» entomologists ami associated technical work- 
