1958 - Young, M. R„, and J. S. Roussel. The effects of temperature on the efficiency of 



insecticides applies topically to boll weevils differing in susceptibility to 

 chlorinated hydrocarbon insecticides. J„ Econ. Ent. 51(1):93- 100. 



Greater mortality of the boll weevil resulted at the higher, rather than at 

 the lower, extreme of the post-treatment range of temperatures, with one excep- 

 tion—the response of the resistant strain to the endrin-malathion combination, 

 wherein greater mortality resulted at the lower extreme of the temperature 

 range. 



The 2 strains (resistant and susceptible, or reference) differed greatly in 

 their susceptibility to the chlorinated hydrocarbons. Toxaphene and endrin were 

 ineffective against the resistant strain. 



Endrin and malathion, when combined, were antagonistic at 90°F., but showed 

 a synergistic effect of 60°F and 80°F. On the other hand, toxaphene and malathion 

 combined were antagonistic at 60°F., but showed synergistic effect at 80° and 

 90°F. 



The resistant and reference strains responded similarly to temperature 

 changes for each insecticide used in respect to antagonistic or synergistic 

 effects. These findings indicated that the mechanism which caused synergistic 

 effect and antagonistic effect had differing temperature coefficients of action for 

 the 2 combinations (endrin-malathion and toxaphene-malathion). 



The fact that the same strain (either resistant or susceptible) responded 

 differently to each of the 3 insecticides (endrin, toxaphene, and malathion) when 

 held at different post-treatment temperatures, indicated that each insecticide 

 had a different mode of action. The difference in the amount of insecticide re- 

 quired to control the reference strain as compared with the amount required to 

 control the resistant strain, when held at varying post-treatment temperature 

 levels, is further supporting evidence for such a conclusion. 



This is the logical expectation in the case of malathion (an organic phosphate) 

 and the chlorinated hydrocarbons as a group. However, it is noteworthy that 

 endrin and toxaphene, both being chlorinated hydrocarbons, appeared to have 

 different modes of action. 



In addition to susceptibility to chlorinated hydrocarbon, there was an indica- 

 tion that the 2 strains differ in other physiological functions. The fact that more 

 malathion was required to control the chlorinated-hydrocarbon- susceptible 

 strain than was required to control the resistant strain prevents the assumption 

 that the susceptibility to malathion and the susceptibility to endrin or toxaphene 

 was controlled by the same mechanism. 



It is also significant that although endrin was relatively non-toxic to the 

 resistant strain, it still influenced the toxicity of malathion to this strain. 



1959 - Blum, M. S., N. W. Earle, and J. S. Roussel. Absorption and metabolism of DDT 



in the boll weevil. J. Econ. Ent. 52(l):17-20. 



The basis for the natural tolerance of the boll weevil for DDT was studied 

 by treating weevils topically or by injection and determining the rate of penetra- 

 tion and metabolism of DDT. The weevil has a natural tolerance for DDT which 

 varies with the strain, age, and time of year collected. Overwintered weevils are 

 more sensitive than first-generation populations. Weevils resistant to chlorinated 

 hydrocarbons, such as endrin, are slightly more resistant to DDT than endrin- 

 susceptible weevils. 



Both resistant and susceptible weevils are very susceptible to injected 

 dosages of DDT. The rates of absorption in susceptible and resistant boll weevils 

 are equal; about 60% of a 5//g. dosage being absorbed in 48 hours. Small amounts 

 of DDT are found in both strains, but slightly more in the susceptible insects. 

 DDE is produced in trace quantities by both strains. After 48 hours about 40% 

 of the applied DDT is converted into unknown metabolites. Neither DDE nor DDA 

 is involved in the primary avenue of DDT detoxication. Compounds reported as 

 outstanding DDT synergists in the house fly increase the toxicity of DDT in the 

 weevil only 3- to 5 -fold. DDT is more toxic to the weevil at lower tempera- 

 tures. 



153 



