365 



with methyl parathlon, azinphosmethyl, malathion, and EPN®, (0-theyl 0-£-nltro- i, 



phenyl phenylphosphonothioate) indicating potentiation of toxicity. It was not i 



possible, however, to attribute significance to the numerical degree of inter- 

 action since the mechanism of potnetiation in these mixtures is unknown. The po- 

 tentiation of methyl parathion by DEF was not supported by statistical evidence, 

 indicating that the addition of DEF may not necessarily result in greater-than- 

 additive toxicity. The potentiating effects of DEF with malathion have previous- 

 ly been attributed largely to inhibition of aliesterase, a type of carboxyesterase. 

 Conversely, EPN, azinphosmethyl, and methyl parathion lack carboxylic ester 

 moieties, and the importance of aliesterase is questionable. / 



716. , and Chambers, H. W. 1970. Temperature relationships in organophosphorus 



poisoning in boll weevils. J. Econ. Entomol. 63: 502-504. 

 A laboratory culture or organophosphorus-susceptible boll weevils are exposed at 

 different temperatures to cotton leaves or filter-paper discs previously treated 

 with insecticide or defoliant. All materials examined showed a positive tempera- 

 ture coefficient of toxicity with methyl parathion and malathion being the most 

 toxic at all temperatures. The toxicities of azinphosmethyl and EPN® (O-ethyl 

 0-p-nitrophenyl phenylphosphonothioate) were severly decreased at lO^C while 

 DEF® (S, S, S-tributyl phosphorotrithioate) showed appreciable toxicity only at 

 32"'C. Studies involving different exposure and holding temperatures indicated 

 that a higher exposure temperature results in increased toxicity, even though 

 the holding temperature is the same for all treatments. Although transferring 

 the insects to a low holding temperature from a high exposure temperature de- 

 creased the effectiveness of the toxicant, the corrected mortality of the in- 

 sects exposed at 32*'C and held at 10*'C was more than twice that of those exposed 

 and held at 10°C. These data suggest that temperature may affect both the innate 

 toxicity and the rate of absorption of the insecticide into the insect. 



J 



