The toxicity and sublethal effects of p,p ‘‐DDT and dieldrin to Aglais urticae (L.) (Lepidoptera: Nymphalidae) and Chorthippus brunneus (Thunberg) (Saltatoria: Acrididae)

SUMMARY Single topical doses of pure p,p '‐DDT and dieldrin (HEOD) were given to the last larval instars of Chorthippus brunneus and Aglais urticae bred under standardized conditions. The symptoms of acute toxicity followed the same pattern in all four insect‐insecticide combinations, and there was a clear inverse correlation between the toxicity of absorbed insecticide and concentration of total lipid when dosed, both being dependent on age. It is probable that developmental changes in concentration of total lipid cause changes in resistance to the lipophilic and hydrophobic organochlorine insecticides. These results illustrate the importance of using the amount of insecticide absorbed rather than the amount applied for the interpretation of data. Unabsorbed insecticide was estimated by methanol rinses; there was some evidence that these remove a small proportion of absorbed insecticide from A. urticae , but not from C. brunneus. Sublethal effects tend to occur at times of lipid mobilization. There was considerable correlation between insecticide persistence and the occurrence of sublethal effects. Both species convert DDT to DDE readily, although only A. urticae retains DDE for long. No obvious effects were detected in C. brunneus. The only effect in A. urticae was retarded pupation when a large dose was applied fairly near the time of pupation. Dieldrin was more toxic and persistent, and caused latent toxicity, deformation of adults, sterility, and hyperactivity of adults in A. urticae , although there were no apparent effects on C. brunneus except for a possible decrease in the time to moult. Neither insecticide affected water uptake in C. brunneus eggs, and development continued normally up to hatch. The hatched nymphs were unaffected by DDT, most of which was in the egg membranes, and the nymphs rapidly metabolized the rest to DDE. Dieldrin did kill nymphs at eclosion. There was no evidence of effects on the genetic constitution of future generations, but the survival and reproductive abilities of individuals can obviously be affected. I conclude, from two measures of the amount of insecticide acquired by A. urticae in the field, and from the amount required to produce sublethal effects, that A. urticae is probably, with present levels of contamination, unaffected by DDT or dieldrin outside sprayed areas, but more information is needed on other possible effects, and on amounts found in wild specimens. I discuss how far this conclusion applies to other insect species.