Systemic effect of aldicarb, dimethoate and ethiofencarb on mortality and population dynamics of the spirea aphid, Aphis citricola Van der Goot

Abstract A bioassay using detached citrus leaves, the petioles of which were immersed in solutions containing insecticides, was used to assess the systemic activity of aldicarb, dimethoate and ethiofencarb on the spirea aphid, Aphis citricola Van der Goot (Homoptera: Aphididae). At identical concentrations in the treatment solutions the order of toxicity to insects of these compounds was aldicarb > dimethoate > ethiofencarb. The toxicity of the residue of aldicarb in the leaves (LC 50 =2·5 μg/g) resembled that of dimethoate (LC 50 =1·8 μg/g) and both were more potent than ethiofencarb (LC 50 =30 μg/g). The amount of aldicarb accumulated in the leaves, 3 days after application, was 25±0·5% of that present in the treatment solution, compared with 4±0·4% of dimethoate and 3±0·3% of ethiofencarb. Thus, the more efficient uptake of aldicarb may be the reason for its high toxicity. When sublethal concentrations of aldicarb incorporated in treatment solutions were taken up by detached leaves, a significant reduction in the pre-reproductive development time, and increased longevity and fecundity were observed. This hormoligosis phenomenon was further emphasized by a considerable increase in aphid weight. This effect seems to be plant mediated, as it was not observed when aldicarb was added to a synthetic diet. Dimethoate showed an effect similar to that of aldicarb, but less pronounced and not statistically significant, whereas ethiofencarb had no such effect.