Possible amplification of insecticide hormoligosis from resistance in the diamondback moth, Plutella xylostella (Lepidoptera : Yponomeutidae)

The possibility that insecticide hormoligosis might be amplified by resistance in the diamondback moth, Plutella xylostella, was tested. The fecundity of females treated with sublethal doses (LD12.5 LD25 and LD50) of fenvalerate or methomyl in the non-selected generation increased in comparison with the control group treated with acetone. The number of eggs laid by treated females in the 10th generation of the fenvalerate-selected strain, which had developed about 10, 000-fold resistance, was the same or smaller than that of the control. On the other hand, fecundity in the 8th generation of the methomyl-selected strain, which had about 4.9-fold resistance, was slightly higher in the LD12.5 and LD25 than that of control. The intensity of insecticide hormoligosis did not depend on the dose of the insecticide although a sublethal dose of the insecticides stimulated reproduction in the susceptible DBM. Furthermore, the hormoligosis was not amplified in concert with the development of resistance in the DBM.