MONITORING OF CROSS RESISTANCE AMONG SEVERAL INSECTICIDES IN THE COTTON LEAFWORM, Spodoptera littoralis (BOISDUVAL)

The pattern of cross resistance for 14 compounds representing the newest promising and main conventional groups of insecticides (spinosyn, spinosoid, avermectin, pyrethroids, carbamates, organophosphates, oxadiazines, nicotinoides, chitin synthesis inhibitors and chlorinated hydrocarbons) in spinosad and abamectin resistant selected strains were studied. Moreover, the cross-resistance of spinosad and abamectin insecticides in cypermethrin resistant strain and methomyl resistant strain were also studied. Spinosad dipping resistant strain (SDRS), showed clear cross resistance against spinetoram and abamectin where resistance factor (RF) values were 48.81 and 18.39, respectively. Negative cross-resistance was observed against seven of tested compounds i.e., fenvalerate, methomyl, chlorpyrifos-methyl, cyanophos, profenofos, indoxacarb and hexaflumuron. Values of RF for those compounds were 0.79, 0.80, 0.08, 0.98, 0.86, 0.47 and 0.76, respectively. Spinosad feeding resistant strain (SFRS) showed considerable cross-resistance against spinetoram, abamectin and profenofos where RF values were 74.90, 23.24 and 9.36, respectively. RF values for chlorpyrifos, hexaflumuron and endrin were around 2. Negative cross resistance was detected against the rest of tested compounds. Values of RF for only three insecticides (thiodicarb, methomyl and chlorpyrifos-methyl) revealed clear cross–resistance with abamectin dipping resistant strain (ADRS). The values of RF were 16.79, 14.90 and 10.04 fold, respectively. Cross resistance of the rest tested insecticides exhibited either slight cross-resistance levels or negative cross resistance. Using abamectin against adults from parent field strain (PS) revealed that no difference in susceptibility to abamectin between males and females. In cypermethrin dipping resistant strain (CDRS), spinosad had negative cross-resistance representing 0.019 fold as RF value. While it had low level of cross-resistance in methomyl dipping resistant strain (MDRS)(RF=3.44-fold).