Spodoptera litura (F.) is an obnoxious cosmopolitan pest that causes serious damage to different economic crops. Entomopathogenic nematodes (EPN) have the potential to control the S. litura larvae. Fifteen EPN isolates were screened, and Steinernema sp. 64-2, four isolates of S. carpocapsae (Weiser), S. longicaudum (Shen & Wang) X-7, and two isolates of H. indica (Poinar, Karunaka & David) were found to cause higher mortality of the second, third, and fourth instars of S. litura than the other tested isolates, with larval mortality rates > 90% after 48 h of exposure. An exposure rate of 12.5 infective juveniles per larva was enough for S. carpocapsae A24, All, and G-R3a-2 and S. longicaudum X-7 to cause 100% mortality of the second instar, and for S. longicaudum X-7 and H. indica 212-2 to cause 100% mortality of the third instar. Five EPN isolates were tested on their virulence at different temperatures and found that all the five EPN isolates performed well against the S. litura larvae at 25 and 30°C, but were not active at 10 and 15°C. Two S. carpocapsae isolates (All and Mex) were virulent against the S. litura larvae at lower temperatures. The five tested EPN isolates were also found to have the ability to infect and kill the pupae of S. litura in the laboratory. The present study further proves that EPN are effective at controlling S. litura, which may partially substitute the use of chemical insecticides, thus reduce the overuse of chemical insecticides.

Insecticide resistance is a major challenge in successful insect pest control as the insects have the ability to develop resistance to various widely used insecticides. Butene-fipronil is a novel compound with high toxicity to insects and less toxicity to the non-target organisms. In the present study, the effect of butene-fipronil alone and in combination with three enzyme inhibitors, piperonyl butoxide (PBO), diethyl maleate (DEM), and triphenyl phosphate (TPP), was carried out on larvae and adults of Drosophilia melanogaster. Our results indicated that the co-toxicity indices of butene-fipronil + PBO, butene-fipronil + TPP, and butene-fipronil + DEM mixtures were 437.3, 335.0, and 210.3, respectively, in the second-instar larvae, while 186.6, 256.2, and 238.5, respectively, in the adults, indicating synergistic effects. Interestingly, butene-fipronil increased the expression of CYP28A5 in the larvae; CYP9F2, CYP304A1, CYP28A5, and CYP318A1 in the female adults; and CYP303A1 and CYP28A5 in the male adults. Furthermore, high-level expression of Est-7 was observed in the female adults compared to larvae and male adults. Our results suggest that there is no difference in butene-fipronil metabolism in larvae and male and female adults of D. melanogaster.

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The toxicities of butene-fipronil to Drosophila melanogaster were evaluated, in comparison to nine conventional insecticides. According to the mean LD50 values of the larvae from CS, w(1118) and Oregan strains, butene-fipronil,abamectin, spinosad and chlorpyrifos exhibited high levels of toxicity. Imidacloprid, α-cypermethrin and clothianidin showed middle levels of toxicity. And acephate,methomyl and acetamiprid had low levels of toxicity. To the adults, butene-fipronil, α-cypermethrin, spinosad, and chlorpyrifos were relatively more toxic, whereas acephate,methomyl, acetamiprid, imidacloprid, clothianidin and abamectin were relatively less toxic. Butene-fipronil and abamectin were more toxic to larvae. In contrast, spinosad,a-cypermethrin, and clothianidin were more toxic to adults.Moreover, the toxic risk assessment using a risk quotient value revealed that butene-fipronil was safe to D. melanogaster adults. Thus, our results suggested that butene-fipronil is harmful to D. melanogaster larvae, but it is relatively safe to the adults.

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