Transgenerational hormesis and sublethal effects of five key insecticides for controlling Spodoptera frugiperda on its endoparasitoid Cotesia marginiventris.

BACKGROUND: The endoparasitoid Cotesia marginiventris (Cresson) is a promising biological control agent of the fall armyworm (FAW) Spodoptera frugiperda (Smith). Because the application of insecticides is one of the prime choices in pest management, we evaluated the sublethal and transgenerational effects of the five key insecticides-chlorantraniliprole, emamectin benzoate, spinetoram, Bacillus thuringiensis (Bt), and Mamestra brassicae nucleopolyhedrovirus (MbNPV)-on the parasitoid. RESULTS: Exposure to five insecticides at a concentration causing 10% mortality (LC10 ) caused hormetic effects in the parent generation (F0 ) by increasing the parasitism and reducing the immature duration. Interestingly, the hormetic response was also observed in the offspring generation indirectly exposed to the insecticides. Furthermore, insecticides increased the parasitism rate by 6.32-14.73% in the F1 generation, which was similar to that of the F0 generation (3.96-11.81%) compared with the control. No significant adverse effect was observed on the number of emerged parasitoids of the F1 and F2 generations. However, insecticides had a detrimental impact on body size and fecundity in the F1 and F2 generations, which showed a small body size with shorter hind tibiae and a significant reduction in the female ratio compared with the control; the exception was that chlorantraniliprole significantly improved the female ratio in the F2 generation. CONCLUSIONS: Five insecticides at LC10 induced transgenerational hormetic and sublethal effects on C. marginiventris. Our results provide a scientific basis for a better understanding of the long-term impacts of insecticides at sublethal doses on parasitoids, facilitating the development of improved integrated pest management programs for FAW control. © 2023 Society of Chemical Industry.

Identification of Chelonus sp. from Zambia and Its Performance on Different Aged Eggs of Spodoptera frugiperda.

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a migratory pest endemic, to tropical and subtropical regions of America. Biological control can effectively and sustainably control pests over a long period of time while reducing the frequency of pesticide use and ensuring the safety of agricultural produce. In our study, the egg-larval Chelonus species (Chelonus bifoveolatus) from parasitized eggs of Spodoptera frugiperda in Zambia were described and identified based on morphological and genetic characteristics. To evaluate the efficiency of C. bifoveolatus, their parasitism suitability on 0- to 2-day FAW eggs under laboratory conditions was compared. The results showed that C. bifoveolatus could accept all FAW eggs at 0-, 1- and 2-day-old age and complete development successfully. Significant differences were found among 0-, 1-, and 2-day-old host eggs with respect to egg-larva developmental duration of C. bifoveolatus, and the egg-larva developmental duration on 2-day-old eggs was significantly lower than those on 0- and 1-day-old eggs. No significant differences were observed in the parasitism, pupation, emergence, and female rates for C. bifoveolatus on various age eggs of FAW. Generally, the parasitism rate, pupal rate, and emergence rate at various ages of FAW eggs were higher than 90%, 75%, and 82%, respectively, and the longevity of female parasitoids was longer than male parasitoids, and the sex ratio of females to males was nearly 1:1. Our results indicate that C. bifoveolatus performed well on various ages of FAW eggs and is a potential biological control agent against FAW in Africa.