Effects Of Potent Fungal-Based Biopesticides On Promising Indigenous Fall Armyworm (Spodoptera Frugiperda) (J. E. Smith) (Lepidoptera: Noctuidae) Associated Parasitoids In Kenya.

Abstract

Maize is a major staple food crop in sub-Saharan Africa, mainly grown by resource-poor farmers. It is the third most important agricultural commodity worldwide after rice and wheat. However, its production is threatened by several biotic and abiotic factors such as cereal pests, parasitic weeds (striga), moisture stress, low fertility and diseases that inflict 15 – 90% yield losses. Arthropod pests are among the main factors leading to low maize yield and are central to many of today's major maize production challenges. These losses have been aggravated by the recent invasion of Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), a highly polyphagous pest that affects many crops with a great preference for cereal crops such as maize, sorghum, and rice. Many control strategies have focused on the use of synthetic chemical pesticides which has a lot of adverse effects to human and environmentand has been ineffective. Biological control of FAW using parasitoids; Telenomus remus, Cotesia icipe and entomopathogenic fungal-based biopesticides have been explored. However, the combination of these biocontrol agents against FAW has not been evaluated in the invaded areas. In this study, four most potent entomopathogenic fungal isolates mainly Metarhizium anisopliae (ICIPE 7, ICIPE 41 and ICIPE 78) and Beauveria bassiana ICIPE 621) were screened against FAW in the laboratory through direct and indirect fungal infections to assess their pathogenicity and virulence against T. remus and C. icipe, and determined their effects on the oviposition, emergence and parasitism rates of these parasitoids. The results showed high susceptibility of the parasitoids through direct infection, where M. anisopliae ICIPE 78 caused the highest mortality rate on adult T. remus (95.83 ± 4.17%) after direct infection of dry conidia to the adult parasitoids, whereas both M. anisopliae ICIPE 7 and ICIPE 41 caused 100% mortality to adult C. icipe seven day post-infection. However, the infected adult parasitoids were able to parasitize FAW larvae that were exposed to them prior to their death, but their F1 generation emergence was also significantly affected by direct fungal infection, with highest number of parasitoids recorded in the control (83.25 ± 5.94%) compared to fungal treatments. In the indirect infection where infected second instar FAW larvae were exposed to the parasitoids, M. anisopliae ICIPE 7 and ICIPE 41 and B. bassiana ICIPE 621 caused moderate mortality rates to T. remus, except M. anisopliae ICIPE 78 that caused >60% mortality to this egg parasitoid at all the concentrations (1 x 105 – 1 x 109 conidia/ml). However, the mortality rates of the endoparasitoid C. icipe increased when

the fungal isolates concentrations also increased. In both direct and indirect infections, additional induced mortality of FAW eggs and larvae was also obtained. Furthermore, high parasitism rates were obtained for both parasitoids in indirect fungal treatments as well as in the controls compared to direct infection experiment where the parasitism rates were lower (~40%) in fungal treatments than the controls (83.25%) for T. remus; while high parasitism rates were observed in M. anisopliae ICIPE 78 (62%) and B. bassiana ICIPE 621 (58%) compared to 35.75 and 36.75% in M. anisopliae ICIPE 7 and ICIPE 41, respectively for C. icipe. This study demonstrated that effective combination of entomopathogenic fungal-based biopesticides with both parasitoid species through indirect infection provide better suppression of FAW populations and consequently could be integrated into FAW-IPM strategies.

Maize is a major staple food crop in sub-Saharan Africa, mainly grown by resource-poor farmers. It is the third most important agricultural commodity worldwide after rice and wheat. However, its production is threatened by several biotic and abiotic factors such as cereal pests, parasitic weeds (striga), moisture stress, low fertility and diseases that inflict 15 – 90% yield losses. Arthropod pests are among the main factors leading to low maize yield and are central to many of today's major maize production challenges. These losses have been aggravated by the recent invasion of Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), a highly polyphagous pest that affects many crops with a great preference for cereal crops such as maize, sorghum, and rice. Many control strategies have focused on the use of synthetic chemical pesticides which has a lot of adverse effects to human and environmentand has been ineffective. Biological control of FAW using parasitoids; Telenomus remus, Cotesia icipe and entomopathogenic fungal-based biopesticides have been explored. However, the combination of these biocontrol agents against FAW has not been evaluated in the invaded areas. In this study, four most potent entomopathogenic fungal isolates mainly Metarhizium anisopliae (ICIPE 7, ICIPE 41 and ICIPE 78) and Beauveria bassiana ICIPE 621) were screened against FAW in the laboratory through direct and indirect fungal infections to assess their pathogenicity and virulence against T. remus and C. icipe, and determined their effects on the oviposition, emergence and parasitism rates of these parasitoids. The results showed high susceptibility of the parasitoids through direct infection, where M. anisopliae ICIPE 78 caused the highest mortality rate on adult T. remus (95.83 ± 4.17%) after direct infection of dry conidia to the adult parasitoids, whereas both M. anisopliae ICIPE 7 and ICIPE 41 caused 100% mortality to adult C. icipe seven day post-infection. However, the infected adult parasitoids were able to parasitize FAW larvae that were exposed to them prior to their death, but their F1 generation emergence was also significantly affected by direct fungal infection, with highest number of parasitoids recorded in the control (83.25 ± 5.94%) compared to fungal treatments. In the indirect infection where infected second instar FAW larvae were exposed to the parasitoids, M. anisopliae ICIPE 7 and ICIPE 41 and B. bassiana ICIPE 621 caused moderate mortality rates to T. remus, except M. anisopliae ICIPE 78 that caused >60% mortality to this egg parasitoid at all the concentrations (1 x 105 – 1 x 109 conidia/ml). However, the mortality rates of the endoparasitoid C. icipe increased when

the fungal isolates concentrations also increased. In both direct and indirect infections, additional induced mortality of FAW eggs and larvae was also obtained. Furthermore, high parasitism rates were obtained for both parasitoids in indirect fungal treatments as well as in the controls compared to direct infection experiment where the parasitism rates were lower (~40%) in fungal treatments than the controls (83.25%) for T. remus; while high parasitism rates were observed in M. anisopliae ICIPE 78 (62%) and B. bassiana ICIPE 621 (58%) compared to 35.75 and 36.75% in M. anisopliae ICIPE 7 and ICIPE 41, respectively for C. icipe. This study demonstrated that effective combination of entomopathogenic fungal-based biopesticides with both parasitoid species through indirect infection provide better suppression of FAW populations and consequently could be integrated into FAW-IPM strategies.