Distribution of entomopathogenic nematodes in some selected insect species in Osogbo local government area of Osun state, Nigeria

Abstract Entomopathogenic nematodes (EPNs) are leading biological control agents used to combat many insect pests. This study investigated the distribution of EPNs in Zonocerus variegatus (Variegated grasshopper), Mantis religiosa (Preying mantis), butterfly, and moth across dry and rainy seasons in Osogbo Local Government Area, Osun State, Nigeria. Insect samples were collected from cultivated farmlands, grasslands and forested lands using an entomological sweep net. The collected insects were characterized and dissected in normal saline medium for EPNs’ presence. Additionally, 60 soil samples were retrieved from the disturbed agroecosystems (where insects were sampled) and the undisturbed agroecosystem (Osun-Osogbo Groove). The soil samples were screened for EPN presence using Phyllophaga spp. (White grubs) larvae as baits, while infected baits were placed on modified white traps to recover EPNs. A total of 876 insect samples were collected: Zonocerus variegatus (63.5%), Mantis religiosa (4.1%), butterflies (18.0%), and moths (14.4%). After screening, only one Mantis religiosa (0.1%) harbored an EPN, identified as Mermis spp. Statistical analysis showed that season and insect age did not influence EPN distribution ( P > 0.05). The low infectivity of EPN in sampled insects was presumed to be due to EPNs’ foraging strategies, flooding, and other factors. Of 36 soil samples from the disturbed agroecosystem, EPN prevalence was zero, whereas all 24 soil samples from the undisturbed agroecosystem contained Heterorhabditis spp. The absolute frequency of EPN occurrence was zero in the disturbed agroecosystem compared to 100% in the undisturbed agroecosystem. This study infers that anthropogenic activities adversely affect EPN occurrence, dispersal, and persistence.