Distribution of Entomopathogenic Nematodes in Some Selected Insect Species in Osogbo Local Government Area of Osun State, Nigeria

Abstract

Entomopathogenic nematodes are leading biological control agents used to combat many insect pests in many regions of the world. This study investigated the distribution of entomopathogenic nematodes in four insect species;Zonocerus variegatus,Mantis religiosa, Butterfly and Moth across dry and rainy seasons in Osogbo Local Government Area of Osun State. Insect samples were collected from different sampling stations; cultivated farmlands, vegetation of grasses, and forested lands using an entomological sweep net. The insects were dissected in a normal saline medium for the presence of EPN. A further verification was made, 36 and 24 soil samples were retrieved randomly from the disturbed agroecosystem; where insects were sampled, and an undisturbed agroecosystem; Osun-Osogbo Groove, respectively. The soil samples were screened for EPN presence usingTenebrio molitor, mealworm as baits, while infected baits are placed on modified white traps to recover EPNs. A total of 876 insects samples comprising;Zonocerus variegatus556 (63.5%),Mantis religiosa36 (4.1%), Butterfly 158 (18.0%) and Moth 126 (14.4%) were collected from the disturbed agroecosystem based on sweep net efficiency and species availability. After screening, only one (1) insect (Mantis religiosa) specimen successfully harbour an EPN, identified asMermisspp. Result from statistical analysis indicates that both season and insects age do not have influence on the distribution of EPN (P>0.05). Moreover, the low infectivity of EPN in the sampled insect was presumed to be caused by EPNs foraging strategies, flooding and other host of factors. This led to further probing through screening of soil samples. Of all 36 soil samples screened from the disturbed agroecosystem, EPNs had zero prevalence. However, from all the (24) soil samples collected from the undisturbed agroecosystem, EPNs belonging to the genusHeterorhabditiswere recovered and identified using morphological and morphometric characters. The absolute frequency of occurrence of EPN in the disturbed agroecosystem was zero compared to 100% recorded for the undisturbed agroecosystem. This study infers that EPN occurrence, dispersal, and persistence in the ecosystem are found to be adversely affected by intense anthropogenic activities.