Host-foraging strategies of five local entomopathogenic nematode species in South Africa

Abstract

Entomopathogenic nematodes (EPNs) are obligate parasites of soil-dwelling insects and are used as biological control agents for many insect pests. These nematodes have a free-living third growth stage called infective juveniles (IJs), which are responsible for foraging and infecting suitable insect hosts. Infective juveniles exhibit three host-foraging strategies: cruising, ambushing, and intermediate foraging strategies. The foraging strategy of EPNs is important for successful infection but is poorly understood. The current study investigated the host-foraging strategies of five local South African EPN species including Heterorhabditis noenieputensis, H. safricana, Steinernema fabii, S. jeffreyense, and S. yirgalemense by assessing their dispersal behavior. Of the five EPN species, H. noenieputensis, H. safricana, S. jeffreyense, and S. yirgalemense showed a positive response to the presence of the wax moth larvae, whereas S. fabii showed a negative response. The four EPN species that showed a positive response to the presence of the host also caused 100% mortality of wax moth larvae that were buried in sand at a depth of 10 cm, whereas S. fabii caused the lowest mortality of 34%. The average distance traveled by all five EPN species decreased on rough textured substrate compared with smooth textured substrate. The observed behavioral patterns suggested that H. noenieputensis, H. safricana, S. jeffreyense, and S. yirgalemense use a cruiser foraging strategy whereas S. fabii uses an ambusher foraging strategy.