Changes in foraging behaviour during the infective stage of entomopathogenic nematodes

SUMMARY Studies of foraging strategies are often complicated by competing goals of the forager. In contrast, non-feeding infective juvenile entomopathogenic nematodes forage exclusively for a single host. Two questions were posed: (1) what is the relationship between metabolic rate, energy reserves and foraging strategy and (2) when a foraging strategy fails, will an infective-stage parasite switch strategies? Three species of entomopathogenic nematodes were stored in water and changes in their behaviour, metabolic rate, energy reserves, and infectivity were measured throughout the storage period.Steinernema carpocapsaeambushes insect hosts, whereas S.glaseriandHeterorhabditis bacteriophoracruise forage.Steinernema carpocapsaewas least active and had the lowest metabolic rate.Heterorhabditis bacteriophorawas more active and had the highest metabolic rate.Steinernema glaseriwas most active and had an intermediate metabolic rate. Neither cruising species changed foraging strategy.Steinernema carpocapsaedecreased nictation (a behaviour associated with ambushing only) and increased their locomotory rate. Any change in searching strategy occurred without assessment of the profitability or distribution of potential hosts, but the advantage this confers is unknown.