CHANGES IN FORAGING BEHAVIOR DURING THE INFECTIVE STAGE OF ENTOMOPATHOGENIC NEMATODES

Studies of foraging strategies are often complicated by competing goal s of the forager. In contrast, non-feeding infective juvenile entomopa thogenic nematodes forage exclusively for a single host. Two questions were posed: (1) what is the relationship between metabolic rate, ener gy reserves and foraging strategy and (2) when a foraging strategy fai ls, will an infective-stage parasite switch strategies? Three species of entomopathogenic nematodes were stored in water and changes in thei r behaviour, metabolic rate, energy reserves, and infectivity were mea sured throughout the storage period. Steinernema carpocapsae ambushes insect hosts, whereas S. glaseri and Heterorhabditis bacteriophora cru ise forage. Steinernema carpocapsae was least active and had the lowes t metabolic rate. Heterorhabditis bacteriophora was more active and ha d the highest metabolic rate. Steinernema glaseri was most active and had an intermediate metabolic rate. Neither cruising species changed f oraging strategy. Steinernema carpocapsae decreased nictation (a behav iour associated with ambushing only) and increased their locomotory ra te. Any change in searching strategy occurred without assessment of th e profitability or distribution of potential hosts, but the advantage this confers is unknown.