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.