Hierarchical order of host cues in parasite foraging strategies

Abstract

SUMMARY The importance of host cues to three species of steinernematid nematodes (Rhabdita: Steinernematidae) with different foraging strategies was compared. We presented host materials to nematodes in series to test responses to combinations of host cues. If a fixed hierarchy of cues is followed during foraging, parasites should respond most strongly to cues offered in natural order. Steinernema carpocapsae , an ambush forager, aggregated at the source of volatile host cues only after attachment to host cuticle. They also parasitized hosts more efficiently after contact with cuticle. Steinernema glaseri , a cruise forager, was unaffected by exposure to combinations of host cues. Steinernema feltiae , a nematode with characteristics of both ambushing and cruising, was affected by cue hierarchies when either contact or volatile cues were presented first. Host-associated materials encountered out of the context may not qualify as host cues for the ambush forager, S. carpocapsae . Perhaps the order in which cues are encountered is more predictable for ambushers than for cruisers. Therefore an ambusher's response to host materials has a more fixed contextual framework.