Effects of contact kairomone and experience on initial giving‐up time

The foraging efficiency of a parasitoid is defined as the number of hosts parasitized per unit of time. Thus, the search time allocation of the species is an important component of foraging efficiency. Such efficiencies are generally measured within host-containing patches, where a patch is defined as a spatial subunit of the foraging area in which aggregations of resource items occur (Hassell & Southwood, 1978; Li et al., 1992). However, non-host-containing patches may also (negatively) contribute to total efficiency, because parasitism cannot occur in such patches and foraging time is wasted. Hence, the time spent in nonhost-containing patches is important to overall parasitism rates. This component has been greatly ignored in the past, because the goal in most studies has been to evaluate patch residence time as a function of host density. In this paper we consider the cues that parasitoids use to determine how long to search in patches when no hosts have been contacted. To do this, we will employ the concept of initial giving up time (IGUT), defined as the amount of time which a parasitoid allocates to any kairomone-contaminated patch before abandoning it if no hosts are encountered (Morrison & Lewis, 1981). This concept was derived from results on the parasitoid, Trichogramma pretiosum, which frequently abandoned host-containing patches before encountering and parasitizing individual hosts. Here, we extend the concept of IGUT to include non-host-containing patches. The time investment for a patch should be the same or similar among host-containing-patches without encounters occurred and non-host-containingpatches where hosts were removed or left already, as long as the patch contains kairomone. The only published study that considered this problem was that of Nelson & Roitberg (1995) in which the leafminer parasitoid Opius dimidiatus was found to actively search mined leaves (with hosts removed) more than 4 times longer than unmined leaves. Nelson & Roitberg (1995) suggested that host products might cause parasitoids to alter their behaviour. Our goal is to examine how the existence of host cues and past experience with patch quality influences the IGUT, using the solitary parasitoid species, Aphelinus asychis Walker (Hymenoptera: Aphelinidae), and its pea aphid host, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae). We tested the hypothesis that a contact kairomone, present in aphid honeydew, is the first cue used by inexperienced or naive wasps (those that have never had the chance to assess any hosts) to locate their hosts, and that with increasing foraging experience, the role of this cue becomes less important in determining search effort. Our aforementioned hypothesis arises from the functions of honeydew cues, which serve as a general cue as to the possible presence of aphids. As shown by Bouchard & Cloutier (1985), the aphid parasitoid, Aphidius nigripes, not only responds to honeydew odors from a preferred host, Macrosiphum euphorbiae, but also to the less preferred hosts, Myzus persicae and Aphis nasturtii, and even to a nonhost aphid, Rhopalosiphum maidis. When a wasp attacks more than one species of aphid and the identity of potential hosts cannot be predicted in advance, then experience must be used to evaluate other criteria (e.g., visual cues). These other cues may be more accurate, but the specifics of them cannot be predicted in advance. Thus, a good rule would be to use honeydew cues until individual