Odour‐mediated long‐range avoidance of interspecific competition by a solitary endoparasitoid: a time‐saving foraging strategy

Abstract

Summary 1.In studies on optimal foraging strategies, long-range decisions in the pursuit of resource are rarely considered. This is also the case for sympatric parasitoids, which may be confronted with the decision to accept or reject host larvae that are already parasitized by a competing species. They can be expected to reject already parasitized hosts if it is likely that they will lose the resulting intrinsic competition. However, examples of such interspecific host discrimination are rare. 2. We propose that parasitoids that are not egg-limited should reject inferior hosts only if it saves them time, and that this will be achieved mainly when the parasitoids are able to detect competitors from a distance. We tested this hypothesis using the sympatric parasitoids Cotesia marginiventris (Cresson) and Campoletis sonorensis (Cameron). 3. C. sonorensis was found to be the superior intrinsic competitor but, upon contact with a host larva, both wasps readily accepted hosts that had already been parasitized by the other species. However, in an olfactometer experiment, C. marginiventris females were found to strongly avoid the odour of their superior competitor. 4. These results are in accordance with a time optimization scenario, whereby the inferior competitor accepts competition if it costs only an egg, but avoids competition if it may save time that can be allocated to the search for more profitable hosts. 5. Models on host discrimination strategies in parasitoids had not yet considered discrimination from a distance. Long-range foraging decisions can also be expected for other organisms that have to choose between resources of varying suitability and profitability.

Do past experience and competitive ability influence foraging strategies of parasitoids under interspecific competition?

“…When the time interval between the two ovipositions is very short, the survival of equally aged parasitoid larvae is independent of the oviposition sequence ( Bai & Mackauer, 1991;Mackauer et al , 1992;Tamò et al , 2006 ). For this purpose, individual aphids isolated on a piece of wheat leaf were offered to an A. rhopalosiphi female.…”

“…In the case of multi-parasitism, parasitoid larvae compete for the possession of the host by physical fights or physiological suppression, leading to the death of supernumerary immatures ( Salt, 1961;Bai & Mackauer, 1991;Godfray, 1994 ). Until now, only a few studies have addressed the question of the effect of interspecific competition on the foraging strategies of parasitoids ( Vet et al , 1984;McBrien & Mackauer, 1990;Janssen et al , 1995;Takasu et al , 1998;Tamò et al , 2006 ). Females may interact directly (interference competition), by attacking and chasing other parasitoids arriving on the patch ( Godfray, 1994;Fields et al , 1998 ), or, more often, indirectly by reducing the proportion of healthy hosts available for the others (exploitative competition).…”

New parasitoid-predator associations: female parasitoids do not avoid competition with generalist predators when sharing invasive prey

“…Avoidance of conspecific competitors has been reported for parasitoid species, but few studies have focused on avoidance of heterospecific competitors. In arthropods, avoidance of heterospecific competitors has been demonstrated in bark beetles (Byers 1993), phytophagous mites (Pallini et al 1997), predatory mites Gnanvossou et al 2003), and parasitoids (Janssen et al 1995;Tamo et al 2006;Cancino et al 2012). However, avoidance is not always systematic (Janssen et al 1999) and avoidance mechanisms are often not clearly identified.…”

Population genetic structure of two primary parasitoids of Spodoptera frugiperda (Lepidoptera), Chelonus insularis and Campoletis sonorensis (Hymenoptera): to what extent is the host plant important?

“…The larval parasitoid C. sonorensis, like many others of its kind, relies on volatiles emitted by caterpillar-damaged plants to locate hosts (Elzen et al 1983;McAuslane et al 1991;Tamò et al 2006). Chelonus insularis is an egg-larval parasitoid and could use cues coming directly from the eggs and traces of pheromones or other chemicals left by ovipositing females to locate host eggs, but evidence is mounting that eggs, once deposited on plants, may also trigger the emission of volatiles by plants that attract egg parasitoids (reviewed by Fatouros et al 2008).…”