In the Nick of Time: Males of the Parasitoid Wasp Pimpla disparis Respond to Semiochemicals from Emerging Mates

Abstract

Males of the parasitoid wasp Pimpla disparis Viereck (Hymenoptera: Ichneumonidae) aggregate on parasitized gypsy moth, Lymantria dispar, host pupae when the emergence of a prospective mate is imminent or under way. We tested the hypotheses that the developing parasitoid ("DePa") inside the host pupal case produces a pheromone that attracts and arrests mate-seeking males, and that the pheromone is most effective during the emergence of the parasitoid from the host. Results obtained in two-choice laboratory experiments, with 4-7-d-old virgin males, indicate that (1) DePa-derived semiochemicals arrest males, (2) the opening of a host pupal case strongly arrests males, and (3) the arrestment cue emanates from oral fluid secreted by both female and male parasitoids while they chew their way out of a host pupal case. This phenomenon implies that emerging females, which are haplodiploid and can reproduce without mating, do not engage in active pheromone signaling to attract males, and that mate-seeking males co-opt chemicals involved in eclosion as a mate-finding cue, taking a 50% chance that the prospective mate is a female.

Chemically Mediated Mate Finding of the Polyphagous Solitary Parasitoid Itoplectis naranyae (Hymenoptera: Ichneumonidae)

“…Searching for emergence sites will be favored if females mate only once and are immediately receptive after emergence (Godfray 1994). In fact, male parasitoids are known to aggregate at female emergence sites (Matthews et al 1979, Hrabar et al 2012. Hrabar et al (2012) suggested that oral ßuids that soften the host cuticle during eclosion function as sex pheromones.…”

“…In fact, male parasitoids are known to aggregate at female emergence sites (Matthews et al 1979, Hrabar et al 2012. Hrabar et al (2012) suggested that oral ßuids that soften the host cuticle during eclosion function as sex pheromones. Males of I. naranyae also search for female emergence sites.…”

“…Jewett and Carpenter (2001) showed seasonal abundance of the parasitoid relating with seasonal prevalence of one of the host species, demonstrating that polyphagous parasitoids would effectively search hosts containing a female with sex pheromones. However, in an ichneumonid, Pimpla disparis Viereck, oral ßuids secreted from both sexes to soften the host cuticle during eclosion play a role as a semiochemical in sexual communication (Hrabar et al 2012). Mate-Þnding cues in polyphagous parasitoids may vary in each parasitoid species that emerges from different host species with species-speciÞc habitats and varying seasonal phenology.…”

Learning provides mating opportunities for males of a parasitoid wasp

“…and to arrest in response to a semiochemical cue associated with the emergence of a prospective mate from the host pupa (Hrabar et al., ). As emerging females do not engage in active long‐range signalling (Hrabar et al., ), the males' ability to time their presence at parasitized host pupae prior to or during emergence of a prospective mate is intriguing. A simple strategy for these males would be to stay for days on the same parasitized pupa, and to await the emergence of the prospective mate.…”

“…A simple strategy for these males would be to stay for days on the same parasitized pupa, and to await the emergence of the prospective mate. For P. disparis , waiting seems a risky strategy, considering that males would take a 50% chance that the prospective mate is indeed a female (Hrabar et al., ), and that they would miss other mating opportunities elsewhere. Alternatively, if males were capable of identifying and memorizing the location of many parasitized pupae, they could repeatedly visit them, track their development, and more likely be present at the time of parasitoid emergence.…”