An alternative reproductive tactic: a parasitoid wasp gathers and guards a harem by pheromone-tagging virgins.

Alternative reproductive tactics (ARTs) are the outcome of decisions to obtain copulations in reproductive competition. Mating tactics male insects exhibit can be based on their competitive ability, or be dependent on conditions such as a competitive setting and the spatial and temporal distribution of receptive females. When females are clustered and numerous, two or more mating tactics can coexist. We predicted that this concept is applicable to the egg parasitoid wasp Ooencyrtus kuvanae (Hymenoptera: Encyrtidae), because wasps emerge en masse as sexually mature adults from gypsy moth, Lymantria dispar, egg masses. We reveal that male O. kuvanae exhibit two ARTs, a mate-at-once (MAO) tactic, and a harem-gathering and -guarding (HGG) tactic. MAO males invariably and immediately mate females they encounter. HGG males (i) typically mate the first receptive female they encounter, (ii) then find and assess other females, (iii) tag those without prior male contact, and finally (iv) return to, and mate with, all females they themselves have tagged. Females do not incur a direct fitness cost by mating with multiply-mated males. HGG males rely on their speed, unique tag pheromone, and on the females' rejection of HGG males except the one that pheromone-tagged them. The tagging pheromone mediates mate recognition and assessment.

Does the stereochemistry of methylated cuticular hydrocarbons contribute to mate recognition in the egg parasitoid wasp Ooencyrtus kuvanae?

Close-range sexual communication of the egg parasitoid wasp Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) takes place on host gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae), egg masses. We tested the hypothesis that mate recognition in O. kuvanae is mediated, in part, by low-volatility cuticular hydrocarbon (CHC) pheromone components. Gas chromatographic and GC-mass spectrometric analyses of body surface extracts of male and female wasps revealed no sex-specific components, but 5-methylheptacosane (5-me-27Hy) and 5,17-dimethylheptacosane (5,17-dime-27Hy) were consistently more abundant in extracts of males. The ratio of 5-me-27Hy and 5,17-dime-27Hy was similar in extracts of males and females, and quantitative differences alone seemed insufficient to impart sex-specific CHC profiles. Therefore, we further hypothesized that the absolute configuration of 5-me-27Hy and 5,17-dime-27Hy contributes to mate recognition or attraction. As the stereoisomers of 5-me-27Hy and 5,17-dime-27Hy cannot currently be separated chromatographically, we could not determine the stereochemistry of the insect-produced components. Instead, we synthesized all stereoisomers and bioassayed synthetic blends in laboratory experiments. Of eight 2-component blends, each blend containing one of the two enantiomers of 5-me-27Hy and one of the four stereoisomers of 5,17-dime-27Hy, the blend of (5S)-methylheptacosane and (5R,17S)-dimethylheptacosane attracted males, whereas the blend of (5R)-methylheptacosane and (5R,17R)-dimethylheptacosane repelled males. Apparent recognition of both pheromone components and pheromone antagonists by males supports the hypothesis that the stereochemistry of 5-me-27Hy and 5,17-dime-27Hy, and possibly other methylated CHCs, may differ between male and female O. kuvanae, and that these differences may serve in mate attraction and recognition.