1. In nature, competitive interactions occur when different species exploit similar niches. Parasitic wasps (parasitoids) often have narrow host ranges and need to cope with competitors that use the same host species for development of their offspring. When larvae of different parasitoid species develop in the same host, this leads to intrinsic and often contest com.petition. Thus far, m.ost studies on intrinsic competition have focused on primary parasitoids. However, competition among primary.hyperparasitoids, parasitic wasps that use primary parasitoids as a host, has been little studied. 2. This study investigated intrinsic competition between two primary hyperparasitoids, the gregarious Baryscapus galactopus and the solitary Mesochoru,s gemellu,s, which lay their eggs in primary parasitoid larvae of tesla rubecula, while those in turn are developing inside their herbivore host, Pieris rapae. The aims were to identify: (i) which hyperparasitoid is the superior competitor; and (ii) whether oviposition sequence affects the outcome of intrinsic competition. 3. The results show that B. galactopus won 70% of contests when the two hyperparasitoids parasitised the host at the same time, and 90% when 13. galactopus oviposited first. When M. gemellus had a 48 h head start, the two hyperparasitoids had an equal chance to win the competition. This suggests that M. galactopus is an intrinsically superior competitor to M. gemellu,s, Moreover, the outcome of competition is affected by time lags in oviposition events. 4. In contrast to what has been reported for primary parasitoids, we found that a. gregarious hyperparasitoid species had a competitive advantage over a solitary species.
- Baryscapus galactopus contest competition insect parasitoid intrinsic competition Mesochorus gemeilus primary hyperparasitoid. induced plant volatiles parasitoid wasps interspecific competition gregarious development heliothis-virescens larval competition pieris-brassicae aphidius-ervi host hymenoptera Entomology