Intrinsic competition between primary hyperparasitoids of the solitary endoparasitoid Cotesia rubecula

Abstract

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 competition. Thus far, most 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 Mesochorus gemellus, which lay their eggs in primary parasitoid larvae of Cotesia 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 B. 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 B. galactopus is an intrinsically superior competitor to M. gemellus. 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.

Evolution of larval competitiveness and associated life‐history traits in response to host shifts in a seed beetle

“…Success in agonistic interactions between larvae can be affected by a variety of traits, such as intrinsic fighting ability or mobility (Mayhew & van Alphen, ; Pexton & Mayhew, ), but most notable among these is body size, with an advantage to large size. This is often observed, for example, when larger, older larvae outcompete smaller, younger ones (Messina, ; Tena et al ., ; Zhu et al ., ; Mackauer, ). The body size of juvenile insects is in turn affected by egg size, particularly early in development.…”

The Ecology of Hyperparasitoids

“…In both aphid-and caterpillar-associated hyperparasitoids, the ectohyperparasitoids attacking aphid mummies or parasitoid larvae that have egressed from their caterpillar host develop facultatively on primary endohyperparasitoids and thus may develop as fifth trophic level hyperparasitoids (45,81,141). The outcome of competition between hyperparasitoid species follows intrinsic competition patterns observed in primary parasitoids (22,46).…”

“…The large majority of described hyperparasitoids are known as solitary, perhaps because they are phylogenetically closely related and similar in size to their hosts. Examples of gregarious species include Baryscapus galactopus, Tachinobia repanda, Pediobius bruchicida (all Eulophidae) (111,136,141). Among aphid-associated hyperparasitoids, Dendrocerus liebscheri is an exception with up to eight individuals recorded from a single host mummy (32), while the congeneric D. carpenteri is solitary but may sometimes produce two or three offspring per host (70).…”

“…The outcome of competition between hyperparasitoid species follows intrinsic competition patterns observed in primary parasitoids (22,46). Superiority as competitor is determined by the breadth of host stages that can be hyperparasitized (15), egg hatching and development time of the larvae (141), and a head start in competition (127). However, ovicidal and host feeding behaviors by hyperparasitoids also may reduce the reproductive success of competing hyperparasitoids (81).…”