Foraging behavior by six fruit fly parasitoids (Hymenoptera: Braconidae) released as single- or multiple-species cohorts in field cages: Influence of fruit location and host density

In Mexico, both native and exotic fruit fly parasitoids exhibit spatial and temporal overlaps in distribution. To better characterize the spatial component of foraging in the braconid portion of this guild, and to examine the effects of intra- and interspecific competition on resource partitioning, we conducted two field-cage experiments aimed at: (1) assessing the host-finding ability of parasitoids when single- or multiple-species cohorts were confronted with very low host-densities only at canopy level; (2) determining the height level preference (canopy vs. ground) for parasitoid foraging activity when single- or multiple-species cohorts were present and host density was high; (3) identifying candidate species for biological control programs using multiple-species releases. We studied two species exotic to Mexico, Diachasmimorpha longicaudata and D. tryoni, and four species native to Mexico, Doryctobracon areolatus, D. crawfordi, Opius hirtus, and Utetes anastrephae (all Braconidae, Opiinae). Parasitoids were allowed to forage for 8-h as single- or multiple-species cohorts in a room-sized cage containing potted trees with guavas artificially infested with Anastrepha ludens larvae and attached to the branches. When parasitoids were released as single-species cohorts into low host-density environments (fruit only at canopy level), D. longicaudata, D. tryoni and O. hirtus clearly distinguished uninfested from infested fruit and exerted the highest rates of parasitism with a significantly female-biased offspring sex ratio. When multiple-species cohorts were released, the same pattern was observed but, D. crawfordi and D. areolatus did not parasitize any larvae. In the case of the high host-density condition and with fruit at canopy and ground levels, when parasitoids were released in single-species cohorts, only D. crawfordi and D. longicaudata parasitized larvae at ground level. At canopy level, D. longicaudata, D. tryoni and D. crawfordi achieved the highest parasitism rates. When parasitoids were released as multiple-species cohorts, individuals of none of the species foraged at ground level, and in the canopy foraging activity and parasitism rates dropped dramatically in all species, except O. hirtus. Given the performance of O. hirtus, it should be considered a potential candidate to complement D. longicaudata in low-host density prevalence areas.