Intraguild interactions between two egg parasitoids of a true bug: from laboratory to field investigations

Intraguild interactions can play a role in species coexistence and in sizing and shaping community structures. In addition, understanding how competitive interactions between parasitoid guilds can affect pest suppression may improve biological control. Interspecific competitive effects can be divided in “extrinsic competition”, the indirect interactions between adult females searching for or exploiting hosts, and “intrinsic competition”, the competition that occurs between larvae developing in the same host. In this work we performed both laboratory and field investigations to address on intraguild interactions occurring between Trissolcus basalis (Hymenoptera: Scelionidae) and Ooencyrtus telenomicida (Hymenoptera: Encyrtidae), two egg parasitoids of the Southern Green Stink Bug, Nezara viridula (Heteroptera: Pentatomidae). These parasitoid species can exploit the same host egg mass and they naturally co-occur from fields. In laboratory conditions, bioassays were developed to study 1) extrinsic competition via comparative host location strategies and 2) intrinsic competition by investigating the outcome of multiparasitism. Field investigations were conducted 1) to score the “discovery efficiency”, the “parasitism efficiency” and the “parasitoid impact” of both species using N. viridula egg masses naturally laid in the fields; 2) to assess the seasonal occurrence and abundance of parasitoid species from sentinel N. viridula egg masses artificially placed in the fields. Results are discussed in terms of ecological factors that play a role in coexistence of competing species (counterbalanced-competition) and the influence of intraguild interaction in biological control.