Abstract
Research on interspecific competitive interactions among insect parasitoids has often been characterized by laboratory studies in which host insects are exposed to female parasitoids of different species in various sequences and combinations. In the last years, an increasing number of studies have investigated interspecific interactions under field and semi-field conditions although just a few number of works focused on egg parasitoids. In this work, we undertook a two-year study to investigate interspecific interactions between Trissolcus basalis (Wollaston) (Hymenoptera: Platygastridae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae), two egg parasitoids of the pest Nezara viridula (L.) (Heteroptera: Pentatomidae) that co-occur in cultivated crops. Under semi-field (in out-door mesh cages) and field conditions, we investigated: 1) the seasonal occurrence of competing parasitoid species on sentinel egg masses; 2) the impact achieved by competing species on the shared host on naturally laid egg masses; 3) the outcome of intraguild interactions under controlled conditions. Results from sentinel egg masses showed that T. basalis occurs in May and successfully parasitizes hosts until the end of September/beginning of October, whereas O. telenomicida is mainly occurring in July-August. In both years, it was found that T. basalis is predominant. From naturally laid egg masses, results indicated that T. basalis achieves higher impact on the hosts, even in those egg masses which are parasitized by more than one female of different species ( = multiparasitism). Results from manipulating intraguild interactions showed that T. basalis achieves higher impact on N. viridula when released alone, but it suffers from competition with O. telenomicida. The ecological factors that play a role in intraguild interactions in the context of biological control perspective are discussed.
Highlights
During the host location process, parasitoids may experience complex interactions with other parasitoids, hyperparasitoids, predators, and entomopathogens [1,2,3]
When parasitoid species compete for the same host ( = interspecific competitive interactions) the interactions can be divided into two broad categories: the interactions that occur among adult females searching for or exploiting hosts ( = extrinsic competition) and the interactions that occur among supernumerary larvae developing in the same host ( = intrinsic competition) [6,7]
Seasonal occurrence under natural conditions In 2011, successful parasitism by T. basalis was first recorded on sentinel eggs deployed on June 4 and this species always occurred until October 2
Summary
During the host location process, parasitoids may experience complex interactions with other parasitoids, hyperparasitoids, predators, and entomopathogens [1,2,3]. An increasing number of studies investigated interspecific interactions in field and semi-field conditions just a few number of works focused on egg parasitoids [18,19,20] Such studies have shed light on the mechanisms explaining how competing parasitoid species can coexist. It is still unclear whether multiple biological control agents are more effective than single species in host suppression [21,22]; it has been recently shown that transient dynamics of hostparasitoid communities can play a major role in pest suppression [23]
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