Raw data on acceptance and emergence in intrinsic competition experiments, and guarding behavior in extrinsic competition: Trissolcus cultratus and Trissolcus japonicus

<p>Understanding competition between scelionid parasitoids that exploit the same host may provide insight into strategies that allow co-existence on a shared resource. Competition studies typically focus on interactions between native and exotic parasitoids that do not share an evolutionary history; however, co-evolved parasitoids may be more likely to demonstrate strategies to avoid or exploit a shared resource. We examined intrinsic and extrinsic competition between Asian <i>Trissolcus japonicus</i> Ashmead and <i>T. cultratus</i> Mayr (Hymenoptera: Scelionidae) associated with <i>Halyomorpha halys</i> Stål (Hemiptera: Pentatomidae) that share an evolutionary history. Interspecific interactions were assessed by providing parasitized egg masses to each species at various intervals post-parasitism, and measuring host acceptance, developmental suitability, and guarding behaviour. <i>Trissolcus japonicus</i> showed high acceptance of parasitized hosts up to 72h following oviposition by <i>T. cultratus</i>, despite a very poor developmental outcome. In contrast, <i>T. cultratus</i> generally avoided ovipositing in <i>H. halys</i> eggs containing <i>T. japonicus</i> early-instar larvae, but did not avoid parasitizing <i>H. halys</i> that contained eggs and third instar larvae. The adaptive value of this behaviour was supported by developmental outcome: <i>T. cultratus</i> outcompeted <i>T. japonicus</i> eggs but not early-instar larvae, and a trophic shift occurred wherein <i>T. cultratus</i> developed as a facultative hyperparasitoid on third instar <i>T. japonicus</i> larvae. <i>Trissolcus japonicus</i> guarded egg masses 8 – 12x longer and displayed more aggressive interactions than <i>T. cultratus</i>, suggesting <i>T. japonicus</i> is the superior extrinsic competitor. Development as a facultative hyperparasitoid provided a competitive niche for Asian <i>T. cultratus</i> and confirms its instrinsic competitive superiority. This also occurs in a biologically-distinct European population of <i>T. cultratus</i>, suggesting that facultative hyperparasitism as a competitive strategy is retained in geographically-separated populations that have not co-evolved with <i>H. halys</i> or <i>T. japonicus.</i></p>