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

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 Trissolcus japonicus Ashmead and
T. cultratus Mayr (Hymenoptera: Scelionidae) associated with Halyomorpha
halys 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.
Trissolcus japonicus showed high acceptance of parasitized hosts up to 72h
following oviposition by T. cultratus, despite a very poor developmental
outcome. In contrast, T. cultratus generally avoided ovipositing in H.
halys eggs containing T. japonicus early-instar larvae, but did not avoid
parasitizing H. halys that contained eggs and third instar larvae. The
adaptive value of this behaviour was supported by developmental outcome:
T. cultratus outcompeted T. japonicus eggs but not early-instar larvae,
and a trophic shift occurred wherein T. cultratus developed as a
facultative hyperparasitoid on third instar T. japonicus larvae.
Trissolcus japonicus guarded egg masses 8 – 12x longer and displayed more
aggressive interactions than T. cultratus, suggesting T. japonicus is the
superior extrinsic competitor. Development as a facultative
hyperparasitoid provided a competitive niche for Asian T. cultratus and
confirms its instrinsic competitive superiority. This also occurs in a
biologically-distinct European population of T. cultratus, suggesting that
facultative hyperparasitism as a competitive strategy is retained in
geographically-separated populations that have not co-evolved with H.
halys or T. japonicus.