Comparative susceptibility to hyperparasitism of two primary aphid parasitoids, Binodoxys communis and Aphidius colemani (Hymenoptera: Aphidiidae), introduced to Hawaii

We evaluated a newly introduced aphid parasitoid in Hawaii, Binodoxys communis (Gahan), in comparison with a previously introduced aphid parasitoid, Aphidius colemani (Viereck), for susceptibility to attack by extant hyperparasitoids under laboratory conditions. This study was initiated to help explain the low abundance of B. communis in the field in contrast to A. colemani, possibly as a result of apparent competition mediated by the hyperparasitoid Syrphophagus aphidovorus (Mayr). Mummies of the two primary parasitoid species were exposed to adult female S. aphidovorus under both choice and no-choice conditions. B. communis was susceptible to S. aphidovorus attack, but A. colemani was a more suitable host, as shown by higher rates of hyperparasitism when both parasitoid species were exposed simultaneously, and a more female-biased sex ratio of hyperparasitoids emerging from A. colemani mummies. The higher suitability of Aphidius colemani for hyperparasitoid development is likely influenced by its larger size, implying more resources for the hyperparasitoids. Contrary to what was expected, no evidence of apparent competition (in terms of the hyperparasitoid’s host finding ability or host suitability) was found to be comparatively more unfavorable towards B. communis. This may have positive implications for B. communis establishment and efficacy in the long run.