Life history traits of the aphid hyperparasitoid Alloxysta brevis and interactions with Aphelinus certus, a parasitoid of the soybean aphid

Aphelinus certus Yasnosh is a primary parasitoid of the soybean aphid (Aphis glycines Matsumura), an invasive pest of soybeans in North America. Although Ap. certus has displayed the capacity to suppress aphid infestations below pesticide spray thresholds, control levels are variable. Previous research has found hyperparasitoids attacking Ap. certus in the field, but the impact of hyperparasitism on the control of aphid populations remains unclear. This laboratory study investigates some key life history attributes of Alloxysta brevis (Thomson), an aphid hyperparasitoid in North America, and its impact on Ap. certus and soybean aphid populations. First, we dissected Al. brevis adults to show that females emerge with an average of 10 mature eggs, continue to produce eggs after adult eclosion, and can hold over 20 mature eggs at a time. We then investigated hyperparasitism across different Ap. certus larval instars and demonstrated that the highest proportion of Al. brevis adults emerges from first-instar larvae. These results provided context for a mesocosm cage study evaluating the population dynamics between soybean aphid, Ap. certus, and Al. brevis. Hyperparasitism by Al. brevis significantly reduced Ap. certus abundance but did not eliminate its ability to suppress aphid populations in a caged setting, indicating that even under high hyperparasitism pressure Ap. certus can still provide substantial biological control of soybean aphid. Results of the cage study suggest that hyperparasitism could have a stabilizing effect on the Ap. certus population, highlighting the need for further investigation into the impact of hyperparasitoids on pest suppression by primary parasitoids.