Endosymbiont-mediated resistance: effects of Hamiltonella defensa (Enterobacterales: Enterobacteriaceae) on parasitism of Aphidius colemani and Praon volucre (Hymenoptera: Braconidae) in Aphis craccivora (Hemiptera: Aphididae).

Abstract

The present study investigated the influence of the Hamiltonella defensa-APSE association, a functional defensive unit in aphids, on the performance of 2 aphidiine parasitoids, Aphidius colemani Viereck, 1912 and Praon volucre (Haliday, 1833), attacking the cowpea aphid, Aphis craccivora, on alfalfa. To assess the effects of H. defensa, naturally infected cowpea aphids with this bacterium (Hd+) were treated with a combination of antibiotics to eliminate the symbiont, generating uninfected cowpea aphids (Hd-). The results showed that A. colemani had similar parasitism success in Hd+ and Hd- cowpea aphids, suggesting that H. defensa had a limited effect on the overall parasitism success of this species. However, H. defensa significantly prolonged the time to mummification of A. colemani developing in Hd+ aphids, while post-mummification emergence and the mummification-to-emergence interval were not significantly affected. In P. volucre, H. defensa had a strong negative effect on parasitoid performance. Hd+ aphids showed significantly lower parasitism success and post-mummification emergence, together with significantly longer time to mummification and mummification-to-emergence interval. Neither female sex ratio nor body size showed a treatment effect that met the Bonferroni-corrected significance threshold in either parasitoid species. These findings show that the H. defensa-APSE association can influence several key components of parasitoid performance and highlight the potential importance of defensive symbionts in shaping aphid-parasitoid interactions.