Effects of Milkweed Host Species on Interactions between Aphis nerii (Hemiptera: Aphididae) and Its Parasitoids

Abstract

The oleander aphid, Aphis nerii Boyer de Fonscolombe, feeds on members of the Apocynaceae family. In Kentucky, A. nerii colonizes several Asclepias species and Cynanchum laeve. The prevalence of milkweeds and A. nerii in Kentucky ecosystems allow natural enemies, including the primary parasitoid Lysiphlebus testaceipes, to utilize this aphid as a resource. The efficacy of L. testaceipes when utilizing A. nerii reared on different host plant species was studied in the field and in the laboratory. In the laboratory, the time until first host contact and the number of ovipositional attempts by L. testaceipes did not vary among aphids from different host plant species. However significantly more aphids were mummified and more parasitoids successfully emerged from aphids on C. laeve than from aphids on tested Asclepias species. The successful emergence rates of L. testaceipes from A. nerii colonizing four species of milkweed were also determined in a naturally infested field plot. While no significant differences were detected in 2009, significantly more L. testaceipes emerged in 2010 from A. nerii mummies collected from C. laeve than from mummies on A. syriaca and A. incarnata with numbers emerging from mummies on A. tuberosa being indistinguishable from those on C. laeve or A. syriaca. Five hyperparasitoid species were also recovered from A. nerii mummies over a two year period. A comparison of hyperparasitoid emergence among A. nerii mummies collected from four species of milkweed found that with the exception of one species during 2009, emergence rates did not differ significantly among aphid host plants. Our results suggest that parasitoid development may be affected by aphid host plant and that adverse effects of A. nerii on L. testaceipes are less severe when aphids develop on C. laeve compared to tested Asclepias species.