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Biological Control of Arthropod Pests and Weeds
Department of Entomology
The growing emphasis on environmental and food safety issues has intensified interest in the development of biological controls as a means for controlling pests. The effective use of natural enemies in biological control programs is contingent upon understanding their ecology and that of their targets, their interaction with production practices, and the most effective means of using them. The purpose of this project is to improve the use of biological control in controlling pests and weeds.
2011 Project Description
We continued studies of the tritrophic effects of four native milkweed species on parasitoids and predators of the milkweed-infesting aphid, Aphis nerii. The most abundant of the natural enemies of Aphis nerii also are commonly found in crops where they attack pests. We found that swamp milkweed had higher concentrations of cardenolides (secondary plant compounds) than did the other three milkweed species tested.
Our results were the first to demonstrate presence of cardenolides in honeyvine milkweed, although concentrations were low in this plant species. We also confirmed presence of cardenolides in the bodies of Aphis nerii that had fed on each of the four milkweed species. In the laboratory, aphid fitness was greatest on honeyvine milkweed.
We hypothesized that natural enemies would be least affected (adversely) by feeding on aphids on honeyvine milkweed species compared with the other three milkweed species. Our experiments with the parasitoid Lysiphlebus testaceipes supported this hypothesis, but our results with the coccinellid predators Harmonia axyridis and Cycloneda munda were less conclusive because these predators generally did poorly when fed Aphis nerii, regardless of milkweed species on which the aphid had fed. Cycloneda munda appeared to be less adversely affected by feeding on Aphis nerii than was Harmonia axyridis but both suffered adverse effects (low survival, low fecundity).
The parasitoid Lysiphlebus testaceipes contributes to the biological control of the soybean aphid and other aphid pests. This parasitoid attacks numerous aphid species on many host plant species, including Aphis nerii, which feeds on potentially toxic milkweed species within and near agricultural plantings. If use of Aphis nerii as a host adversely affects the biology of this parasitoid, this could reduce its effectiveness as a biological control agent in nearby crops. Our results with Lysiphlebus testaceipes suggest that the effects on the parasitoid of using Aphis nerii on honeyvine milkweed are less severe than effects of using these aphids on other milkweed species. Honeyvine milkweed is the most abundant species of milkweed in and near Kentucky crops, while the other three milkweed species are much less abundant in Kentucky.
S.M. Colvin. 2011. Tritrophic effects of milkweed species on natural enemies of Aphis nerii. Ph.D. Dissertation, University of Kentucky.