Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Entomology

First Advisor

Dr. Kenneth F. Haynes

Second Advisor

Dr. Douglas W. Johnson

Abstract

Aphids (Hemiptera: Aphididae) are pests of multiple cropping systems, primarily due to the viruses they vector and direct crop damage that is exacerbated by their rapid population growth. In Kentucky, grain aphids (Rhopalosiphum padi and Sitobion avenae) cause significant yield loss to winter wheat as vectors of Barley Yellow Dwarf virus (BYDV), prompting the routine application of insecticides. Coupled with increasing human populations and decreasing arable land, it is increasingly evident that biological control services provided by natural enemies represent a viable long-term management option. Aphids are preyed upon by a diverse array of predators that can be exploited in conservation biological control. I designed a field experiment to monitor dispersal into and out of wheat fields, and how these movements were affected by the surrounding habitat. Analysis revealed there are significant movements of R. padi into the wheat in the fall, and S. avenae in spring, and that these movements are slowed down by forested edges. Natural, field-bordering weed strips were used as a conservation biological technique to enhance predator populations. Results showed that while weed strips did not affect the yield of the crop, aphid abundance, or BYDV incidence, it did significantly increase the abundance of natural enemies. Dominant predators included Coccinellidae, Anthocoridae, Chrysopidae larvae, and Braconidae. Using molecular gut-content analysis, I screened multiple species of predators and found strong trophic linkages between aphids and Orius insidiosus and multiple species of coccinellids, namely Coccinella septempunctata and Coleomegilla maculata. In aphidophagous systems, intraguild predation (IGP) can interfere with the biological control potential so I also screened coccinellids for IGP using newly designed primers. To identify intraguild prey DNA in coccinellids, I designed species-specific primers for C. maculata and C. septempunctata to use in PCR-based molecular gut-content analysis. Results revealed high frequencies of IGP between coccinellids that are significantly higher in weed strip plots. However, I observed no detectable impact on aphid predation during these increased times of IGP, suggesting it does not interfere with biological control of aphids in this system. I discuss the role of weed strips in winter wheat as part of an integrative pest management strategy.

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