Date of Graduation

12-2017

Document Type

Thesis

Degree Name

Master of Science in Entomology (MS)

Degree Level

Graduate

Department

Entomology

Advisor

Gus Lorenz

Committee Member

Jeremy Ross

Second Committee Member

Nicholas Seiter

Keywords

Biocontrol, Biopesticide, Helicoverpa Zea, Nucleopolyhedrovirus, Soybean, Transmission

Abstract

Helicoverpa armigera Nucleopolyhedrovirus (HearNPV) is a commercially available viral biopesticide that targets Heliothines, including Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), the most damaging pest of soybean (Glycine max (L.) Merrill) in the Mid-South. Previous formulations of HearNPV have been well studied; however, no research has been published on current formulations. The first objective of this thesis was to assess the rate of horizontal transmission of HearNPV in a soybean field infested with H. zea when HearNPV was applied as a bio-insecticide, and to identify arthropods that are important obligate carriers in dissemination. HearNPV spread 200 feet in 3 fields, and was present between 13 and 21 days post application. Ceresa festina (Hemiptera: Membracidae), H. zea larvae, and Geocoris spp. (Hemiptera: Geocoridae) were identified as important carriers, while spiders (Araneae) were determined to be suppressors of HearNPV. The second objective was to identify arthropods in contact with infected larvae and determine their importance in dissemination. HearNPV was found as far away as 200 feet by 3 days; however, only 2 samples were positive past 3 days. Several previously undocumented carriers were observed, including several families of Diptera and Lygus lineolaris (Hemiptera: Miridae). The third objective was to determine the ability of HearNPV to kill each H. zea instar, and a second infestation. HearNPV was successful in controlling 1st-3rd instars in 5 days. The second generation was controlled in 3.5 days. If applied to a soybean field as an insecticide when 1st-3rd instar H. zea populations are present, HearNPV should be able to spread 200 feet, utilizing several over-sprayed arthropods such as Ceresa festina, and remain in the canopy from 3 to 21 days. Five days after the application, several arthropods can disseminate HearNPV from liquefied to healthy larvae for 3 days before the majority of active HearNPV leaves the canopy. If another generation of healthy larvae infest during this time period, the epizootic event should continue, thus repeating this cycle.

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