Issuing Body

Mississippi State University

Advisor

Catchot, Angus L. Jr.

Committee Member

Gore, Jeffrey

Committee Member

Cook, Donald R.

Committee Member

Caprio, Michael A.

Committee Member

Daves, Chris

Date of Degree

5-1-2020

Document Type

Dissertation - Open Access

Abstract

Helicoverpa zea (Boddie), a pest of cotton that also occurs in field corn, is commonly controlled through the use of foliar-applied insecticides or transgenic crops expressing Bt genes. To prevent the selection of resistant populations, refuge systems have been implemented into the agroecosystem. Historically, structured refuge compliance among growers has been low, leading to the commercialization of seed blended refugia. To test the viability of seed blended refugia in the southern U.S., field studies were conducted in Mississippi and Georgia during the 2016, 2017, and 2018 growing seasons. To quantify adult H. zea emergence from structured and seed blended refuge options, emergence traps were utilized. Kernel damage and moth emergence timings were recorded. Various percentages of stand loss ranging from 0% to 50% were also simulated to determine yield effects in unprotected seed blended refugia. Lastly, H. zea feeding and emergence in a two-gene field corn variety expressing Cry1A.105 and Cry2Ab2 were compared to non-Bt field corn. When compared to a structured refuge, H. zea adult moth emergence from seed blended refugia did not significantly differ. Kernel damage was not different between seed blended treatments and structured refuge treatments. Moth emergence timings were not significantly delayed between the structured refuge and seed blended refuge treatments. Significant yield losses were observed when stand loss was simulated at various levels in field corn, suggesting that there is an opportunity to see yield losses in an unprotected seed blended refuge field corn landscape. Kernel damage did not significantly differ between field corn expressing Cry1A.105 and Cry2Ab2 and non-Bt field corn, possibly due to H. zea resistance to the Cry genes. However, there was a significant difference in emergence from two-gene expressing field corn and non-Bt field corn. This suggests that there may be high pupal mortality in two-gene corn plots. Based on these data, seed blended refuge could be a viable option to replace structured refuge strategies in the southern U.S., however, if left unprotected, yield loss could be observed in a case of high boring insect pressure. The significant loss of refuge plants can also compromise refuge effectiveness.

URI

https://hdl.handle.net/11668/16541

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