Emergence of walnut husk maggot adults in Central Illinois and potential for control with Metarhizium brunneum

Authors: Behle, Robert

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2020
Publication Date: 12/11/2020
Publication URL: https://handle.nal.usda.gov/10113/7367989
Citation: Behle, R.W. 2020. Emergence of walnut husk maggot adults in Central Illinois and potential for control with Metarhizium brunneum. Journal of Insect Science. 20(6). Article 33. https://doi.org/10.1093/jisesa/ieaa134.
DOI: https://doi.org/10.1093/jisesa/ieaa134

Interpretive Summary: Many insect pests spend a portion of their life cycle in the soil, an environment that limits pest control options especially when considering biological control methods. Some beneficial fungi used as bioinsecticides create a structure called a microsclerotium that is naturally adapted for the soil environment. In this research, granules laced with microsclerotia of the Metarhizium fungus, produced using industrial techniques, were applied to soil under walnut trees to target a fruit fly known as the walnut husk maggot. These maggots are closely related to the apple maggot and cause damage while feeding within the protection of the walnut husk, but exit the husk of the fallen nut to pupate in the soil and overwinter. For two consecutive years, fungal treatments applied in September reduced the number of flies emerging the following summer by 35%. These results support additional exploration into the use of beneficial fungi to provide environmentally friendly pest control and contribute to integrated management of soil inhabiting insect pests.

Technical Abstract: The walnut husk maggot, Rhagoletis sauvis (Loew) (Diptera: Tephritidae), causes damage to walnuts when maggots feed inside the husk. September applications of the entomopathogenic fungi Metarhizium brunneum F52 as microsclerotia laced granules to the soil in Illinois were evaluated for pest control based on adult emergence during the following summer. Over three years in central Illinois, adult emergence began near July 1, peaked before July 23, and emergence extended as late as August 23. One summer application of fungus (June 30) when pupae were present, did not reduce fly emergence. One of two September applications targeting maggots as they move to the soil to pupate significantly reduced the number of flies emerging from treated plots when compared with untreated plots. Emergence trap data show a defined peak adult emergence in July for central Illinois while September applications of Metarhizium granules reduced subsequent fly emergence nearly 35%.