Comparative study of egg parasitism by Gryon pennsylvanicum (Hymenoptera: Scelionidae) on two squash bug species Anasa tristis and Anasa armigera (Hemiptera: Coreidae)

Authors: CORNELIUS, MARY; Hu, Jing - Hu; Vinyard, Bryan

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2018
Publication Date: 9/25/2018
Citation: Cornelius, M.L., Hu, J.S., Vinyard, B.T. 2018. Comparative study of egg parasitism by Gryon pennsylvanicum (Hymenoptera: Scelionidae) on two squash bug species Anasa tristis and Anasa armigera (Hemiptera: Coreidae). Environmental Entomology. https://doi.org/10.1093/ee/nvy145.
DOI: https://doi.org/10.1093/ee/nvy145

Interpretive Summary: Because of the growing demand for organic produce, there is interest in the development of biological control programs for squash production. Gryon pennsylvanicum is the primary egg parasitoid of squash bugs and has the potential to be effective as a biological control agent of squash bugs. This study evaluated the effects of egg mass size and the physiological state of the parasitoid on parasitism rates by Gryon pennsylvanicum Ashmead on egg masses of two squash bug species, Anasa tristis DeGeer and Anasa armigera Say. There were no published reports available on egg parasitism of A. armigera. In choice tests, there was no difference in the host acceptance of egg masses of the two squash bug species. In no-choice tests, parasitism rates were significantly higher on A. armigera egg masses with 11-15 eggs, 21-25 eggs, and >25 eggs per egg mass compared with A. tristis egg masses. Naive parasitoids had significantly higher parasitism rates than experienced parasitoids for both squash bug species. For egg masses with > 25 eggs, both naive and experienced parasitoids parasitized a greater number of A. armigera eggs than A. tristis eggs. It is possible that A. armigera is a more suitable host than A. tristis for G. pennsylvanicum, but further studies are necessary. This study on how factors such as the physiological state of the parasitoid and the numbers of eggs per egg mass influence parasitism rates provides valuable information on the efficacy of G. pennsylvanicum as a biological control agent of squash bug pests.

Technical Abstract: This study evaluated the effects of egg mass size and the physiological state of the parasitoid on parasitism rates by Gryon pennsylvanicum Ashmead on egg masses of two squash bug species, Anasa tristis DeGeer and Anasa armigera Say. Gryon pennsylvanicum is the primary egg parasitoid of A. tristis. There were no published reports available on egg parasitism of A. armigera. In choice tests, there was no difference in the host acceptance of egg masses of the two squash bug species. In no-choice tests, parasitism rates were significantly higher on A. armigera egg masses with 11-15 eggs, 21-25 eggs, and >25 eggs per egg mass compared with A. tristis egg masses. Naive parasitoids had significantly higher parasitism rates than experienced parasitoids for both squash bug species. For egg masses with > 25 eggs, both naive and experienced parasitoids parasitized a greater number of A. armigera eggs than A. tristis eggs. It is possible that A. armigera is a more suitable host than A. tristis for G. pennsylvanicum, but further studies are necessary. In a comparison of parasitism rates of field-collected and laboratory-tested A. tristis egg masses of different sizes, there was only a higher parasitism rate on field-collected egg masses with > 25 eggs than on laboratory-tested egg masses. The average parasitism rate of field-collected A. tristis egg masses of > 25 eggs was only 36.4%, indicating that G. pennsylvanicum frequently fails to parasitize all of the eggs in larger egg masses in the field.