Irrigation and grass cover effects on pupal survival rates in soil and adult emergence patterns of Rhagoletis indifferens (Diptera: Tephritidae)

Authors: Yee, Wee; Chapman, Peter

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2017
Publication Date: 4/5/2018
Citation: Yee, W.L., Chapman, P.S. 2018. Irrigation and grass cover effects on pupal survival rates in soil and adult emergence patterns of Rhagoletis indifferens (Diptera: Tephritidae). Environmental Entomology. 47(2):457-466. https://doi.org/10.1093/ee/nvx209.
DOI: https://doi.org/10.1093/ee/nvx209

Interpretive Summary: Cherry fruit fly is a threat to the commercial cherry industry in the western U.S. The fly’s ability to survive in dry climates affects its distribution and pest status, but it is unclear if its surival rates are increased by irrigation in different soils. Personnel at USDA-ARS, Wapato, WA determined the effects of adding water to bare and grass-covered soils on survival rates of fly pupae in central Washington. Results showed that fly pupae survived equally well in irrigated and unirrigated bare soils, but suffered relatively high mortality in unirrigated grass-covered soils. Results are important because they show that unirrigated, grass-covered soils or mulch barriers in mid- and late-summer could reduce fly survival, thus suppressing fly abundance.

Technical Abstract: Western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), occurs in unmanaged cherries (Prunus spp.) across dry climates in Washington State and other regions in western U.S.A. and Canada. To help explain the fly’s distribution in arid climates, we determined the effects of adding water to bare and grass-covered soils on pupal survival rates and adult emergence patterns of R. indifferens in central Washington. Water was added (irrigated) or not to bare soil and grass-covered soils in open-ended pots pressed into the ground. Larvae were added to pots and pupal survival and adult fly emergence determined over three seasons. Moisture was higher in irrigated than unirrigated treatments but within irrigated treatments, moisture in bare versus grass-covered soil did not differ. Even in unirrigated treatments, humidity in soil 5 cm below the surface where many pupae reside was >60%, including during summers. Pupal survival was greater in bare (24.5-47.7%) than grass-covered soil (6.7-17.0%). Irrigating bare soil had no effect on pupal survival or adult emergence, but in grass-covered soil, irrigation increased pupal survival (15.2-17.0% versus 6.7-9.5%) and adult emergence (two of three years, 12.8 and 24.1 versus 1.1 and 11.6%). Results suggest R. indifferens pupae tolerate unirrigated soils during summer because soil moisture and high humidity there prevents desiccation, contributing to the fly’s wide distribution and abundance in dry climates, and that dry, grass-covered soils or mulch barriers in mid- and late-summer could reduce fly survival.