Dispersal From Overwintering Sites, Action Thresholds for Blueberry Maggot Fly (Diptera: Tephritidae), and Factors That Can Influence Variation in Predicted Fruit Infestation Levels in Maine Wild Blueberry: Part I.

Abstract

Between 1996 and 2003 field studies were conducted in wild blueberry, Vaccinium angustifolium Aiton (Ericales: Ericaceae) to determine action thresholds for the blueberry maggot fly, Rhagoletis mendax Curran (Diptera: Tephritidae). Thresholds were based upon cumulative fly trap captures on baited Pherocon AM traps. The cumulative numbers of R. mendax flies captured over time was a significant predictor of infested fruit levels (maggots/liter blueberries). Fifty percent of the variance in fruit infestation is explained by fly captures. Based upon this relationship, the University of Maine Cooperative Extension has recommended action threshold of 10 cumulative fly captures/trap. However, this threshold is liberal in terms of risk as only 50% of the variance in fruit infestation is explained by fly captures. The dynamics of colonization rate and fly physiological status entering fruit-bearing fields might partially explain the variance in the action threshold. The majority of flies emerge from pruned fields or along forest scrub/shrub field edges, and it takes between 1 and 10 d (mean = 4.1 ± 0.9 d) for the populations to enter adjacent fruit-bearing fields. Flies dispersed from pruned fields at a decreasing rate the farther they dispersed. The rate of dispersal into fruit-bearing wild blueberry fields also depends upon the overwintering site quality. Sites with fruit exhibited both delayed colonization and lower colonization rates into fruit-bearing fields than adjacent pruned fields with no fruit. We also found that as the season progressed the proportion of flies capable of laying eggs varied greatly by location and year.