Concordance of eclosion life history timing across trophic levels in communities of host plants, fruit flies, and parasitoid wasps in the Pacific Northwest, USA.

Abstract

Whether host plant fruiting phenology variation affects eclosion times and generates allochronic isolation across trophic levels for Rhagoletis flies (Diptera: Tephritidae) and their braconid parasitoids is largely unknown, except in the Rhagoletis pomonella (Walsh) hawthorn-apple system. Here, we investigated how fly and wasp eclosion times in 4 systems-Oregon grape, Rhagoletis berberis Curran; red osier dogwood, Rhagoletis tabellaria (Fitch); bitter cherry, Rhagoletis indifferens Curran; and snowberry, Rhagoletis zephyria Snow-in Washington state, USA correspond to host phenology. Fruiting patterns differed among plants. Oregon grape and bitter cherry fruited once in relatively narrow temporal windows, while red osier dogwood and snowberry fruited multiple times or more widely through the season. Fruiting times differed for plants from earlier to later: based on fruit set, Oregon grape < red osier dogwood = bitter cherry < snowberry; first ripening fruit, Oregon grape < bitter cherry = snowberry; percent mature fruit in early August, Oregon grape = red osier dogwood < bitter cherry < snowberry. Mean fly eclosion times generally matched host fruiting times: red osier dogwood fly < Oregon grape fly = bitter cherry fly < snowberry fly. Parasitoid and fly eclosion matched except snowberry fly wasps eclosed before bitter cherry fly wasps. Differences in eclosion times between flies or wasps resulted in allochronic isolation from 1% to 96%. Nonconcordance between timing of fruit maturity and fly/wasp eclosion may be related to differences in precise host fruit or fly stages attacked by different species. Fruiting phenology may select for variable fly eclosion times, leading to a range of allochronic isolation between different Rhagoletis species and their associated guilds of parasitoid wasps.