Phenological and ecological differences between two tephritid flies (Diptera) in golden currant (Grossulariaceae) and implications for species coexistence

Abstract

Communities comprising multiple temperate tephritid flies infesting the same host fruit may provide insights into how species partition resources to avoid competitive exclusion. Using Euphranta canadensis (Loew) and Rhagoletis ribicola Doane (Diptera: Tephritidae) that share golden currant, Ribes aureum Pursh (Grossulariaceae), as a model, we hypothesised that adults and larvae of these flies temporally divide host fruit to coexist. Fruit loads, fruiting phenology, fly catches, and larval infestation levels were determined in central Washington state, United States of America, in 2023, 2024, and 2025. Adult E . canadensis abundance peaked in May when most currants were immature and that of R . ribicola peaked in June when most currants were mature. Only E . canadensis larvae emerged from fruit collected in May; both species emerged from fruit collected in June; and only R . ribicola emerged from fruit collected in July. In June, larval niche overlap was 0.543–0.996, but no larvae emerged from 94–99% of fruit collected, suggesting currants can be an unlimited resource. Our results suggest that temporal partitioning of fruit resources and low infestation rates may help mitigate interspecific competition between E . canadensis and R . ribicola , with implications for monitoring or management of tephritid pests that co-occur in fruit trees.