Reproductive compatibility of two lines of Delia platura

Accurate identification of agricultural pests is a major component of integrated pest management. The seedcorn maggot, Delia platura (Meigen) (Diptera: Anthomyiidae), is a cosmopolitan polyphagous pest species that may be found in high numbers in numerous crops. Two morphologically identical genetic lines of D. platura (H and N) with distinct distributions were recently identified. To date, no study has investigated the reproductive compatibility of the two lines and thus the possibility that they may actually be two unique biological entities. A previous study described the reproductive traits of the two lines and suggested that H-line females are highly selective toward the male with which they mate, pointing to a possible pre-mating isolation mechanism between the lines. Using laboratory-reared colonies originating from the Montérégie region in Québec, Canada, this study investigates the reproductive compatibility of the two D. platura lines. We found that only one of 30 H-line females was inseminated by an N-line male, further suggesting mate choice as a pre-mating isolation mechanism between the lines. However, N-line females were readily inseminated by H-line males, suggesting a lack of pre-mating isolation in this type of cross. The eggs laid by N-line females mated with H-line males had a lower hatching rate than the ones laid by females of intraline crosses, suggesting either post-mating pre-zygotic or post-zygotic partial isolation. However, the larvae that did hatch had a comparable developmental success to those from intraline crosses in terms of survival and developmental time from larval hatching to adult emergence, pupal mass, and adult sex ratio, suggesting a lack of post-zygotic isolation for these life stages. Considering the different biological traits of the two lines, we suggest the use of the ‘biotype’ terminology to designate the two biological entities and discuss their implications for integrated pest management.