Illuminating new host-parasitoid relationships of Apocephalus Coquillett (Diptera: Phoridae) parasites of fireflies (Coleoptera: Lampyridae)

Some parasitic insects maintain associations with several different hosts, while for others the use of multiple hosts can lead to the evolution of reproductive isolation between different host-associated populations. Why some species tend to specialise while other closely related species stay generalists is an open question. The parasitic fly genus Apocephalus Coquillett (Diptera: Phoridae) contains both specialist and generalist species. One species, Apocephalus antennatus Coquillett, is recognised as a single, widely dispersed and highly generalist species that parasitizes many different genera of fireflies (Coleoptera: Lampyridae). However, the species status of A. antennatus has not been investigated genetically and other putatively generalist Apocephalus have proved to consist of several cryptic specialist species, each with a more limited host range. To test for cryptic host-associated diversity in A. antennatus, we collected adult Lampyridae from across the eastern half of the United States and from Costa Rica and reared their Apocephalus parasitoids. We analysed genetic sequences, host associations and morphology to delimit putative species. Our results maintain the status of A. antennatus as a single species that attacks different firefly hosts, both nocturnal and diurnal. We did not recover A. antennatus from Costa Rica, but other Apocephalus in Costa Rica were more species-rich and appeared more specialised on lampyrid hosts than A. antennatus. Site of mating and host discrimination may be important determinants of whether phorids specialise or are able to use multiple different host species.