Synopeas ruficoxum Buhl (Hymenoptera, Platygastridae) is a natural enemy of soybean gall midge, Resseliella maxima Gagné (Diptera, Cecidomyiidae)

Platygastridae (Hymenoptera) is known as a ‘ dark taxon’ as it is highly diverse and understudied. Within Platygastridae, one of the largest genera is Synopeas Förster, species of which parasitize Cecidomyiidae (Diptera). This study identifies a new host association between these two families, with Synopeas ruficoxum Buhl as the second reported parasitoid of soybean gall midge, Resseliella maxima Gagné.

Parasitoids were reared from soybean stems infested with R. maxima collected in Nebraska, USA. Furthermore, PCR assays confirmed that R. maxima larvae are parasitized by S. ruficoxum in the field. All S. ruficoxum specimens were female, suggesting that this may be an asexually reproducing population.

We found that some, but not all, S. ruficoxum were infected with a bacterium, Wolbachia, known to mediate asexual reproduction in other insects, suggesting other factors may be responsible for the all-female population. Publicly available barcoding data allowed us to determine that S. ruficoxum is also present in Eastern Canada, which is beyond the known geographic range of R. maxima. This suggests that S. ruficoxum has other hosts or that the geographic range of R. maxima is broader than currently documented.

A redescription and diagnostic data for S. ruficoxum are provided, advancing the ability to use this parasitoid for biological control of R. maxima.