Molecular gut content analysis reveals in-field consumption of Resseliella maxima Gagné (Diptera: Cecidomyiidae) by Pterostichus melanarius (Illiger) (Coleoptera: Carabidae)

Soybean gall midge, Resseliella maxima Gagné (Diptera: Cecidomyiidae), is a soybean pest in the midwestern United States. Pterostichus melanarius (Illiger) (Coleoptera: Carabidae), an abundant predator in R. maxima-infested fields, feeds on and prefers R. maxima in the laboratory. However, it remains unknown if P. melanarius feeds on R. maxima in the field. We used experiments to assess whether P. melanarius feeds on R. maxima in the field and determine how quickly R. maxima DNA degrades in P. melanarius guts (ie the half-life). Molecular gut content analysis of P. melanarius adults collected from soybean fields in 2021 and 2022 detected R. maxima DNA in P. melanarius guts in both years (3.5% of all P. melanarius in 2021, and 10% in 2022). Across pitfall traps deployed on a single sampling date, up to 20% of P. melanarius had recently fed on R. maxima. Pterostichus melanarius predation on R. maxima was density dependent, and the half-life for detection of DNA from a single R. maxima larva in P. melanarius guts was 6.59 h. Overall, results confirm that (i) P. melanarius is a predator of R. maxima in the field, (ii) predation of R. maxima is dependent on R. maxima density, and (iii) field predation estimates are likely an underestimate due to the short detection half-life. These findings indicate P. melanarius may contribute to natural control of R. maxima in the field.