Impact of larval and cocoon burial depth on emergence of adult soybean gall midge (Diptera: Cecidomyiidae)

Soybean gall midge, Resseliella maxima Gagné, is a pest of soybean that causes severe yield loss, with no specific management tactics currently being widely implemented. Due to R. maxima forming cocoons and pupating in soil, characterizing its cocooning behavior and studying the effects of artificial burial on adult emergence may reveal possible cultural control tactics like tillage. R. maxima larvae were released and allowed to pupate in vials filled with sand, which were then dissected into cross-sections to identify the depth at which cocoons were formed. R. maxima tended to form cocoons within the first 1 cm of sand when 10 larvae were released, and within the first 1.5 cm of sand when 50 larvae were released. In a second experiment, cocoons were buried at depths up to 3 cm in 0.5 cm increments. When cocoons were buried, adult emergence decreased and was delayed as depth increased, with no adult emergence when cocoons were buried deeper than 1.5 cm. In a third experiment, larvae were buried at depths up to 12 cm in 1 cm increments. When larvae were buried, adult emergence decreased and was delayed as depth increased; however, there was emergence from the deepest tested depth. Upward movement of larvae plateaued and decreased as burial depth increased, with greater burial depths also associated with lower cocooning rates. These findings suggest that burial of cocooned R. maxima can effectively reduce adult emergence, and that tillage should be explored as a potential management tactic to control this pest.