Substrate and Moisture Affect the Pupation Depth of the Corn Silk Flies Chaetopsis massyla and Euxesta eluta (Diptera: Ulidiidae)

SIMPLE SUMMARY: Corn silk flies are among the major pests of fresh market sweet corn production in tropical and semi-tropical regions. They have been reported as particularly impactful in Argentina and southern and central Florida. Insecticides are used heavily to protect crops; however, lapses in treatment or pest resistance can result in sufficient damage to render the cobs unmarketable. To provide better insight into the development of alternative management strategies, research was conducted to better understand the pupation behavior of two major species of corn silk flies. In a laboratory study, three soil types were tested across six different levels of moisture to evaluate the pupation behavior of the flies. Both soil and moisture levels impacted pupation depths, and these factors are important for optimizing management strategies such as tilling or the use of parasitoids as biological control agents. ABSTRACT: Corn silk flies, or picture-winged flies (Diptera: Ulidiidae), are important pests of fresh market sweet corn in commercial production areas in southern Florida. Issues with pest management related to insecticide resistance, problems in insecticide application, and alternate crop population sources constitute a significant challenge for the protection of developing corn ears. Developed larvae leave cobs and pupate in the soil; however, relatively little is known about these behaviors. In this study, two soil types collected from fields were compared with sand under six different moisture levels in the laboratory to determine the pupation depths of the larvae. Comparisons were carried out concerning the pupation depth of Chaetopsis massyla and Euxesta eluta, which are major pest species in Florida. Both soil type (muck, loamy sand, and sand) and moisture levels (0, 10, 25, 50, 75, 100% field holding capacity) significantly affected pupation depth, with shallow pupation observed under dry or saturated wet conditions. The addition of structures such as pipe cleaners simulating corn roots resulted in deeper pupation under most conditions.