Making control decisions for Sitodiplosis mosellana (Diptera: Cecidomyiidae) in wheat (Gramineae) using sticky traps

Abstract

Wheat midge larvae, Sitodiplosis mosellana (Géhin), attack developing seeds and cause losses of common wheat, Triticum aestivum L., and durum wheat, Triticum durum Desf. (Olfert et al. 1985; Lamb et al. 1999). Insecticide applied as the crop flowers can reduce damage (Elliott 1988). The economic threshold varies from 4 to 7% of common wheat seeds infested by larvae, depending upon grade of wheat and cost of insecticidal control (Lamb et al. 2000). To make control decisions, farmers count adults at sunset during the period from heading to flowering (Elliott and Mann 1996), and apply insecticide if densities reach a nominal threshold of one adult per four or five wheat spikes (Anonymous 1993). Decisions must be made although no relationship has been detected between the number of adults in the crop and subsequent densities of damaging larvae (Oakley et al. 1998), and farmers have little confidence in their counts. The pest is difficult to sample because adults are small, short-lived, crepuscular, and are usually hidden in the crop canopy (Pivnick and Labbé 1993); eggs are microscopic (Mukerji et al. 1988); larvae feed inside florets (Lamb et al. 2000); and mature larvae and pupae are in the soil (Lamb et al. 1999). Sticky traps have been used to sample midges in sorghum (Merchant and Teetes 1992) and in wheat (Oakley et al. 1998), with mixed results. Our objective was to determine if catches of wheat midge adults on sticky traps can effectively guide farmers in making control decisions.