Occurrence of the new invasive insect Contarinia nasturtii (Diptera: Cecidomyiidae) on cruciferous weeds.

Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae), a common insect pest in Europe and a new invasive pest in North America, causes severe damage to cruciferous crops. In the United States, C. nasturtii was first reported in western New York in 2004. From 2005 to 2007, field surveys were conducted in western New York to investigate the occurrence of C. nasturtii in weeds that might serve as a reservoir for this pest. The results indicate that 12 cruciferous weed species were found in and around commercial vegetable crucifer plantings, and C. nasturtii emergence was detected from most of them. The number of C. nasturtii that emerged from the weeds was low and varied by species, year, and the timing of sampling. Peak emergence from weeds in fallow fields occurred in June. Nonchoice tests in the laboratory showed that significantly fewer larvae were found on cruciferous weeds than on cauliflower plants, although C. nasturtii could lay eggs on the weeds. When weeds and cauliflower plants were simultaneously exposed to C. nasturtii adults for egg laying (choice tests), 97.3% of the C. nasturtii larvae were found on the cauliflower plants 8 d after oviposition, 2.7% on Sinapis arvensis L., and none on the other five weed species tested. Our results suggest that cruciferous weeds can serve as alternative host plants of C. nasturtii but are less suitable than cauliflower. A method of detecting C. nasturtii on weeds and control of C. nasturtii through weed management are discussed.