Onion thrips colonization of onion fields bordering crop and noncrop habitats in muck cropping systems

Onion thrips, Thrips tabaci Lindeman, colonization of onion fields may be influenced by bordering crop and non-crop habitats. Identifying habitats adjacent to onion fields associated with high T. tabaci infestations would be valuable for improving scouting efforts and management decisions. A 3-year study examined adult T. tabaci colonization patterns within onion fields early (June through early July) and late in the season (August) in three muck regions in New York (USA). We hypothesized that early-season adult densities would be greater in onion fields bordering other crops (e.g. carrot, corn and potato) and non-crops (e.g. woods) than those bordering other onion fields and that more adults would occur along onion field edges than field centres. Results indicated similar adult densities in onion fields regardless of bordering crop and non-crop habitats in seven of nine muck region 9 year data sets; exceptions were more adults in onion fields bordering potato (Elba region only) and corn (Potter region only) than those bordering other onion fields. Adult densities decreased as distance into onion fields increased in only four of nine muck region 9 year data sets; in these cases only 38% more adults were found along field edges than field centres. Later in the season, we hypothesized that adult densities would be greater in non-mature onion fields bordering mature onion fields, and densities would be greater along field edges than field centres. Results indicated that adult densities in nonmature onion fields bordering mature onion fields were 54 times greater than those bordering other non-mature onion fields, and four times more adults occurred along field edges than field centres; adult densities were similar along field edges and centres in non-mature onion fields bordering other non-mature onion fields. Implications for T. tabaci management in onion based on these colonization patterns are discussed.