PoPulation dynamics of Harmonia axyridis and apHis glycines in niagara Peninsula soybean fields and vineyards

J. ent. Soc. Ont. 140: 27-39 Multicoloured Asian lady beetle (Harmonia axyridis) is an occasional pest of wine and juice grapes in vineyards throughout northeastern North America. in late season, beetles aggregate on grape clusters immediately before harvest, and are difficult and expensive to remove before processing. Outbreaks of H. axyridis are thought to be related to soybean aphid (Aphis glycines) populations. heavy infestations of aphids occur late in the season on soybeans and can sustain large numbers of H. axyridis. Each summer from 2004 to 2006, 23-29 soybean fields along the escarpment of the Niagara Peninsula were monitored each week for soybean aphid infestation, and all life stages of H. axyridis were recorded. Where substantial populations of A. glycines were found, larvae and adults of H. axyridis soon followed. Severity of H. axyridis infestation in vineyards was still high even when A. glycines populations were reduced by insecticides in soybean fields in 2005. Outbreaks of H. axyridis in vineyards are correlated with substantial populations of soybean aphid that occur early in the season. Outbreak populations of H. axyridis in vineyards were observed in years where A. glycines eggs were not abundant on overwintering hosts, thus H. axyridis density appears to be negatively correlated with numbers of overwintering A. glycines eggs on its primary host, Rhamnus cathartica. A model of interaction between the two species is proposed.