Managing resistance to the insect growth regulator, pyriproxyfen, in Bemisia tabaci

The insect growth regulator pyriproxyfen (a juvenoid) effectively inhibits the hatching of eggs of the tobacco or cotton whitefly, Bemisia tabaci, as well as causing pupal mortality. Since 1991, this insecticide has been one of the main agents for controlling B tabaci on Israeli cotton. Seasonal tre nds of susceptibility to pyriproxyfen in field populations were monitored f rom June (prior to treatment) through late summer at different locations in Israel. After seven years of pyriproxyfen use within an insecticide resist ance management strategy that limits this insecticide to a single applicati on per season, susceptibility has been maintained in many areas. In other l ocations where pyriproxyfen had been used against geographically isolated p opulations of B tabaci, moderate to high levels of resistance have been obs erved. Ecological and agronomic factors that may contribute to geographical variation in selection for resistance are discussed. The dynamics of pyriproxyfen-susceptible and -resistant populations of B ta baci following a single application of pyriproxyfen were investigated under simulated field conditions in the laboratory. The susceptible population w as suppressed very effectively, whereas effects of pyriproxyfen against the resistant population were much more transient. Differences in the producti vity of susceptible and resistant strains in the absence of pyriproxyfen tr eatment could reflect a fitness cost accounting for observed reductions in resistance levels between seasons in the held. They may also explain why, f ollowing a recent reduction in the use of pyriproxyfen in cotton fields, re sistance in 1998 declined to levels observed in 1995/6. (C) 1999 Society of Chemical Industry.