No abstract

Comparative bioassays of two chloronicotinyl insecticides, acetamiprid and imidacloprid, against the whitefly Bemisia tabaci (Gennadius), using foliar and systemic applications, were conducted under laboratory conditions and in field trials. Under controlled conditions, the ovicidal activity of foliar applications of acetamiprid on cotton seedlings was much higher than that of imidacloprid. According to LC50 and LC90 values, acetamiprid was 10- and 18-fold more potent than imidacloprid. Both compounds were effective when applied to soil against whitefly adults; however, the potency of imidacloprid was somewhat higher than that of acetamiprid 2, 7 and 14 days after application; resulting (with the concentration of 25 ml a.i./l) in adult mortality of 90, 93, and 96% and 76, 84, and 76% respectively. In an experimental cotton field, the efficacy of foliar applications of 60 g a.i./ha acetamiprid and 210 g a.i./ha imidacloprid was compared. Field residual activity of acetamiprid to whitefly adults lasted for approximately ten days, compared with three days for imidacloprid.

No abstract

: The insect growth regulator pyriproxyfen (a juvenoid) eþ ectively inhibits the hatching of eggs of the tobacco or cotton whiteýy, 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 trends of susceptibility to pyriproxyfen in üeld populations were monitored from June (prior to treatment) through late summer at diþ erent locations in Israel. After seven years of pyriproxyfen use within an insecticide resistance management strategy that limits this insecticide to a single application per season, susceptibility has been maintained in many areas. In other locations where pyriproxyfen had been used against geographically isolated populations of B tabaci, moderate to high levels of resistance have been observed. 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 tabaci following a single application of pyriproxyfen were investigated under simulated üeld conditions in the laboratory. The susceptible population was suppressed very eþ ectively, whereas eþ ects of pyriproxyfen against the resistant population were much more transient. Diþ erences in the productivity of susceptible and resistant strains in the absence of pyriproxyfen treatment could reýect a ütness cost accounting for observed reductions in resistance levels between seasons in the üeld. They may also explain why, following a recent reduction in the use of pyriproxyfen in cotton üelds, resistance in 1998 declined to levels observed in 1995/6.