Effect of milbemectin on the sweetpotato whitefly, Bemisia tabaci

Milbemectin has a chemical structure close to the group of avermectins, which are derived from Streptomyces avermitilis, and is considered primarily an efficient miticide. Effects of milbemectin on the sweetpotato whitefly, Bemisia tabaci Gennadius, were investigated under laboratory and field conditions. In bioassays conducted under controlled chamber conditions, the compound affected Ist instars of B. tabaci, resulting in a LC90 of 0.06 mg a.i. 1(-1). Later stage larvae were much less affected. Milbemectin is highly photodegradable in sunlight. In laboratory assays, when treated cotton seedlings were subjected to 3 h of sunlight before being exposed to B, tabaci adults, no mortality of the whiteflies was observed. Milbemectin at a concentration of 2 mg a.i. 1(-1) applied in combination with 0.2% 'Ultra Fine' mineral oil showed a residual activity of 67% adult mortality 10 days after application, whereas milbemectin alone had no appreciable activity. The effect of milbemectin on whitefly populations in a cotton field was compared with that of cypermethrin and of untreated control. Although milbemectin was not applied with mineral oil, it was more effective than cypermethrin in controlling the whitefly populations. This insecticide/miticide seems not to affect appreciably natural enemies of B. tabaci. Milbemectin may be considered a compound with the potential for controlling B. tabaci populations. Mineral oils enhanced the potency of milbemectin on both whitefly larvae and adults.