Effect of milbemectin on the sweetpotato whitefly, Bemisia tabaci

Milbemectin has a chemical structure close to the group of avermectins, whi ch are derived from Streptomyces avermitilis, and is considered primarily a n efficient miticide. Effects of milbemectin on the sweetpotato whitefly, B emisia tabaci Gennadius, were investigated under laboratory and field condi tions. In bioassays conducted under controlled chamber conditions, the comp ound 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 p hotodegradable in sunlight. In laboratory assays, when treated cotton seedl ings were subjected to 3 h of sunlight before being exposed to B, tabaci ad ults, no mortality of the whiteflies was observed. Milbemectin at a concent ration of 2 mg a.i. 1(-1) applied in combination with 0.2% 'Ultra Fine' min eral oil showed a residual activity of 67% adult mortality 10 days after ap plication, whereas milbemectin alone had no appreciable activity. The effec t of milbemectin on whitefly populations in a cotton field was compared wit h that of cypermethrin and of untreated control. Although milbemectin was n ot applied with mineral oil, it was more effective than cypermethrin in con trolling the whitefly populations. This insecticide/miticide seems not to a ffect appreciably natural enemies of B. tabaci. Milbemectin may be consider ed a compound with the potential for controlling B. tabaci populations. Min eral oils enhanced the potency of milbemectin on both whitefly larvae and a dults.