Assessment of biological control of Bemisia tabaci (Homoptera: Aleyrodidae) on common bean in Honduras

Two experimental field trials assessed the effect of natural enemies on immature stages of Bemisa tabaci (Gennadius) infesting two varieties of common bean (Phaseolus vulgaris L.), 'Dorado 364' (Bean Golden Mosaic Virus (BGMV) tolerant) and 'Catrachita' (BGMV susceptible). Studies were carried out at Zamorano, Honduras during 'primera' (May-August) 1995 and 'postrera' (September-January), 1995-96. Treatments corresponded to two types of exclusion cages (1 x 1 x 0.5 m) and a no cage treatment. Cages were covered with organdy to exclude all natural enemies or with a net material to exclude larger predators but allow smaller parasitoids to enter the cages. Percentage parasitism ranged from 21 to 32% in 'primera' and from 10 to 37% in 'postrera'. The nymphal density of B. tabaci was relatively low and ranged from 2 to 7 nymphs per leaf in 'primera' and between 0.4 to 0.9 nymphs per leaf in 'postrera'. The most common parasitoids collected from B. tabaci were Encarsia pergandiella Howard and E. nigricephala Dozier (Aphelinidae). Our results suggest that parasitism is host-density independent. Parasitism at low host densities (< 1 nymph per leaf) may be a contributing factor preventing B. tabaci outbreaks.