Abstract:
Whitefly, Bemisia tabaci infestation is observed on Hygrophila corymbosa, a newly established aquatic plant in Green Farms Ltd., Marawilla, Negombo. This study was carried out to understand the biology of B. tabaci, alternative host and the efficacy of Lecanicillium lecanii against B. tabaci. Eggs, nymphs and adults of B. tabaci was reared and studied their development stages and damaging stages. Six life stages of B. tabaci are egg, four instars, and the adult. All the life stages of B. tabaci occurred on the lower surface of the leaf. Crawler, the first instar had legs and the only mobile instar that moved to feed sites. Nymphs and adults of B. tabaci caused infestation on H. corymbosa. Solanum lycopersicum, Solanum melongena, Capsicum annuum, Crossandra infundibuliformis, Euphorbia pulcherrima and Plectranthus scutellarioide and those identified as alternative hosts for B. tacbaci. Under in-vitro conditions the L. lecanii formulation was used to control B. tabaci. All the experiments were designed according to complete randomized design (CRD). Data were statistically analyzed using the SAS package. Significance among the treatments was determined according to Dunnett mean separation test at 95% of a confidence interval. Application of L. lecanii suspensions at 1 g/L, 3 g/L, 6 g/L and 10 g/L against B. tabaci nymphal stage resulted in 88%, 97%, 97% and 98% mean mortality respectively at 15 days after treatment (DAT). The results also revealed that the percentage of mean mortality of eggs was very less at different concentrations of L. lecanii. No mortality had been observed until 9 DAT. Mean mortality of B. tabaci eggs at 1 g/L, 3 g/L, 6 g/L and 10 g/L of L. lecanii suspension were 8%, 12%, 12%, and 15% respectively at 15 DAT. Application of L. lecanii suspension at 2 g/L, 3 g/L and 4 g/L against the nymphal stage of B. tabaci has resulted in 97%, 99% and 99% of mean mortality, respectively at 15 DAT. Hence, 3 g/L of L. lecanii was the optimum concentration to control B. tabaci nymphs under in-vitro conditions.
