Influence of Moisture on the Toxicity of Some Biopesticides on Bombyx Mori L.

Abstract

Adverse effect of moisture on some microbial insecticides such as Halt (Bacillus thuriengiensis var kurstaki, B.t.k.- 55000 S.U./mg), Biolep (B.t.k.- 32000 I.U. /mg), Vertimec (product of Streptomyces avermitilis - Avermectin1.8% w/v) and Bassina (formulation of Beauvaria bassiana-1 x 107 spore / ml) were studied against third instar larvae of mulberry silkworm, Bombyx mori L. under four levels of relative humidity ( 30%, 60%, 80% and 90% R.H.) and constant temperature (20 0 C ± 2 0 C). The biocide avermectin at 1000 ppm caused 96.66% and 95.00% mortality after 72 h of treatment at 80% and 90% relative humidity respectively. Whereas, halt and biolep caused 95.00%, 90.00% and 81.66%, 80.00% mortality after 72 h at the two respective humidies level. Through fungal formulation of B. bassiana proved to be less harmful against B. mori at 30% and 60% R.H. it inflicted 40 – 43.33% mortality at higher moisture level (>70% R.H.). Relative humidity was found to play a major role towards pathogenecity of all the tested microbials against B. mori. Increasing mortality was recorded with increase in days after treatment and maximum effect was noticed at 80% R.H. The overall effect followed the same trend for all the microbial insecticides, and the observed descending order was Avermectin > Halt > biolep > B. bassiana at four levels of relative humidity, respectively.