Toxicity of Bacillus thuringiensis wild strains of Sardinia on Lymantria dispar (Lepidoptera: Lymantriidae) and a comparison with commercial preparations.

In a laboratory bioassay the toxicity of Bt wild strains was compared with the effectiveness of isolates obtained from Bt commercial preparations (Foray® serotype H 3A3B, Dipel® HD1 and Rapax® serotype EG 2348). Native colonies were isolated by Ohba and Aizawa (1986) method from soils collected in different areas of Sardinia. All isolates were grown following the method of Karamanlidou et al. (1991). The pellets were suspended in water and analysed by spectrophotometry at 600 nm and the suspensions were adjusted with water so that 8 x 109 spores and crystals could be counted at optical density 1. One millilitre of this suspension was centrifuged in order to obtain the relative weight of pellet (~ 0.00625 g).