Susceptibility of Tortrix viridiana L. to Bacillus thuringiensis var. kurstaki at different level of larval development.

Abstract

Recently out-breaks of the green oak leaf roller Tortrix viridana L. (Lepidoptera, Tortricidae) were recorded in Natural Reserve in Sicily (Italy) where treatments are generally forbidden. The commercial, social and environmental value of the wood in the forest needs to be preserved and biological control could be applied in particular case. To optimise the permitted biological treatment, not only in terms of product amount but also for the time of application baseline susceptibility of T. viridiana from the Natural Reserve of Ficuzza (Palermo, Italy) to a commercial formulation of Bacillus thuringiensis was determined for neonates and 2, 5, 10 and 15 day old larvae. The differences in susceptibility of the different larval development were recorded. For neonates the calculated DL50 was 0.63 μg/ml, while after five days it was 10.01 μg/ml. The same doses had little effect on the older larvae, showing a clear decrease in susceptibility with age and larval growth. A relationship was also found between susceptibility and body length. The implications of these data in controlling this pest in the natural reserve are discussed.