Evaluation of different Bacillus thuringiensis sv kurstaki formulations against Lymantria dispar and Malacosoma neustria larvae infesting Quercus suber trees

Lepidopteran defoliators such as Lymantria dispar and Malacosoma neustria represent a major concern for cork oak forest, especially during population outbreaks. To contain their infestations over large areas, the use of entomopathogenic microorganisms such as Bacillus thuringiensis serovar kurstaki (Btk) is one of the available option. However, the features of the microbial control agent formulations represent a key factor for the success of application programs. The results of two years efficacy trials with different formulations of Btk, conducted in 2012 and 2013 in a cork oak forest in North-Western Sardinia, are reported. In the first year, trials were carried out on a M. neustria population, while in the second year a mixed population of L. dispar and M. neustria was involved. Trials included two formulations of Btk strain EG 2348 (Rapax® and Rapax Experimental) in comparison with two other commercial formulations (Foray 48B® and Delfin®). Both formulations of Btk strain EG 2348 proved to be effective in controlling the two pest species, showing a forest protection potential comparable to that of the reference products, Foray 48B® and Delfin®, containing spores and insecticidal Cry proteins of strains HD-1 and SA-11, respectively. Also the defoliation levels were significantly higher in untreated control trees than in treated ones.