Abstract: Cork oak forest protection and management require continuous monitoring of defoliator moth species. Among these, the European tent caterpillar, Malacosoma neustrium L., can cause widespread and extensive defoliation of host plants, and the implementation of appropriate management programs becomes necessary. Sustainable control methods may include the use of entomopathogenic microrganisms, such as Bacillus thuringiensis serovar kurstaki (Btk). However, the formulation of the microbial control agents can be a key factor for the success of application programs. The results of an efficacy trial with different formulations of Btk strain EG 2348 against larvae of M. neustrium conducted in a cork oak forest in Sardinia (Italy) are reported. In the trial, a commercial and an experimental formulation of Btk strain EG 2348 were tested (henceforth Rapax® and Rapax Experimental) in comparison to two Btk-based reference products (Foray 48B® and Delfin®). Both formulations of Btk strain EG 2348 proved to be effective in controlling the pest.