Virulence of two entomopathogenic nematodes through their interaction with Beauveria bassiana and Bacillus thuringiensis against Pieris brassicae (Lepidoptera: Pieridae)

Pieris brassicae L. is one of the most important pests of Brassicaceae. The insecticidal effect of two entomopathogenic nematodes (EPNs), Heterorhabditis bacteriophora and Steinernema feltiae, was determined through their interaction with Beauveria bassiana and Bacillus thuringiensis subsp. kurstaki (Btk) against P. brassicae. In the interaction tests, the EPNs were applied at LC50 level 0, 12 or 24h after treating the larvae with LC10 or LC25 of the B. bassiana or Btk. The interaction between the EPNs and B. bassiana was entirely different from the interaction of the EPNs and Btk. The interaction with B. bassiana was dependant on time intervals, while the interaction of the EPNs with Btk was almost additive or synergistic. An antagonistic effect was seen when the EPNs were applied immediately after the B. bassiana. However, the application of the EPNs 24h after their treatment with B. bassiana caused additive or synergistic effects. The results also showed the best mortality effect when the EPNs were used with Btk at 12 h and 24 h time intervals. Based on the results, a simultaneous use of the EPNs and B. bassiana is not recommended against P. brassica. However, the EPNs could be used simultaneously after Btk but it is better to allow a time interval to increase mortality.