Effects of Bacillus thuringiensis var. israelensis Strains and Toxins on the Pine Processionary Moth Thaumetopoea wilkinsoni (Lepidoptera: Notodontidae)

Abstract

The pine processionary moth Thaumetopoea wilkinsoni (Tams, 1926) (Lepidoptera: Notodontidae) is one of the most harmful species that causes destruction in pine ecosystems and also causes critical skin reactions in humans and animals due to its urticating hairs. This study aimed to evaluate the efficacy of different strains [Bti ATCC 35646 (wild-type strain), Bti pHT315, and Bti pHTppk (mutant strain)] of Diptera-targeted Bacillus thuringiensis subsp. israelensis (Bti) and toxins (spore/crystal mixtures) obtained from these strains against the 4th larval stage of T. wilkinsoni under laboratory conditions. T. wilkinsoni eggs were collected from pine trees at Ondokuz Mayıs University in Samsun, Turkey, in 2022. Pine needles were contaminated with bacterial strains of different concentrations (1 × 10⁷, 1 × 10⁸, 1 × 10⁹ cfu/mL) in 5 mL and toxins in different concentrations (0.15, 0.3, 0.6, 1.25, 2.5, 5 mg/mL) in 2 mL. Larvae were placed in containers with 30 larvae in each group and were observed for 25 days. As a result of the study, Bti ATCC 35646 with 63.4% mortality and the lowest LC₅₀ value of 1.2 × 10⁹ cfu/mL among the three strains of Bti and Bti pHTppk with 76.7% mortality and the lowest LC₅₀ value of 1.2 mL among the toxins from the Bti strains had found to be virulent for T. wilkinsoni. The results obtained from our study suggest that Diptera-targeted Bti is virulent to T. wilkinsoni and that this strain and spore/crystal mixture can be used in the biological control of this species.