Extended plant protection by an epiphytic Pseudomonas sp. derivative carrying the cry9Aa gene from Bacillus thuringiensis galleriae against the pine processionary moth Thaumetopoea pityocampa

Abstract

A strain of Pseudomonas sp. isolated from the phyllosphere of Pinus nigra in northern Italy was used for the introduction and high expression level of the gene encoding the Cry9Aa entomocidal toxin from Bacillus thuringiensis spp. galleriae. Laboratory tests showed that the resulting bacterial construct was more efficacious in terms of LC50 when compared to the purified toxin alone, against the first instar larvae of the pine processionary moth (Thaumetopoea pityocampa), suggesting that the encapsulation of the toxin within the bacterial cell may prevent the degradation of the protein. When the efficacy of the strain was compared in a long-term greenhouse experiment (102 days) with that of a commercial preparation of Btk (Foray 48B), the latter was superior in terms of total mortality, but its effectiveness decreased with time at a faster rate than that of the cry9Aa-Pseudomonas. Overall data indicate that the expression of Bt toxins in heterologous epiphytic bacteria offers potential for more efficient and persistent delivery of toxins to the target insect pests.