Screening of cry gene contents of Bacillus thuringiensis strains isolated from avocado orchards in Mexico, and their insecticidal activity towards Argyrotaenia sp. (Lepidoptera: Tortricidae) larvae

Aims: To screen for Bacillus thuringiensis strains from avocado orchards in two Mexican states with lepidopteran-specific cry gene content and evaluate their insecticidal activity against Argyrotaenia sp., an undescribed species present in avocado orchards. Methods and Results: Lepidopteran-active cry1, cry2 and cry9 genes were detected by PCR analysis in 37 isolates. cry1 genes were more frequent in Michoacán, but were undetected in Nayarit isolates. cry9 and cry2 genes were detected in isolates from both states, although cry2 genes were less frequent. A variety of crystal shapes were observed among the isolates. According to gene profile, eight isolates were selected and tested against 2-day old Argyrotaenia sp. larvae. Standard strain HD-125 caused the highest mortality followed by strain MR-26 from Michoacán at a concentration of 500 μg ml^-1, respectively. Conclusions: Bacillus thuringiensis strains isolated from avocado orchards exhibit a low toxic activity towards Argyrotaenia sp. larvae, in spite of their specific cry gene content. Significance and Impact of the Study: Toxic activity of B. thuringiensis is not necessarily related to insect pest habitat and neither to specific cry gene content associated to other lepidopterans.