Behavioral responses and development of larvae and adult of Cnaphalocrocis medinalis (Guenée) on transgenic Bt rice

Abstract Background In general, it was observed that the transgene expression in transgenic plants did not alter the biochemical composition and phenotypes of transformed plants. The oviposition preference of gravid female moths is expected to correlate with the host plant fitness for their offspring development. Since many neonate larvae of lepidopteran species are relatively immobile, female adults must choose a more favorable site for laying eggs to increase the probability of larval survival. With this background, the present investigation was carried out to study the behavior of larvae and adults of leaf folder, Cnaphalocrosis medinalis (Guenee) on transgenic rice lines expressing cry2AX1 gene which were previously generated in our laboratory. Results PCR positive transgenic plants were subjected to quantitative ELISA for their level of expression. The expression level of Cry2AX1 ranged between 18±0.01 to 128±0.06 ng/gram of fresh leaf tissues, while the non-transformed ASD16 did not show any detectable level of expression. Among the transgenic events tested, the maximum expression level (128 ng/g) of Cry protein was observed in GR-ASD16-1-91-1. The results revealed that the adults did not exhibit oviposition preference towards transgenic and non-transgenic plants in choice as well as no choice test as the adults could not differentiate the test and control plants for laying the eggs. However, significant differences in larval survival and adult emergence indicated the deleterious effect of transgenic plants harboring the cry2AX1 gene in both larval and adult development, irrespective of the test condition of choice and no choice. Prolonged settling time and reduced folding length and binds spun by the larvae on transgenic plants lead to the hypothesis that the larvae could not behave normally and make congenial niche as in non-transgenic plants, exposing the larvae to the risk of both biotic and abiotic factors. The larvae fed on transgenic plants could not behave normally as in wild type and exposing their body parts to the risk of both biotic and abiotic factors.ConclusionsIt was concluded that transgenic plants with a moderate level of insect toxicity can also be used in IPM of rice leaf folder by introducing larval parasitoids or predators for effective management of rice leaf folder.