Background: The pink bollworm Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) is one of the world's most important pests of cotton. Insecticide sprays and transgenic cotton producing toxins of the bacterium Bacillus thuringiensis (Bt) are currently used to manage this pest. Bt toxins kill susceptible insects by specifically binding to and destroying midgut cells, but they are not toxic to most other organisms. Pink bollworm is useful as a model for understanding insect responses to Bt toxins, yet advances in understanding at the molecular level have been limited because basic genomic information is lacking for this cosmopolitan pest. Here, we have sequenced, de novo assembled and annotated a comprehensive larval midgut transcriptome from a susceptible strain of pink bollworm. Findings: A de novo transcriptome assembly for the midgut of P. gossypiella was generated containing 46,458 transcripts (average length of 770 bp) derived from 39,874 unigenes. The size of the transcriptome is similar to published midgut transcriptomes of other Lepidoptera and includes up to 91 % annotated contigs. The dataset is publicly available in NCBI and GigaDB as a resource for researchers. Conclusions: Foundational knowledge of protein-coding genes from the pink bollworm midgut is critical for understanding how this important insect pest functions. The transcriptome data presented here represent the first large-scale molecular resource for this species, and may be used for deciphering relevant midgut proteins critical for xenobiotic detoxification, nutrient digestion and allocation, as well as for the discovery of protein receptors important for Bt intoxication.

Insecticidal proteins from Bacillus thuringiensis (Bt) are used widely in sprays and transgenic plants to control insect pests. Although much research has elucidated the effects of Bt toxins on larvae, relatively little is known about their effects on adults. Here, we evaluated the effects of exposing adults to Bt toxin Cry1Ac on the life span and reproduction of two strains of pink bollworm (Pectinophora gossypiella (Saunders)). In larval diet bioassays, the concentration of Cry1Ac killing 50% of larvae (LC50) was 640 times higher for the laboratory-selected resistant strain (AZP-R) than the susceptible strain (APHIS-S). In experiments with adults, the highest concentrations of Cry1Ac tested (160 and 640 mu g Cry1Ac per ml of 5% honey water) reduced life span for both strains. Treatments with 10, 40, and 160 mg Cry1Ac per ml reduced the duration of the oviposition period as well as the number of eggs laid by both strains, but did not affect the percentage of pairs producing eggs, the duration of the preoviposition period, or the percentage of eggs hatching for either strain. Adult life span did not differ between strains at low to moderate concentrations of Cry1Ac, but it was significantly greater for the resistant strain than the susceptible strain at the two highest concentrations of Cry1Ac tested. The reduced susceptibility to high concentrations of Cry1Ac in adults of the AZP-R strain relative to the APHIS-S strain provides the first evidence of expression of resistance to a Bt toxin in adult Lepidoptera.