Seasonal pink bollworm, Pectinophora gossypiella (Saunders), infestations of transgenic and non-transgenic cottons

The susceptibility of pink bollworm (PBW), Pectinophora gossypiella (Saunders), larvae to NuCOTN 33B (Bt) and Delta and Pineland (DPL) 5415 cotton, Gossypium hirsutum L., bolls developing on early- and late-season plant nodes was studied. Bolls were artificially infested with PBW eggs from a laboratory colony or exposed to feral PBW populations in the field. For artificial egg infestations, PBW entrance holes in Bt and DPL 5415 bolls averaged 19.6 ± 2.2 and 14.4 ± 1.2 per boll, respectively, over seven sampling dates. No larval exit holes were found in Bt cotton bolls, and an average of 1.8 ± 0.2 exit holes per boll occurred in DPL 5415 cotton bolls. Larval survival as percentages of the numbers of entrance holes were 21.5 for DPL 5415 and < 0.1 for Bt. The extremely low larval survival in Bt cotton from more that 11,000 entrance holes suggests, at least for the laboratory strain in this study, a high level of Bt susceptibility. Live and dead first instars in Bt bolls ranged from < 0.1 to 2.1 per boll. No living or dead second- or third-instar larvae occurred. Seven surviving PBW (living fourth instars or pupae in boll boxes) were found in Bt bolls over all sampling dates. All F1 larvae obtained from survivors in the putative Bt bolls died on Bt bolls, but 50% boll infestation with 0.6 larvae per boll occurred following release on DPL 5415 bolls. No tests were conducted with Bt bolls to verify the presence of CrylAc toxic protein but the complete mortality of the F1 larvae suggests that the surviving larvae were from non-Bt bolls. In contrast to Bt bolls, no dead first instars, 0.0 to 0.1 live second instar, 0.1 to 0.2 live third instar, and 0.6 to 5.5 live fourth instars were found per DPL 5415 boll. Immature Bt cotton bolls developing on plants 180 days after planting (DAP) were as toxic to PBW larvae as immature bolls developing on plants 83 DAP. Random boll sampling in plots showed an average of 31 and < 1% boll infestations in DPL 5415 and Bt cottons. respectively. Average numbers of entrance holes per DPL 5415 and Bt cotton boll were 1.5 and 1.0, respectively. Percentages of surviving larvae were 21.2% for DPL 5415 and 0.7% for Bt. Whole cotton plant sampling showed PBW infestations of 17.2% of the open mature and 10.5% of the immature green bolls for DPL 5415, and 0.0% of the open Bt bolls infested Bt and 1.7% infested immature green bolls. Briefly, our study showed that the Bt toxic protein technology continues to be outstanding in season-long effectiveness for PBW control. There were no indications of reduced efficacy for late-season bolls.