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Studies were conducted to follow seasonal susceptibility of feral pink bollworm (PBW), Pectinophora gossypiella (Saunders) larvae to NuCOTN 33B (Bt) and Deltapine (DPL) 5414 in furrow and furrow plus supplementary drip-irrigated cotton field plots. Laboratory bioassays of laboratory - reared PBW larvae to flower buds and bolls and cabbage looper (CL), Trichoplusia ni (Hübner), larval mortality feeding on DPL 5415 and Bt cottons leaves were also conducted. Cry1Ac insect toxic protein contents in the different plant tissue were determined by Enzyme Linked ImmunoSorbent Assay (ELISA) throughout the season to compare in relation to PBW and CL mortality data. Irrigation type had no effect on PBW or CL larval mortality parameters measured. DPL 5415 bolls had 0.15 feral live larvae per boll and no dead larvae per boll compared with no live and 0.12 dead feral larvae per Bt boll. Whole plant samples showed 0.5 to 8.6% live larvae boll infestations compared to no live PBW life stages and no exit holes for Bt bolls. No PBW larvae survived on day four following bioassay infestation of one-third grown Bt flower buds with PBW neonate larvae as compared to 90% larval survival on DPL 5415 flower buds. Immature bolls harvested in the field and artificially infested with PBW larvae in the laboratory showed averages of 3 to 52% live larvae per boll, all in fourth instar of development, for DPL 5415 bolls compared to no live larvae, no development beyond the first instar, and no exit holes for Bt bolls. Cry1Ac protein level in flower buds were 0.11 to 0.16 ppm and 0.14, 0.11 and 0.05 ppm, in each case, per wet weight gram of boll tissue in bolls during the season. For CL leaf bioassays, larval mortalities after 7 days feeding on Bt leaves were variable ranging from 82 to 94% from node 8 on 61 and 82 days after planting (DAP) to 32, 38 and 7% on leaves from node 16 on 82, 117, and 159 DAP, respectively, and 28 and 6% on leaves from node 24 on 117 and 159 DAP. Cry1Ac amounts were 0.96 and 0.85 ppm (wet wgt per g of Bt leaf tissue), from leaves from node 8 (61 and 82 DAP), 0.53, 0.50 and 0.22 ppm (node 16, 82, 117, and 159 DAP) and 0.44 and 0.18 ppm (node 24, 117 and 159 DAP). Numbers of cotton bolls, lint and seed per acre were significantly greater from plots that were furrow plus drip irrigated as compared to furrow irrigated alone. DPL 5415 and Bt cotton yields were not significantly different. |
