Seasonal abundance of whitefly nymphs, primarily sweetpotato whitefly, Bemisia tabaci (Gennadius), and bandedwinged whitefly, Trialeurodes abutilonea (Haldeman), on leaves of germplasm lines and cultivars of cotton, Gossypium hirsutum L., were determined in field plots at Maricopa, AZ, in 1987. In general, the germplasm lines with the greatest numbers of leaf trichomes (range 2 to 98 per cm2) had the greatest numbers of nymphs (range 0.4 to 11.3 nymphs per leaf on 23 September). The okra-leaf characteristic did not have a consistent effect on the numbers of nymphs. Deltapine 20, Centennial, and Stoneville 506 cultivars planted on 30 April had significantly greater infestations (range 20.3 to 121.3 nymphs per leaf) on 16 October than did the same cultivars planted 21 May (range 4.5 to 53.0) or 11 June (range 7.0 to 31.5). The nectariless okra-leaf line WC-12NL and cultivar Deltapine 61 had 1.1 and 1.5 nymphs per leaf on 22 September, respectively, not significantly different.
Infestations of pink bollworm, Pectinophora gossypiella (Saunders), (Lepidoptera: Gelechiidae), and numbers of beneficial insects in two cottons, Gossypium hirsutum, were compared at Maricopa, Arizona, and Brawley, California, during the 1986-1988 seasons. Plots (0.8 ha) of WC-12NL (nectariless, okraleaf, and early maturing) had significantly lower boll infestations than DPL-61 (nectaried, normal leaf, and later maturing) for each location and year. The three year average (range) PBW/100 bolls for WC-12NL and DPL-61 at Maricopa were 6.8 (5.7-10.7) compared to 11.2 (6.8-15.7), respectively. At Brawley the averages were 18.9 (9.3-27.6) compared to 39.2 (15.5-52.5), respectively. With the exception of 1986 at Maricopa, the percentage of bolls with eggs was significantly greater for DPL-61 (average 8.1, range 3.4-16.0) than for WC-12NL (average 4.2, range 1.1-12.1) for each location and year. Both cottons averaged about four eggs per oviposited boll; not significantly different. The numbers of Lygus spp. and three beneficial species of insects were not different in the two cottons. Collops vittatus (Say) (Coleoptera: Melyridae) was collected in significantly greater numbers in WC-12NL (1.0 per 50 sweeps compared to 0.9 for DPL-61), while Hippodamia convergens (Guerin-Meneville) (Coleoptera: Coccinellidae) was collected in greater numbers in DPL-61 (0.6 per 50 sweeps compared to 0.3 for WC-12NL). WC-12NL is the culmination of a 20-year breeding programme for resistance to P. gossypiella and has characteristics attractive for cotton production in areas where a shorter growing season is desirable.
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