Aspectos biológicos e preferência para oviposição por Bemisia tabaci (Gennadius, 1889) biótipo B (Hemiptera: Aleyrodidae) em cultivares de algodoeiro

Abstract

The purpose of this work was to evaluate some biological aspects of egg and nymphal stages of Bemisia tabaci (Gennadius, 1889) biotype B (Hemiptera: Aleyrodidae) and to study its preference for oviposition and the effect of the presence, number and type of trichomes on the cotton cultivars BRS Ipê, BRS 186-Precoce 3, BRS Acala, BRS Verde, BRS-200 Marrom, BRS Cedro, BRS Ita 90-2 and BRS Aroeira. The experiments took place in climatic chambers at 28 ± 2°C, 70% RH and photophase of 12 hours, and in green houses, both at the Department of Entomology, Federal University of Lavras (UFLA), Minas Gerais, Brazil. Two seedlings/cup of each cultivar were placed in small plastic cups for the biological studies. Observations were made on ten eggs/cup (one egg/leaf) and on resulting nymphs up to the adult stage. Oviposition preference tests (with and without oviposition choice) were carried out in cages covered with nylon organdi ("voil") containing 100 adults; eggs were counted in 4 cm2 areas on lower surface of the leaves. Egg fertility was not affected by the cotton cultivars but survival in egg-adult period was influenced by the host plant. There was no influence of cultivars neither in the duration of egg stage, nymphs of 2nd, 3rd and 4th instars nor in the duration of the period egg-adult but nymphs reared in the cultivar BRS Ipê had their 1st instar period extended. Low oviposition was detected in BRS Aroeira, BRS Verde and BRS Ita 90-2 cultivars in experiments with and without choice of oviposition, indicating a possible source of resistance, but no correlation can be established between trichome densisty an oviposition preference among the cultivars studied at this time.