Influence of trichomes on ovipositional preference of Bemisia tabaci (Genn.) Biotype B (Hemiptera: Aleyrodidae) for bean genotyes

The oviposition preference (free-choice tests) of Bemisia tabaci (Germ.) Biotype B for 20 bean genotypes was tested. The genotypes were divided into two plots and set up in a block-randomized design with 20 replications. New expanded bean leaves were sectioned and placed in glass tubes containing distilled water and disposed in acrylic cages containing approximately 500 insects. After 24h, the total number of eggs laid on the abaxial surface of leaves and the density of straight and hooked trichomes in two areas of 4.9 mm(2) on the abaxial surface were counted. The leaf area was measured as well as the maximum and minimum length of hooked and straight trichomes, which were classified in short, medium or long. No significant correlation was found between the number of eggs and the density of total trichomes (straight + hooked) or between hooked or straight trichomes. Significant correlation was detected between the number of eggs and long straight trichomes type A(1) (r = 2.85) and short hooked trichomes type B-3 (r = -2.44). In this way, the ovipositional preference of B. tabaci for Bolinha genotype (4.8 eggs/cm(2)) in a free-choice test could be associated to the larger number of long straight trichomes type A(1) (31.7 trichomes/4.9 mm(2)) on its leaves surface. In addition, the whitefly ovipositional nonpreference for G13028 wild genotype (1.1 eggs/cm(2)) could be related with the numerous short hooked trichomes type B-3 (64.1 trichomes/4.9 mm(2)) on its leaves surface.