The genetic basis of larval host-plant preference was investigated in reciprocal F 1 , F 2 , and backcrossed generations derived from hybrid crosses between the generalist species Helicoverpa armigera (Hübner) and the closely related specialist species Helicoverpa assulta (Guenée) (Lepidoptera: Noctuidae). Host-plant preference for cotton [ Gossypium arboreum L. (Malvaceae)] and pepper [ Capsicum frutescens L. (Solanaceae)] of fifth-instar caterpillars was tested by using a two-choice leaf-disk assay. Helicoverpa armigera and H. assulta were significantly different in their feeding preferences, but the difference was not significant in the reciprocal hybrids, which showed there were no maternal/cytoplasmic effects. Comparisons of feeding preference between different groups of females or males demonstrated that the trait was not controlled by sex-linked loci. The distributions of feeding preference index values for crosses that carried similar complements of autosomal genes were not significantly different, whereas crosses with different complements of autosomal genes were associated with significantly different feeding preferences, indicating that feeding preference of the two species for cotton and pepper, respectively, is controlled by autosomal genes. It was found that one major autosomal locus affected this feeding preference, with the H . armigera -derived alleles being partially dominant to those carried by H. assulta . The genetic analysis of hybrids contributes to understand the evolution of feeding preference in these closely related species.

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Experiments were carried out to study the relationship between the quantity of honeydew and rmof green peach aphid infesting 50 tobacco varieties in the field from 1990 to 1992. The results showed that the range for rm is from 0.102 to 0.498, for honeydew secreted during 24 hours is 3.862 mm2/aphid to 29. 356 mm2/aphid. It also showed that the resistance of tobacco varieties to green peach aphid manifested in the reduction of net reproductive rate. Both rm and honeydew had significant relations to the population of green peach aphid in the field, and therefore the quantity of honeydew can be used as an index in determination of tobacco resistance to green peach aphid.