Assessing Cotton Genotypes for Resistance to Aphis gossypii (Hemiptera: Aphididae).

Aphis gossypii Glover (Hemiptera: Aphididae) is a polyphagous species frequently associated with the presence of sooty mold and viruses lethal to plants. The purpose of this work was to characterize possible resistance categories of cotton genotypes against A. gossypii. Initially, a preliminary test was carried out with 78 genotypes, 15 of which were selected for infestation ability assays and the determination of the cumulative aphid-day rates. Posteriorly, these genotypes were also evaluated through antixenosis and antibiosis assays. The genotypes FM 910, FM 966 LL, Mocó, Gossypium hirsutum var. punctatum L. (Malvaceae), Variedade Reba = BTK-12, Deltapine, Hi-Bred, Acala 4-42, IAC PV010-1664, IAC 21, Reba B-50 PR and FMT 709 inhibited the aphid colonization. In the infestation ability assay, G. hirsutum punctatum, IAC PV010-1664 and Acala 4-42 were the least infested. In a multiple-choice assay, Deltapine Smooth Leaf and Variedade Reba = BTK-12 were significantly less infested, suggesting antixenosis. In the antibiosis assay, Gossypium arboreum L. (Malvaceae) 1 showed the lowest number of nymphs, number of nymphs per adult per day and, number of nymphs at 10 d after the birth of the first nymph in addition to reducing the reproductive period, nymphal survival, adult longevity and, developmental time. In the FM 910, the number of nymphs produced per day and, at 10 d after the birth of the first nymph decreased, which also indicated resistance. The results obtained here are unprecedented and can be explored in breeding programs to develop insect-resistant cotton cultivars.

Role of nutritional composition in the development and survival of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on artificial diet and natural hosts.

Helicoverpa armigera is a pest of several crops causing significant economic impact. We evaluated the insect development on different vegetative and reproductive structures of cotton, maize, and soybean compared to artificial diet. One hundred individuals were evaluated per structure (cotton leaves and bolls; maize leaves, grains, and silk; soybean leaves and pods) and artificial diet. Centesimal analyses were performed on quantifiable nutrient contents in diets. The viability of immatures (eggs, larvae, and pupae) ranged from 30% on maize leaf to 74% on cotton bolls, while on the artificial diet, it was 70%. Maize, cotton, and soybean leaves provided viability of 30, 37, and 42%, respectively, revealing these leaves tissues are less favorable to the development of H. armigera immatures compared to 'reproductive tissues'. Centesimal composition of diets compared 14 common components in all diets, which correlated significantly with larval and pupal stages and/or pupal weight. Of the 12 dietary components that significantly affected larval development time, half were negatively correlated, indicating a decrease in developmental time from their increments. In general, when insects were confined separately to substrates, the artificial diet was the most suitable for H. armigera development compared to the evaluated natural diets. However, in natural conditions, the variability of available hosts must be considered. In addition, it is acceptable for moths to select more suitable hosts for oviposition, while their larvae move to other more suitable tissues of the same plant or even migrate to other plants.