EVALUATION OF CULTIVARS, GERMPLASM LINES, AND SPECIES OF GOSSYPIUM FOR RESISTANCE TO BIOTYPE-B OF SWEET-POTATO WHITEFLY (HOMOPTERA, ALEYRODIDAE)

We evaluated 19 cultivars, germplasm lines, and species accessions of cotton and wild relatives, Gossypium spp., in a field, plot experiment for resistance to biotype ''B'' of the sweetpotato whitefly, Bemisia tabaci (Gennadius). We collected leaf samples on eight dates from 9 Ju ne to 14 September and counted eggs and nymphs. Egg and nymph numbers were <1 per g of leaf weight through June, then began to increase rapi dly, reaching 5,100 eggs by mid-August and 2,000 nymphs by mid-Septemb er. The rate of increase in Arizona-wild cotton, G. thurberi Todaro, w as significantly slower and numbers of eggs and nymphs were significan tly lower than in the two upland, G. hirsutum L., control cultivars 'D eltapine 50' and 'Stoneville 506'. The 19 cotton entries were divided into four leaf pubescence classes: glabrous, moderately pubescent, pub escent, and highly pubescent. Although no differences in numbers of eg gs were observed among the pubescence classes, the glabrous entries av eraged fewer nymphs than the moderately pubescent or pubescent entries , but not fewer than the single highly pubescent entry, G. raimondii U lbrich. The control upland cultivars, three upland germplasm lines, an d the single G. barbadense L. cultivar 'Pima S-6' wilted, defoliated, and opened bolls prematurely because of extreme sweetpotato whitefly p ressure. In spite of very high numbers of insects, none of the other e ntries except G. raimondii showed visible wilting and defoliation.