Comparative Nutrition and Developmental Biology of Xylem-Feeding Leafhoppers Reared on Four Genotypes of <I>Glycine max</I>

Abstract

A simplified protocol for rearing the glassy-winged sharpshooter, Homalodisca coagulata (Say) (Homoptera: Cicadellidae), was tested on four genotypes of soybean, Glycine max (L.) Merrill. Growth and development of leafhoppers were examined on three glabrous isolines (D88-5320, D88-5328, and D90-9216) and one pubescent genotype (Hagood). All three glabrous isolines were adequate hosts producing an average of >100 adults from eight original mating pairs of leafhoppers. Pubescent Hagood produced significantly fewer adults with longer developmental times. Isoline D88-5328 produced 30% more adults than the other glabrous isolines. Genotype also had significant effects on total developmental times, developmental rates within instars, growth rates, and adult masses at eclosion with insect performance being enhanced on isoline D88-5328. All genotypes of G. max had similar xylem chemistry at the initiation of the rearing experiment (6-week-old plants), but as G. max matured (14–18 wk), isoline D88-5328 provided significantly more organic nitrogen. Chemical analyses of xylem fluid and developmental data support the hypothesis that young H. coagulata required balanced profiles of organic nitrogen for development but benefited from increased organic nitrogen as they approached maturation. Poor performance on pubescent Hagood was not related to xylem chemistry and was assumed to result from the inhibitory effect of trichomes. Xylem fluid analysis suggests that some plants may have eventually experienced nitrogen deprivation from high leafhopper loads; this, in turn, resulted in slow development and small body size at maturation for some insects. Although this protocol provides a simplified technique for rearing H. coagulata, it is likely that manipulation of xylem chemistry via fertilization would further maximize growth and developmental rates.