REPRODUCTIVE AND DEVELOPMENTAL RATES OF 2 GREENBUG BIOTYPES IN RELATION TO 2 WHEAT HOST-RESISTANCE GENES

The reproductive and developmental parameters of biotypes C and E gree nbug, Schizaphis graminum (Rondani), restricted to feeding on each of four host wheat, Triticum aestivum L., genotypes was investigated. Whe n reared on TAM105 and TAM107 winter wheat cultivars (susceptible and resistant, respectively, to biotype C greenbug based on allelic variat ion at the Gb2 locus), biotype C greenbugs differed significantly in c umulative number of nymphs produced (72.60 and 19.74, respectively), i ntrinsic rate of increase (0.244 and 0.113, respectively), and total d ays required for nymphal development (5.37 and 6.73), respectively. Bi otype E greenbugs reared on the same cultivars (both of which are susc eptible to biotype E), exhibited significant differences in cumulative nymphs per adult (64.02 and 53.46, respectively) and in total lifespa n (26.61 and 17.78, respectively), but not in intrinsic rate of increa se (0.212 and 0.217, respectively). Two near-isogenic wheat breeding l ines, each closely related to TAM105 and TAM107, were also evaluated. Biotype-E resistant TXGBE273 and biotyye-E-susceptible TXGBE307 are di stinguished by differing alleles at the Gb3 locus. While the two breed ing lines were not distinguished by any measures of biotype C developm ent or reproduction, biotype E aphids produced significantly more cumu lative nymphs per adult on susceptible TXGBE307 (42.27) than on resist ant TXGBE273 (25.00). The antibiotic factors contributing to resistanc e to both biotypes were generally more related to effects on reproduct ion than to developmental effects. Significant effects of biotype C re sistance were observed on reproduction in biotype E, although that eff ect was offset by differences in mean generation time in one of the wh eat lines.