effect of four wheat cultivars on life table parameters of schizaphis graminum (hemiptera: aphididae)

the life table parameters of schizaphis graminum (rondani) (hemiptera: aphididae) on four commercial cultivars of wheat (kohdasht, pastor, tajan and zagros) were determined in laboratory conditions. fertility life table were constructed using age-specific survivorship (lx) and age-specific fecundity (mx) and subsequently analyzed using jackknife method and anova. there were significant differences among pre-imaginal period and adult longevity of the aphid on the four wheat cultivars. the highest mortality occurred at first nymphal instar on all of wheat cultivars tested. the life expectancy (ex) of one-day-old adults was estimated to be 23.5, 24.6, 30.36 and 26.83 days on kohdasht, pastor, tajan and zagros, respectively. the gross reproductive rate was significantly higher on tajan (102.39 ± 1.42 females/female/generation) compared with other three cultivars. the net reproductive rate (r­0) significantly differed on different wheat cultivars examined. the r0-value was highest on tajan (82.21 ± 1.21) and lowest on zagros (38.23 ± 0.63 females/female/generation). the highest and lowest values of the intrinsic rate of increase (rm) were 0.276 ± 0.002 (on pastor) and 0.222 ± 0.001 day-1 (on zagros), respectively. the finite rate of increase (l) differed significantly among four wheat cultivars, ranging from 1.25 ± 0.00 (on zagros) to 1.32 ± 0.00 days-1 (on pastor). doubling time ranged from 2.51 ± 0.02 (on pastor) to 3.12 ± 0.02 days (on zagros). the longest mean generation time (t) of the aphid was obtained on tajan cultivar. the results showed that the zagros cultivar had the highest antibiotic effect on population growth of s. graminum.