Biology of aphids infesting wheat.
The biology of two aphid species, i.e. Rhopalosiphum padi and Macrosiphum miscanthi, was studied on excised wheat (cv. H 2329) earheads at room temperature. R. padi produced four nymphal instars with a mean nymphal period of 4.92 days, adult longevity of 7.85 days, and mean pre-reproductive, reproductive and post-reproductive periods of 0.70, 6.0 and 0.69 days, respectively. The total life cycle showed a gradual decline from 18.5 days in the first generation to 11.0 days in the seventh generation. The total fecundity per female was highest in the first generation (53 nymphs) then declined in subsequent generations, reaching 13.25 nymphs in the seventh generation. A fifth nymphal period was observed in M. miscanthi. However, it did not affect the total nymphal period (7.16 days) and adult longevity (8.68 days). The mean pre-reproductive, reproductive and post-reproductive periods were 1.01, 6.63 and 1.04 days, respectively. The total life cycle varied between 16.0 and 13.4 days, with a mean value of 15.18 days. Unlike R. padi, the adult longevity, reproductive period and total life cycle of M. miscanthi did not decline in successive generations. The total fecundity and the daily fecundity per female, which decreased in successive generations, had mean values of 21.91 and 3.26 days, respectively. The gradual decline observed in adult longevity, reproductive period, total life cycle and fecundity was possibly due to the gradual increase in the ambient temperature from late February to mid-April.