Study on population increase parameters of greenbug, Schizaphis graminum (Hem.: Aphididae), on common wheat varieties in Varamin region, Iran

The biology of greenbug, Schizaphis graminum Rondani, one of the most important pests of cereals in Varamin region of Iran, was studied in laboratory at 20 ± 1˚C, 60-70% R.H. and a photoperiod of 16: 8 (L: D) hours. The experiment was carried out by rearing aphids on the leaves of six common wheat varieties including: Mahdavi, Kavir, Niknezhad, Azadi, Tabasi, and Ghods using leaf cages. The nymphal development time, mortality, longevity and adult fertility of the aphid were recorded daily. The intrinsic rate of increase (rm), finite rate of increase (λ), and doubling time (DT) parameters were calculated. Results revealed that nymphal mortality rate was very low resembling that on sensitive wheat varieties. The aphid had relatively high longevity and short nymphal development time on all mentioned wheat varieties. The lowest aphid fertility rate was obtained on Kavir comparing to the fertility yielded on Mahdavi and Tabasi that was significantly higher (P < 0.01). Estimation of the intrinsic rate of increase revealed that the wheat varieties studied were susceptible to aphid, for the reason that the aphid population increased by constant exponential rate of 0.252-0.310 female/female/day. This showed high population increase potential at suitable conditions in the absence of natural enemies. Results proved that the Niknezhad, Tabasi and Ghods were the most suitable wheat varieties for rearing the aphid. The lowest rate of fertility, intrinsic rate of increase, and finite rate of increase, and the longest doubling time of aphid population were observed on Kavir, due to lower fecundity and longer nymphal development period. Therefore, the aphid population increase potential on Kavir was lower than that on the other varieties and so, expansion of sowing Kavir in Varamin region most probably may not result in aphid population increase.