The biology of the red and green morphs of the tobacco aphid, Myzus persicae nicotianae (Blackman) on flue-cured tobacco

The tobacco aphid, Myzus persicae nicotianae is aneconomically important pest of tobacco. Damage is throughdirect injury by sucking sap of infested plants as well asreduction of the quality of the leaf by leaving honey-dewwhich encourages the subsequent growth of sooty-mould. Inaddition to this, aphids also transmit economically importantvirus diseases such as the bushy-top virus, the alfalfa mosaicvirus and the potato virus-Y. Before 2002, the main colourform of the tobacco aphid in Zimbabwe was green. However,during the 2003/2004 tobacco season, concerns were raisedwhere red forms of the tobacco aphid were observed to bemore prevalent than the green form. During the 2004/2005tobacco season, green forms of the tobacco aphid could onlybe found with difficulty. In intensive research spanning threeyears, the days to adulthood, days to 1st nymph, nymphs/day,longevity, fecundity and survival of the red morph werecompared to that of the green aphid. Across all years, days toadulthood were the same for the two forms. The red morphproduced more nymphs/day than the green morph. Longevitywas similar but fecundity was 1½ to 2 times higher for the redmorph than the green aphid. The red morph survived longerthan the green aphid. These parameters combined to give thered morph of the tobacco aphid a greater reproductivepotential and rate of population increase over the green morphthereby partly explaining the sudden increase in this pest inthe recent past. -- aphid ; red morph ; green morph ; flue-cured tobacco