Peach potato aphids Myzus persicae (Sulzer) (Homoptera: Aphididae) were reared on artificial diets containing the steroidal glycoalkaloids (GAs) a-solanine and a- chaconine in concentrations lower or similar to those observed in potato leaves. The parameters used to measure the aphid performance were the total individual adult cumulative fecundity, diet uptake and mortality the mean relative growth rate (MRGR) and the intrinsic rate of natural increase (IRI). The adults proved to be susceptible to high concentrations (80-160 mg GA /100ml of diet) showing reduced fecundity, diet uptake and increased mortality in comparison to controls. Ingestion of these artificial diets by nymphs delayed maturity and decreased the intrinsic rate of natural increase. GAs in low concentrations marginally stimulated the reproductive performance and diet acceptability of this aphid.
The effects of nitrogen fertilisation and pesticide (Aldicarb) application on the foliar total and individual GA production of two potato cultivars King Edward and Maris Piper were examined using a semi-hydroponic culture system. Nitrogen deficient potato plants produced elevated concentrations of GAs. The two cultivars reacted in a different way on pesticide application. Cv. King Edward produced elevated amounts of GAs in the low pesticide treatment when no differences were observed between pesticide treatments on cv. Maris Piper.
Glycoalkaloid production of potato plants subjected to stress induced by peach potato aphid M. persicae infestation was investigated in a glasshouse, a plant growth room, and an open-air field experiment. In both glasshouse and plant growth room experiments aphid infested potato plants produced reduced amounts of total and individual GAs compared to these produced by non infested plants. This reduction was attributed to the sugar deficiency induced to the plants due to the dense aphid colonisation. However results from the field experiment showed a temporal increase of the glycoalkaloids produced by the potato cv. King Edward plants subjected to aphid infestation. It is concluded that aphid infestation as a stress inducing factor possibly affects that part of secondary metabolism responsible for the glycoalkaloid production in potato.