Abstract
Innate capacities for increase of the aphids Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas) were determined by demographic analysis of experimental parthenogenetic populations at constant temperatures between 5° and 30 °C. Both species showed capacities for increase between 5° and 25 °C as indicated by calculated values of intrinsic and finite rates of increase. Upper temperature threshold for growth of populations of both species was estimated as between 25° and 30 °C, and the lower temperature threshold as below 5 °C. Optimum temperatures for increase were 25 °C for M. persicae and 20 °C for M. euphorbiae. Innate capacity for increase of M. persicae was generally higher than that of M. euphorbiae, particularly at temperatures between 15° and 25 °C, because of more rapid development and earlier attainment of maximum fecundity rate by M. persicae. Temperature influenced the innate capacity for increase by modification of developmental time, survival rate, and fecundity rate. Age at which maximum fecundity occurred was more important in determining the innate capacity for increase than total fecundity. Intrinsic rates of increase were largely determined by the first one or two weeks of adult life of the members of a population.
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