VARIATION IN APHID WEIGHT AND REPRODUCTIVE POTENTIAL IN RELATION TO PLANT-GROWTH FORM

Plants used as hosts by aphids were classified into 9 categories, based on phenology and growth form. The relative abundance of each category changes with the successional age of the habitat. The adult body weight and reproductive potential of 90 aphid species on 120 host-plants are analyzed. Both alate and apterous morphs are considered. Total embryo number and number of mature embryos are used as indices of potential fecundity and short-term reproductive effort. Aphids occurring on woody plants (evergreens and deciduous trees and shrubs) are generally heavier than those on annuals, biennials and perennials. The reproductive potential of aphids varies according to the host-plant category on which they are found. Aphids on herbaceous plants are potentially more fecund than those on woody plants. Within these categories, alate aphids on annuals have a higher reproductive potential than those on biennials and perennials while shrub-associated aphids are potentially more fecund than aphids on trees. Species on grasses and ferns have a low reproductive potential. Seasonal trends in aphid weight and reproductive potential are discussed in terms of established patterns in host-plant phenology and nutrient levels. Results lend support to classical life-cycle theory and to the successional models of Margalef and Odum.