VARIATION IN PEA APHID POPULATION DEVELOPMENT IN 3 DIFFERENT HABITATS

1. Seasonal population growth rates for the pea aphid, Acyrthosiphon p isum Harris, were determined in three different host plant habitats; a lfalfa, Medicago sativa (L.), clover, Trifolium pratense (L.), and pea s, Pisum sativum (L.); over four years and eight places, It was possib le to estimate a common intrinsic rate of increase for each host plant habitat. 2. An analysis of the relative influence of temporal, spatia l and host plant habitat variation showed that the host plant habitat was most important in determining the growth rates of the populations, both in rate of build-up and decline. 3. Patterns of alate production in the three different habitats differed substantially between the an nual peas and the two perennial legumes. During the summer, alate prod uction was large and rapid in peas and remained low and constant in cl over and alfalfa 4. Parasitism was highest in peas. The species compos ition of parasitoids differed between crops. 5. Aphids in annual peas had a higher intrinsic rate of increase and a faster rate of decline t han in the two perennial legumes. This explains the presence of both m i,oratory and sedentary forms among pea aphids.