LIFE TABLES AND INTRINSIC RATES OF INCREASE OF APTEROUS BLACK BEAN APHIDS AND PEA APHIDS, ON BROAD BEAN (HOMOPTERA: APHIDIDAE)

Abstract

Abstract Life tables were prepared from daily fecundity and survival data on 69 apterous black bean aphids, Aphis fabae Scopoli, and 47 apterous pea aphids, Acyrthosiphon pisum (Harris). Both were on broad beans in 20° ± 0.5 °C, 70–80% R.H., and 16 hr light per day. The intrinsic rates of natural increase (r m ) computed from the life tables were 0.359 ♀/♀ day for the bean aphid and 0.404 ♀/♀ day for the pea aphid. Mortality was not important in determining the rates of increase because very few aphids died during their reproductive periods. Only 5 of 116 reproducing aphids died, all from inability to extrude nymphs which had died before bursting their embryonic membranes. These nymphs became covered with a discharge from the mother which cemented them in place and prevented the birth of succeeding nymphs. The resulting engorged females died in 3–4 days. An analysis of and comparison with life tables of two other aphid species in addition to those produced here showed that the differences in r m were due almost entirely to differences in fecundity. Two fecundity patterns, correlated with aphid phylogeny, were recognized.