Abstract
The frequency distribution of the durations of development of 516 larvae of Adalia bipunctata is unimodal, and the fast- and slow-developing larvae can be identified at the beginning of the fourth (= last) instar. To determine the advantages of fast and slow development, the survival, duration of development, growth and number of aphids consumed by fast- and slow-developing fourth instar larvae fed different numbers aphids were recorded.
The percentages of fast- and slow-developing fourth instar larvae that survived when fed 0.5, 1 or an excess of aphids per day, surprisingly, did not differ. The slow-developing larvae of both sexes took longer to complete their development than the fast- developing larvae when fed 1 or an excess of aphids per day, and although the weights of the fast- and slow-developing fourth instar larvae differed at the beginning of the instar, they did not differ at the end of this instar when fed 1 aphid per day.
However, when reared on an excess of aphids per day, the adult weights of the fast- developing individuals was greater than that of slow-developing individuals. The average durations for which the larvae in the two groups survived when fed 0.5 aphids/day differed with the larvae of the fast- developing individuals surviving for 9.8 +/- 0.5 days and slow-developing individuals 17 +/- 1.3 days.
Assuming that it is the rate of predator biomass increase, which is maximized by evolution, a model of the relationship between the rate of development/growth of a predator and that of its prey indicates that the optimum growth rate of a predator is positively associated with that of its prey. The evolutionary implications of these results are discussed.