larvae, which never moult and always die when the reproductive larvae
finish consuming the host. Precocious larvae are also morphologically
distinguished from reproductive larvae by having larger mandibles and a
distinctly serpentine body, which facilitates movement in the host (Fig.
7.4). Cruz (1981) determined that precocious larvae function as a sterile
soldier caste, which kill interspecific competitors by piercing them with
their mandibles. This altruistic behaviour is advantageous, because pre-
cocious larvae increase their own fitness by assuring the survival of their
reproductive siblings. Since selection acts at the level of both the individ-
ual and the brood, the ratio of investment in reproductive and precocious
larvae would also be predicted to vary depending on how large or small
the threat from competitors might be. Such adaptive phenotypic plasticity
occurs in the polyembryonic waspCopidosoma floridanum, where the
proportion of embryos developing into soldiers changes from 4% in hosts
that are not attacked by another parasitoid to 24% in hosts that are
attacked by a competitor (Harveyet al., 2000b).144 M.R. Strand
Fig. 7.4. Light micrograph of a reproductive larva (a) and precocious larva (b) from
the polyembryonic parasitoidCopidosoma floridanum. The head of each larva is
orientated to the right. Scale bar, 100μm. (Adapted from Harveyet al., 2000b.)