SOCIAL INFLUENCES ON NYMPHAL DEVELOPMENT IN THE COCKROACH, DIPLOPTERA-PUNCTATA

Solitary male nymphs of the cockroach Diploptera punctata (Eschscholtz ) (Blattaria: Blaberidae) took significantly longer to reach adulthood than males paired with either a male or female nymph or grouped with four other male nymphs since birth. When isolated throughout nymphal d evelopment, 15.8% of males passed through 3 stadia before adult eclosi on, and the remainder went through 4 stadia. In contrast, 61.3% of pai red males became adults in 3 stadia. Males need not, however, be isola ted or paired for the entire nymphal period to express isolated or pai red patterns of development. About 60% of males paired in just the fir st stadium or its initial 9 days became adults in 3 stadia, and only 2 0.4% of males isolated in the first stadium and the first 3 days of th e second reached adulthood within 3 stadia. Although the first stadium was a critical period in which social condition determined the course of future development, analyses of covariance showed that isolated ma les gained less weight than paired ones, not only in the first stadium , but in the second as well. Moreover, the degree of growth of a male in the second stadium, measured as either weight gain or relative grow th rate, did not depend on the male's social condition in the first st adium, because isolated second-instar males grew less than paired ones , even when both sets of insects had been paired in the first stadium. Female nymphal development, unlike that of males, was not greatly aff ected by social factors.