INTERMEDIATE-WINGED APHIDS AND THE TIME-OF-DETERMINATION THEORY

Abstract

Aphids of the species Macrosiphum solanifolii, intermediate between winged and wingless, were experimentally produced, and a histological study was made of these. Two theories attempting to explain the combination of characters (wings, ocelli, wing muscle) found in intermediate-winged aphids are discussed in this paper. More than 2/3rds of the aphids of this study gave evidence of supporting the theory that the combination of characters in intermediates is due to the fact that differentiating organs are detd. at different times in the embryogeny (time-of-detn. theory). This indicates that organs are detd. in a serial order in aphids as has been found to be true for certain vertebrates. The order of embryonic detn. of the structures distinguishing winged from wingless is wings, ocelli, and wing muscles. Though the time between the detn. of these organs appears short the period of embryonic segmentation for the 3 structures is of considerable duration. The irregularities found in the combination of characters are considered the result of a variation in the time of detn. for a given organ in different individuals.