Variability and genetic basis for migratory behaviour in a spring population of the aphid, Aphis gossypii Glover in the Yangtze River Valley of China

The population dynamics, development of gonads, takeoff and flight behaviour of Aphis gossypii Glover were investigated in order to test whether there was variation of migratory ability in the spring population. Field surveys showed that not all the aphids overwintering on hibiscus migrated to the secondary host plants, and the host-alternating and host-specific life-cycle forms coexisted in Nanjing, China. Substantial variation in flight capacity of winged individuals, development of gonads and takeoff behaviour were found within the spring population. The frequency distribution of flight duration and the number of ovarioles per individual alatae exhibited two peaks, representing the migratory and sedentary genotypes, respectively. Significant response to directional selection on takeoff behaviour demonstrated the additive genetic component of this variation. Selection for 'takeoff' individuals caused a significant increase in takeoff angle from 39.8 degrees in the first selection to 68.7 degrees in the fifth; and, hence, screened out the migratory genotype (M), while selection for the sedentary individuals increased the rate of non-takeoffs significantly, and screened out the sedentary genotype (S). The reciprocal cross, M(female) x S(male), produced hybrid offspring performing significantly steeper takeoff angles compared with those from the cross S(female) x M(male), suggesting the presence of a maternal effect. On the other hand, takeoff rate was ranked as M(female) x S(male)=S(female) x M(male)>M>S, involving no sex-linkage and maternal effect. The coexistence of host-alternating and host-specific life-cycle forms of A. gossypii on the primary host has, as deduced from the present studies, a genetic basis.

Electrophoretic variation at flight-related enzyme loci and its possible association with flight capacity in Epiphyas postvittana

Variations at three flight-related enzyme loci, delta-glycerophosphate dehydrogenase (delta-Gpdh), glucose-6-phosphate dehydrogenase (G6pd), and phosphoglucomutase (Pgm), of Epiphyas postvittana (Walker) moths were investigated using starch gel electrophoresis. Among the three enzyme loci, delta-Gpdh and G6pd were found to be monomorphic, but Pgm was polymorphic, with a total of seven different genotypes and five alleles identified in this study. Comparisons of allozyme variability at the Pgm locus showed significant differentiation among five natural populations sampled from geographically distinct localities in New Zealand and Australia and between laboratory populations differentiated by artificial selection on flight capacity. The Pgm polymorphism was shown to be associated with the variation of flight capacity, but the role of the enzyme locus in the evolution of flight behavior is to be demonstrated in this species.