MIGRATION AND GENETIC-REGULATION OF THE PRE-REPRODUCTIVE PERIOD IN THE COTTON-BOLLWORM MOTH, HELICOVERPA-ARMIGERA

The pre-reproductive period (PRP) is of interest in the study of noctuid migration because it approximates to the number of nights in which migratory flight can occur. This study examined the pre-calling period (PCP = female PRP) distribution of Indian, Malawian and Chinese Helicoverpa armigera strains and found them to be significantly different. A PCP sib-analysis experiment was conducted both on the Malawian and on the Chinese strains. In both sib-analysis experiments, the sire component of variance was significant and greater than that of the dam component. As females are the heterogametic sex in Lepidoptera, this suggests that some genes influencing the PCP are X-linked. Male moths were also shown to have PRPs, the distribution of which was not significantly different from that of their female siblings. A selection experiment, based on the PCP only, produced two divergent lines of early- and late-maturing females after only two generations of selection. After three generations of selection, the male PRP distributions in the two lines were examined and were found to differ significantly. The divergence occurred in the same direction as for females, suggesting that the same set of genes regulates the PRP in both sexes. The results of this study are considered in relation to the evolution of migration in H. armigera.