Isoenzymes and migration in the African armyworm Spodoptera exempta (Lepidoptera, Noctuidae)

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Abstract
Techniques for the separation of proteins have proved to be powerful tools in the study of genetic variation. Polymorphisms on protein levels can be used to study the structure of populations. In general, differences in allele frequencies can be found among populations in different parts of the distribution area of a species. If, however, enough gene flow occurs by migration, the whole system can be regarded as one panmictic unit and similar frequencies can be expected in the whole area.African armyworms are caterpillars of the noctuid moth Spodoptera exempta. They live on all sorts of graminaceous plants on which vast outbreaks can occur. Their economic importance can be considerable since they eat the main human food crops as well as pasture grasses. The occurrence of migration in S. exempta is known but its importance is a main controversial point. Outbreaks move during the year. These outbreaks could be caused by migrating animals or by increasing local populations when conditions are favourable.The aim of this study has been to determine the relative importance of migration. Allele frequencies have been determined of six alleloenzymes that proved to be genetically polymorphic, an EST, 0‐HBDH, ODH, a‐GPDH, ME and LDH. Seventeen armyworm samples have been collected at a maximal distance of 2000 km in Kenya, Tanzania and Rhodesia on different food plants during 1975 and 1976.No heterogeneity among these samples could be detected in the allele frequencies. A comparison with data from relevant literature on insects showed that the lack of heterogeneity cannot be described to inadequacy of the data. The occurrence of extensive migration is concluded to cause the similarity in allele frequencies.

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