The Australian Species of Heliothis: Identification, Genetic Variation and Migration

Abstract

The Australian Heliothis complex consists of five described species of which two, H. armigera (Hubner) and H. punctigera Wallengren, are serious agricultural pests. Both are highly polyphagous but only H. armigera attacks cereal crops, including maize. H. armigera has developed resistance to insecticides but H. punctigera has not. The two pest species are very similar but can be separated on morphological criteria in the adult, pupal and late larval stages. The eggs and small larvae are indistinguishable except through electrophoretic variation, being fixed or almost so for different alleles at seven loci. Differences in the ICD and PGD bands can be used to indicate when the potentially resistant species H. armigera is present. The genetic distance between H. armigera and H. punctigera is 0.34, lower than the comparable value for the two American pest species. The percentage of loci which are polymorphic and the average heterozygosity are also relatively low. Genetic distances between widely separated populations are less than 0.01 in both species, and the same rare alleles are present in most populations. These results can be explained by extensive migration. Both species are long distance migrants and can be found in areas remote from cultivated hosts. The rapid spread of resistance in H. armigera is probably due to migration.