Resistance to insecticides has repeatedly developed in Helicoverpa armigera around the world and is of major concern to the cotton industry in Australia. CYP337B3, the gene responsible for fenvalerate resistance was identified in 2012 (Joußen et al.) Different alleles of this resistance gene have been identified at different frequencies in different regions of the world. Identifying the variants present in Northern Australia gives us an insight into movement of H. armigera from Asia in Australia. A total of 91 samples from N. Australia, were tested. In this data set, the majority of individuals collected from the field in Northern Australia (80%) were positive for CYP337B3, either as a homozygote or a heterozygote. Almost half (47%) of the alleles sequenced from Northern Australia were found to be the allele predominantly found in Asia (CYP337B3v2) as compared to 20% of alleles from the cotton growing regions identified as Asian. The major implication from this work is that there is gene flow between Asian populations and Australia. F2 testing of an individual collected from the Ord River showed that this CYP337B3v2 gene was associated with survival of a discriminating dose of fenvalerate. Further work is required to examine connectivity between these populations and the potential risk of other resistance alleles arriving from Asia.