Professor McKenzie has studied the genetic response of natural populations to environmental change, using insecticide residues in the Australian Sheep Blowfly, Lucilia cuprina as the primary model system. In practical terms, a clearer understanding of the genetic response, (both major and minor gene substitutions), and the precise environmental circumstances evoking the genetic response, has provided one of the soundest conceptual bases for the management of pesticide resistance. In more general terms, the laboratory and field studies of McKenzie has provided one of the most fascinating analyses of modern ecological genetics. For his theoretical and practical contributions, McKenzie is regarded as a world leader in ecological and evolutionary genetics.