An investigation into the possibility of reversion towards susceptibility in a N.Z. insecticidal strain of Tetranychus urticae Koch: a dissertation submitted in partial fulfilment of the requirement for the degree of Bachelor of Horticultural Science with Honours in the University of Canterbury [Lincoln College]

Abstract

The wide occurrence of resistance to insecticides in many pest species is a prime example of rapid evolution or what is termed microevolution in the Darwinian sense (Brown, 1967). This process embraces the principles of mutation, migration and selection. As a matter of survival, pest insect species have begun a passive retaliation. In resistance, the population gene pool is being dealt with. Insecticides act as powerful “sieves”, selecting out the few pre-adapted resistant individuals within the population (Plapp, 1970) and eventually concentrating these resistant mutants (Crow, 1957) that were initially low in frequency within the population. Thus the rate of acquirement, but not mere possession of resistance depends on the recessiveness or dominance of the resistant genes. Given adequate pressure to spark off this evolutionary change, nearly all insect species are capable of developing some form of tolerance to a particular insecticide (Georghiou, 1972).