Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)




S.F.H. Threlkeld


i) the more neglected of the two components of the adaptive response of insects to biocides, the behavioural (avoidance) response was investigated and found to be made up of a basic aversive and a secondary dispersive component. ii) natural populations were found to possess a large amount of genetically determined variation in both physiological and behavioural responses to malathion. There is also evidence that these characteristics have been affected by selection in the local populations. iii) the relationship between avoidance and resistance in natural populations indicates that both responses are independently modifiable by selection. iv) a class of X-linked mutations was induced which show a negative correlation between resistance and avoidance. These mutations may prove useful in further studies of resistance and avoidance mechanisms (eg. via genetic mosaic studies), and they may also represent a class of mutations which provide co-adapted changes in responses that may prove to be important in some evolutionary situations. v) practical methods (already published) for assaying avoidance and resistance were developed, which may prove themselves to be useful in studies of economically important insects.

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