Biometrical and population genetic studies of the dimethoate resistance of Danish houseflies
The resistance of houseflies to a particular insecticide is often
complex, involving several genes. In this light, the work detailed in this
thesis set out to examine (i)o alternatives to standard chromosome isolation
procedures, for genetic analysis of multi-factorial resistances, and (ii)
available data on the evolution of a multifactorial resistance (dimethoate)
in the field, in order to see whether they would afford inferences of the
population genetic processes involved.
Preliminary laboratory studies demonstrated a partial dependence
of LOG LDSO on LOG weight. Therefore, in all experiments the covariance of
LOG LDSO and LOG weight was taken into account and used for a partial control
A Cavalli design (comparison of two inbred parental strains,
their FI, F2, and first backcross generations) was employed in a biometrical
genetic analysis of dimethoate resistance, and found to yield
acceptable results when both parents were inbred, but to be of little use
when one parent was not inbred. The main use of this design would be
where mutant markers suitable for chromosome isolation are not available.
A heterozygous chromosome assay proved straight forward and,
given its speed and accuracy, was thought to have several advantages over
standard chromosome isolation procedures.
Analysis of data on the evolution of dimethoate resistance in
farm populations of houseoflies in Denmark, faced severe problems caused
by migration of flies between farms, which was hitherto thought to be of
little importance. Apart from this difficulty, modelling of the evolution
of dime tho ate resistance was thought':oto be inappropriate as estimates of
many essential parameters were lacking.
A trial of the Lincoln Index method for estimating the sizes of
farm populations of houseflies was largely unsuccessful due to the failure
of several assumptions of the method.
A population cage for the continuous rearing of houseflies was
developed Q.nd its possible rele in future population genetic studies of
insecticide resistance is discussed.