| Summary: | Genetics, gene flow, and distribution of pesticide
resistance traits were examined for organophosphate (OP)
resistance in three beneficial phytoseiid mites. Levels
and genetics of OP resistance in Amblyseius andersoni
were examined first. Laboratory strains from Italy and
Oregon, USA, were compared in susceptibility to
insecticides used in western Oregon fruit crops. The
Italian strain was 80-100 times more resistant to the OPs
azinphosmethyl, diazinon, malathion, and phosalone, as
well as carbaryl, a carbamate. Significant differences
were not found between strains for endosulfan or
fenvalerate. Using backcross analysis, response of F1
hybrids to azinphosmethyl indicated OP resistance was
semidominant. Through novel statistical analysis,
backcross of F1 to parent strains revealed resistance was
polygenic, with at least two loci. Reciprocal crosses
demonstrated the presence of maternal effects, with
increased variation associated with progeny of Oregon
females.
In the next set of experiments, electrophoresis of
allozymes was used to estimate gene flow for Typhlodromus
pyri. Ten populations from two apple growing valleys of
Oregon were compared. Subpopulations were collected from
in and around commercial apple orchards. Four loci
unaffected by pesticide use were examined. FST was
calculated at 0.115, and Nm as 2.08. No allelic patterns
could be discerned for populations among or within
valleys; however, more variation was present for mite
populations within valleys than between them. Some
inbreeding was found within populations. While from
dispersal studies one would conclude T. pyri is nondispersive,
allozymic analysis indicates there is
moderate gene flow.
Factors affecting OP resistance distribution in T.
pyri and Metaseiulus occidentalis were examined. A
diagnostic concentration of azinphosmethyl was used to
determine OP resistance frequencies for populations of
each species, collected in and near commercial apple
orchards in two valleys. OP resistance in T. pyri
populations was localized: mites from 10 m or more
outside orchards were OP susceptible, while those within
orchards were resistant. This indicated limited gene
flow. All M. occidentalis populations were resistant,
indicating a regional resistance pattern and high gene
flow. Factors which were not significant in the
distribution of OP resistance were: valley, degree of
orchard isolation, host plant, and seasonality. === Graduation date: 1994
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