Toxicological studies were carried out to evaluate the
susceptibility of codling moth, Cydia pomonella L. to
different insecticides. Bioassay procedures for adults and
larvae were standardized in terms of posttreatment holding
and temperature, age and sex of insects, insecticide
formulations and selection of a reference strain.
This study detected a low level of resistance to
azinphosmethyl in codling moth from Oregon. The LD50 value
of the most susceptible strain was 0.038 ug AI/moth, while
that of the most resistant population was approximately 4.3
times higher as determined by the topical application
method on pheromone traps. The adult topical bioassay using
moths reared in the laboratory showed that two of the seven
strains tested (Crippens and Medford) had 4-5 fold higher
LD50 values than reference (Saint Cloud) strain. In the
topical and residual studies with first instar larvae,
similar but slightly lower differences were observed among
the different populations.
There was a strong indication of low levels of
resistance in populations to diazinon and fenvalerate in
topical tests applied to both males and females. However,
there was no significant difference for carbaryl or
endosulfan. Larval topical bioassays showed a significant
difference only to diazinon. Correlation analysis suggests
that a degree of cross-resistance exists between
azinphosmethyl and diazinon and to some extent to
fenvalerate.
Codling moths exposed to the residues of diflubenzuron
showed a maximum of 2-fold difference between the
susceptible and resistant populations. The differences were
visible in terms of egg hatch and first instar larval
entries. The pupal and adult stages emerging from the
treated apples exposed to ovipositing females showed
insignificant sublethal effects. A strong positive
correlation between the resistance to azinphosmethyl and
resistance to diflubenzuron was noticed. Selection of
codling moths for resistance to diflubenzuron for six
generations in the laboratory decreased susceptibility by
5-fold.
Application of synergists such as PBO and DEF,
combined with azinphosmethyl and diflubenzuron, showed
slightly different effects on all strains of codling moth.
Use of PBO (a P-450 inhibiting compound) with
azinphosmethyl and diflubenzuron did not change toxicity of
either of the compounds. However, the combination of DEF (an esterase inhibiting compound) with the insecticides
significantly increased the toxicity of azinphosmethyl and
to some extent diflubenzuron. The maximum synergistic
ratios obtained were 8 and 2 for azinphosmethyl and
diflubenzuron, respectively. These results indicate a
possible involvement of esterases in development of
resistance in codling moth to azinphosmethyl and maybe to
diflubenzuron. The optimal synergistic ratio determined on
a resistant strain of codling moth to various combinations
of azinphosmethyl and DEF was 1:4 (50 ppm of azinphosmethyl
200 ppm of DEF). The phytotoxicity studies on young apple
trees showed that DEF should be used at or below 500 ppm to
avoid phytotoxicity while maintaining effective control of
codling moth with a reduced dose of azinphosmethyl. / Graduation date: 1997
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34156 |
| Date | 18 July 1996 |
| Creators | Arshad, Muhammad, 1958- |
| Contributors | AliNiazee, M. T. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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