Helicoverpa zea is one of the most costly insect pests of food and fiber crops
throughout the Americas. Pyrethroid insecticides are widely applied for control as they
are effective and relatively inexpensive; however, resistance threatens sustainability
because alternative insecticides are often more expensive or less effective. Pyrethroid
resistance has been identified since 1990 and monitoring has utilized cypermethrin in the
adult vial test, but resistance mechanisms have not yet been elucidated at the molecular
level. Here we examined field-collected H. zea males resistant to cypermethrin for
target site and metabolic resistance mechanisms.
We report the cDNA sequence of the H. zea sodium channel a-subunit
homologous to the Drosophila para gene and identified known resistance-conferring
mutations L1029H and V421M, along with two novel mutations at the V421 residue,
V421A and V421G. An additional mutation, I951V, may be the first example of a
pyrethroid resistance mutation caused by RNA-editing. We identified other specimens
with significantly higher transcriptional expression levels of cytochrome P450 genes CYP6B8 and CYP6B9 compared to the susceptible, ranging from a factor of 3.7 to 34.9
and 5.6 to 39.6, respectively.
In addition, we investigated if differences in insect growth stage and pyrethroid
structure affect our ability to predict resistance in the adult vial test. Vial bioassays with
cypermethrin, esfenvalerate, and bifenthrin were conducted on third instars and male
moths from a susceptible laboratory colony and the F1 generation of a resistant field
population. For the resistant population, vial assays using either growth stage gave
similar resistance ratios for each of the three pyrethroids, respectively, proving the adult
vial test accurately reflects larval resistance. However, resistance ratios varied
considerably depending on the pyrethroid used, so values obtained with one pyrethroid
may not be predictive of another.
This dissertation is the first to identify molecular mechanisms associated with H.
zea pyrethroid resistance. Our results suggest carefully chosen pyrethroid structures
diagnostic for specific resistance mechanisms could improve regional monitoring
programs and development of high throughput assays to detect the resistance
mechanisms used in tandem with traditional monitoring may greatly improve our ability
to identify and predict resistance and make better control recommendations.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-7891 |
| Date | 2010 May 1900 |
| Creators | Hopkins, Bradley Wayne |
| Contributors | Pietrantonio, Patricia V. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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