Willamette mite (WM), Eotetranychus willamettei, is a major pest throughout most winegrape regions in coastal California and Oregon. These mites puncture leaf tissue with their chelicerae and cause loss of photosynthetically active area. Chemical control treatments on grape include nearly ten registered synthetic miticides, plus soaps and oils. Oils can be petroleum based (mineral oil) or botanical (from seeds of various plants). There has been a lot of interest of late in the use of botanical oils other than soybean, including those derived from the seeds of plants including spearmint, rosemary and clove. This project tested for differences in the efficacy of a mineral vs. a botanical oil. The botanical oil was a blend of rosemary and peppermint oil (Ecotrol®) and was tested against a petroleum based oil (Omni Oil®), then compared to a commonly used synthetic miticide (Nexter®, common chemical name pyridaben). The field experiment (San Juan Vineyards in Shandon, CA) tested effects on adult mite and egg populations, with five treatments: Omni Oil®, Ecotrol®, Nexter®, Ecotrol® + Nexter®, and water as a control. Laboratory experiments tested effects on adult females and eggs. Treatments were Omni Oil®, Ecotrol® (1.0%), Ecotrol® (0.5%) and water as a control. Field data showed that Omni Oil® (at 1.5%) was the only effective treatment, Ecotrol® (at 0.5% or 1.0%) did not differ from the control. Omni Oil® was the most effective treatment against adult mites in the laboratory studies, followed by Ecotrol® at 1.0%, with Ecotrol® at 0.5 % not very effective. Egg mortality was high with Omni Oil® 1.5% or Ecotrol® 1.0% but low with Ecotrol® 0.5%.

The effects of miticides on the reproductive physiology of queens and drones were examined. The first study examined the effects of Apistan (fluvalinate), Check Mite+ (coumaphos), and Apilife VAR (74% thymol) on sperm production and viability in drones. Drones from colonies treated with each miticide were collected at sexual maturity. Sperm production was determined by counting the number of sperm in the seminal vesicles. Sperm for viability assays was analyzed by dual fluorescent staining. Apilife VAR and coumaphos significantly lowered (P<0.0001) sperm production and coumaphos treatments caused a significant decrease (P<0.0001) in the sperm viability. The effects of miticides on queens was examined by treating queen-rearing colonies and examining the number and viability of sperm in the spermathecae of newly mated queens. Queens from each treatment group were collected after mating and the spermathecae were removed and analyzed. Colonies treated with coumaphos failed to provide viable queens and were excluded. Apilife VAR was found to significantly decrease (P<0.0016) sperm viability. No significant differences in sperm numbers were found between treatments. The effect of miticides on sperm viability over time was also examined. Drones were reared as described, but the spermatozoa were collected as pooled samples from groups of drones. The pooled samples from each treatment were subdivided and analyzed periods of up to 6 weeks. Random samples were taken from each treatment (n = 6 pools) over a period of 6 weeks. The exposure of drones to coumaphos during development significantly reduced sperm viability for all 6 weeks, and caused a large decline in week 6. The potential impacts of these results on queen performance and failure are discussed. / Master of Science in Life Sciences