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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2016)

The predatory mite, Galendromus flumenis (Chant) (Acari: Phytoseiidae), is the most abundant predator and the only phytoseiid species on date bunches infested with Banks grass mite, Oligonychus pratensis (Banks) (Acari: Tetranychidae). Biological studies were conducted on this predatory mite in order to develop and optimize biological control strategies against the Banks grass mite.

In the first chapter, studies showed that G. flumenis feeds on all immature stages of Banks grass mite, but it prefers eggs over the other stages. Functional response studies indicated that the predator displays a type II response on all immature stages of the prey. The mutual interference study in Chapter 2 revealed that total predation increased with increasing G. flumenis density in two arena sizes. However, there was not a proportional increase in per capita predation due to mutual interference. The interference effect was high in small arenas due to higher encounter rates between predators. Also, higher predator density and smaller arena size caused significantly higher dispersal rate of predators.

In Chapter 3 data show that G. flumenis develops under a wide range of temperatures from 18°C to 42°C, but survival rates were highest between 26°C and 38°C. The optimal temperature for development (Topt) was calculated to be 37.6°C. Further work on the population growth and reproduction of G. flumenis (Chapter 4) showed that predators cannot oviposit at 38°C (Topt). At 34°C, the next temperature with the shortest developmental time for the predator, G. flumenis showed medium reproductive capacity (1.6 eggs/ day and 19.9 eggs/ ovipositional period), which is inferior to its prey. The net reproductive rate of prey can reach three times the maximum potential of G. flumenis, contributing to an intrinsic rate of natural increase of the prey that is more than double that of the predator.

In the final chapter, treatment with the miticide hexythiazox had little or no effect on immature development and reproduction of emerging adult predators. Hexythiazox did not have any adverse effect on the fecundity of treated females, hatch rate of eggs, progeny development, or sex ratio.

    Cover page: Biological Studies on Galendromus flumenis (Acari: Phytoseiidae), a Predator of Banks Grass Mite
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2019)
    The pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is a pest of many plants, and a new problem on dates in California. The effects of seven insecticides and water on different life stages of this mealybug were studied to identify the best material for control. Water did not have any significant effect on mealybugs, but the insecticide treatments significantly affected all life stages tested. The egg hatch rate ranged from 28.5% to 17.2% for spirotetramat, bifenthrin, flupyradifurone, fenpropathrin, and buprofezin treatments, and was lower for sulfoxaflor (2.8%) and acetamiprid (0.1%). Despite high survival of neonate crawlers in the non-treated control and water treatments, 53.1% and 34.6% survived in the spirotetramat and buprofezin treatments, respectively; survival was zero in the other treatments. Spirotetramat and buprofezin caused very low mortality of nymphs in the first day post-treatment, but mortality significantly increased over time and reached 42.8% and 50.6% by day 6, respectively. The other treatments were highly toxic to the nymphs (79.4⁻99.4% on day 6). Insecticides also had a significant effect on the feeding ability of nymphs. By day 6 after treatment, 73.9% to 100% of nymphs treated with different insecticides stopped feeding although they were still alive. Insecticides showed no effect on the mortality of adult females, but the percentages of ovipositing females were significantly reduced (51.1% to 10.6%) in all insecticide treatments, except buprofezin, which was not statistically different from water and the non-treated control. In the process of our studies, we identified abnormalities in the appearance of eggs from females treated with various insecticides, and these aberrant eggs are described.
      Cover page: Lethal and Sub-Lethal Effects of Insecticides on the Pink Hibiscus Mealybug, Maconellicoccus hirsutus (Hemiptera: Pseudococcidae)
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2024)
      Drosophila suzukii lay eggs in soft-skinned, ripening fruits, making this insect a serious threat to berry production. Since its 2008 introduction into North America, growers have used insecticides, such as pyrethroids and spinosads, as the primary approach for D. suzukii management, resulting in development of insecticide resistance in this pest. This study sought to identify the molecular mechanisms conferring insecticide resistance in these populations. We sequenced the transcriptomes of two pyrethroid- and two spinosad-resistant isofemale lines. In both pyrethroid-resistant lines and one spinosad-resistant line, we identified overexpression of metabolic genes that are implicated in resistance in other insect pests. In the other spinosad-resistant line, we observed an overexpression of cuticular genes that have been linked to resistance. Our findings enabled the development of molecular diagnostics that we used to confirm persistence of insecticide resistance in California, U.S.A. To validate these findings, we leveraged D. melanogaster mutants with reduced expression of metabolic or cuticular genes that were found to be upregulated in resistant D. suzukii to demonstrate that these genes are involved in promoting resistance. This study is the first to characterize the molecular mechanisms of insecticide resistance in D. suzukii and provides insights into how current management practices can be optimized.
        Cover page: Transcriptome analysis of Drosophila suzukii reveals molecular mechanisms conferring pyrethroid and spinosad resistance.
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2023)
        The invasion of Drosophila suzukii, spotted-wing drosophila, across Europe and the US has led to economic losses for berry and cherry growers, and increased insecticide applications to protect fruit from damage. Commercial production relies heavily on unsustainable use of conventional toxic insecticides. Non-toxic insecticide strategies are necessary to alleviate the disadvantages and non-target impacts of toxic conventional insecticides and improve Integrated Pest Management (IPM). A novel food-grade gum deployed on dispenser pads (GUM dispensers) was evaluated to mitigate D. suzukii crop damage in five commercial crops and nine locations. Trials were conducted at a rate of 124 dispensers per hectare in cherry, wine grape, blueberry, raspberry, and blackberry in California and Oregon, USA during 2019 and 2020. The majority of trials with the food-grade gum resulted in a reduction of D. suzukii egg laying in susceptible fruit. In some cases, such damage was reduced by up to 78%. Overall, results from our meta-analysis showed highly significant differences between GUM treatments and the untreated control. Modeling simulations suggest a synergistic reduction of D. suzukii damage when used in combination with Spinosad (Entrust SC) insecticide. These data illustrate commercial value of this tool as a sustainable alternative to manage D. suzukii populations within a systems approach.
          Cover page: Open field trials of food-grade gum in California and Oregon as a behavioral control for Drosophila suzukii Matsumura (Diptera: Drosophilidae).
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