Mites alight! Sunflower crop area and pollen supplementation enhance honey bee resistance to Varroa destructor

Anthropogenic landscape changes can affect parasite epidemiology in wild and agricultural animals. Honey bees are agricultural animals whose services are threatened by loss of floral resources and by parasites, most notably the invasive mite Varroa destructor. Existing mite control strategies rely heavily on chemical treatments that can adversely affect bees. Alternative, pesticide-free control methods are urgently needed to maintain effective pollination services. Many flowering plants provide nectar and pollen that enhance resistance to parasites in animals. Enrichment of landscapes with antiparasitic floral resources could therefore provide a sustainable means of parasite control in pollinators. Floral rewards of Asteraceae plants have been shown to reduce parasitic infection in diverse bee species, including honey and bumble bees. Here, we tested the effects of sunflower (Helianthus annuus) cropland and pollen supplementation on honey bee resistance to macro- and microparasites. Our results show that each doubling of sunflower crop area is associated with a 28% reduction in mite infestation intensity. Late-summer supplementation of colonies with sunflower pollen reduced mite infestation by 2.75-fold relative to an artificial pollen. Our findings suggest the potential for sunflower plantings or pollen supplements to counteract a main driver of honey bee losses worldwide.

Management of the Wheat Curl Mite and Wheat Streak Mosaic Virus With Insecticides on Spring and Winter Wheat

The wheat curl mite (WCM, Aceria tosichella, Keifer) is an eriophyid mite species complex that causes damage to cereal crops in the Northern Great Plains by feeding damage and through the transmission of plant viruses, such as wheat streak mosaic virus. Insecticide treatments were evaluated in the greenhouse and field for efficacy at managing the WCM complex on wheat. Treatments tested were carbamates, organophosphates, pyrethroids, a neonicotinoid seed treatment, mite growth inhibitors, and Organic Materials Review Institute–approved biocontrols, soaps, and oils. Treatment with carbamates, organophosphates, and pyrethroids decreased WCM in greenhouse trials compared with untreated controls 14 days after infestation. The seed treatment, mite growth inhibitors, and organic pesticides did not reduce WCM populations effectively and consistently. The timing of application was tested using a sulfur solution as the experimental treatment. Treating plants with sulfur seven days after mite infestation reduced mites compared with the untreated control. In contrast, prophylactically applied sulfur and sulfur applied 14 days after mite infestation were not effective. When tested under field conditions with plots infested with viruliferous mites, there was no yield difference detected between untreated control plots and plots sprayed with insecticides. Select carbamates, organophosphates, and pyrethroids have a potential for use in greenhouse mite management when appropriate.

Defense Responses in the Interactions between Medicinal Plants from Lamiaceae Family and the Two-Spotted Spider Mite Tetranychus urticae Koch (Acari: Tetranychidae)

This study aimed to determine the effects of plant species on the biological parameters of Tetranychus urticae Koch and the time of mite infestation on plant physiology in Ocimum basilicum L., Melissa officinalis L. and Salvia officinalis L. Mite infestation induced various levels of oxidative stress depending on plant species and the duration of infestation. Host plants affected T. urticae life table parameters. The low level of susceptibility was characteristic of S. officinalis, which appeared to be the least infected plant species and reduced mites demographic parameters. Infested leaves of S. officinalis contained elevated levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) compared to control. In addition, higher membrane lipid peroxidation and higher activity of guaiacol peroxidase (GPX) and lower activity of catalase (CAT) were recorded with a longer mite infestation. In contrast, O. basilicum appeared to be a suitable host on which T. urticae could develop and increase in number. In basil leaves, increasing levels of hydrogen peroxide and MDA with elevated GPX activity and strongly decreased catalase activity were recorded. Knowledge of the differences in mite susceptibility of the tested medicinal plants described in this study has the potential to be applied in breeding strategies and integrated T. urticae pest management in medicinal plant cultivations.

Tomato Cultivars Resistant or Susceptible to Spider Mites Differ in Their Biosynthesis and Metabolic Profile of the Monoterpenoid Pathway

The two-spotted spider mite (TSSM; Tetranychus urticae) is a ubiquitous polyphagous arthropod pest that has a major economic impact on the tomato (Solanum lycopersicum) industry. Tomato plants have evolved broad defense mechanisms regulated by the expression of defense genes, phytohormones, and secondary metabolites present constitutively and/or induced upon infestation. Although tomato defense mechanisms have been studied for more than three decades, only a few studies have compared domesticated cultivars' natural mite resistance at the molecular level. The main goal of our research was to reveal the molecular differences between two tomato cultivars with similar physical (trichome morphology and density) and agronomic traits (fruit size, shape, color, cluster architecture), but with contrasting TSSM susceptibility. A net house experiment indicated a mite-resistance difference between the cultivars, and a climate-controlled performance and oviposition bioassay supported these findings. A transcriptome analysis of the two cultivars after 3 days of TSSM infestation, revealed changes in the genes associated with primary and secondary metabolism, including salicylic acid and volatile biosynthesis (volatile benzenoid ester and monoterpenes). The Terpene synthase genes, TPS5, TPS7, and TPS19/20, encoding enzymes that synthesize the monoterpenes linalool, β-myrcene, limonene, and β-phellandrene were highly expressed in the resistant cultivar. The volatile profile of these cultivars upon mite infestation for 1, 3, 5, and 7 days, revealed substantial differences in monoterpenoid and phenylpropanoid volatiles, results consistent with the transcriptomic data. Comparing the metabolic changes that occurred in each cultivar and upon mite-infestation indicated that monoterpenes are the main metabolites that differ between cultivars (constitutive levels), while only minor changes occurred upon TSSM attack. To test the effect of these volatile variations on mites, we subjected both the TSSM and its corresponding predator, Phytoseiulus persimilis, to an olfactory choice bioassay. The predator mites were only significantly attracted to the TSSM pre-infested resistant cultivar and not to the susceptible cultivar, while the TSSM itself showed no preference. Overall, our findings revealed the contribution of constitutive and inducible levels of volatiles on mite performance. This study highlights monoterpenoids' function in plant resistance to pests and may inform the development of new resistant tomato cultivars.

Oryza sativa cv. Nipponbare and Oryza barthii as Unexpected Tolerance and Susceptibility Sources Against Schizotetranychus oryzae (Acari: Tetranychidae) Mite Infestation

Cultivated rice (Oryza sativa L.) is frequently exposed to multiple stresses, including Schizotetranychus oryzae mite infestation. Rice domestication has narrowed the genetic diversity of the species, leading to a wide susceptibility. This work aimed to analyze the response of two African rice species (Oryza barthii and Oryza glaberrima), weedy rice (O. sativa f. spontanea), and O. sativa cv. Nipponbare to S. oryzae infestation. Surprisingly, leaf damage, histochemistry, and chlorophyll concentration/fluorescence indicated that the African species present a higher level of leaf damage, increased accumulation of H2O2, and lower photosynthetic capacity when compared to O. sativa plants under infested conditions. Infestation decreased tiller number, except in Nipponbare, and caused the death of O. barthii and O. glaberrima plants during the reproductive stage. While infestation did not affect the weight of 1,000 grains in both O. sativa, the number of panicles per plant was affected only in O. sativa f. spontanea, and the percentage of full seeds per panicle and seed length were increased only in Nipponbare. Using proteomic analysis, we identified 195 differentially abundant proteins when comparing susceptible (O. barthii) and tolerant (Nipponbare) plants under control and infested conditions. O. barthii presents a less abundant antioxidant arsenal and is unable to modulate proteins involved in general metabolism and energy production under infested condition. Nipponbare presents high abundance of detoxification-related proteins, general metabolic processes, and energy production, suggesting that the primary metabolism is maintained more active compared to O. barthii under infested condition. Also, under infested conditions, Nipponbare presents higher levels of proline and a greater abundance of defense-related proteins, such as osmotin, ricin B-like lectin, and protease inhibitors (PIs). These differentially abundant proteins can be used as biotechnological tools in breeding programs aiming at increased tolerance to mite infestation.

Injurious status of Schizotetranychus schizopus (Zacher, 1913) (Acari: Tetranychidae) on Indian Thorny Bamboo

Spider mites, especially members of Schizotetranychus represent a common and dominant group of bamboo pests, enjoying worldwide distribution. The present paper highlights the feeding attributes of a notorious species of bamboo spider mite, viz. Schizotetranychus schizopus (Zacher, 1913) infesting the Indian Thorny Bamboo, Bambusa bambos (L.) Voss. Observations on feeding behavior of the mite were completed in the laboratory by collecting mite specimens from infested leaves of bamboo plants grown in Calicut University Botanical Garden. The species showed initial colonization on the abaxial surface of bamboo leaves, adjacent to the midrib and feeding activity of the members of the colony resulted in the development of damage symptoms like chlorotic spots, white patches, yellowing etc. Comparative analysis of the biochemical constituents of mite infested and uninfested leaves of B. bambos revealed significant alterations. Mite infested bamboo leaves presented significantly reduced values of chlorophyll fluorescence (30.10% loss in Fv/Fm ratio) thereby indicating a decline of photosynthetic efficiency. Significant reduction in total carbohydrate (58.87%) and total protein (21.02%) contents also could be accounted in mite infested leaves. Meanwhile, mite infestation was found to enhance the production of stress compounds such as Total Phenol (22.86%) and Proline (69.05%). An increase in the uptake of micro and macronutrients like Potassium (18.87%), Calcium (36.66%), Copper (48.76%) and Zinc (19.62%) was also observed in mite infested leaves. Despite this, the uptake of nutrients such as Phosphorus (8.22%), Magnesium (3.55%), Sulphur (1.54%), Iron (11.46%), Manganese (13.64%) and Boron (30.09%) significantly decreased owing to mite infestation. Significant decrease in moisture content also was evident in the mite infested bamboo leaves. The results of the study helped to evidence the biotic stress induced by the mite on its bamboo host, by promoting enhanced production of Total Phenol, Proline, Potassium, Calcium, Copper and Zinc which would play a substantial role in the defense mechanism of the plant.