Acaricidal activity and sublethal effects of an oxymatrine-based biopesticide on two-spotted spider mite (Acari: Tetranychidae)

Testing new compounds for efficacy against Varroa destructor and safety to honey bees (Apis mellifera)

BACKGROUND

Varroa destructor is among the greatest threats to honey bee health worldwide. Acaricides used to control Varroa are becoming increasingly ineffective due to resistance issues, prompting the need for new compounds that can be used for control purposes. Ideally, such compounds would exhibit high toxicity to Varroa while maintaining relatively low toxicity to bees and beekeepers. We characterized the lethal concentrations (LC₅₀ ) of amitraz, matrine, FlyNap®, the experimental carbamates 2-((2-ethylbutyl)thio)phenyl methylcarbamate (1) and 2-(2-ethylbutoxy)phenyl methylcarbamate (2), and dimethoate (positive control) for Varroa using a glass vial assay. The test compounds also were applied to honey bees using an acute contact toxicity assay to determine the adult bee LD₅₀ for each compound.

RESULTS

Amitraz was the most toxic compound to Varroa, but carbamate 2 was nearly as active (within 2-fold) and the most selective due to its lower bee toxicity, demonstrating its promise as a Varroa control. While carbamate 1 was less toxic to honey bees than was amitraz, it was also 4.7-fold less toxic to the mites. Both matrine and FlyNap® were relatively ineffective at killing Varroa and were moderately toxic to honey bees.

CONCLUSION

Additional testing is required to determine if carbamate 2 can be used as an effective Varroa control. As new chemical treatments are identified, it will be necessary to determine how they can be utilized best alongside other control techniques as part of an integrated pest management program. © 2021 Society of Chemical Industry.

Integrated Pest Management Control of Varroa destructor (Acari: Varroidae), the Most Damaging Pest of (Apis mellifera L. (Hymenoptera: Apidae)) Colonies

Varroa destructor is among the greatest biological threats to western honey bee (Apis mellifera L.) health worldwide. Beekeepers routinely use chemical treatments to control this parasite, though overuse and mismanagement of these treatments have led to widespread resistance in Varroa populations. Integrated Pest Management (IPM) is an ecologically based, sustainable approach to pest management that relies on a combination of control tactics that minimize environmental impacts. Herein, we provide an in-depth review of the components of IPM in a Varroa control context. These include determining economic thresholds for the mite, identification of and monitoring for Varroa, prevention strategies, and risk conscious treatments. Furthermore, we provide a detailed review of cultural, mechanical, biological, and chemical control strategies, both longstanding and emerging, used against Varroa globally. For each control type, we describe all available treatments, their efficacies against Varroa as described in the primary scientific literature, and the obstacles to their adoption. Unfortunately, reliable IPM protocols do not exist for Varroa due to the complex biology of the mite and strong reliance on chemical control by beekeepers. To encourage beekeeper adoption, a successful IPM approach to Varroa control in managed colonies must be an improvement over conventional control methods and include cost-effective treatments that can be employed readily by beekeepers. It is our intention to provide the most thorough review of Varroa control options available, ultimately framing our discussion within the context of IPM. We hope this article is a call-to-arms against the most damaging pest managed honey bee colonies face worldwide.

Bioacaricidal Potential of Moringa oleifera Ethanol Extract for Tetranychus merganser Boudreaux (Acari: Tetranychidae) Control

The Tetranychidae family includes mites causing severe damage to agricultural fields. The red spider mite, Tetranychus merganser Boudreaux (Acari: Tetranychidae), causes severe damage to several plant species grown as cash crops. Current red spider mite control depends mainly on chemical insecticides. There is a need for alternate control measures that are environmentally friendlier than chemical pesticides. The aim of the study was to assess the effects of Moringa oleifera leaf ethanolic extract at different concentrations (0.1, 0.5, 1, 5, 10, 15, and 20% (v/v)) against T. merganser females. Such effects can serve as a basis to include this compound in integrated pest management programs for the control of red spider mites. Mites treated with 20% (v/v) killed 86.67%, 13.70%, and 96.30% at 24, 48, and 72 h, respectively, as compared to the control treatment. Oviposition, egg hatching, and the damage caused by red spider mites were all reduced at high concentrations. Moringa oleifera leaf ethanolic extract can be used as a powerful bioacaricide for the control of T. merganser.

Evaluation of Ethanol Extract of Moringa oleifera Lam. as Acaricide against Oligonychus punicae Hirst (Trombidiformes: Tetranychidae)

Tetranychidae family is a major group of mites causing serious damage in agricultural, vegetable and ornamental crops. Avocado bronze mite (ABM), Oligonychus punicae Hirst (Acari: Tetranychidae) causes major crop damage, defoliation and fruit abortion. At present, the control of this mite depends mainly on agrochemicals. Therefore it is necessary to find alternatives to synthetic pesticides that can help minimize environmental impact and health risks for the consumers. The aim of this research was to assess the effect of different concentrations (0.1, 0.5, 1, 5, 10, 15 and 20% (v/v)) of ethanolic extract of Moringa oleifera leaves against adult ABM females. Mites treated with 0.1 and 20% (v/v) of the extract showed mortality of 0.00% and 46.67%, 6.67% and 86.67%, 13.70% and 96.67%, at 24, 48 and 72 h, as compared to the control treatment, respectively. The number of eggs laid and hatch, as well as ABM feeding rates, depended on the extract concentration, which led to a reduction in the growth rate. M. oleifera leaf ethanolic extract has potential to control O. punicae.

Sublethal effects of spirodiclofen on biological and demographic parameters of the citrus leprosis mite Brevipalpus yothersi (Acari: Tenuipalpidae)

BACKGROUND

Brevipalpus yothersi Baker is one of the main vectors of citrus leprosis. Knowing the biology of this mite species when under chemical control is extremely important to understand its population dynamics, and then to solve problems of management of this pest. Therefore, we assessed the effects of one sublethal dose of spirodiclofen (0.48 ppm) on biological and demographic parameters of B. yothersi under laboratory and greenhouse conditions, comparing them with non-exposed mite population.

RESULTS

Under laboratory conditions, where citrus fruits were used as a substrate, the duration of developmental stages (pre-egg-laying and egg-laying) and mite longevity showed no differences between treatments. However, the number of laid eggs increased in acaricide-treated fruits. In the greenhouse experiment, where citrus plants were used as a substrate, the instantaneous growth rate (ri) of mites was positive in all untreated plots. In contrast, in treated plants, ri was negative in 12 experimental units, and mite populations were suppressed in five of them. Moreover, mite population dynamics had a positive ri in three treated plants.

CONCLUSIONS

Spirodiclofen sublethal dose had no negative effect on the offspring of B. yothersi females. However, it is not safe for citrus leprosis mite since it may increase egg number per female in some conditions. Biological and demographic differences could influence mite population dynamics in the field, requiring appropriate management strategies to improve citrus leprosis control. © 2019 Society of Chemical Industry.

Botanicals Against Tetranychus urticae Koch Under Laboratory Conditions: A Survey of Alternatives for Controlling Pest Mites

Tetranychus urticae Koch is a phytophagous mite capable of altering the physiological processes of plants, causing damages estimated at USD$ 4500 per hectare, corresponding to approximately 30% of the total cost of pesticides used in some important crops. Several tools are used in the management of this pest, with chemical control being the most frequently exploited. Nevertheless, the use of chemically synthesized acaricides brings a number of disadvantages, such as the development of resistance by the pest, hormolygosis, incompatibility with natural predators, phytotoxicity, environmental pollution, and risks to human health. In that sense, the continuous search for botanical pesticides arises as a complementary alternative in the control of T. urticae Koch. Although a lot of information is unknown about its mechanisms of action and composition, there are multiple experiments in lab conditions that have been performed to determine the toxic effects of botanicals on this mite. Among the most studied botanical families for this purpose are plants from the Lamiaceae, the Asteraceae, the Myrtaceae, and the Apiaceae taxons. These are particularly abundant and exhibit several results at different levels; therefore, many of them can be considered as promising elements to be included into integrated pest management for controlling T. urticae.

Bioactivity of an oxymatrine-based commercial formulation against Brevipalpus yothersi Baker and its effects on predatory mites in citrus groves

The acaricidal bioactivity of an oxymatrine-based commercial formulation against Brevipalpus yothersi Baker (Acari: Tenuipalpidae), a vector mite of the Citrus leprosis virus (CiLV), and its impact on predatory mites were assessed. For this purpose, laboratory and field assays using bioacaricide concentrations ranging from 0.5 to 2.0 mg L^-1 of oxymatrine were performed during the years from 2015 to 2016. Laboratory results showed that the oxymatrine-based commercial formulation does not cause deleterious effects on B. yothersi eggs; however, it causes high larval mortality. For adult females, the bioacaricide caused high acute toxicity and residual effect for at least 5 days after application. In the field, the bioacaricide exhibited high acaricidal activity against B. yothersi, with efficacy levels similar to that of synthetic acaricide spirodiclofen (48 mg L^-1) until 49 days after the application. The application of the bioacaricide did not negatively affect the population levels of phytoseiid predatory mites. Therefore, our results suggest that the oxymatrine-based commercial formulation is an important tool for management of the citrus leprosis mite in citrus groves.

Ruta graveolens Extracts and Metabolites against Spodoptera frugiperda

The biological activity of Ruta graveolens leaf tissue extracts obtained with different solvents (ethyl acetate, ethanol, and water) and metabolites (psoralen, 2-undecanone and rutin) against Spodoptera frugiperda was evaluated. Metabolites levels in extracts were quantified by HPLC and GC. Ethyl acetate and ethanol extracts showed 94% and 78% mortality, respectively. Additionally, psoralen metabolite showed a high mortality as cypermethrin. Metabolite quantification in extracts shows the presence of 2-undecanone (87.9 μmoles mg−1 DW), psoralen (3.6 μmoles mg−1 DW) and rutin (0.001 μmoles mg−1 DW). We suggest that these concentrations of 2-undecanone and psoralen in R. graveolens leaf tissue extracts could be responsible for S. frugiperda mortality.

Reproductive parameters of Tetranychus urticae (Acari: Tetranychidae) affected by neonicotinoid insecticides

Two-spotted spider mite is a major pest of many agricultural and ornamental crops worldwide. Some reports have indicated that application of neonicotinoid insecticides may lead to increased fecundity of this pest. If this is found to be true, the use of these pesticides may cause an outbreak of spider mite populations. Sublethal effects of three neonicotinoids, namely thiacloprid, acetamiprid and thiamethoxam were studied on T. urticae adults at field recommended doses. The experiments were carried out using bean leaf pieces in plastic Petri dishes. The adult mites were treated using two methods: (1) drench application and (2) spraying of leaves with Potter Spray Tower. Our results indicated that all neonicotinoids tested increased T. urticae population. In both treatment methods, acetamiprid treated mites had the highest intrinsic rate of population increase (rm) and finite rate of population increase (λ); and the lowest mean generation time (T) and doubling time among the treatments. If similar results are obtained from greenhouse and field trials, the use of these insecticides requires necessary precautions such as avoiding repeated use of neonicotinoid insecticide for controlling insect pests.