Alternative food sources for Amblydromella caudiglans (Phytoseiidae) and effects on predation.

The addition of supplemental food sources for natural enemies is a growing component of conservation and augmentative biological control. Supplemental foods can be used to retain natural enemies when prey are scarce and to promote survival, fecundity, longevity, and development of natural enemy populations, especially generalist natural enemies. Amblydromella caudiglans (Schuster) (Acari: Phytoseiidae) is one of the most abundant predatory mites found in commercial apple orchards in Washington, USA, and contributes to spider mite control. However, because its widespread presence in commercial apple orchards was only recently discovered, how supplementary food sources affect its performance is unknown. In laboratory studies, we evaluated the performance (fecundity, retention, prey consumption) of the generalist phytoseiid A. caudiglans on commercially available supplemental food sources, including factitious prey (Ephestia eggs and Artemia brine shrimp cysts), and pollens of apple, pear, and cattail. We determined that A. caudiglans will not consume Ephestia eggs and performs best on cattail and pear pollens. Combinations of food sources did not enhance the performance of this predator compared to the best performing single-sources. The presence of alternative food sources did not decrease A. caudiglans predation of twospotted spider mite nymphs, except for Artemia brine shrimp cysts, which had a substantial handling time. These results lay the groundwork for identifying a way to promote and retain this natural enemy in tree fruit cropping systems through the use of food resource applications or floral plantings.

Whole genome comparisons reveal panmixia among fall armyworm (Spodoptera frugiperda) from diverse locations.

BACKGROUND: The fall armyworm (Spodoptera frugiperda (J.E. Smith)) is a highly polyphagous agricultural pest with long-distance migratory behavior threatening food security worldwide. This pest has a host range of > 80 plant species, but two host strains are recognized based on their association with corn (C-strain) or rice and smaller grasses (R-strain). The population genomics of the United States (USA) fall armyworm remains poorly characterized to date despite its agricultural threat. RESULTS: In this study, the population structure and genetic diversity in 55 S. frugiperda samples from Argentina, Brazil, Kenya, Puerto Rico and USA were surveyed to further our understanding of whole genome nuclear diversity. Comparisons at the genomic level suggest a panmictic S. frugiperda population, with only a minor reduction in gene flow between the two overwintering populations in the continental USA, also corresponding to distinct host strains at the mitochondrial level. Two maternal lines were detected from analysis of mitochondrial genomes. We found members from the Eastern Hemisphere interspersed within both continental USA overwintering subpopulations, suggesting multiple individuals were likely introduced to Africa. CONCLUSIONS: Our research is the largest diverse collection of United States S. frugiperda whole genome sequences characterized to date, covering eight continental states and a USA territory (Puerto Rico). The genomic resources presented provide foundational information to understand gene flow at the whole genome level among S. frugiperda populations. Based on the genomic similarities found between host strains and laboratory vs. field samples, our findings validate the experimental use of laboratory strains and the host strain differentiation based on mitochondria and sex-linked genetic markers extends to minor genome wide differences with some exceptions showing mixture between host strains is likely occurring in field populations.

Spider mite resistance to miticides in South Carolina strawberry and implications for improved integrated pest management.

Tetranychus urticae Koch (Acari: Tetranychidae), twospotted spider mite, is a major secondary pest of strawberry and can cause significant yield loss. Tetranychus urticae is typically controlled using miticides, which has led to rapid resistance development. In South Carolina (USA), extension agents and growers have reported field failures of miticides (inadequate pest suppression), but resistance has not been quantitatively determined. In 2018, we determined the level of miticide resistance of six T. urticae populations found on strawberry across South Carolina. We examined efficacy of all miticides registered for use on US strawberry by conducting an initial diagnostic bioassay at 20% of the maximum labeled field rate. Any population × active ingredient combination resulting in < 55% mortality was identified as 'potentially resistant' and concentration-response bioassays were then conducted to calculate LC50 values for an individual population. These values were compared with those of a known-susceptible laboratory population to calculate resistance ratios (RR). Our results indicate that examined South Carolina populations of T. urticae from strawberry were highly resistant to bifenthrin (RR = 100-60,000) and there was reduced susceptibility to fenbutatin-oxide (RR = 25-123). The 'Sardinia' population had decreased abamectin susceptibility (RR = 25). No resistance to hexythiazox, etoxazole, acequinocyl, bifenazate, fenpyroximate, spiromesifen, or cyflumetofen was found. Based on available data, it appears that miticide resistance is not a likely cause of field failures and issues related to application error and coverage should be investigated. Overall, this work supports the need to reduce the use of broad-spectrum pesticides and older products, in favor of newer miticide chemistries due to resistance issues.

Evaluation of Tarsonemus bilobatus and Podosphaera xanthii as suitable resources for Proprioseiopsis mexicanus in cucurbit systems in the Southeast USA.

Tritrophic relationships involving tarsonemids and predatory phytoseiids are common in a variety of agroecosystems, but due to the wide range of diets in both families, it is necessary to understand what food resources they are consuming to determine potential impact on crops. We investigated a frequent association of cucurbit powdery mildew (Podosphaera xanthii), Tarsonemus bilobatus, and Proprioseiopsis mexicanus in watermelon and pumpkin fields to determine whether P. mexicanus is consuming either or both of the other organisms. We also examined developmental and reproductive capability of P. mexicanus on these diets. If P. mexicanus is an effective predator of T. bilobatus, it may also be useful in controlling pest tarsonemids, such as broad mites. Proprioseiopsis mexicanus either starved or escaped from arenas rather than consume P. xanthii. When consuming T. bilobatus, P. mexicanus females developed from larva to adult in ca. 3 days. On this diet, the preoviposition period was ca. 2 days and P. mexicanus laid 1.7 eggs/day. These results are comparable to some of the higher-quality non-prey resources investigated in the literature. Starved female P. mexicanus consumed 6.5 T. bilobatus of mixed stages in 1 h. This study provides support for further research into the importance of non-pest tarsonemids as a resource to maintain the presence of generalist predatory mites as an early-intervention natural enemy. Further work should examine the efficacy of P. mexicanus as a natural enemy of economically important pest tarsonemids.

Suitability of food resources for Proprioseiopsis mexicanus, a potentially important natural enemy in eastern USA agroecosystems.

The phytoseiid Proprioseiopsis mexicanus has been collected from a wide range of plants in the western hemisphere, including many cucurbit agroecosystems in South Carolina, USA. Our aim was to characterize the lifestyle of P. mexicanus and its potential as a natural enemy of Tetranychus urticae, a common pest in cucurbits. We determined developmental time, pre-oviposition time, and fecundity of females on pollen-only diets from a commercial Typha spp. supplement source, Citrullus lanatus, Cucurbita maxima, Cucurbita moschata, Cucurbita pepo, Delosperma cooperi, Trifolium incarnatum, and on T. urticae and a combination of T. urticae and Typha spp. pollen. Female development time differed based on diet-development was fastest on C. lanatus and D. cooperi diets (ca. 3 days) and slowest on Typha pollen diet (ca. 5 days). Pre-oviposition time was shorter for females fed C. lanatus and T. incarnatum (1.6 days) and longest when fed Typha pollen (3.1 days). Citrullus lanatus, T. incarnatum, and D. cooperi pollen diets resulted in more eggs/day compared to other diets. Cucurbita moschata pollen resulted in the lowest oviposition rate (0.69 eggs/day). Because these pollens varied in size, we examined pollen size as a factor in developmental and reproductive success. With the exception of Typha pollen, small-pollen diets (C. lanatus, D. cooperi, and T. incarnatum) resulted in faster development, shorter pre-oviposition time, and higher fecundity than large-pollen diets (Cucurbita spp.). We concluded that P. mexicanus is a generalist predator that may require pollen for survival and reproduction, but alone this species may not be an effective predator of T. urticae.

Importance of Transplanted Onions Contributing to Late-Season Iris yellow spot virus Epidemics in New York.

Iris yellow spot virus (IYSV) is an economically significant tospovirus of onion transmitted by onion thrips (Thrips tabaci Lindeman). IYSV epidemics in onion fields are common in New York; however, the role of various habitats contributing to viruliferous onion thrips populations and IYSV epidemics is not known. In a 2-year field study in New York, the abundance of dispersing onion thrips, including those determined to be viruliferous via reverse-transcriptase polymerase chain reaction, was recorded in habitats known to harbor both IYSV and its vector. Results showed that viruliferous thrips were encountered in all habitats; however, transplanted onion sites accounted for 49 to 51% of the total estimated numbers of viruliferous thrips. During early to midseason, transplanted onion sites had 9 to 11 times more viruliferous thrips than the other habitats. These results indicate that transplanted onion fields are the most important habitat for generating IYSV epidemics in all onion fields (transplanted and direct-seeded) in New York. Our findings suggest that onion growers should control onion thrips in transplanted fields early in the season to minimize risk of IYSV epidemics later in the season.

Phenology and structure of a phytoseiid community in an insecticide-free apple orchard.

Commercial orchards have acarine communities that are reduced in biological diversity compared to their undisturbed counterparts. Examining the phenology of an unsprayed orchard allows for the examination of non-pesticide factors that drive changes in populations. This study examined the mite community in a largely unsprayed research orchard in 2013­2014. The phytoseiids Galendromus flumenis (Chant), Amblydromella caudiglans (Schuster), Kampimodromus corylosus Kolodochka, and Galendromus occidentalis (Nesbitt) were found, in addition to Zetzellia mali (Ewing) and Aculus schlechtendali (Nalepa). Although G. occidentalis is typically the dominant phytoseiid in commercial orchards, G. flumenis was much more abundant in this unsprayed block. Aculus schlechtendali appeared to be the main source of prey for all predator species. The availability of this prey item and the lack of pesticides are likely the factors that allowed for G. flumenis to reach high abundances. Tetranychids were scarce, emphasizing the role of these mites as induced pests; without the application of disruptive sprays, the predatory mite community was able to maintain biological control. This study demonstrates that the species complex of generalist phytoseiids that is present in orchard systems undisturbed by pesticides is sufficient to maintain spider mite populations below damaging levels throughout the season.

Effects of Orchard Pesticides on Galendromus occidentalis (Acari: Phytoseiidae): Repellency and Irritancy.

The effects of repellency or irritancy in Galendromus occidentalis (Nesbitt) were studied for three rates of 16 pesticides commonly used in apple production. Adult female mites were exposed to residues in a series of choice bioassays (treated and untreated half of bean leaf disks). Novaluron, carbaryl, mancozeb+copper hydroxide, and sulfur were the most repellent materials to G. occidentalis, with females consistently avoiding the treated side of the leaf disk. Spirotetramat, flubendiamide, and cyantriniliprole caused an intermediate or inconsistent degree of repellency; azinphosmethyl, lambda-cyhalothrin, acetamiprid, thiacloprid, imidacloprid, spinetoram, spinosad, and chlorantriniliprole caused little to no repellency. Irritancy (running off of the disk, as opposed to resting on the untreated half) was the most pronounced in the acetamiprid and lambda-cyhalothrin treatments. Acute toxicity (within the 6 h test period) was highest in the lambda-cyhalothrin and spinetoram treatments; in the former case, the mortality at all rates tested was substantial enough to interfere with the measurement of behavioral effects. Although irritancy may be considered the more extreme form of repellency, there were several pesticides (carbaryl, cyantraniliprole, mancozeb+copper hydroxide, novaluron) where a moderate to high degree of repellency did not correspond to a high degree of irritancy. Similarly, repellency was not consistently related to acute toxicity; one of the most repellent materials (novaluron) was not acutely toxic. Behavioral effects may help explain instances where lethal or sublethal bioassays do not fully predict the effects of pesticides seen in orchard use.

Comparative biology and pesticide susceptibility of Amblydromella caudiglans and Galendromus occidentalis as spider mite predators in apple orchards.

The successful integrated mite management program for Washington apples was based on conservation of the mite predator Galendromus occidentalis (Nesbitt). In the 1960s, this mite was assumed to be the only phytoseiid in Washington commercial apple orchards, due to its preference for the most common mite pest of that period, Tetranychus mcdanieli McGregor, as well as its resistance to organophosphate pesticides. A recent survey of phytoseiids in Washington apple found that another phytoseiid, Amblydromella caudiglans (Schuster) has become common. It is a more generalized predator than G. occidentalis (it is not a Tetranychus spp. specialist) and is not known to be organophosphate-resistant. A series of experiments was conducted to compare the life history, prey consumption, and pesticide tolerance of these two species. Galendromus occidentalis developed more quickly than A. caudiglans, but had slightly lower egg survival. Although A. caudiglans attacked more Tetranychus urticae Koch eggs than G. occidentalis, it could not reproduce on this diet. Both predators performed equally well on a diet of T. urticae protonymphs. Unlike G. occidentalis, A. caudiglans experienced significant mortality when exposed to carbaryl, azinphosmethyl, and bifenazate. Both predators experienced significant mortality due to imidacloprid and spinetoram. These results highlight the key differences between these two predators; the shift away from organophosphate use as well as the change in dominant mite pest to Panonychus ulmi (Koch) may be driving factors for the observed increased abundance of A. caudiglans in Washington apple.

Phytoseiids in Washington commercial apple orchards: biodiversity and factors affecting abundance.

Galendromus occidentalis (Nesbitt) is an important biological control agent of spider mites (Acari: Tetranychidae) in Washington apple orchards. It was thought to be essentially the sole phytoseiid existing in this system, due in part to its resistance to commonly used orchard pesticides, and organophosphates in particular. To test this assumption, we conducted a survey of 102 commercial apple blocks in Washington to characterize the community of phytoseiid species. Seven phytoseiid species were found in our samples; G. occidentalis and Amblydromella caudiglans (Schuster) were found in the greatest abundance. We hypothesized that the gradual shift away from the use of organophosphates in recent decades may have caused the change in phytoseiid community structure. The survey data and information regarding the management, location, and surrounding habitat of each block were used to determine what factors affect phytoseiid abundances. Galendromus occidentalis abundance was positively affected by the use of conventional (vs. organic) spray programs, and the use of the acaricide bifenazate. Amblydromella caudiglans abundance was negatively affected by bifenazate use and positively affected by herbicide strip weediness; it was also less prevalent in 'Golden Delicious' blocks compared to other cultivars. These results indicate that A. caudiglans reaches higher abundances in orchards that lack certain agricultural disturbances, whereas G. occidentalis can survive in more disturbed environments. Surveys of this nature can provide valuable insight to potential drivers of community structure, allowing for the improvement of integrated pest management programs that incorporate conservation of newly recognized biological control agents such as A. caudiglans.

Nontarget pesticide impacts on pest natural enemies: progress and gaps in current knowledge.

Avoiding pesticide nontarget effects on natural enemies is a cornerstone of conservation biological control. Recent advances in this field have included increased examination of nuanced sublethal effects, including microbiome changes. There is an interest in lifetable-based approaches, while also simplifying results to reduce the amount of information a grower needs to interpret to make a judicious application decision. Newer pesticides are showing promise for selectivity to both natural enemies and humans. Major research gaps still remain, with few published studies on ground-dwelling natural enemies, herbicides, adjuvants, or pesticide mixes. Translating the results of laboratory assays to field-level effects remains a major challenge. Field studies examining entire management programs and meta-analyses of laboratory studies may begin to address this issue.

Herbicides Harm Key Orchard Predatory Mites.

The phytoseiid mites Galendromus occidentalis and Amblydromella caudiglans are critical for conservation biological control of pest mites in Washington State, U.S.A. apples. While the non-target effects of insecticides on phytoseiids are well described, research on herbicide effects is limited. Using laboratory bioassays, we examined lethal (female mortality) and sublethal (fecundity, egg hatch, larval survival) effects of seven herbicides and five adjuvants on A. caudiglans and G. occidentalis. The effects of mixing herbicides with recommended adjuvants were also tested to determine if the addition of an adjuvant increased herbicide toxicity. Glufosinate was the least selective herbicide tested, causing 100% mortality in both species. Paraquat caused 100% mortality in A. caudiglans and 56% mortality in G. occidentalis. Sublethal effects were significant for both species when exposed to oxyfluorfen. Adjuvants did not cause non-target effects in A. caudiglans. The non-ionic surfactant and methylated seed oil increased mortality and decreased reproduction in G. occidentalis. The high toxicity of glufosinate and paraquat for both predators is concerning; these are the primary "burn down" herbicide alternatives to glyphosate, which is decreasing in use due to consumer toxicity concerns. Field studies are needed to determine the extent to which herbicides disrupt orchard biological control, focusing on glufosinate, paraquat, and oxyfluorfen. Consumer preferences will need to be balanced with natural enemy conservation.

Updating integrated mite management 50 years later: comparing laboratory pesticide susceptibility of a 'new' generalist predatory mite to a cornerstone specialist predator.

BACKGROUND: Historically, integrated mite management in Washington apple orchards has focused on conservation of the predatory mite Galendromus occidentalis (Nesbitt) to reduce secondary pest mite pressure. However, pesticide use has changed to include more selective products, coinciding with a shift in the predatory mite community composition to include a new major predator, Amblydromella caudiglans (Schuster). There is evidence that A. caudiglans is more pesticide sensitive than G. occidentalis. Therefore, updates to pesticide selectivity recommendations are needed to conserve this 'new' key predator. Using bioassays, we examined the lethal (female mortality) and sublethal effects (fecundity, egg hatch, larval survival) of 4 fungicides and 11 insecticides on A. caudiglans, to determine whether existing conservation recommendations can be applied to this predatory mite. Susceptibility was compared with prior research on G. occidentalis. RESULTS: Mancozeb was the least selective fungicide tested on A. caudiglans; it caused high acute toxicity and sublethal effects. Carbaryl was the least selective insecticide and caused 100% mortality. Captan was the most selective fungicide. Chlorantraniliprole and cyantraniliprole were the most selective insecticides and therefore least likely to disrupt biological control by A. caudiglans. Non-target effects on A. caudiglans and G. occidentalis were similar, but A. caudiglans experienced higher mortality to some broad-spectrum insecticides. CONCLUSIONS: All the products tested had some non-target effects on A. caudiglans. However, A. caudiglans sensitivity to most tested pesticides was similar to that of G. occidentalis. In general, existing spray recommendations for conserving G. occidentalis can be adjusted slightly and applied to A. caudiglans conservation. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Turning a Pest into a Natural Enemy: Removing Earwigs from Stone Fruit and Releasing Them in Pome Fruit Enhances Pest Control.

The European earwig Forficula auricularia (L.) (Dermaptera: Forficulidae) is an omnivorous insect that is considered a minor pest of stone fruit and a key predator of pests in pome fruit orchards. In many pome fruit orchards, earwigs are absent or in low abundance due to broad-spectrum spray programs and the slow recolonization rate of earwigs. Orchards in transition to organic or "selective" conventional programs often struggle to achieve effective levels of biological control, and thus, may benefit from inoculating earwigs to expedite their re-establishment. In a two-year study, we evaluated the potential for mass trapping earwigs from stone fruit using rolled cardboard traps to reduce fruit damage and provide earwigs for augmentation in pome fruit. We also tested whether a single mass release or five releases (on alternating weeks) of the same total number of earwigs in apples and pears reduced pests relative to plots where no releases occurred. Mass trapping did not decrease earwig abundance or substantially reduce fruit damage in stone fruit orchards. However, trapping was an efficient method for providing earwigs for augmentation. Earwig abundances were only increased in orchards where earwigs were previously low or absent; however, multiple orchards with varying prior levels of earwigs exhibited reductions in key pests (woolly apple aphid and pear psylla). For some other pests evaluated, plots with mass releases of earwigs had a slight trend in overall lower pest density when compared with control plots. A strategy for moving earwigs out of stone fruit orchards and into pome fruit orchards could be an effective method for augmenting orchard predator populations.

Meta-Analysis of Herbicide Non-Target Effects on Pest Natural Enemies.

A critical component of integrated pest management is minimizing disruption of biological control by reducing the use of pesticides with significant non-target effects on natural enemies. Insecticide non-target effects testing for natural enemies has become increasingly common, but research examining the non-target effects of herbicides on natural enemies is scarce, and recommendations regarding herbicide selectivity are non-existent. We used meta-analysis to summarize laboratory bioassays testing non-target effects of herbicides on arthropod natural enemies and identify patterns in taxon susceptibility and active ingredient toxicity. Data were extracted from 78 papers representing 801 total observations. Herbicides increased natural enemy mortality and decreased longevity, reproduction, and predation. Mesostigmatan mites and hemipterans were the most sensitive to herbicides, and spiders, neuropterans, and hymenopterans were the least sensitive. Mortality was higher in juvenile predators versus parasitoids but did not differ between adults; parasitoid juveniles are likely better protected within the host. In terms of acute mortality, metribuzin, glufosinate, and oxyfluorfen were the most harmful herbicides. Only nicosulfuron, rimsulfuron, pendimethalin, phenmedipham, atrazine, and urea did not increase natural enemy mortality. The large effect size of glufosinate is particularly concerning, as it is the most likely replacement herbicide for glyphosate in many crops. Many active ingredients remain under-studied. Our analysis indicates that herbicides have a strong potential to disrupt biological control in cropping systems.

Seasonal activity of Trechnites insidiosus (Hymenoptera: Encyrtidae) and its host Cacopsylla pyricola (Hemiptera: Psyllidae) in pear.

Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae) is the most expensive and challenging insect pest of commercial pear trees in the Pacific Northwest. Integrated pest management (IPM) programs are working toward relying more heavily on natural enemies to reduce insecticide use. Trechnites insidiosus (Crawford) (Hymenoptera: Encyrtidae) is the main parasitoid of C. pyricola, but little is known about its biology in the region. Developing sampling tools is important for the deployment of IPM programs, including monitoring of natural enemies. In this study, we examined 2 conventional monitoring methods: beat trays and yellow sticky cards, in addition to screened sticky cards and 3D-printed cylinder traps. Additionally, we tested an overwintering trap for the collection of parasitized C. pyricola. The trapping methods were tested in orchards in Oregon and Washington. Unscreened cards caught the most T. insidiosus and C. pyricola, followed by screened cards, cylinder traps, and then beat trays. Beat trays sometimes failed to catch any T. insidiosus, even when it was found in abundance via other methods. Screened cards and cylinder traps reduced bycatch and increased ease of identifying T. insidiosus. Specimens from the cylinder traps were also more suitable for use in molecular analysis. The overwintering traps were effective at capturing parasitized C. pyricola, but were highly variable year to year. The ideal trapping method will vary based on research needs (e.g., DNA preservation, reducing bycatch, catching higher numbers), but both screened sticky cards and cylinder traps were viable methods for monitoring T. insidiosus and its host.

Nontarget Impacts of Herbicides on Spiders in Orchards.

Spiders are key predators in many agroecosystems, including orchards. Despite the importance of spiders in biological control, pesticide nontarget effects on this group are poorly described. This is especially true for herbicides, which spiders frequently encounter as they move between the ground cover and tree canopy. We sought to determine the nontarget effects of seven herbicides used in orchards on three species of spiders that are commonly found in Washington state (USA) orchards: Pelegrina aeneola (Curtis) (Araneae: Salticidae), Philodromus cespitum (Walckenaer) (Araneae: Philodromidae), and Phanias watonus (Chamberlin & Ivie) (Araneae: Salticidae). Immature spiders were collected from orchards and used in laboratory assays. Single spiders were placed in vials with dried herbicide residues and mortality was evaluated after 1, 2, and 5 d. We also evaluated herbicide impacts on prey consumption rates and on spider movement using motion-tracking software. Only oxyfluorfen caused significant spider mortality. P. cespitum seemed to be less acutely sensitive to oxyfluorfen than the two salticid species. Several herbicide treatments significantly increased locomotion in P. cespitum, whereas rimsulfuron numerically decreased movement of P. aeneola. Sulfonylurea herbicides (rimsulfuron, halosulfuron) decreased prey consumption of P. aeneola. Our work indicates that although spiders may be less acutely sensitive to some pesticides than beneficial insects, they can be affected by sublethal effects of herbicides. Future work should determine if herbicide applications impact spider abundance in the field and reduce biological control services. In general, more work is needed on the impacts of herbicides on natural enemies.

Meta-analysis and review of pesticide non-target effects on phytoseiids, key biological control agents.

Understanding pesticide non-target effects on natural enemies is a key element of successful conservation biological control. Due to their importance in agroecosystems worldwide, the phytoseiid mites are the most well-studied natural enemies in pesticide selectivity research. The wealth of literature associated with this topic allows for a thorough meta-analysis of pesticide non-target effects and may also indicate general trends relevant to many cropping systems. We conducted a meta-analysis using 2386 observations from 154 published papers examining the impact of pesticides on lethal (adult and juvenile mortality) and sublethal (fecundity, egg hatch) effects. Insecticides and herbicides did not statistically differ in toxicity to phytoseiids, but research on herbicide non-target effects is scarce. Specific insecticides, fungicides, and miticides were sorted into least and most harmful categories. Phytoseiid species also differed in sensitivity, with Galendromus occidentalis (Nesbitt), Neoseiulus californicus (McGregor), and Typhlodromus pyri Scheuten among the least sensitive species. Sensitivity variation may be partly due to pesticide resistance; the greatest differences between species were within older mode of action (MOA) groups, where resistance development has been documented. It has been speculated that specialist phytoseiids, which closely associate with Tetranychus spp. spider mites, have more opportunities for resistance development due to their necessary proximity to a pest that rapidly develops resistance. Effect sizes were higher for generalist phytoseiid species, supporting this hypothesis. This meta-analysis highlights pesticide types (herbicides) and MOA groups where more research is clearly needed. Our analysis also allows for more robust generalizations regarding which pesticides are harmful or selective to phytoseiids. © 2021 Society of Chemical Industry. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Residual Activity of Acaricides for Controlling Spider Mites in Watermelon and Their Impacts on Resident Predatory Mites.

Twospotted spider mite, Tetranychus urticae Koch (Trombidiformes: Tetranychidae), is an important, worldwide pest of watermelon, Citrullus lanatus L. (Thunb.) Matsum. & Nakai (Cucurbitales: Cucurbitaceae). Feeding results in chlorotic spots and leaf necrosis, which can substantially reduce yields. In watermelon, T. urticae is managed solely with acaricides. Issues with acaricide resistance and pesticide label restrictions on number of applications per season require research-based recommendations on products with effective, long-lasting residues. To improve recommendations for T. urticae management in watermelon and to measure possible effects on non-target beneficial mites, we conducted acaricide efficacy trials in two locations in South Carolina, United States. The adulticidal products abamectin, bifenazate, fenpyroximate, and tolfenpyrad and the ovicidal products spiromesifen and etoxazole were tested. We also conducted two bioassays to better determine duration of acaricide residues. In the field trials, all acaricides except tolfenpyrad reduced T. urticae abundance, but all acaricides also reduced abundance of the most common predatory mite, Neoseiulus fallacis (Garman) (Mesostigmata: Phytoseiidae). In the bioassays, abamectin and bifenazate residues caused high adult T. urticae mortality at up to 21 d after treatment, performing better than fenpyroximate and tolfenpyrad. Etoxazole and spiromesifen were longer lasting, with <1 offspring per treated female in the etoxazole treatment at 28 d after treatment. Based on efficacy, abamectin or bifenazate should be rotated with etoxazole for fast knockdown of active stages while reducing reproduction, respectively. However, development and registration of more selective acaricides in watermelon is needed to preserve biological control of T. urticae by predatory mites.

Erythritol, an Artificial Sweetener, Is Acaricidal Against Pest Mites and Minimally Harmful to a Predatory Mite.

Erythritol, an artificial sweetener, has shown promise as an organic, human-safe insecticide. Recently, erythritol applications were shown to be successful at controlling pear psylla (Cacopsylla pyricola (Förster)) (Hempitera: Psyllidae), the most important pest of pear in the Pacific Northwest, USA. Twospotted spider mite (Tetranychus urticae Koch) (Trombidiformes: Tetranychidae) and pear rust mite (Epitrimerus pyri (Nalepa)) (Trombidiformes: Eriophyidae) can also be highly damaging pear pests. Their common natural enemy, Galendromus occidentalis (Nesbitt) (Mesostigmata: Phytoseiidae), can provide biological control if selective pesticides are used for managing other pests. Through a series of bioassays, we sought to determine whether erythritol could also be used for controlling either species of pest mite. We also examined whether erythritol had acute or sublethal impacts on G. occidentalis, through a variety of exposure methods. Effects examined included mortality, fecundity, prey consumption, and locomotion. We determined that a high concentration of erythritol (30%) had efficacy against both pest mite species and caused arresting behavior in twospotted spider mite. Erythritol caused little acute mortality in G. occidentalis, but did reduce fecundity and prey consumption through some exposure methods. Through motion-capture software, we determined that this is primarily due to reduced movement, likely caused by difficulty walking on residues and excessive grooming behavior. Because the predatory mite non-target effects were less acute than those for the two pest mites, we concluded that erythritol could likely be integrated into pear IPM with little or no disruption of mite biological control.