Nontarget Impacts of Herbicides on Spiders in Orchards

Glyphosate-based herbicides reduced overwintering population and reproduction of agrobiont spiders

Spiders are important in ecosystem and serve as predators in the biological control of pest insects in agroecosystem, where they encounter various harsh challenges including pesticides and low temperature in winter. Glyphosate-based herbicides (GBH) are widely and frequently applied to diminish weeds, exposing spiders a disturbed habitat, especially to overwintering spiders. We conducted a study combining field surveys and lab assays, to assess the effects of a GBH on the overwintering of the agrobiont wolf spider, Pardosa pseudoannulata. The GBH significantly reduced the overall overwintering spider population by about 69 %, and reduced the number of vulnerable juveniles by about 80 %. The survivors exhibited substantial fitness costs such as reproductive dysfunctions and enhanced oxidative stress responses. We then mimicked the overwinter process in lab. We housed spiders on soil patches with and without weeds to examine whether weeds contributed to the GBH's sublethal effects. Spiders overwintered independent of weeds when GBH was not applied. When GBH was applied before or during overwintering, juvenile spiders overwintered in weedy habitats exhibited reduced survival and fecundity, and increased oxidative stress compared to their counterparts in weed-free habitats. Therefore, GBH-containing weeds contributed to the persistent adverse effects of GBH on overwintering spiders. The findings revealed the cross-talk among weeds, herbicides, low temperature, and non-target organisms. The study provides novel information on the environmental risk assessment of pesticides and rational scheduling of pesticide application.

Herbicides may threaten advances in biological control of diseases and pests

Advances in agriculture include integrated methods of controlling pests, diseases, and weeds with biocontrollers, which are constantly increasing, along with herbicides. The objective is to present a systematic review of the main reports of herbicide effects on non-target organisms used in applied biological control and those naturally occurring in the ecosystems controlling pests. The categories were divided into predatory and parasitoid arthropods. Three hundred and fifty reports were analyzed, being 58.3% with parasitoids and 41.7% with predators. Lethal or sublethal effects of herbicides on reproduction, predation, genotoxicity, and abundance of biological control organisms have been reported. Two hundred and four reports of the impact of herbicides on parasitoids were analyzed. The largest number of reports was with parasitoids of the genus Trichogramma, with wide use in managing pests of the herbicide-tolerant transgenic plants. Most tests evaluating effects on parasitism, emergence, and mortality of natural enemies subjected to herbicides are with parasitoids of Lepidoptera eggs with a high diversity and use in managing these pests in different crops. Additive and synergistic effects of molecules increase the risks of herbicide mixtures. Herbicide use for weed management must integrate other control methods, as the chemical can impact natural enemies, reducing the biological control of pests.

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.

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.

Non-target pesticide impacts on pest natural enemies: Progress and gaps in current knowledge

Avoiding pesticide non-target 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.

Overhauling the ecotoxicological impact of synthetic pesticides using plants' natural products: a focus on Zanthoxylum metabolites

The reduction in agricultural production due to the negative impact of insects and weeds, as well as the health and economic burden associated with vector-borne diseases, has promoted the wide use of chemicals that control these "enemies." However, the use of these synthetic chemicals has been recognized to elicit negative impacts on the environment as well as the health and wellbeing of man. In this study, we presented an overview of recent updates on the environmental and health impacts of synthetic pesticides against agro-pest and disease vectors while exhaustive reviewing the potentials of natural plant products from Zanthoxylum species (Rutaceae) as sustainable alternatives. This study is expected to spur further research on exploiting these plants and their chemicals as safe and effective pesticide entities to minimize the impact of their chemical and synthetic counterparts on health and the environment.