Risk assessment of maize damage by wireworms (Coleoptera: Elateridae) as the first step in implementing IPM and in reducing the environmental impact of soil insecticides

Influence of Wireworm Diet on its Susceptibility to and Control With the Entomopathogenic Fungus Metarhizium brunneum (Hypocreales: Clavicipitaceae) in Laboratory and Field Settings

Entomopathogenic fungi (EPF) represent promising control agents against wireworms but success in field experiments is inconsistent. The physiological condition of the targeted insect is crucial for its ability to withstand fungal infection. In particular, nutritional status is among the most important determinants of the insects' immune defense. In this study, we investigated the effects of diet on the development of the wireworm Agriotes obscurus (L.) (Coleoptera: Elateridae) and its subsequent susceptibility to the fungal pathogen Metarhizium brunneum (Petch) (Hypocreales: Clavicipitaceae) in a pot experiment. After being reared on one of five plant diets for eight weeks, wireworms were exposed to an environment inoculated with the EPF and monitored for their susceptibility to fungal infection. We then performed a field experiment in which three plant diets (clover, radish, and a cover crop mix), selected according to the insects' performance in the laboratory experiment, were grown as a cover crop with EPF application. Plant diet influenced growth and development of larvae, but there were no strong differences in susceptibility toward fungal infection in the laboratory experiment. Damage levels in EPF-treated plots in the field varied depending on the cover crop. Damage was highest in plots planted with a mix of cover crop species, whereas damage was lowest in plots with clover or radish alone. This agrees with the laboratory results where insect performance was inferior when fed on clover or radish. Cover crop effects on wireworm damage in the subsequent cash crop may thus vary depending on the cover crop species selected.

Evaluation of Entomopathogenic Nematodes against Common Wireworm Species in Potato Cultivation

Wireworms (Coleoptera: Elateridae) are common insect pests that attack a wide range of economically important crops including potatoes. The control of wireworms is of prime importance in potato production due to the potential damage of the larvae to tuber quantity and quality. Chemical insecticides, the main control strategy against wireworms, generally fail to provide satisfactory control due to the lack of available chemicals and the soil-dwelling habits of the larvae. In the last decades, new eco-friendly concepts have emerged in the sustainable control of wireworms, one of which is entomopathogenic nematodes (EPNs). EPNs are soil-inhabitant organisms and represent an ecological approach to controlling a great variety of soil-dwelling insect pests. In this study, the susceptibility of Agriotes sputator Linnaeus and A. rufipalpis Brullé larvae, the most common wireworm species in potato cultivation in Türkiye, to native EPN strains [Steinernema carpocapsae (Sc_BL22), S. feltiae (Sf_BL24 and Sf_KAY4), and Heterorhabditis bacteriophora (Hb_KAY10 and Hb_AF12)] were evaluated at two temperatures (25 and 30 °C) in pot experiments. Heterorhabditis bacteriophora Hb_AF12 was the most effective strain at 30 °C six days post-inoculation and caused 37.5% mortality to A. rufipalpis larvae. Agriotes sputator larvae were more susceptible to tested EPNs at the same exposure time, and 50% mortality was achieved by two EPNs species, Hb_AF12 and Sc_BL22. All EPN species/strains induced mortality over 70% to both wireworm species at both temperatures at 100 IJs/cm², 18 days post-treatment. The results suggest that tested EPN species/strains have great potential in the control of A. sputator and A. rufipalpis larvae.

Integrated Pest Management of Wireworms (Coleoptera: Elateridae) and the Rhizosphere in Agroecosystems

The rhizosphere is where plant roots, physical soil, and subterranean organisms interact to contribute to soil fertility and plant growth. In agroecosystems, the nature of the ecological interactions within the rhizosphere is highly dynamic due to constant disruptions from agricultural practices. The concept of integrated pest management (IPM) was developed in order to promote an approach which is complementary to the environment and non-target organisms, including natural enemies, by reducing the sole reliance on synthetic pesticides to control pests. However, some of the implemented integrated cultural and biological control practices may impact the rhizosphere, especially when targeting subterranean pests. Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are generalist herbivores and a voracious group of pests that are difficult to control. This paper introduces some existing challenges in wireworm IPM, and discusses the potential impacts of various control methods on the rhizosphere. The awareness of the potential implications of different pest management approaches on the rhizosphere will assist in decision-making and the selection of the control tactics with the least long-term adverse effects on the rhizosphere.

Risk Assessment and Area-Wide Crop Rotation to Keep Western Corn Rootworm Below Damage Thresholds and Avoid Insecticide Use in European Maize Production

Simple Summary

Diabrotica virgifera virgifera LeConte, the Western corn rootworm (WCR), is a maize-specific pest that has been a serious threat in Europe since the mid-1990s. To properly implement integrated pest management, it is necessary to identify the key factors associated with risks of crop damage from WCR and to evaluate the effectiveness of area-wide strategies based on agronomic measures, such as crop rotation, in reducing those risks. In Italy and Croatia, a survey of agronomic and cultural factors in fields damaged by WCR allowed us to determine that the beetle population size accounts for most of the risk of maize damage from WCR. Crop rotation (without insecticide use), both structural and flexible, was the most effective strategy for keeping WCR populations below the damage threshold. This indicates that WCR management can be carried out in accordance with European Union regulations to limit or avoid insecticide treatments and reduce environmental impacts.

Abstract

The Western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, has been a serious quarantine pest to maize in Europe since the mid-1990s. The integrated pest management of WCR requires an accurate knowledge of the factors that contribute most to risks of crop damage, as well as knowledge of effective area-wide strategies based on agronomic measures, such as crop rotation. In Italy and Croatia, agronomic and cultural factors in fields damaged by WCR were evaluated through a long-term survey. Based on the survey results, high-WCR densities contribute most to risks of damage to maize. Extensive field research in north-eastern Italy compared large areas of continuous maize production with areas under different crop rotation systems (i.e., a structural one with one-time maize planting in a three-year rotation and a flexible one with continuous maize planting interrupted when beetle populations exceed the threshold). The objective was to evaluate the effectiveness of different rotation regimes as possible best practices for WCR management. Captures of beetles in yellow sticky traps, root damage, larval densities, and damage to maize plants (e.g., lodging) were assessed at the center of each area. The results demonstrated the both structural and flexible crop rotation systems were effective strategies for maintaining WCR below damage threshold densities without the need for insecticides.

Field Evaluation of Selected Plant Volatiles and Conspecific Pheromones as Attractants for Agriotes obscurus and A. lineatus (Coleoptera: Elateridae)

Sex pheromones are commonly used in traps to monitor populations and movements of male click beetles, but to date few attractants have been identified for females. Notable exceptions are plant-derived kairomones for female Agriotes brevis and A. ustulatus, allowing the monitoring of both males and females of these species with lures containing both pheromones and plant volatiles. The attractiveness of these plant volatiles for two congeners, A. obscurus and A. lineatus, which are agricultural pests in Europe and North America, was evaluated in the current study. Both the four-component MINIM plant-derived lure for A. brevis, and the blend of (E)-anethol and (E)-cinnamaldehyde for A. ustulatus, were not attractive to A. obscurus and A. lineatus, and instead appeared to reduce captures—both when compared to blank controls, and when blended with and compared to the sex pheromones of these species. This was most pronounced in A. obscurus, where (E)-anethol and (E)-cinnamaldehyde reduced male captures by 43 and 37%, respectively. Combining the pheromones of A. obscurus and A. lineatus reduced captures of these species by 77 and 19%, respectively, compared to these pheromones singly. This suggests that attractants for female click beetles can be highly species-specific, and that the blending of pheromones of congeneric species with each other, or with plant volatiles, can reduce captures. Further research into developing such attractants for economic species is urgently needed.

Three years of surveillance associates agro-environmental factors with wireworm infestations in Manitoba, Canada

BACKGROUND

Wireworms, the soil-dwelling larvae of click beetles, are a major threat to global agricultural production. This is largely due to their generalist polyphagous feeding capabilities, extended and cryptic life cycles, and limited management options available. Although wireworms are well-documented as economically important pests in the Canadian Prairies, including Manitoba, there are gaps in knowledge on species distributions, subterranean behaviour and life cycles, feeding ecology and damage capacity, and economic thresholds for crop yield loss.

RESULTS

We carried out 3 years (2018-2020) of intensive surveillance of larval populations across Manitoba. A total of 31 fields (24 in ≥ 2 consecutive years) were surveyed in early spring using standardized bait trapping approaches. Wireworms were present in 94% of surveyed sites, but the catch within fields varied year to year. While Hypnoidus bicolor predominated (94% of larvae), several other pest species were identified. We then explored the relationships between wireworm trap numbers and agro-environmental factors. The larval catch tended to decrease under conditions of low soil temperatures and increased clay content, coupled with high soil moisture and precipitation during the trapping period. Treatment and cultural methods appeared less influential; however, wheat production in either of the previous two growing seasons was associated with increased wireworm catch. Our models failed to predict a relationship between wireworm catch and crop yields, although infestations were rare in our region.

CONCLUSION

Our findings better infer the risks posed by wireworms to crop production in the Canadian Prairies, and the agro-environmental factors that represent the greatest contributors to these risks. This information should be incorporated into future integrated pest management (IPM) strategies for wireworms. © 2021 Her Majesty the Queen in Right of Canada Pest Management Science © 2021 Society of Chemical Industry Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Assessment of the Attraction Range of Sex Pheromone Traps to Agriotes (Coleoptera, Elateridae) Male Click Beetles in South-Eastern Europe

Simple Summary

Click beetles are the adults of wireworms, soil-dwelling larvae that damage multiple arable crops. The attraction range of YATLORf pheromone traps to click beetles of four species of Agriotes wireworms was studied to provide additional information about the implementation of integrated pest management against these harmful pests in Europe. This should allow a significant reduction in insecticide use. Male click beetles were marked and released at different distances from a pheromone trap. Recapture rate, maximum sampling ranges, and effective sampling areas were calculated. The recapture rate was significantly affected by distance, species, and wind direction and decreased as distance increased. The majority of beetles were caught from short distances (up to 10 m) within the first five days. The estimated attraction range was low for all the considered Agriotes species, suggesting that pheromone traps were unsuitable for use as mass trapping instruments to disrupt mating. However, after results and previous research outputs were evaluated, it seems possible to use the traps not only as monitoring tools, but also as attract-and-kill strategies for most beetle populations.

Abstract

The attraction range of YATLORf pheromone traps to adults of four species of Agriotes (A. brevis, A. sordidus, A. litigiosus, and A. ustulatus) was studied to provide additional information about the most harmful Agriotes species in Europe. Male click beetles were marked and released at different distances from a pheromone trap. The recapture rate was calculated and analyzed using analysis of variance. The recapture rate was significantly affected by distance, species, and wind direction. The recapture rate decreased as distance increased. The majority of beetles were caught from short distances (up to 10 m) within the first five days. A. brevis, a mainly crawling species, showed the lowest recapture rate. The wind direction affected the recovery rate, with a significantly lower number of beetles moving downwind from the release points. Maximum sampling ranges and effective sampling areas were calculated. The obtained estimations were low (53 to 86 m and 509 to 2602 m², respectively) for all the considered Agriotes species, suggesting that they were unsuitable for use as mass trapping instruments to disrupt mating. However, it seems possible to use the traps not only as monitoring tools, but also as attract-and-kill strategies for most beetle populations.

Future of Insecticide Seed Treatment

Seed treatment as a method of local application of pesticides in precise agriculture reduces the amount of pesticides used per unit area and is considered to be the safest, cheapest and most ecologically acceptable method of protecting seeds and young plants from pests in the early stages of their development. With the introduction of insecticides from the neonicotinoid group in the mid-1990s, the frequency of seed treatment increased. Due to suspected negative effects on pollinators, most of these insecticides are banned in the European Union. The ban has therefore led to a reduction in the number of active substances approved for seed treatment and to an increased re-use of active substances from the group of pyrethroids as well as other organophosphorus insecticides, which pose potentially very serious risks, perhaps even greater than those of the banned neonicotinoids. The objective of this review is to analyze the advantages and disadvantages of seed treatment and the potential role of insecticide seed treatment in reducing the negative impact of pesticides on the environment. The main disadvantage of this method is that it has been widely accepted and has become a prophylactic protective measure applied to almost all fields. This is contrary to the principles of integrated pest management and leads to an increased input of insecticides into the environment, by treating a larger number of hectares with a lower amount of active ingredient, and a negative impact on beneficial entomofauna. In addition, studies show that due to the prophylactic approach, the economic and technical justification of this method is often questionable. Extremely important for a quality implementation are the correct processing and implementation of the treatment procedure as well as the selection of appropriate insecticides, which have proven to be problematic in the case of neonicotinoids. The ban on neonicotinoids and the withdrawal of seed treatments in oilseed rape and sugar beet has led to increased problems with a range of pests affecting these crops at an early stage of growth. The results of the present studies indicate good efficacy of active ingredients belonging to the group of anthranilic diamides, cyantraniliprole and chlorantraniliprole in the treatment of maize, soybean, sugar beet and rice seeds on pests of the above-ground part of the plant, but not on wireworms. Good efficacy in controlling wireworms in maize is shown by an insecticide in the naturalites group, spinosad, but it is currently used to treat seeds of vegetable crops, mainly onions, to control onion flies and flies on other vegetable crops. Seed treatment as a method only fits in with the principles of integrated pest management when treated seeds are sown on land where there is a positive prognosis for pest infestation.

Newer characters, same story: neonicotinoid insecticides disrupt food webs through direct and indirect effects

During the Green Revolution, older classes of insecticides contributed to biodiversity loss by decreasing insect populations and bioaccumulating across food webs. Introduction of Integrated Pest Management (IPM) improved stewardship of insecticides and promised fewer non-target effects. IPM adoption has waned in recent decades, and popularity of newer classes of insecticides, like the neonicotinoids, has surged, posing new and unique threats to insect populations. In this review, we first address how older classes of insecticides can affect trophic interactions, and then consider the influence of neonicotinoids on food webs and the role they may be playing in insect declines. We conclude by discussing challenges posed by current use patterns of neonicotinoids and how their risk can be addressed.

Species Identification of Wireworms (Agriotes spp.; Coleoptera: Elateridae) of Agricultural Importance in Europe: A New "Horizontal Identification Table"

Simple Summary

Wireworms are soil-dwelling larvae that damage multiple arable crops. The most common wireworms found in European cultivated fields belong to the genus Agriotes. Large amounts of insecticides are applied on a prophylactic basis to control them; before any treatment can be applied, however, legislation imposes an assessment of whether pest population levels exceed a damage threshold above which a significant yield reduction is expected. Thresholds vary greatly among species, thus quick and reliable larval identification is needed. This will result in the implementation of the appropriate integrated pest management practices. Furthermore, research into non-chemical strategies involves carrying out tests with live wireworms identified to species. Wireworms were observed to identify live larvae rapidly on site to assess density and compared with species-specific thresholds before sowing, and for laboratory experiments to be performed. This work led to a “synoptic key” that reliably identifies most live larvae, while traditional keys consider only single characters step by step. The key considers several discriminating morphological characters in order of stability. Identification becomes reliable when at least two main discriminating characters are found and attributed to a single species.

Abstract

Wireworms are yellowish soil-dwelling larvae that damage a wide range of arable crops. The most common wireworms found in European cultivated fields (except for the Caucasus) belong to the genus Agriotes (Coleoptera: Elateridae). In several European countries, environment-impacting insecticides are applied on a prophylactic basis to control them. However, before any treatment can be applied, European legislation requires that an assessment is done when pest population levels exceed a damage threshold. The threshold substantially depends on wireworm species, thus quick reliable larval identification is needed to implement the appropriate integrated pest management practices. Furthermore, research into non-chemical strategies involves carrying out tests with live and identified wireworms. Thus, thousands of wireworms were observed in a bid to identify live larvae so that larval density could be assessed and compared with species-specific thresholds before sowing, and laboratory experiments were carried out. This work led to a horizontal identification table that allows for quick and accurate identification of live larvae. This key, unlike traditional dichotomous keys, simultaneously considers a set of multiple discriminating morphological characters in order of stability. The key can be reliably used by less experienced users and, once minimum familiarity is acquired, most larvae can be identified rapidly, with high precision.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 3: alternatives to systemic insecticides

Over-reliance on pesticides for pest control is inflicting serious damage to the environmental services that underpin agricultural productivity. The widespread use of systemic insecticides, neonicotinoids, and the phenylpyrazole fipronil in particular is assessed here in terms of their actual use in pest management, effects on crop yields, and the development of pest resistance to these compounds in many crops after two decades of usage. Resistance can only be overcome in the longterm by implementing methods that are not exclusively based on synthetic pesticides. A diverse range of pest management tactics is already available, all of which can achieve efficient pest control below the economic injury level while maintaining the productivity of the crops. A novel insurance method against crop failure is shown here as an example of alternative methods that can protect farmer's crops and their livelihoods without having to use insecticides. Finally, some concluding remarks about the need for a new framework for a truly sustainable agriculture that relies mainly on natural ecosystem services instead of chemicals are included; this reinforcing the previous WIA conclusions (van der Sluijs et al. Environ Sci Pollut Res 22:148-154, 2015).

Development of precise micro analytical tool to identify potential insecticide hazards to bees in guttation fluid using LC-ESI-MS/MS

This paper illustrates the development of a miniaturized and precise analytical tool for biomonitoring of honey bee exposure to insecticides. This is the first work describing an analytical method for determination of very low concentrations of a wide range of insecticides in maize guttation fluid. Seed treatment with systemic insecticides or their foliar application causes the accumulation of compounds in the guttation liquid, which consists of excess water and compounds removed by plants and is a source of water for bees. A micro-QuEChERS protocol using 1 g of sample was used for analysis of over 140 insecticides belonging to 30 different chemical classes by LC-ESI-MS/MS. The determination of insecticides in guttation fluid is a difficult analytical task due to 1) the complexity of the sample matrix, 2) small amounts of test samples and 3) trace levels of analytes (often equal sublethal dose of insecticide for bees). An efficient sample treatment is proposed, involving 1 g of sample, extraction with 1% formic acid in acetonitrile, frozen, ultrasound-assisted, centrifugation and dispersive solid phase extraction with nano graphene oxide. Other tested sorbents: Fe₃O₄MNPs and two mixtures PSA/C18/GCB and Z-Sep did not give satisfactory parameters during sample purification. The graphene oxide proved to be the best, ensuring negligible matrix effects and analyte recoveries between 70% and 120% with relative standard deviations <20% for most of the compounds studied. The proposed method enables assessment of risk to honey bees resulting from exposure to guttation fluids containing toxic insecticides at very low concentrations.

An update of the Worldwide Integrated Assessment (WIA) on systemic pesticides. Part 4: Alternatives in major cropping systems

We present a synthetic review and expert consultation that assesses the actual risks posed by arthropod pests in four major crops, identifies targets for integrated pest management (IPM) in terms of cultivated land needing pest control and gauges the implementation "readiness" of non-chemical alternatives. Our assessment focuses on the world's primary target pests for neonicotinoid-based management: western corn rootworm (WCR, Diabrotica virgifera virgifera) in maize; wireworms (Agriotes spp.) in maize and winter wheat; bird cherry-oat aphid (Rhopalosiphum padi) in winter wheat; brown planthopper (BPH, Nilaparvata lugens) in rice; cotton aphid (Aphis gossypii) and silver-leaf whitefly (SLW, Bemisia tabaci) in cotton. First, we queried scientific literature databases and consulted experts from different countries in Europe, North America, and Asia about available IPM tools for each crop-pest system. Next, using an online survey, we quantitatively assessed the economic relevance of target pests by compiling country-level records of crop damage, yield impacts, extent of insecticide usage, and "readiness" status of various pest management alternatives (i.e., research, plot-scale validation, grower-uptake). Biological control received considerable scientific attention, while agronomic strategies (e.g., crop rotation), insurance schemes, decision support systems (DSS), and innovative pesticide application modes were listed as key alternatives. Our study identifies opportunities to advance applied research, IPM technology validation, and grower education to halt or drastically reduce our over-reliance on systemic insecticides globally.

The use of click beetle pheromone traps to optimize the risk assessment of wireworm (Coleoptera: Elateridae) maize damage

Maize seeds are routinely coated with insecticide to target Agriotes spp. larvae (wireworms). However, in order to find fields where pest control is actually needed, it might be useful to estimate the adult Agriotes population levels and thus the pressure they exert, with a low-cost risk assessment tool, such as YATLORf (Yf) sex pheromone traps. A database containing 17 consecutive years (1998–2014) of field monitoring was analyzed, with information including both pheromone-trap catches of adults and maize-plant damage by wireworms. Significant associations were discovered between seasonal adult catches in-field, subsequent wireworm populations, and plant damage/yield reduction. When each trap contained over 1,100 A. sordidus adults and over 210 A. brevis adults one year prior (Y-1), the risk of 15%-plus plant damage in Year 0 (Y0) increased by 6 times and 37 times respectively when compared with lower numbers. More than 1,000 A. brevis adults/trap two years prior (Y-2) increased the risk of 15%-plus plant damage in Y0 by 13 times when compared with lower numbers. Cumulative thresholds were also found in Y-1 and Y-2 at the same site. Yf threshold values allowed us to detect fields with a negligible crop-damage risk and thus to reduce the use of insecticides.

Movement of the Neonicotinoid Seed Treatment Clothianidin into Groundwater, Aquatic Plants, and Insect Herbivores

Agricultural use of the neonicotinoid clothianidin (CLO) as a seed treatment of corn and soybeans has been linked to contamination of waterways and irrigation water. By analyzing samples collected from field lysimeters with liquid chromatography tandem mass spectrometry (LC-MS), this study reports the highest CLO concentrations within leachate following planting, with maximum concentrations occurring 4 weeks post-planting (3370 ng L^-1). This concentration is approximately 10× greater than previously reported CLO concentrations in streams/rivers and prairie wetlands, likely the result of reduced dilution and photolysis impacts. To document nontarget vegetation translocation dynamics, the macrophyte Lemna gibba was exposed to varying CLO concentrations for 12 h within a laboratory setting. Quantification of CLO uptake occurred every 4 h. Finally, trophic level impacts were investigated by exposing the water lily aphid Rhopalosiphum nymphaeae to L. gibba grown in CLO-contaminated water. Aphids lived and fed on contaminated duckweed for 48 h, after which an LC₅₀ of 8.71 ng g of the plant tissue^-1 was calculated. While uptake of CLO by duckweed was rapid, aphids are unlikely to suffer acute mortality at previously reported environmental CLO concentrations. Future research should expand on this work with other macrophytes/herbivores and longer-term experiments to more realistically mimic chronic field exposures.

In-Field Habitat Management to Optimize Pest Control of Novel Soil Communities in Agroecosystems

The challenge of managing agroecosystems on a landscape scale and the novel structure of soil communities in agroecosystems both provide reason to focus on in-field management practices, including cover crop adoption, reduced tillage, and judicial pesticide use, to promote soil community diversity. Belowground and epigeal arthropods, especially exotic generalist predators, play a significant role in controlling insect pests, weeds, and pathogens in agroecosystems. However, the preventative pest management tactics that dominate field-crop production in the United States do not promote biological control. In this review, we argue that by reducing disturbance, mitigating the effects of necessary field activities, and controlling pests within an Integrated Pest Management framework, farmers can facilitate the diversity and activity of native and exotic arthropod predators.