Willem G. van Herk

Wireworm Management I: Stand Protection Versus Wireworm Mortality With Wheat Seed Treatments

ABSTRACT The efficacy of various insecticidal seed treatments in protecting wheat, Triticum aestivum L., from wireworm damage as well as reducing wireworm (Coleoptera: Elateridae) populations was studied over 3 yr. Protection from wireworm damage was measured by postplanting stand counts, and effects on wireworm populations were measured by within-row core samples and by bait traps placed in plots the following spring. The effects of treatments on populations of larger wireworms already present at planting were distinguished from their effects on neonate wireworms produced that growing season. Neonicotinoid seed treatments (imidacloprid, clothianidin, and thiamethoxam) provided excellent wheat stand protection, likely through prolonged wireworm intoxication, but populations of larger and neonate wireworms were not significantly reduced in bait traps the following spring. The pyrethroid tefluthrin, applied to seed with and without a neonicotinoid insecticide (thiamethoxam), provided excellent crop protection, but populations of wireworms also were not significantly reduced. This and additional laboratory data suggest that wheat stand establishment provided by tefluthrin is due to a combination of repulsion and short term morbidity events. The phenyl pyrazole fipronil provided excellent crop protection, and populations of both larger and neonate wireworms could not be detected in plots the following spring. The previously registered organochlorine lindane, although reducing wireworm feeding, was phytotoxic in 2 of 3 yr. Next to fipronil, lindane was the most consistent seed treatment in reducing populations of larger and neonate wireworms. These studies indicate that stand and yield protection provided by contemporary wheat seed treatments cannot automatically be equated with wireworm population mortality. This is an important consideration when choosing a suitable seed treatment to replace lindane, which historically provided both stand protection and wireworm reduction, and did not have to be applied every year.

Biology, Ecology, and Control of Elaterid Beetles in Agricultural Land*

Wireworms, the larvae of click beetles (Coleoptera: Elateridae), have had a centuries-long role as major soil insect pests worldwide. With insecticidal control options dwindling, research on click beetle biology and ecology is of increasing importance in the development of new control tactics. Methodological improvements have deepened our understanding of how larvae and adults spatially and temporarily utilize agricultural habitats and interact with their environment. This progress, however, rests with a few pest species, and efforts to obtain comparable knowledge on other economically important elaterids are crucial. There are still considerable gaps in our understanding of female and larval ecology; movement of elaterids within landscapes; and the impact of natural enemies, cultivation practices, and environmental change on elaterid population dynamics. This knowledge will allow generation of multifaceted control strategies, including cultural, physical, and chemical measures, tailored toward species complexes and crops across a range of appropriate spatial scales.

Soil Bioassay for Studying Behavioral Responses of Wireworms (Coleoptera: Elateridae) to Insecticide-Treated Wheat Seed

Abstract A bioassay for observing wireworm behavior in soil is described. The bioassay permits analysis of orientation, feeding, repellency, and postcontact toxicity behaviors of wireworms in response to insecticide-treated wheat seeds. Wireworm positions were recorded every 5 min for 3 h, and the time required to orient to and contact seeds, and the duration of individual feeding events, was calculated. Both avoidance (before contact with seeds) and repellency (after contact) were quantified. A high proportion of Agriotes obscurus (0.95), Limonius canus (1.00), Ctenicera pruinina (0.80), Melanotus communis/dietrichi (0.80), and Hypolithus sp. (0.70) larvae contacted untreated wheat seeds and began feeding within 120 min when seeds were preincubated for 60 min in soil with 20% moisture. A smaller proportion of A. obscurus contacted seeds if seeds were not incubated in the bioassay before wireworm introduction (0.80) or in soil with 10% moisture (0.65). L. canus larvae required a significantly shorter time (25.3 min) to contact seeds if seeds were incubated for 60 min than if seeds were not incubated before wireworm introduction (43.1 min). Wireworms exposed to untreated seeds and seeds treated with the fungicide Dividend XLRTA fed normally (i.e., sustained feeding for at least 60 min), but a significant proportion of wireworms exposed to seeds treated with Tefluthrin 20 CS (containing the synthetic pyrethroid tefluthrin) fed for 15 min or less and were subsequently repelled. Wireworms exposed to Vitavax Dual (containing the organochlorine lindane) were not repelled after feeding and showed symptoms of illness for up to 28 d before making a full recovery (89%) or dying (11%).

Wireworms as Pests of Potato

Wireworms (Coleoptera: Elateridae) of several species cause severe cosmetic and economic injury to daughter tubers. Populations are expanding globally, due largely to the attrition of most organochlorine and organophosphate insecticides used since the 1950s. Where wireworms could once be controlled for several years with organochlorine insecticides, contemporary management strategies for wireworms are taking on more regional, species-specific and multi-tactical approaches. The requisite knowledge and expertise underlying these approaches involves taxonomy (traditional and molecular); biology and ecology (life history, behavior, distribution, habitat and host preferences, chemical ecology, phenology); surveillance (wireworm and adult sampling and risk assessment); and species-specific response(s) to a variety of integrated pest management approaches (e.g. crop rotation, cultivation, tolerant varieties, soil amendments, biological and semiochemical controls and low-risk insecticides). These topics are reviewed in this chapter, along with suggestions as to the more likely and productive avenues of research to address now and in the future.

Further Studies on Wireworm Management in Canada: Damage Protection Versus Wireworm Mortality in Potatoes

ABSTRACT The efficacy of various insecticides and application methods in protecting potatoes from wireworm (Agriotes obscurus L.) damage as well as reducing wireworm populations was studied over 5 yr in Agassiz, British Columbia. Protection from wireworm damage was measured by the number of blemishes to daughter tubers, and effects on wireworm populations were measured by sampling soil around seed potatoes and/or by bait traps the following spring. Organophosphates registered for wireworm control in the United States and/or Canada (phorate and chlorpyrifos), significantly reduced blemishes to tubers by, respectively, 92.2 and 90.2%, and populations of large (≥9 mm long = ‘resident’) wireworms by 83.4 and 71.0% relative to controls. Similar reductions in smaller (<9 mm long = ‘neonate‘) wireworms were also observed. Neonicotinoids (imidacloprid, clothianidin, and thiamethoxam) tested as seed piece treatments at ≈12.5 g active ingredient/100 kg potato seed reduced blemishes by, respectively, 19.1, 71.6, and 90.6%, but resident wireworms were only reduced by, respectively, 22.0, 29.1, and 51.8%. Significant mortality of neonates was not observed with any neonicotinoid treatment. With the possible exception of thiamethoxam, where significant reduction in resident wireworms occurred, it is likely that the blemish protection provided without significant wireworm mortality with imidacloprid and clothianidin treatments was because of long-term wireworm intoxication followed by population recovery. The phenyl pyrazole, fipronil, applied as an in-furrow spray reduced blemishes by 94.3%, and resident wireworm populations could not be detected in plots the following spring. Neonates were reduced by 93.3%, indicating excellent residual control had occurred with fipronil. These studies indicate that tuber protection by fipronil and currently registered organophosphates is likely because of significant early season mortality of wireworms, whereas neonicotinoids generally provide control through long-term morbidity without high levels of mortality occurring.

Possible aversion learning in the Pacific Coast wireworm

The effects of carbon dioxide and the induction of morbidity on aversion learning in larvae of the Pacific Coast wireworm Limonius canus LeConte (Coleoptera: Elateridae) are discussed. Wireworms preconditioned by exposing them one or four times to odour of Tefluthrin 20SC and Dividend XLRTA [Syngenta Crop Protection (Canada), Inc., Canada] during the induction of temporary morbidity subsequently contact tefluthrin‐treated wheat seeds in soil bioassays for as long as naïve (i.e. not preconditioned) larvae but are repelled four to five‐fold more frequently by Dividend‐treated seeds in soil bioassays than naïve wireworms, suggesting that wireworms are capable of associating a novel odour (i.e. Dividend) with morbidity but require a minimum of 10–15 min subsequent contact time with treated seeds before being repelled. Wireworms preconditioned by exposure to peppermint odour during the induction of morbidity are not subsequently repelled by peppermint odour in soil bioassays, suggesting that wireworms are either not capable of aversion learning or that the presence of a CO2 source and/or a suitable host plant may override a negative cue (i.e. peppermint odour). In studies conducted in the absence of soil, a host plant and CO2 production, wireworms are repelled slightly by droplets of 1.0% but not 0.1% peppermint oil. Previous exposure to peppermint odour or contact with peppermint oil‐treated filter paper during one induction of morbidity does not increase the repellency of wireworms to 1.0% peppermint oil significantly. Repellency to 1.0% peppermint oil is almost eliminated when morbidity is induced five times in the absence of peppermint odour but is restored when peppermint odour is present during preconditioning. These findings suggest that wireworm sensitivity to repellent compounds decreases when repeatedly made moribund, although the results are not sufficient to conclude that wireworms are capable of associative learning.

Mark–recapture of Agriotes obscurus and Agriotes lineatus with dense arrays of pheromone traps in an undisturbed grassland population reservoir

The present study was conducted using mark–released populations of male Agriotes obscurus (AO) and Agriotes lineatus (AL) adults to simulate the spatial and temporal capture rates of wild beetle populations in dense arrays of pheromone traps in a confined, nonfarmed habitat. Two parallel rows of traps, spaced 3 m apart along corridors of grassy dyke, recaptured 85.6% of AO and 77.8% of AL with arrays of their respective pheromone traps, mostly within the first week of release. In arrays of mixed AO and AL traps, recapture rates were 77.8% and 83.3%, respectively. In arrays with only AO traps, 31.2% of AL males released within the arrays mistakenly entered the AO traps, which declined to only 2.2% when released in arrays with both AO and AL traps. In arrays with only AL traps, only 0.7% of released AO were mistakenly taken in the AL traps, and only 0.3% mistakenly entered AL traps in mixed AO and AL trap arrays. Between 34.4–38.9% of AO and 21.1–25.6% of AL released in areas immediately adjacent to the trapping arrays were caught, mostly in the outermost traps. The implications of these results for determining the efficacy of mass trapping as a click beetle management approach are discussed.

Mass trapping wild Agriotes obscurus and Agriotes lineatus males with pheromone traps in a permanent grassland population reservoir

A study was conducted to determine whether arrays of pheromone traps could be used to reduce populations of male Agriotes obscurus (AO) and Agriotes lineatus (AL) adults in a confined nonfarmed habitat (grassy dyke). Traps placed 3 m apart in 15 × 2 arrays captured significantly more AL than AO, although the trap catch varied with location for both species and was inversely related to the number of nearby competing traps. Models of beetle movement indicated that a considerable proportion of males (AL: 18.4–71.8%; AO: 35.0–58.3%) collected in the arrays had moved in from elsewhere and that AL beetles are more active than AO beetles. AL beetles frequently entered AO traps unless both trap types were present in the array, whereas AO rarely entered AL traps. Concurrent catches in pitfall traps placed inside and outside pheromone trapping zones indicated the trap arrays significantly reduced male (but not female) AO and AL beetles inside their respective arrays, that AO traps reduced AL beetles in AO arrays, and that both AL and AO traps could potentially reduce the number of mating pairs in these arrays. The implications of these results in determining the efficacy of this approach as a click beetle management approach are discussed.

Determination of Agriotes obscurus (Coleoptera: Elateridae) sex pheromone attraction range using target male behavioural responses

A study was conducted to determine the attractive range of traps baited with Agriotes obscurus pheromone to male beetles in both still air and wind conditions. This information is crucial for evaluating the potential of mass trapping when aiming to reduce beetle populations. Groups of 10 beetles were released at 14 points spaced 1 m apart along a linear track, at one end of which was a pheromone and wind source. Beetle response to the pheromone and/or wind was recorded 150 s after release and characterized as orienting either towards or away from the pheromone and/or wind source. Data analysis indicated the attraction range of the sex pheromone is <5 m in still air, which is considerably lower than estimates from previous studies and emphasizes the challenge of mass trapping this species in the field. The attraction range increased when there was air flow. Unexpectedly, not all male beetles respond to the pheromone, and beetles are inclined to move downwind even in the presence of pheromone. The latter finding suggests that wind direction may influence beetle dispersal and mate finding in the field. The implications of these results for determining the efficacy of mass trapping as a management approach are discussed.

Erratum to: Companion planting attract-and-kill method for wireworm management in potatoes

Management of wireworms in potatoes is commonly through the use of insecticides applied at planting. With many insecticides for wireworm control now disappearing worldwide, there is an urgent need for lower risk, efficacious, and cost-effective alternative strategies for use in the twenty first century. To address this need, a novel intercrop attract-and-kill (A&K) method for controlling wireworm damage to tubers and reducing wireworms was evaluated in British Columbia (Agriotes obscurus), and Ontario (Melanotus spp.). Wheat seed treated with fipronil and/or thiamethoxam was planted in-furrow alongside untreatedmother tubers. In BC trials, wheat seed treatedwith fipronil, or fipronil plus thiamethoxam, provided comparable blemish reductions to in-furrow granular applications of Thimet 15G, containing phorate. With these A&K treatments, mean reduction in wireworms relative to untreated controls ranged from 89 to 100 %, as compared to a 59.2 % reduction with Thimet. In the Ontario studies, mean blemish reductions of 81.2 % occurred with intercropped fiproniltreated wheat, and a 66.6 % reduction in damage with fipronil plus thiamethoxam in comparison to Thimet (83.4 % reduction). Reduction in potato yield due to competitionwith intercropped wheat was seldom observed. It is concluded that an A&K strategy with wheat treated with fipronil at 5 g active ingredient (AI)/100 kg seed would require only 3.4 g AI/ha, relative to 3250 g AI of phorate/ha to achieve comparable control. This A&K strategy offers a highly effective means of wireworm blemish and population control; has low environmental risk; and would be comparable to the cost of currently used prophylactic insecticide treatments such as phorate.