W. G. van Herk

Mortality of a Wireworm, Agriotes obscurus (Coleoptera: Elateridae), after Topical Application of Various Insecticides

Abstract Ten insecticides representing seven chemical groups were applied at various concentrations topically by using a Potter Spray Tower to evaluate their relative toxicities on the European wireworm Agriotes obscurus L. (Coleoptera: Elateridae). Wireworms were stored at 15°C after exposure to organophosphate (OP) (chlorpyrifos, diazinon), pyrethroid (tefluthrin), thianicotinoid (thiamethoxam, clothianidin), chloronicotinoid (imidacloprid, acetamiprid), phenyl pyrazole (fipronil), organochlorine (lindane), and spinosyn (spinosad) insecticides, and their postapplication health was evaluated weekly for up to 301 d. LC50, LC90, LT50, and LT90 values were calculated for each chemical except acetamiprid, and compared with those of lindane, clothianidin, and chlorpyrifos. Wireworms exposed to OPs died or recovered more quickly (LT50 < 20 d, LT90 < 50 d), than those exposed to all other insecticides tested except tefluthrin (LT50 = 25.5 d, LT90 = 66.5 d). Wireworms exposed to sublethal concentrations of all neonicotinoids quickly became moribund after application but made a full recovery. Wireworms exposed to fipronil at concentrations near the LC90 value showed no intoxication symptoms for up to 35 d, and they did not recover after symptoms developed. For each chemical, increasing the concentration increased the time required for wireworms to recover but decreased the time required to kill wireworms. Fipronil was highly toxic to wireworms (LC50 = 0.0001%), but acetamiprid (LC50 = 1.82%), imidacloprid (LC50 = 0.83%), tefluthrin (LC50 = 0.23%), diazinon (LC50 = 0.54%), and spinosad (LC50 = 0.51%) were not. The toxicity of both clothianidin (LC50 = 0.07%) and thiamethoxam (LC50 = 0.17%) were similar to those of lindane (LC50 = 0.06%) and chlorpyrifos (LC50 = 0.10%).

Repellency of a Wireworm, Agriotes obscurus (Coleoptera: Elateridae), on Exposure to Synthetic Insecticides in a Soil-Less Bioassay

Abstract A soil-less bioassay arena to test repellency of wireworms (A. obscurus) to insecticides and carrier solvents is described. The bioassay and variables measured distinguish between shorter-range (contact and/or volatile) and longer-range (volatile) repellency. Wireworm positions are recorded every 3 s for 20 min, and average speed, rate of slowing, and longer- and shorter-range repellent behaviors calculated. Shorter-range repellency is determined with a Wireworm Repellency Score (WRS, range 0–100), calculated before contact and after contact with test chemicals. Of two carrier solvents tested, wireworms were strongly repelled by acetone (WRS = 57) but not by water (WRS = 1) when introduced to the bioassay arenas immediately after chemical inoculation. When bioassay arenas were assembled/sealed 2 min after inoculation, acetone elicited no repellency (WRS = 2). When dissolved in acetone in bioassays assembled with a 2-min delay, imidacloprid, chlorpyrifos, lindane, and tefluthrin elicited slight to moderate repellency at the highest concentrations tested (WRS = 30, 48, 42, and 49, respectively). Both longer- and shorter-range repellency increased over the duration of the observation period for lindane and tefluthrin, and shorter-range repellency also increased over the duration of the observation period for chlorpyrifos. Removal of volatiles in the bioassay arena by vacuum considerably affected wireworm movement in the arena, with the repellency elicited by acetone and lindane being significantly reduced. Clothianidin elicited no longer- or shorter-range repellency.

Morbidity and recovery of the Pacific Coast wireworm, Limonius canus, following contact with tefluthrin-treated wheat seeds

Late instars of the Pacific Coast wireworm, Limonius canus (LeConte) (Coleoptera: Elateridae), were exposed to wheat seeds treated with tefluthrin at 5, 10, 15, 20, or 30 g active ingredient (a.i.) per 100 kg wheat seed for 1, 2, 4, 8, or 16 min. All wireworms were moribund within 20 min of first exposure and recovered fully within 12 h. The time required for recovery (tr) after a single exposure increased with duration of exposure (e) and concentration (c), but decreased with wireworm weight (w), expressed as (tr)0.5 = 5.2812 + 0.9407e – 0.0259e2 + 0.1569c + 0.0254ec – 0.0174w – 0.0057ew. For wireworms exposed to treated seeds for 2 min, the time required for induction of morbidity decreased as concentration of tefluthrin increased and as wireworm weight decreased, expressed as (ti)0.5 = 2.613 – 0.039c + 0.018w, where ti is the induction time of morbidity, and c and w are as above. Wireworms re‐exposed to tefluthrin‐treated seeds after recovery from previous exposure were again moribund within 20 min of exposure, but recovery was significantly more rapid if the second exposure was 2, 4, 6, 8, 12, 18, 24, and 48 h after recovery from first exposure. Recovery from a second exposure was not significantly faster when the second exposure was 96 h after recovery from the first exposure. The ability of wireworms to recover from tefluthrin‐induced morbidity may seriously limit the efficacy of this insecticide in actually reducing wireworm populations in the field.

Effect of temperature on the morbidity and recovery of the Pacific Coast wireworm, Limonius canus, following contact with tefluthrin-treated wheat seeds

Late instars of the Pacific Coast wireworm, Limonius canus (LeConte) (Coleoptera: Elateridae), were exposed to wheat seeds treated with tefluthrin at 10 g active ingredient/100 kg wheat seed, for 2 min, at 10, 15, 20, and 25 °C. All wireworms were moribund within 20 min of first exposure and recovered fully within 7 h. Morbidity induction time (i) decreased considerably as the temperature (t) was increased from 10 to 15 °C, but did not decrease further when the temperature was increased from 15 to 25 °C. For each temperature, induction time decreased as wireworm weight (w) increased, so that . A strong negative temperature coefficient was observed in wireworm recovery, the time required for recovery (r) after exposure decreasing as both temperature (t) and wireworm weight (w) increased, so that r = 1102.47(w)−0.1848 * e−0.1012t. The temperature at which wireworms contact insecticides in the field may significantly affect the induction and duration of morbidity, and determine whether wireworms will become moribund before they are repelled by tefluthrin. The ability of wireworms to recover from tefluthrin‐induced morbidity may seriously limit the efficacy of this insecticide in reducing wireworm populations in the field.

Field Evaluation of Insecticides for Control of Cabbage Maggot (Diptera: Anthomyiidae) in Rutabaga in Canada

Abstract At the time of this research, there were only two insecticides registered for control of cabbage maggot, Delia radicum L., in rutabaga in Canada, one of which (diazinon) will be deregistered by 2017, and resistance having been reported in some areas for the other (chlorpyrifos). To screen for chemistries to replace these organophosphates, and obtain efficacy data comparable between key vegetable brassica production areas in Canada, four small plot field studies were conducted concurrently in British Columbia, Saskatchewan, Ontario, and Quebec in 2009. These studies followed standardized protocols for seeding, application of insecticide drenches, sampling and damage assessment, and generally tested the same products. Of the insecticides evaluated, none provided maggot control comparable with the industry standard, chlorpyrifos. However, cyantraniliprole (Cyazypyr 200SC; registered in 2015 as Verimark) applied at 3 g AI (15.0 ml product)/100 m row of seeded rutabagas consistently provided the next highest reduction in % culls, suggesting the efficacy of this chemical may be improved if used at higher rates. The results of these studies are discussed in the context of current literature on D. radicum management in rutabaga. Future management strategies are also discussed, including a transplant plug treatment approach for increasing the dosage per plant and efficacy of chemistries such as Cyazypyr 200SC in the field.

Predation of Thereva nobilitata (Fabricius) (Diptera: Therevidae) on Agriotes obscurus L. (Coleoptera: Elateridae).

Little is known about the natural enemies of wireworms (Coleoptera: Elateridae), but there are frequent anecdotal reports of (usually unnamed) stiletto fly larvae (Diptera: Therevidae) preying on various species. We observed larvae of Thereva nobilitata (Fabricius) feeding on larvae of the dusky wireworm, Agriotes obscurus L., during the summer of 2011, in Agassiz, British Columbia. This finding is of interest as: both the predator and the wireworm are introduced species to this area from Europe; T. nobilitata is uncommon in North America; and this predator has not been associated with any wireworm species previously. We observed that larvae of male and female T. nobilitata will feed on various sizes of A. obscurus larvae, most feeding being carried out by the smallest T. nobilitata larvae. These findings suggest future work should assess the potential for therevid larvae as top‐down regulators of Agriotes larvae under field conditions.

Blending of pheromone lures for two exotic European pest elaterid beetles

Abstract Two exotic European click beetle species, Agriotes obscurus and Agriotes lineatus, were introduced into the lower Fraser valley of British Columbia over a century ago, and are now predominant pests of a number of arable crops. A semiochemical-based method of monitoring both species has been developed as a part of an integrated pest management plan, and there is interest in mass trapping with pheromones as a management tool. A. obscurus females produce primarily geranyl octanoate (G8) and geranyl hexanoate (G6), while A. lineatus females produce both G8 and geranyl butanoate (G4). The current studies examined the possibility of using a blend of G8, G6, and G4 components in a single lure to trap both species simultaneously. A blended G8, G6 and G4 lure in a 1:1:1 ratio was, on average, 1.42 times more attractive to A. lineatus males than standard A. lineatus pheromone lures, but caught only 0.24 times the number of A. obscurus in standard A. obscurus traps. Blended traps, therefore, are effective for monitoring and mass trapping of A. lineatus, but only for detection of A. obscurus.

Wireworm and Flea Beetle IPM in Potatoes in Canada: Implications for Managing Emergent Problems in Europe

Three species of wireworms (Coleoptera: Elateridae) known to cause severe damage to potatoes in Europe and Asia have been introduced to Canada and are now well established as pests in the westernmost province of British Columbia (BC) (Agriotes obscurus and A. lineatus) and the eastern provinces of Nova Scotia and Prince Edward Island (A. obscurus, A. lineatus and A. sputator). Conventional insecticide-based efforts to control these invasive pests have had serious environmental impacts, or are failing to prevent severe economic damage from occurring to potatoes in some key potato production areas. Research toward developing an IPM programme for these exotic species has been completed or is underway in Canada, including the following: biological and ecological studies, development of monitoring and risk assessment programmes, and development of insecticidal and alternative control strategies. This research is summarized and implications for wireworm management in Europe are discussed. In addition to wireworms, one of the primary economic insect pests of potatoes in BC is the tuber flea beetle, Epitrix tuberis (Coleoptera: Chrysomelidae). The larvae of this beetle feed on developing or mature daughter tubers, producing surface channels or tracks and holes directly into the tuber. In the past, growers would apply 7–10 foliar sprays of broad-spectrum insecticides per growing season, which was not always successful in controlling this pest. In the EU, a newly identified flea beetle, Epitrix papa sp. n., as well as the North American species, E. cucumeris, have been identified as attacking potatoes initially in Portugal (2004) and later also in Spain. The potential spread of these emergent pests to various EU and non-EU countries is of concern, and if established would require the development of management strategies. The former development of a highly effective IPM programme developed in BC for E. tuberis is discussed, as is its potential for E. papa and E. cucumeris management in Europe.

Wireworm in Quebec Field Crops: Specific Community Composition in North America

Abstract Wireworms are important economic pests that attack the seeds and roots of numerous vegetable and field crops worldwide. A 5-yr study was conducted in the main agricultural regions of the province of Quebec (Canada), to identify and characterize the wireworm communities (Coleoptera: Elateridae) that occur in fields planted with economically important crops (maize, soybean, cereals, canola, and grasslands). Bait traps were used to collect wireworms each spring from 2011 to 2015. More than 600 sites were sampled in total, involving ca. 14,000 traps. Wireworms were found in 69% of the sites and 73% of the traps. A total of 6,014 wireworms were collected and identified to genus, or to species when possible. The results show that nine genera occur in Quebec and that Hypnoidus abbreviatus (Say) is currently the most abundant species in arable land in Quebec, representing 72% of all collected wireworms. The other genera collected were Melanotus (8% of all wireworms collected), Ampedus (7%), Limonius (6%), and Agriotes (4%). Wireworms from the genera Aeolus, Dalopius, Hemicrepidius, and Oestodes constituted ca. 3% together. The predominance of H. abbreviatus appeared to be specific to Quebec compared with the other Canadian provinces and the rest of North America. We observed differences in the relative abundance of wireworm genera among the agricultural regions sampled. However, no effect of current and preceding crops was observed in this study. Our results suggest that integrated pest management strategies for managing wireworms in Quebec fields should take into consideration the species present in each agronomical region.