Wireworm (Coleoptera: Elateridae) Species Composition and Management in Sweet Potato Grown in North Florida Using Chemical Insecticides and Entomopathogenic Nematodes

Wireworms are immature stages of click beetles (Coleoptera: Elateridae) and are considered a serious threat to sweet potato production in the southern United States. The major wireworm species collected in North Florida sweet potato fields in 2017 and 2018 were Conoderus scissus, C. rudis, C. amplicollis, and C. falli. These species vary in their behavior and biology. During a 2-yr study period, we conducted two insecticide field trials using eleven insecticides belonging to organophosphates, neonicotinoids, pyrethroids, and botanical classes, and three field trials using entomopathogenic nematode (EPN) species to control wireworms. In 2017, all insecticide treatments significantly reduced new feeding holes and total holes (old + new + other) as compared to the untreated control. In 2018, the result was similar with a few variations. In both years, all insecticides showed a percentage reduction in wireworm damage holes (2017: 34.88–96.19%; 2018: 12.38–97.02%) with the highest by Regent. In the EPN field study, one application of EPN near planting significantly reduced soil insects. In a laboratory study conducted at the Tropical Research and Education Center, UF-IFAS, chlorpyrifos caused higher percentage mortality of C. rudis (55.5%) than C. scissus (22.2%). At the present experiment rates, none of the insecticides caused the mortality of C. amplicollis. Heterorhabditids strain ‘FL-2122’ was more susceptible to chlorpyrifos than other strains of EPN.

Entomopathogens in conjunction with imidacloprid could be used to manage wireworms (Coleoptera: Elateridae) on spring wheat

We examined the effect of biopesticides used alone, mixed with other biopesticides, or in conjunction with an imidacloprid against wireworms (Coleoptera: Elateridae) in spring wheat Triticum aestivum Linnaeus (Poaceae) (variety: Duclair). The study was conducted at Ledger and Valier, Montana, United States of America in 2015 and 2016. Ten biopesticides (spinosad, azadirachtin, pyrethrin, Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Fungi: Clavicipitaceae) GHA (Mycotrol), B. bassiana ANT-03 (BioCeres), Chromobacterium subtsugae Martin et al. (Bacteria: Neisseriaceae), Burkholderia Yabuuchi et al. (Burkholderiaceae) species, Metarhizium brunneum Petch (Fungi: Clavicipitaceae) ESC1 (MbESC1), and M. brunneum F52 (MetF52) as microsclerotial and corn grit-based granules) were tested in addition to thimet and imidacloprid. Treatment efficacy was based on plant stand protection, wireworm populations, and yield. In 2015, there was considerable variation between sites in treatment efficacy. Mycotrol, BioCeres, MetF52+spinosad, and MetF52+imidacloprid applications protected seedlings from wireworm damage better than the control at Ledger, while only MetF52 at Valier. Wireworm populations were significantly higher with Mycotrol, spinosad, MetF52+spinosad, MbESC1 (25 g/L), and MetF52 treatments, compared with control, at 14 and 28 days post application at Ledger, but without effect at Valier, 2015. We found significantly higher yield in plots treated with imidacloprid+MetF52 and Mycotrol+azadirachtin (Xpulse) compared with control at Ledger. In 2016, no significant treatment effects were observed at either site. In summary, this study provides insight on what treatments should be explored in more detail despite variable results.

Potential Application of Pheromones in Monitoring, Mating Disruption, and Control of Click Beetles (Coleoptera: Elateridae)

Wireworms, the larvae stage of click beetles (family, Elateridae), are serious soil dwelling pests of small grain, corn, sugar beet, and potato crops globally. Since the 1950s, conventional insecticides such as lindane provided effective and inexpensive protection from wireworms, and little integrated pest management research (IPM) was conducted. The removal of these products from the agricultural market, particularly Lindane, has resulted in increasing levels of wireworm damage to small grain, corn, and potato crops. The wireworm damage has become an increasing problem for growers, so the demand for a meaningful risk assessment and useful methods to restrict damage is increasing. However, due to the cryptic habitat of the wireworms, pest control is very difficult and leads to unsatisfying results. The prospective appropriateness of sex pheromone traps for employing management strategies against wireworm’s populations was first suggested with experimentation in Hungary and Italy. Simultaneously, considerable work has been done on the identification and use of pheromone traps to monitor population of click beetles. The work has been mostly done in European and former Soviet Union countries. For this paper, we reviewed what work has been done in monitoring the click beetle which was considered as pests and how the pheromones can be used in IPM to monitor and control wireworms/click beetles. Also, the possibilities of using the pheromone-baited traps for mating disruption and control tested in the fields were summarized.

Control of Tobacco Wireworms with Spring Applications of Lorsban, 1997

The objective of this experiment was to evaluate the efficacy of broadcast, ppi Lorsban 4 E and Mocap 6 EC against tobacco wireworms in the field. Plots were established at the Border Belt Tobacco Research Station, Whiteville, NC, on 30 Apr in a field with a Norfolk loamy sand soil. Individual plots were 4 rows (1.14 m apart) wide by 22 plants (ca. 13.7 m) long and were arranged in a RCB design with 3 treatments (untreated check included) and 4 blocks. On 24 Apr, the foliar materials were applied using a COz-powered backpack sprayer fitted with Spraying Systems flat-fan nozzles, 20" apart on a 6.7" boom at 30 psi and 25 gpa. Tobacco was transplanted on 30 Apr with a single-row transplanter. At 20 days after transplanting, 10 plants from rows 2 and 3 were pulled and rated for damage. Wireworm damage ratings were subjected to ANOV and WD, K = 100, was used to separate treatment means.

Seasonal Abundance and Mathematical Distribution of Wireworms and Wireworm Feeding Damage in Sweet Potato

Seasonal abundance and spatial distribution of wireworm feeding damage were determined for sweet potato by examining storage roots. Spatial distribution of wireworms was determined by sampling corn-wheat seed baits. Wireworm feeding damage (deep, shallow and healed holes) increased as the season progressed. The distribution of wireworms in sweet potato fields was clumped as was feeding damage distribution. The spatial distribution of wireworm damage on sweet potato roots fits the negative binomial distribution. Values for the negative binomial parameter k for two fields indicated a clustered distribution of wireworm feeding damage. Greater k-values for healed feeding damage and total feeding damage than for deep and shallow feeding damage indicate that sample size could be adjusted, depending on seasons, to achieve optimal sampling efficiency. As feeding damage can predict wireworm populations, a sampling strategy based on early-season wireworm damage data is particularly timely, efficient and economical for evaluating wireworm damage data.