Categorization and numerical assessment of wireworm mobility over time following exposure to bifenthrin

We discuss the effect of the pyrethroid insecticide bifenthrin incorporated into soil at 100, 200, and 300 g AI/ha on late-instar larvae of the dusky wireworm, Agriotes obscurus (Coleoptera: Elateridae), and present a method of assessing wireworm health and mobility over time. Wireworms became moribund within 1 h of placement in soil amended with bifenthrin at all rates. After 2 weeks of morbidity in amended soils, wireworms recovered within 7 days of being placed in clean soil. A considerable proportion (0.13–0.93) of wireworms placed in amended soil moved to the soil surface and remained there for 2 weeks or more in a moribund state; wireworms transferred to clean soil no longer moved to the soil surface. Eight distinct mobility categories were observed and are described, and a new method for assessing wireworm health and mobility over time is discussed.     

Crop protection and mortality of Agriotes obscurus wireworms with blended insecticidal wheat seed treatments

In Canada, as in much of the northern hemisphere, insecticidal seed treatments for cereals that both protect crops from damage by wireworms (Coleoptera: Elateridae) and actually reduce wireworm populations to sub-economic levels are lacking. Thiamethoxam and fipronil applied alone or in combination as wheat seed treatments were evaluated in field studies between 2006 and 2008 in protecting wheat from damage and reducing populations of resident and neonate wireworms. Thiamethoxam alone applied at 5 or 10 g a.i./100 kg seed provided adequate wheat stand and yield protection, but did not significantly reduce Agriotes obscurus wireworm populations. Fipronil alone at 5–50 g a.i./100 kg seed provided adequate wheat stand and yield protection, and also killed significant numbers of both resident and neonate wireworms. Thiamethoxam (10 g a.i.) was initially combined with fipronil at 50, 5, 0.5, 0.05, and 0.005 g a.i./100 kg seed, and subsequently with a delimiting range of fipronil at 50, 5, 1, 0.5, and 0.1 g a.i. Blends of thiamethoxam (10 g a.i.) + fipronil at rates of 50, 5, or 1 g a.i. provided stand and yield as good or better than the former industry standard Vitavax Dual (containing lindane). Combinations of thiamethoxam (10 g a.i.) + fipronil at rates of 50, 5, 1, and 0.5 g a.i. had very low numbers of resident or neonate wireworms relative to the untreated check and were comparable to the Vitavax Dual standard. The benefit of combined thiamethoxam + fipronil seed treatments at these rates, is that crop stand and yield are improved over the individual chemicals applied alone, and resident and neonate wireworm mortality is high. The large reductions in resident and neonate wireworms observed with these combined seed treatments would remove the economic threat of wireworms in fields for 3+ years with rates of insecticides much lower than the formerly used Vitavax Dual.     

Wireworm damage to wheat seedlings: effect of temperature and wireworm state

We describe the results of four laboratory studies designed to measure the effect of temperature and wireworm appetence, weight, and degree of Metarhizium infection on their ability to damage wheat seedlings. Wireworm activity, measured from wireworm speed, increased linearly from 6 to 18 °C and leveled off thereafter. Plant emergence and growth increased exponentially from 6 to 22 °C for wheat cultivars AC Barrie and AC Unity VB. Plant root:shoot ratio at Zadoks 13 was highest at 14 °C and lowest at 22 °C for AC Barrie. Wireworm weight and degree of infection with Metarhizium did not affect their ability to kill wheat seedlings, but wireworms in a feeding state caused significantly more damage than those in a non-feeding state when wheat was grown at 10, 14, 18, and 22 °C. Wireworms (ww) in a feeding state destroyed 1.8 seedlings/ww in 14 days at 22 °C if there were 1 or 2 wireworms in a pot, and 1.5 seedlings/ww if there were 4 wireworms in a pot. If 5 wireworms were placed in a pot, wireworms in a feeding state destroyed 0.3, 1.0, 0.9, 1.3, and 1.4 seedlings/ww in 46, 32, 25, 25, and 25 days at 6, 10, 14, 18, and 22 °C, respectively. Wireworm mortality from Metarhizium during 60 days of containment in pots in the study was higher in non-feeding than in feeding wireworms, and higher if wireworms were selected from a Metarhizium-infected colony than those selected from a non-infected colony. Some of the implications of these results for wireworm management and laboratory trials are discussed.     

Response of the dusky wireworm, Agriotes obscurus (Coleoptera: Elateridae), to residual levels of bifenthrin in field soil

To determine if bifenthrin residues elicit morbidity and surfacing behavior in wireworms, larvae of the dusky wireworm, Agriotes obscurus (Coleoptera: Elateridae) were placed in field soil treated with the pyrethroid insecticide bifenthrin ~1 year previous. Morbidity was immediate and lasted as long as wireworms remained in the soil, disappearing quickly after transfer to clean soil. In 2009, field soil treated 336 days previous with bifenthrin at 340 g AI/ha elicited morbidity symptoms similar to that elicited by soil freshly amended with bifenthrin at 100 g AI, and analysis of the field soil confirmed residual levels of bifenthrin exceeding 100 g AI/ha. In 2010, wireworms placed in field soil treated 343 days previous with bifenthrin at 100, 200, and 300 g AI/ha responded as in 2009, with the degree of morbidity increasing with the rate of insecticide, and with wireworms in a non-feeding state more affected than those in a feeding state at each rate. In both 2009 and 2010, moribund wireworms moved to the soil surface within 1 day of placement in the soil containing residual bifenthrin and remained there until reburied, after which they often resurfaced. To confirm that the bifenthrin residues elicited repellency, wireworms were placed in soil window bioassays containing field soil with residual bifenthrin. Wireworms behaved markedly different upon contacting soil containing the residues than when exposed to untreated soil, both in the presence and absence of an attractant, but were less likely to avoid soil containing residual bifenthrin when attracted by wheat seedlings placed inside it.     

Preliminary investigations into the use of trap crops to control Agriotes spp. (Coleoptera: Elateridae) in potato crops

A field trial was conducted to investigate the use of peas (Pisum sativum cv. Valverde), wheat (Triticum aestivum cv. Capo) and oilseed radish (Raphanus sativus var. oleiformis cv. Adagio) as trap crops to control wireworm in potato fields. We investigated the efficacy of trap crops and distance of attraction by counting larvae in both potato and trap crop rows. Wireworms of the genera Agriotes, Adrastus and Hemicrepidius were observed. In the plots planted with peas as a trap crop, significantly more wireworms were observed than in the other treatments, which was clearly due to the influence of the trap crop pea. The potato rows 0.75 m away from the peas showed 2.4 times more larvae than the potato rows 1.5 m away. This may be due to a decrease of the peas’ attractiveness over time (Miles and Petherbridge 1927), with wireworms that were initially attracted to the peas moving back to the nearby potatoes. In the plots planted with wheat, oilseed radish and the control (bare soil instead of a trap crop), there was no significant difference in numbers of larvae between the potato rows. In the control plots, significantly more larvae were found in the potato rows than in the bare soil. We assessed the damage to potato tubers by weighing them and counting the wireworm holes. Our results indicate that peas are more attractive to wireworms than potatoes and might be an effective trap crop if the right timing and spacing relative to the potatoes is found.     

A survey of microbial antagonists of Agriotes wireworms from Germany and Italy

Wireworms of the genus Agriotes (Coleoptera: Elateridae) are severe and widespread agricultural pests affecting numerous crops throughout the world and causing damage of economic importance. Between 2008 and 2011, a survey of the occurrence of natural microbial antagonists of wireworms was conducted. Altogether, 3,420 wireworms and two dead beetles from agricultural habitats and grassland of various parts of Germany and 700 lab-reared wireworms from Italy were screened for the presence of disease. Of these, 283 selected dead and moribund Agriotes specimens were diagnosed by light and electron microscopy for insect pathogens; 66 wireworms contained unspecified bacterial infections; and 86 specimens displayed fungal growth with 25 infected by the entomopathogenic taxa Beauveria bassiana, Metarhizium anisopliae, Isaria fumosorosea, Isaria spp. and Lecanicillium sp. Nematodes were observed in 29 dead individuals, and 141 individuals showed no distinguishable pathogens. In one dead Agriotes larva, an intracellular bacterium was identified as a new Rickettsiella pathotype named ‘Rickettsiella agriotidis’. The survey resulted in a natural infection rate of 0.66 %. The possible use of these pathogens as biocontrol agents is discussed.     

Validation of a sequential sampling plan for wireworms (Coleoptera: Elateridae) at sugarcane planting

Wireworms in Florida are primarily a pest in newly planted sugarcane, and growers usually apply a soil insecticide at planting to protect germinating seedpieces from wireworm damage. However, studies have suggested that this application in many cases may not be necessary. The objective of this research was to test a sequential sampling method to determine the need for soil insecticide at sugarcane planting. Testing was conducted on fields located on King Ranch near South Bay, Florida. Wireworm samples were taken in a transect across the length of each field. We used an economic injury level of nine or more wireworms per 25 samples. Sugarcane yield parameters for each whole field were obtained through standard commercial harvesting procedures. Using our sampling method, 38 fields were judged as not needing insecticide application. There was no significant difference in yield in these fields with versus those without insecticide application.     

The molecular identification and genetic diversity of economically important wireworm species (Coleoptera: Elateridae) in Canada

Click beetle larvae (wireworms) are significant crop pests in Europe and North America. In Canada, there are ~30 economically important species which are morphologically difficult to identify, but for which sequence data are lacking. Accurate knowledge of damage-causing species and the population genetics and phylogeography of elaterids will provide insight into their sustainable management. Here, we use interspecific variation in mitochondrial 16S rRNA as a robust method of identification, consider the intra- and interspecific genetic variation of some important Canadian wireworm pests and assess the genetic structure and isolation by distance for a re-emerging major pest species, Hypnoidus bicolor Eschscholtz. Wireworms were sampled from Canada and the USA, identified as morphospecies, and sequenced at the 16S rRNA region (294–442 bp). Within some species unusually high intraspecific genetic distances between samples suggested the possibility of cryptic wireworm species or misidentifications, though this was <1 % for most species. Phylogenetic analyses gave some indication of the likely identity of these ambiguous samples. There was a significant correlation between genetic and geographic distance and significant genetic structuring within and between H. bicolor populations, which appeared to be composed of two species comprising several haplotypes. These data provide a starting point for determining the distribution of damage-causing species throughout Canada. The inclusion of data from other nuclear and mitochondrial loci, and use of sequence data from known adult samples, would further aid identification and relationships of wireworm species.     

IPM thresholds for Agriotes wireworm species in maize in Southern Europe

Currently, integrated pest management (IPM) of wireworms is not widespread in Europe. Therefore, to estimate the densities of three major wireworm species in southern Europe (Agriotes brevis Candeze, A. sordidus Illiger, and A. ustulatus Schäller), bait traps were deployed pre-seeding in maize fields in north-eastern Italy between 1993 and 2011. Research discovered that there was a significant correlation between all three wireworm species caught in the bait traps and damage to maize plants, but damage symptoms varied. Wherever A. ustulatus was the main species caught, there was no significant damage to maize plants, but seeds were damaged. Most of the symptoms caused by A. brevis and A. sordidus were to the central leaf/leaves, which wilted because of feeding on the collar. A. brevis was the most harmful species; when more than one A. brevis wireworm was caught per trap, plant damage sometimes resulted in reduced yield. Five A. ustulatus larvae per trap caused the same damage to maize as one A. brevis. A. sordidus came second (threshold two larvae/trap). These thresholds are reliable for: (1) bare soil in which there are no alternative food sources; (2) average soil temperature 10 cm beneath the surface of above 8 °C for 10 days; (3) soil humidity near to field water capacity, but days of flooding have not been considered. The implementation of the practical method described herein may lead to effective IPM of wireworms in maize and to a significant reduction in the number of fields treated with soil insecticides.     

筛胸梳爪叩甲监测技术及应用

正害虫预测预报是进行害虫风险评估及制定防治决策的基础,使用有效的监测技术能准确地预测林间害虫发生的时间、种群动态等重要参数,可为害虫防治指标的确定和综合防治措施的实施提供参考依据。当前,我国已有近百种重要害虫建立了系统的监测技术[1]。金针虫是鞘翅目(Coleoptera)叩甲科(Elateridae)昆虫幼虫的通称,广布于世界各地,是一种极为重要的地下害虫[2-3]。金针虫隐蔽性强,且能随环境变化改变活动及危害深度,其虫口密度     

Wireworm damage reduction in potatoes with an attract-and-kill strategy using <Emphasis Type="Italic">Metarhizium brunneum</Emphasis>

Innovative wireworm control strategies are required to implement integrated pest management on the basis of the (EC) No regulation 1107/2009 and Directive 2009/128/EC. Entomopathogenic fungi, such as Metarhizium brunneum (Metschnikoff) Sorokin, are potential biological control agents for wireworm control but do not achieve high control efficacies in the field when applied as a conidia suspension. In a 2-year study, wireworm control with a novel attract-and-kill strategy aimed at enhancing M. brunneum efficacies in organic potato production systems in Lower Saxony, Germany. The approach is based on the attraction of wireworms (Agriotes spp. Eschscholtz) towards an artificial carbon dioxide-emitting source, using baker’s yeast (Saccharomyces cerevisiae Meyen ex Hansen) in combination with M. brunneum conidia for wireworm infection. Both components were encapsulated in alginate as a carrier material and applied in a mixture with two types of beads (one for encapsulated yeast and one for M.brunneum conidia). An application of these beads within the potato rows during potato planting reduced wireworm tuber damage by 37–75% relative to the untreated control and was able to enhance the efficacy of M. brunneum by up to 35% through an attract-and-kill approach compared to beads without a carbon dioxide source only. This strategy offers a high potential to promote biological wireworm control as an alternative to insecticide use by potentially reducing the inoculum compared to an inundate M. brunneum conidia release strategy.     

Relative influence of climate and agroenvironmental factors on wireworm damage risk in maize crops

A large-scale survey was carried out in 336 French fields to investigate the influence of soil characteristics, climate conditions, the presence of wireworms and the identity of predominant species, agricultural practices, field history and local landscape features on the damage caused by wireworms in maize. Boosted regression trees, a statistical model originating from the field of machine learning, were fitted to survey data and then used to hierarchize and weigh the relative influence of a large set of variables on the observed damage. Our study confirmed the relevance of an early assessment of wireworm populations to forecast crop damage. Results have shown that climatic factors were also major determinants of wireworm damage, especially the soil temperature around the sowing date, with a strong decrease in damage when it exceeds 12 °C. Soil characteristics were ranked third in importance with a primary influence of pH, but also of organic matter content, and to a lesser extent of soil texture. Field history ranked next; in particular, our findings confirmed that a long-lasting meadow appeared favourable to wireworm damage. Finally, agriculture practices and landscape context (especially the presence of a meadow in the field vicinity) were also shown to influence wireworm damage but more marginally. Overall, the predicted damage appeared highly correlated with the observed one allowing us to produce the framework of a decision support system to forecast wireworm risk in maize crop.     

Physical exclusion of adult click beetles from wheat with an exclusion trench

Click beetles, the adult stage of wireworms, will enter fields of their preferred hosts (i.e., grasses, pasture, and cereals) from various reservoir habitats, and lay eggs which give rise to wireworm problems in subsequent years. To prevent click beetles, Agriotes obscurus, from immigrating into fields, a portable trench barrier composed of an extruded, PVC plastic trough was evaluated in 2001 in Agassiz, British Columbia, Canada. Plots of wheat or bare ground that were surrounded by trenches had significantly lower numbers of males in pheromone traps and females in pitfall traps relative to non-trenched plots. Exclusion was more pronounced in the first part of the study (about 75 % reduction) than later in the study (30–42 %), likely due to gradual within plot emergence of overwintered beetles and/or flight activity. The potential for use of exclusion devices for click beetle control and future directions for research are discussed.     

Correlations between wireworm damages in potato fields and landscape structure at different scales

Wireworms, the larvae of click beetles are world-wide pests of arable and vegetable crops. Many studies have shown that arthropods are influenced by landscape context. Therefore, for successful wireworm risk assessment, it is important to gain more information on relationships between landscape structure and wireworm infestation level. The aim of this study was to investigate if different landscape variables are related to wireworm infestation, represented by the proportion of wireworm damaged potato tubers. Based on aerial photographs and field surveys landscape variables, such as landscape composition, landscape complexity and ecological variables were characterised around 14 randomly selected potato field plots alongside the gradient from the lower warm-dry “Weinviertel” (region 1) to the cool-humid “Waldviertel” (region 2) in the North-East of Austria at three scales (1, 9 and 25 ha). Relationships between landscape variables and wireworm damage ratings were described by Spearman correlations coefficients. Our results showed that wireworm damage was higher in region 2 than in region 1 and tended to be higher in soils with higher sand content. Among the tested landscape variables only landscape composition, especially grassy field margins were significantly positively correlated with wireworm damage at the 25 ha scale. In areas with high proportion of such grassy habitats, farmers should pay more attention to field characteristics, such as sand content in soil, and management, like crop rotation. Further investigations on appropriate management regimes for grassy landscape elements suppressing wireworm populations but ensuring the maintenance of natural pest control should be conducted.     

Occurrence of Agriotes wireworms in Austrian agricultural land

Agriotes wireworms (Coleoptera: Elateridae) are abundant soil-dwelling herbivores which can inflict considerable damage to field crops. In Europe up to 40 species occur, differing in their ecology and pest status. Their distribution in the larval stage, however, has rarely been assessed because of the considerable effort in collecting wireworms and the difficulties in identifying them to species-level. Here, we examined the occurrence of Agriotes wireworms in Austrian agricultural land with regard to their association with climatic and soil parameters. Using a molecular identification system, 1348 field-collected larvae from 85 sites were identified to species-level. Three species, Agriotes obscurus, Agriotes brevis, Agriotes ustulatus, and two that could not be discerned molecularly (Agriotes lineatus and Agriotes proximus), were assigned to two ecological groups: (i) A. brevis/A. ustulatus, found in areas with a warmer, drier climate and alkaline soils, and (ii) A. obscurus/A. lineatus/proximus which occur mainly at higher altitude characterised by lower temperatures, higher precipitation and acidic, humus-rich soils. Agriotes sputator was abundant throughout Austria, confirming its euryoecious nature. Only one larva of Agriotes litigiosus was found, prohibiting further analysis. These data contribute to a characterisation of species-specific traits in Agriotes larvae in agricultural land, an important prerequisite to develop efficient control strategies for these wireworms.     

Drought effects on water use efficiency, freezing tolerance and survival of Eucalyptus globulus and Eucalyptus globulus × nitens cuttings

Genetic improvement of Eucalyptus genotypes for drought and frost resistance is essential for successful intensive management of commercial plantations. Understanding the physiological mechanisms that relate water use and frost resistance for highly deployed genotypes may allow for better prediction of their future performance, genetic selection and seedling management for site specific purposes. We studied whether instantaneous water use efficiency (WUE _i ) may serve as drought, freezing and photoinhibition tolerance predictor by studying its response on six E. globulus clones (Eg1–Eg6) and four E. globulus × E. nitens hybrid seedlings (Egn1–Egn4) under drought and irrigated (control) treatments. Net photosynthesis (A) and transpiration (E) were studied using a gas exchange system in order to calculate WUE _i (A/E). Simultaneous chlorophyll a fluorescence measurements were performed to assess the non photochemical quenching components. Frost tolerance of plants under control and drought treatments were evaluated by measuring temperatures that exert 50% photoinactivation of photosystem II. Finally, drought tolerance was evaluated by plant survival within each genotype after rehydration. Our results showed significant genotype variability in the rate of soil and xylem water potential decrease during drought. While most of the genotypes reached ?4.0 MPa in about 35 days of drought, genotypes Eg6 and Egn4 required 56 days of drought to reach this xylem water potential. WUE _i exhibited significant differences among genotypes and irrigation treatments. Genotypes Eg5 and Egn4 increased their WUE _i between 70 and 80% after drought. This was associated with a more conservative control of water loss at the stomatal level combined with maintenance of relatively higher rates of net photosynthesis than the other genotypes under drought conditions. Plants exposed to drought were more freezing tolerant than control plants, having in average 3°C lower LT₅₀ than well irrigated ones. There was no a clear correlation between WUE _i and drought tolerance or drought-induced photoinhibition, however WUE _i was inversely correlated with LT₅₀. Our results suggest that WUE _i is not suitable by itself to select drought tolerant genotypes, but may provide evidence for discarding drought sensitive genotypes. In addition, it could provide valuable information to select for freezing tolerance.     

Foraging wireworms are attracted to root-produced volatile aldehydes

Soil-dwelling insects are known to react to chemical cues they encounter in the rhizosphere. Whether wireworms (Coleoptera, Elateridae) use root-emitted volatile organic chemicals to localize their host plant remains, however, poorly understood. Here, we aimed at identifying chemical cues released by barley roots that attract Agriotes sordidus. In a first behavioral experiment, we assessed the ability of wireworms to orient towards live barley roots, using dual-choice olfactometers suitable for belowground insects. Then, we collected the volatile organic compounds (VOC) produced by barley roots using a dynamic head-space sampling approach. VOC were quantified and identified using gas chromatography—mass spectrometry (GC–MS). The odorant blend is composed of four aldehydes, namely hexanal, (E)-hex-2-enal, (E)-non-2-enal, and (E,Z)-nona-2,6-dienal. In a second set of dual-choice bioassays, wireworms were attracted towards a synthetic blend of these four major compounds. However, the synthetic blend was not as attractive as live roots, which is partially explained by the absence of CO₂, commonly known as a strong attractant for soil-dwelling insects. While CO₂ indicates the presence of living material in the vicinity, we hypothesize that additional VOC inform about the plant suitability. A better understanding of these belowground signals would contribute to the development of new integrated control strategies against wireworms.     

金针虫控制技术及其研究进展

金针虫是一类重要地下害虫,其控制技术一直是植物保护工作的难点.文章从作物栽培管理、生物防治、土壤处理、化学防治及成虫诱杀5个方面综述了国内外金针虫控制技术的研究现状及进展,并提出了在金针虫不同发育阶段协调多种控制手段的综合治理策略.     

Similar carbon density of natural and planted forests in the Lüliang Mountains,China

Key message

The carbon density was not different between natural and planted forests, while the biomass carbon density was greater in natural forests than in planted forests. The difference is due primarily to the larger carbon density in the standing trees in natural forests compared to planted forests (at an average age of 50.6 and 15.7 years, respectively).

Context

Afforestation and reforestation programs might have noticeable effect on carbon stock. An integrated assessment of the forest carbon density in mountain regions is vital to evaluate the contribution of planted forests to carbon sequestration.

Aims

We compared the carbon densities and carbon stocks between natural and planted forests in the Lüliang Mountains region where large-scale afforestation and reforestation programs have been implemented. The introduced peashrubs (Caragana spp.), poplars (Populus spp.), black locust (Robinia pseudoacacia), and native Chinese pine (Pinus tabulaeformis) were the four most common species in planted forests. In contrast, the deciduous oaks (Quercus spp.), Asia white birch (Betula platyphylla), wild poplar (Populus davidiana), and Chinese pine (Pinus tabulaeformis) dominated in natural forests.

Methods

Based on the forest inventory data of 3768 sample plots, we estimated the values of carbon densities and carbon stocks of natural and planted forests, and analyzed the spatial patterns of carbon densities and the effects of various factors on carbon densities using semivariogram analysis and nested analysis of variance (nested ANOVA), respectively.

Results

The carbon density was 123.7 and 119.7 Mg ha^?1 for natural and planted forests respectively. Natural and planted forests accounted for 54.8% and 45.2% of the total carbon stock over the whole region, respectively. The biomass carbon density (the above- and belowground biomass plus dead wood and litter biomass carbon density) was greater in natural forests than in planted forests (22.5 versus 13.2 Mg ha^?1). The higher (lower) spatial carbon density variability of natural (planted) forests was featured with a much smaller (larger) range value of 32.7 km (102.0 km) within which a strong (moderate) spatial autocorrelation could be observed. Stand age, stand density, annual mean temperature, and annual precipitation had statistically significant effects on the carbon density of all forests in the region.

Conclusion

No significant difference was detected in the carbon densities between natural and planted forests, and planted forests have made a substantial contribution to the total carbon stock of the region due to the implementation of large-scale afforestation and reforestation programs. The spatial patterns of carbon densities were clearly different between natural and planted forests. Stand age, stand density, temperature, and precipitation were important factors influencing forest carbon density over the mountain region.