Wireworm (Coleoptera: Elateridae) genomic analysis reveals putative cryptic species, population structure, and adaptation to pest control

Pest Elaterids of North America: New Insights and Opportunities for Management

The larval stages of click beetle (Coleoptera: Elateridae) species, several of which are serious agricultural pests, are called wireworms. Their cryptic subterranean habitat, resilience, among-species differences in ecology and biology, and broad host range, as well as the lack of objective economic injury thresholds, have rendered wireworms a challenging pest complex to control. Significant progress has been made in recent years, introducing a new effective class of insecticides and improving species identification and our understanding of species-specific phenology, chemical ecology (i.e., adult sex pheromones and larval olfactory cues), and abiotic and biotic factors influencing the efficacy of biological control agents. These new developments have created opportunities for further research into improving our risk assessment, monitoring, and integrated pest management capabilities.

Cryptic diversity begets challenges and opportunities in biodiversity research

How many species of life are there on Earth? This is a question that we want to know but cannot yet answer. Some scholars speculate that the number of species may reach 2.2 billion when considering cryptic diversity and that each morphology-based insect species may contain an average of 3.1 cryptic species. With nearly two million described species, such high estimates of cryptic diversity would suggest that cryptic species are widespread. The development of molecular species delimitation has led to the discovery of a large number of cryptic species, and cryptic biodiversity has gradually entered our field of vision and attracted more attention. This paper introduces the concept of cryptic species, how they evolve, and methods by which they may be discovered and confirmed, and provides theoretical and methodological guidance for the study of hidden species. A workflow of how to confirm cryptic species is provided. In addition, the importance and reliability of multi-evidence-based integrated taxonomy are reaffirmed as a way to better standardize decision-making processes. Special focus on cryptic diversity and increased funding for taxonomy is needed to ensure that cryptic species in hyperdiverse groups are discoverable and described. An increased focus on cryptic species in the future will naturally arise as more difficult groups are studied, and thereby, we may finally better understand the rules governing the evolution and maintenance of cryptic biodiversity.

Global population genetic structure and lineage differentiation of the stable fly, Stomoxys calcitrans

The bloodsucking fly, Stomoxys calcitrans (Diptera: Muscidae), is a cosmopolitan pest that transmits potential pathogens mechanically. We conduct phylogeographic analyses of S. calcitrans to resolve its global population genetic structure for establishing baseline of molecular studies. Results from mitochondrial gene suggested that the major divergence of S. calcitrans predominantly occurred 0.32-0.47 million years ago (Mya) and the subsequent diversifications took place during 0.13-0.27 Mya. The Ethiopian region was deduced as the most likely origin of S. calcitrans and the Nearctic lineages were considered to have originated from Oriental or Palaearctic regions. Our results further revealed that each biogeographic region of S. calcitrans likely maintains its genetic specialty, and yet, those non-monophyletic relationships were possibly caused by ancestral retention, dispersal with mammals, long-distance migration, and the international livestock industries. Moreover, the three highly diverged Ethiopian lineages may be putative cryptic species that require clarification of their veterinary importance. Unravelling the genetic structure of stable fly and preventing gene flow among biogeographic regions through anthropogenic activities are thus pivotal in livestock industry administration, particularly genetic exchange among differentiated lineages that might lead to the consequence of ecological trait alterations.

Cyantraniliprole seed treatment effectively controls wireworms (Pleonomus canaliculatus Faldermann) and white grubs (Anomala corpulenta Motschulsky) in maize fields

Wireworms and white grubs are destructive underground pests in maize fields in China. Cyantraniliprole has good control effect on coleoptera pests. Here, we evaluated the toxicity of cyantraniliprole to the second instar larvae of Anomala corpulenta Motschulsky and third-instar of larvae of Pleonomus canaliculatus Faldermann and the effects of sublethal concentrations on the activity of antioxidant and detoxification enzymes. We also explored the efficacy of cyantraniliprole on underground pests under indoor and field conditions. The LC₅₀ of cyantraniliprole for the third instar larvae of P. canaliculatus was 23.3712 mg/L, and that for the second instar larvae of A. corpulenta was 5.9715 mg/L. Cyantraniliprole can activate the activity of superoxide dismutase (SOD), peroxidase (POD), and glutathione S-transferase (GST) to different degrees at a sublethal dose. According to the pot experiment and the control efficacy test in the field, the indoor control effect of cyantraniliprole seed treatment on P. canaliculatus and white grubs was approximately 80%, and the maximum increase in yield achieved through cyantraniliprole application was approximately 15% in the field efficacy test. Cyantraniliprole has a strong control effect on wireworms and white grubs, so it can be used to treat seeds to control underground pests in maize fields.

Molecular Species Delimitation Using COI Barcodes of Mealybugs (Hemiptera: Pseudococcidae) from Coffee Plants in Espírito Santo, Brazil

Mealybugs are insects belonging to the family Pseudococcidae. This family includes many plant-pest species with similar morphologies, which may lead to errors in mealybug identification and delimitation. In the present study, we employed molecular-species-delimitation approaches based on distance (ASAP) and coalescence (GMYC and mPTP) methods to identify mealybugs collected from coffee and other plant hosts in the states of Espírito Santo, Bahia, Minas Gerais, and Pernambuco, Brazil. We obtained 171 new COI sequences, and 565 from the BOLD Systems database, representing 26 candidate species of Pseudococcidae. The MOTUs estimated were not congruent across different methods (ASAP-25; GMYC-30; mPTP-22). Misidentifications were revealed in the sequences from the BOLD Systems database involving Phenacoccus solani × Ph. solenopsis, Ph. tucumanus × Ph. baccharidis, and Planacoccus citri × Pl. minor species. Ten mealybug species were collected from coffee plants in Espírito Santo. Due to the incorrect labeling of the species sequences, the COI barcode library of the dataset from the database needs to be carefully analyzed to avoid the misidentification of species. The systematics and taxonomy of mealybugs may be improved by integrative taxonomy which may facilitate the integrated pest management of these pests.

Seasonal turnover and insights into the overwintering biology of wireworms (Coleoptera: Elateridae) in the Canadian Prairies

BACKGROUND

The long-lived terricolous larvae of click beetles, colloquially called wireworms, pose a significant threat to agriculture worldwide. Several economically important pest species have been documented in the Canadian Prairies, including Hypnoidus bicolor, Limonius californicus and Hypnoidus abbreviatus. However, most monitoring activities are performed in the early spring and there is evidence from other geographical regions of seasonal shifts in wireworm species composition and prevalence. Further, little is known about the overwintering physiology or behaviors of wireworms, which undoubtedly contribute to their population dynamics.

RESULTS

We surveyed wireworm populations from four Manitoban fields six times throughout the 2020 and 2021 growing seasons. Both Hypnoidus species were active throughout the spring and summer; however, L. californicus did not become active until later in the spring. Chill-coma recovery assays indicated Hypnoidus species recovered quicker than L. californicus from cold acclimation. Vertical migration assays simulating progressively lower ambient temperatures experienced by overwintering larvae identified H. bicolor throughout the soil profile, with L. californicus preferentially found at cooler, shallower depths. We speculate that these differences in species distribution within the soil column are due to the higher levels of putative cryoprotectants (for example, trehalose, sorbitol, glucose, glycerol) in L. californicus, as identified by targeted liquid chromatography tandem mass spectrometry.

CONCLUSION

Our findings of a stark seasonal turnover in wireworm species prevalence and composition in the Canadian Prairies should be incorporated into future integrated pest management and surveillance activities. This study also advances our understanding of wireworm overwintering biology, which should be factored into current management approaches. © 2022 His Majesty the King in Right of Canada. Pest Management Science © 2022 Society of Chemical Industry. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Seasonal and Diel Communication Periods of Sympatric Pest Limonius Click Beetle Species (Coleoptera: Elateridae) in Western Canada

In western North America, sympatric Limonius click beetle species produce limoniic acid [(E)-4-ethyloct-4-enoic acid] as a sex pheromone component (L. canus (LeConte), L. californicus (Mannerheim)) or respond to it as a sex attractant (L. infuscatus (Motschulsky)). We tested the hypothesis that these three congeners maintain species-specificity of sexual communication through nonoverlapping seasonal occurrence and/or contrasting diel periodicity of sexual communication. Using capture times of beetles in pheromone-baited traps as a proxy for sexual communication periods, our data show that L. canus and L. californicus have seasonally distinct communication periods. Most L. canus males (>90%) were captured in April and most L. californicus males (>95%) were captured in May/June/July. As almost exclusively L. infuscatus males were captured in two separate 24-hr trapping studies, with data recordings every hour, it remains inconclusive whether the three Limonius congeners communicate at different times of the day. Males of L. infuscatus responded to pheromone lures only during daytime hours and during the warmest period each day. Captures of L. infuscatus overlapping with those of L. canus in April and those of L. californicus in May/June imply the presence of reproductive isolating mechanisms other than seasonal separation of sexual communication periods.

Signals of adaptation to agricultural stress in the genomes of two European bumblebees

Human-induced environmental impacts on wildlife are widespread, causing major biodiversity losses. One major threat is agricultural intensification, typically characterised by large areas of monoculture, mechanical tillage, and the use of agrochemicals. Intensification leads to the fragmentation and loss of natural habitats, native vegetation, and nesting and breeding sites. Understanding the adaptability of insects to these changing environmental conditions is critical to predicting their survival. Bumblebees, key pollinators of wild and cultivated plants, are used as model species to assess insect adaptation to anthropogenic stressors. We investigated the effects of agricultural pressures on two common European bumblebees, Bombus pascuorum and B. lapidarius. Restriction-site Associated DNA Sequencing was used to identify loci under selective pressure across agricultural-natural gradients over 97 locations in Europe. 191 unique loci in B. pascuorum and 260 in B. lapidarius were identified as under selective pressure, and associated with agricultural stressors. Further investigation suggested several candidate proteins including several neurodevelopment, muscle, and detoxification proteins, but these have yet to be validated. These results provide insights into agriculture as a stressor for bumblebees, and signal for conservation action in light of ongoing anthropogenic changes.

Genome analysis of Phrixothrix hirtus (Phengodidae) railroad worm shows the expansion of odorant-binding gene families and positive selection on morphogenesis and sex determination genes

Among bioluminescent beetles of the Elateroidea superfamily, Phengodidae is the third largest family, with 244 bioluminescent species distributed only in the Americas, but is still the least studied from the phylogenetic and evolutionary points of view. The railroad worm Phrixothrix hirtus is an essential biological model and symbolic species due to its bicolor bioluminescence, being the only organism that produces true red light among bioluminescent terrestrial species. Here, we performed partial genome assembly of P. hirtus, combining short and long reads generated with Illumina sequencing, providing the first source of genomic information and a framework for comparative analyses of the bioluminescent system in Elateroidea. This is the largest genome described in the Elateroidea superfamily, with an estimated size of ∼3.4 Gb, displaying 32 % GC content, and 67 % transposable elements. Comparative genomic analyses showed a positive selection of genes and gene family expansion events of growths and morphogenesis gene products, which could be associated with the atypical anatomical development and morphogenesis found in paedomorphic females and underdeveloped males. We also observed gene family expansion among distinct odorant-binding receptors, which could be associated with the pheromone communication system typical of these beetles, and retrotransposable elements. Common genes putatively regulating bioluminescence production and control, including two luciferase genes corresponding to lateral lanterns green-emitting and head lanterns red-emitting luciferases with 7 exons and 6 introns, and genes potentially involved in luciferin biosynthesis were found, indicating that there are no clear differences about the presence or absence of gene families associated with bioluminescence in Elateroidea.

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.

Genetic diversity of the two-spotted stink bug Bathycoelia distincta (Pentatomidae) associated with macadamia orchards in South Africa

The South African macadamia industry is severely affected by a complex of stink bugs, dominated by the two-spotted stink bug, Bathycoelia distincta Distant (Pentatomidae). This species was first discovered during the spring of 1984 in the Limpopo province. Although considerable effort has been spent trying to manage this pest, it continues to be a pest of concern for the macadamia industry. Information on the genetic diversity of this species is lacking, despite the potential relevance of such information for management strategies. The present study aimed to characterise the genetic diversity of B. distincta populations in South Africa. The Cytochrome c Oxidase Subunit 1 (COI) and cytochrome b (Cytb) gene regions were sequenced from individuals collected from the three main regions of macadamia production over three different seasons (2018–2020). An overall high haplotype diversity (COI = 0.744, Cytb = 0.549 and COI+Cytb = 0.875) was observed. Pairwise mean genetic distance between populations from each region varied from 0.2–0.4% in both datasets, which suggests the absence of cryptic species. The median joining network for both datasets consisted of one or two central haplotypes shared between the regions in addition to unique haplotypes observed in each region. Finally, low genetic differentiation (F_ST < 0.1), high gene flow (Nm > 1) and the absence of a correlation between genetic and geographic distance were estimated among populations. Overall, these results suggest that the B. distincta populations are not structured among the areas of macadamia production in South Africa. This might be due to its ability to feed and reproduce on various plants and its high dispersal (airborne) between the different growing regions of the country along with the rapid expansion of macadamia plantations in South Africa.

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.

Limoniic Acid and Its Analog as Trap Lures for Pest Limonius Species (Coleoptera: Elateridae) in North America

Four species of Limonius wireworms (Coleoptera: Elateridae), L. californicus, L. canus, L. infuscatus and L. agonus, are serious crop pests in North America. Limoniic acid, (E)-4-ethyloct-4-enoic acid, has been reported as a sex pheromone component of female L. californicus and L. canus, and a sex attractant for male L. infuscatus. In the same study, both limoniic acid and the analog (E)-5-ethyloct-4-enoic acid were highly attractive in field experiments. Moreover, six carboxylic acids in headspace volatiles of Limonius females elicited responses from male antennae but were not tested for behavioral activity. Here, we report trap catch data of Limonius spp. obtained in field experiments at 27 sites across North America. All four Limonius species were attracted to limoniic acid and to the analog but not to the carboxylic acids. Adding these carboxylic acids to limoniic acid, or to the analog, reduced its attractiveness. In dose-response studies, trap lures containing 0.4 mg or 4 mg of limoniic acid afforded large captures of L. californicus and L. infuscatus. Neither limoniic acid nor the analog were deterrent to other elaterid pest species. The broad attractiveness of limoniic acid to Limonius spp., and its non-deterrent effect on heterogeners, may facilitate the development of generic pheromone-based monitoring and management tools for multiple click beetle species.

Distribution of Pest Wireworm (Coleoptera: Elateridae) Species in Alberta, Saskatchewan, and Manitoba (Canada)

We present findings of a general survey of pest wireworms in Alberta, Saskatchewan, and Manitoba conducted from 2004 to 2019; the first such survey of the Canadian Prairie provinces since that published by Glen et al. (1943). Samples were collected from 571 farmland locations where crop damage from wireworms was observed or suspected, and a total of 5,704 specimens (3,548 larvae, 2,156 beetles) were identified. Most specimens (96.9%) were identified as Hypnoidus bicolor (3,278), Selatosomus aeripennis destructor (1,280), Limonius californicus (842), and Aeolus mellillus (125). This suggests that H. bicolor has replaced S. a. destructor as the predominant species and that the relative importance of L. californicus as a pest species has increased since earlier reports. Despite the relatively small number of specimens collected per location (approx. 10), H. bicolor and S. a. destructor, and S. a. destructor and L. californicus were frequently collected at or near the same location (within 1 km). We provide species records and incidence of co-occurrence at different spatial scales, discuss potential reasons for and implications of shifts in species composition, implications of species co-occurrence for managing wireworm pests in crop production, and outline pertinent research needs. A path analysis approach used to correlate incidence of the main species with various soil characteristics indicated that organic matter, cation exchange capacity, and water retention capacity all had a significant species-specific influence on wireworm presence.

Genetic structure and population demographics of Hypnoidus bicolor (Coleoptera: Elateridae) in the Canadian Prairies

BACKGROUND

Following banning of the pesticide lindane in most counties, wireworms (i.e., the soil-living larval stages of click beetles) have become major pests of a variety of economically important field crops. Hypnoidus bicolor is a common pest species in the Canadian Prairies. However, little is known about its life history, which impedes the development of effective integrated pest management (IPM) strategies. Population genetic approaches have the potential to assist in the development of IPM.

RESULTS

We sequenced a 622-bp fragment of the COX1 gene from 326 H. bicolor wireworm and click beetles collected from 13 localities on the Canadian Prairies. Two genetically distinct (>4.66% sequence divergence) clades were identified, suggesting that they may be part of a species complex. Clade A predominated and increased in prevalence the further east samples were collected, whereas the opposite was true for clade B. Clade B appears to be comprised of two mitochondrial DNA groups, however, one group was represented by only one haplotype. Both clades were characterized by uneven gene flow among populations with low levels of regional genetic structuring. Clade A appeared to have undergone population and range expansions, which may coincide with the advent of intensive agriculture practices in the prairies.

CONCLUSION

Knowledge of species composition and population structure is important for the development of effective IPM strategies but is often lacking for wireworms. Our study fills these knowledge gaps for a predominant pest species in the prairies, H. bicolor, by providing robust evidence for cryptic forms and characterizing its dispersal patterns and population dynamics. © 2021 Society of Chemical Industry.

Limoniic Acid - Major Component of the Sex Pheromones of the Click Beetles Limonius canus and L. californicus

Wireworms, the larvae of click beetles (Coleoptera: Elateridae), are soil-dwelling insect pests inflicting major economic damage on many types of agricultural crops worldwide. The objective of this work was to identify the female-produced sex pheromones of the Pacific Coast wireworm, Limonius canus LeConte, and the sugarbeet wireworm, L. californicus (Mannerheim) (Coleoptera: Elateridae). Headspace volatiles from separate groups of female L. canus and L. californicus were collected on Porapak Q and analyzed by gas chromatography with electroantennographic detection (GC-EAD) and GC-mass spectrometry. GC-EAD recordings revealed strong responses from male L. canus and male L. californicus antennae to the same compound, which appeared below GC detection threshold. The structure of this candidate pheromone component was deduced from the results of micro-analytical treatments of extracts, retention index calculations on four GC columns, and by syntheses of more than 25 model compounds which were assessed for their GC retention characteristics and electrophysiological activity. The EAD-active compound was identified as (E)-4-ethyloct-4-enoic acid, which we name limoniic acid. In field experiments in British Columbia and Alberta, Canada, traps baited with synthetic limoniic acid captured large numbers of male Limonius click beetles, whereas unbaited control traps captured few. Compared to traps baited with the analogue, (E)-5-ethyloct-4-enoic acid, traps baited with limoniic acid captured 9-times more male L. californicus, and 6.5-times more male western field wireworms, L. infuscatus Motschulsky, but 2.3-times fewer male L. canus. Limoniic acid can now be developed for detection, monitoring and possibly control of L. californicus, L. infuscatus and L. canus populations.