Dietary history of click beetles and wireworms in the genus Limonius (Coleoptera: Elateridae) revealed by molecular gut content analysis.

Wireworms, the larval stage of pest click beetle species (Coleoptera: Elateridae), are pests of many crops in North America including root vegetables and cereals. There is cause for concern amongst growers who are facing pressure from wireworms because there are a decreasing number of effective pesticides that can be used for wireworm management. Most research on pest elaterids has focused on the wireworm stage, which is the damage causing life stage. Recently, the focus in elaterid research has shifted to the adult click beetle stage, including identification of semiochemicals and development of effective traps. However, there is still a lot to be discovered about the basic biology of click beetles, including their feeding ecology. In an effort to understand the feeding ecology of click beetles, we investigated the presence of plant DNA in the digestive tracts of Limonius californicus (Mann.), L. canus (LeConte), and L. infuscatus (Mots.) beetles collected in 3 different locations within central Washington. To examine dietary histories of beetles and wireworms, specimens were collected from natural habitats and high-throughput sequencing of the plant genes trnF and ITS was used to identify their dietary history. Results revealed that click beetles do feed on a large variety of plants, which included a large quantity of brassicaceous plants commonly found in areas surrounding wireworm infested plots. The identification of the dietary history of the click beetles allowed us to infer their landscape-scale movements thus providing a means to better understand their behavior.

A Symmetrical Diester as the Sex Attractant Pheromone of the North American Click Beetle Parallelostethus attenuatus (Say) (Coleoptera: Elateridae).

Hexanoic acid, 1-octanol, 1,8-octanediol, octyl hexanoate, 1,8-octanediol monohexanoate, and 1,8-octanediol dihexanoate were identified in headspace volatiles collected from the crushed abdomen of a female click beetle of the species Parallelostethus attenuatus (Say) (Elaterinae, tribe Elaterini). In field trials carried out in Illinois, South Carolina, North Carolina, and Virginia, adult male beetles were strongly attracted to 1,8-octanediol dihexanoate alone. Blends of the dihexanoate with one or more of the other compounds proved to be less attractive than the dihexanoate alone, suggesting that the pheromone of this species may consist of a single compound. The symmetrical diester structure of the pheromone is a novel natural product and appears to be structurally unique among insect pheromones.

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.

13-Tetradecenyl acetate, a female-produced sex pheromone component of the economically important click beetle Melanotus communis (Gyllenhal) (Coleoptera: Elateridae).

Species-specific behavior-modifying chemicals have been used for more than 50 years for monitoring and management of insect pests of agriculture and human health. Elaterid beetle larvae are among insect pests in soil that are increasingly problematic, in part due to the lack of effective management strategies. However, little is known about the insect-produced chemicals that mediate the reproductive behavior of these pests. We used chemical and behavioral studies to identify, synthesize, and field test the sex attractant pheromone of adults of Melanotus communis, commonly called the corn wireworm, the larvae of which are economically important pests of U.S. crops. Our results indicated that a single female-produced chemical, 13-tetradecenyl acetate, was strongly attractive to conspecific male beetles, and did not appear to attract other species. In field evaluations, male M. communis exhibited a dose-dependent response to this compound. In a trial comparing different slow-release dispensers, a small rubber septum impregnated with the chemical was as effective as and easier to use than a plastic bag dispenser. Given that the sex attractant of this insect consists of a single compound that can be readily synthesized, its development for monitoring and management of the corn wireworm may be economically feasible.

Identification of Aggregation-Sex Pheromone Components for a "Living Fossil", the False Click Beetle, Palaeoxenus dohrni Horn (Coleoptera: Eucnemidae).

Insect pheromones have rarely been exploited in surveys or studies of rare and endangered species, despite their potential as effective and highly selective attractants for target species. Here, we report the identification, synthesis, and field bioassays of a male-produced aggregation-sex pheromone blend of a rare false click beetle species endemic to southern California, Dohrn's elegant eucnemid beetle, Palaeoxenus dohrni Horn (Coleoptera: Eucnemidae). This species is the only extant species in its genus and subfamily. Analyses of extracts of headspace volatiles collected from adult beetles revealed several male-specific compounds. Two of these compounds, identified as (E)-2-nonen-4-one and (R)-2-nonanol, elicited electroantennographic responses from antennae of beetles of both sexes. In field bioassays, a blend of the two compounds attracted both sexes, whereas the individual compounds were not attractive. The identification of an attractant pheromone should provide a useful tool for bioconservation and ecological studies of this iconic species.

An Unstable Monoterpene Alcohol as a Pheromone Component of the Longhorned Beetle Paranoplium gracile (Coleoptera: Cerambycidae).

We report the identification of p-mentha-1,3-dien-8-ol, an unstable monoterpene alcohol, as a male-produced aggregation-sex pheromone component of the cerambycid beetle Paranoplium gracile (Leconte) (subfamily Cerambycinae, tribe Oemini), a species endemic to California. Headspace volatiles from live males contained a blend of nine cyclic terpenoids that were not detected in analogous samples from females. Volatiles produced by male Eudistenia costipennis Fall, also in the tribe Oemini, contained the same suite of nine compounds. Four compounds, dehydro-p-cymene, p-mentha-1,3-dien-8-ol, p,α,α-trimethylbenzyl alcohol, and an unidentified compound were found to elicit responses from antennae of P. gracile females in coupled gas chromatography-electroantennogram detection (GC-EAD) assays, whereas only p-mentha-1,3-dien-8-ol elicited responses from antennae of males. In field assays, p-mentha-1,3-dien-8-ol stabilized with the antioxidant butylated hydroxytoluene (BHT) attracted P. gracile of both sexes, indicating it functions as an aggregation-sex pheromone, as with other pheromones identified from its subfamily, the Cerambycinae. Adding four of the other compounds found in headspace samples to the dienol lure had no effect on attraction. Because of the instability of p-mentha-1,3-dien-8-ol, it seems likely that at least some of the compounds seen in the extracts of volatiles from both species are artefacts, rather than being components of the pheromone.

Identification of Sex Pheromones and Sex Pheromone Mimics for Two North American Click Beetle Species (Coleoptera: Elateridae) in the Genus Cardiophorus Esch.

To date, all known or suspected pheromones of click beetles (Coleoptera: Elateridae) have been identified solely from species native to Europe and Asia; reports of identifications from North American species dating from the 1970s have since proven to be incorrect. While conducting bioassays of pheromones of a longhorned beetle (Coleoptera: Cerambycidae), we serendipitously discovered that males of Cardiophorus tenebrosus L. and Cardiophorus edwardsi Horn were specifically attracted to the cerambycid pheromone fuscumol acetate, (E)-6,10-dimethylundeca-5,9-dien-2-yl acetate, suggesting that this compound might also be a sex pheromone for the two Cardiophorus species. Further field bioassays and electrophysiological assays with the enantiomers of fuscumol acetate determined that males were specifically attracted by the (R)-enantiomer. However, subsequent analyses of extracts of volatiles from female C. tenebrosus and C. edwardsi showed that the females actually produced a different compound, which was identified as (3R,6E)-3,7,11-trimethyl-6,10-dodecadienoic acid methyl ester (methyl (3R,6E)-2,3-dihydrofarnesoate). In field trials, both the racemate and the (R)-enantiomer of the pheromone attracted similar numbers of male beetles, suggesting that the (S)-enantiomer was not interfering with responses to the insect-produced (R)-enantiomer. This report constitutes the first conclusive identification of sex pheromones for any North American click beetle species. Possible reasons for the strong and specific attraction of males to fuscumol acetate, which is markedly different in structure to the actual pheromone, are discussed.