Evidence that Cerambycid Beetles Mimic Vespid Wasps in Odor as well as Appearance

Life history and bionomics of Glycobius speciosus (Coleoptera: Cerambycidae: Cerambycinae: Clytini)

Glycobius speciosus (Say) was studied in New York State to elucidate poorly known aspects of its biology. Head capsule size from excavated larvae coupled with gallery lengths measured at the time of excavation was used to characterize larval development. Partial life tables indicated nearly 20% of G. speciosus survive to adulthood. Larvae experienced 30% of their mortality during early development, 27% during mid-larval development, and 43% during late larval development. Predation by hairy woodpeckers, Dryobates villosus (Linnaeus) (Piciformes: Picidae), the only unambiguous source of mortality, accounted for 43% mortality in naturally infested trees located and followed 2004-2009, and 74% late instar mortality. One parasitoid, Dolichomitus irritator (Fabricius) (Hymenoptera: Ichneumonidae), was recovered from a single larva. Beetles emerged between 316 accumulated DD (base 10 °C) and 648 DD. Males emerged prior to, or simultaneously with, females and lived longer. Female fecundity averaged 41.3 ± 6 eggs. Larval eclosion occurred 7-10 days after oviposition. Non-functional ovipositors observed in 16% of females represented an appreciable reproductive loss. In 77% of infested trees 1 oviposition site was located and in 70% of oviposition sites examined only 1 or 2 larvae successfully eclosed, penetrated the bark to the phloem-xylem interface, and began feeding. Beetles preferred southern and eastern aspects for oviposition which occurred preferentially on the lower bole (<20 cm). Male beetles had longer and wider antennae than females, pronotal pits containing gland pores, and a straight to concave posterior margin of the terminal sternite compared to the more rounded margin of females.

Conspicuousness, phylogenetic structure, and origins of Müllerian mimicry in 4000 lycid beetles from all zoogeographic regions

Biologists have reported on the chemical defences and the phenetic similarity of net-winged beetles (Coleoptera: Lycidae) and their co-mimics. Nevertheless, our knowledge has remained fragmental, and the evolution of mimetic patterns has not been studied in the phylogenetic context. We illustrate the general appearance of ~ 600 lycid species and ~ 200 co-mimics and their distribution. Further, we assemble the phylogeny using the transcriptomic backbone and ~ 570 species. Using phylogenetic information, we closely scrutinise the relationships among aposematically coloured species, the worldwide diversity, and the distribution of aposematic patterns. The emitted visual signals differ in conspicuousness. The uniform coloured dorsum is ancestral and was followed by the evolution of bicoloured forms. The mottled patterns, i.e. fasciate, striate, punctate, and reticulate, originated later in the course of evolution. The highest number of sympatrically occurring patterns was recovered in New Guinea and the Andean mountain ecosystems (the areas of the highest abundance), and in continental South East Asia (an area of moderate abundance but high in phylogenetic diversity). Consequently, a large number of co-existing aposematic patterns in a single region and/or locality is the rule, in contrast with the theoretical prediction, and predators do not face a simple model-like choice but cope with complex mimetic communities. Lycids display an ancestral aposematic signal even though they sympatrically occur with differently coloured unprofitable relatives. We show that the highly conspicuous patterns evolve within communities predominantly formed by less conspicuous Müllerian mimics and, and often only a single species displays a novel pattern. Our work is a forerunner to the detailed research into the aposematic signalling of net-winged beetles.

The Scent of Life: Phoretic Nematodes Use Wasp Volatiles and Carbon Dioxide to Choose Functional Vehicles for Dispersal

Hitchhikers (phoretic organisms) need vehicles to disperse out of unsuitable habitats. Therefore, finding vehicles with the right functional attributes is essential for phoretic organisms. To locate these vehicles, phoretic organisms employ cues within modalities, ranging from visual to chemical senses. However, how hitchhikers discriminate between individual vehicles has rarely been investigated. Using a phoretic nematode community associated with an obligate fig-fig wasp pollination mutualism, we had earlier established that hitchhiking nematodes make decisions based on vehicle species identity and number of conspecific hitchhikers already present on the vehicle. Here we investigate if hitchhikers can differentiate between physiological states of vehicles. We asked whether phoretic nematodes choose between live or dead vehicles present in a chemically crowded environment and we investigated the basis for any discrimination. We conducted two-choice and single-choice behavioral assays using single nematodes and found that plant- and animal-parasitic nematodes preferred live over dead vehicles and used volatiles as a sensory cue to make this decision. However, in single-choice assays, animal-parasitic nematodes were also attracted towards naturally dead or freeze-killed wasps. The volatile profile of the wasps was dominated by terpenes and spiroketals. We examined the volatile blend emitted by the different wasp physiological states and determined a set of volatiles that the phoretic nematodes might use to discriminate between these states which is likely coupled with respired CO₂. We determined that CO₂ levels emitted by single wasps are sufficient to attract nematodes, demonstrating the high sensitivity of nematodes to this metabolic product.

Sampling technique biases in the analysis of fruit fly volatiles: a case study of Queensland fruit fly

Diverse methods have been used to sample insect semiochemicals. Sampling methods can differ in efficiency and affinity and this can introduce significant biases when interpreting biological patterns. We compare common methods used to sample tephritid fruit fly rectal gland volatiles ('pheromones'), focusing on Queensland fruit fly, Bactrocera tryoni. Solvents of different polarity, n-hexane, dichloromethane and ethanol, were compared using intact and crushed glands. Polydimethylsiloxane, polydimethylsiloxane/divinylbenzene and polyacrylate were compared as adsorbents for solid phase microextraction. Tenax-GR and Porapak Q were compared as adsorbents for dynamic headspace sampling. Along with compounds previously reported for B. tryoni, we detected five previously unreported compounds in males, and three in females. Dichloromethane extracted more amides while there was no significant difference between the three solvents in extraction of spiroacetals except for (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane for which n-hexane extracted higher amount than both dichloromethane and ethanol. Ethanol failed to contain many of the more volatile compounds. Crushed rectal gland samples provided higher concentrations of extracted compounds than intact rectal gland samples, but no compounds were missed in intact samples. Of solid phase microextraction fibers, polyacrylate had low affinity for spiroacetals, ethyl isobutyrate and ethyl-2-methylbutanoate. Polydimethylsiloxane was more efficient for spiroacetals while type of fiber did not affect the amounts of amides and esters. In dynamic headspace sampling, Porapak was more efficient for ethyl isobutyrate and spiroacetals, while Tenax was more efficient for other esters and amides, and sampling time was a critical factor. Biases that can be introduced by sampling methods are important considerations when collecting and interpreting insect semiochemical profiles.

Identification of a Male-Produced Volatile Pheromone for Phymatodes dimidiatus (Coleoptera: Cerambycidae) and Seasonal Flight Phenology of Four Phymatodes Species Endemic to the North American Intermountain West

Research over the last 15 yr has shown widespread pheromone parsimony within the coleopteran family Cerambycidae, with a number of highly conserved pheromone motifs, often shared within and across subfamilies, tribes, and genera. Our goals were to increase our understanding of the evolution of volatile pheromones within the Cerambycidae, their role in reproductive isolation and to identify pheromones for use in the development of lures for monitoring cerambycids. Over 3 yr, we tested 12 compounds known to be cerambycid pheromones as possible attractants at sites across Idaho. This study focused on species within the cerambycine genus Phymatodes (Tribe: Callidiini). We also collected and analyzed headspace volatiles of captured Phymatodes dimidiatus (Kirby). Our results demonstrate that (R)-2-methylbutan-1-ol is a male-produced volatile pheromone for P. dimidiatus. These results are consistent with prior research suggesting that (R)-2-methylbutan-1-ol and (R)-3-hydroxyhexan-2-one, individually or in a blend of both compounds, commonly serve as pheromones for Phymatodes spp. We captured Phymatodes starting in mid-May, continuing through mid-August. Our data indicate that flight periods of Phymatodes spp. in Idaho overlap. These species may be utilizing various mechanisms to ensure reproductive isolation, such as the production of different volatile pheromones, minor components, and/or proportions of components, utilizing different host species and/or host volatiles, differing daily activity periods, and/or occupying different heights in the tree canopy. Our results contribute to the basic understanding of the chemical and behavioral ecology of the Cerambycidae and can be applied to the development of pheromone lures for monitoring of economically important or endangered species.

The Role of Minor Pheromone Components in Segregating 14 Species of Longhorned Beetles (Coleoptera: Cerambycidae) of the Subfamily Cerambycinae

We present research on the chemical ecology of 14 species of longhorned beetles (Coleoptera: Cerambycidae), in four tribes of the subfamily Cerambycinae, conducted in east-central Illinois over 8 yr. Adult males produce aggregation-sex pheromones that attract both sexes. Twenty independent field bioassays explored the pheromone chemistry of the species and tested the possible attractive or antagonistic effects of compounds that are not produced by a given species, but are pheromone components of other species. Analyses of beetle-produced volatiles revealed compounds that had not been reported previously from several of the species. The most common pheromone component was (R)-3-hydroxyhexan-2-one, but pheromones of some species included isomers of the related 2,3-hexanediols. Males of the congeners Phymatodes amoenus (Say) and Phymatodes testaceus (L.) produced pure (R)-2-methylbutan-1-ol. Enantiomers of 2-methylbutan-1-ol also proved to be powerful synergists for Megacyllene caryae (Gahan), Sarosesthes fulminans (F.), and Xylotrechus colonus (F.). The major components of pheromone blends were consistently present in collections of headspace volatiles from male beetles, and only the major components were inherently attractive to a subset of species when tested as single components. Minor components of some species acted as powerful synergists, but in other cases appeared not to influence attraction. Among the minor components identified in headspace extracts from males, 2,3-hexanedione and 2-hydroxyhexan-3-one appeared to be analytical artifacts or biosynthetic by-products, and were neither attractants nor synergists. The antagonistic effects of minor compounds produced by heterospecific males suggest that these compounds serve to maintain prezygotic reproductive isolation among some species that share pheromone components.

Identification of an insect-produced olfactory cue that primes plant defenses

It is increasingly clear that plants perceive and respond to olfactory cues. Yet, knowledge about the specificity and sensitivity of such perception remains limited. We previously documented priming of anti-herbivore defenses in tall goldenrod plants (Solidago altissima) by volatile emissions from a specialist herbivore, the goldenrod gall fly (Eurosta solidaginis). Here, we explore the specific chemical cues mediating this interaction. We report that E,S-conophthorin, the most abundant component of the emission of male flies, elicits a priming response equivalent to that observed for the overall blend. Furthermore, while the strength of priming is dose dependent, plants respond even to very low concentrations of E,S-conophthorin relative to typical fly emissions. Evaluation of other blend components yields results consistent with the hypothesis that priming in this interaction is mediated by a single compound. These findings provide insights into the perceptual capabilities underlying plant defense priming in response to olfactory cues.

Plants are able to prime anti-herbivore defenses in response to olfactory cues of insect pests. Here, Helms et al. identify the insect pheromone E,S-conophthorin produced by the goldenrod gall fly as the specific chemical component that elicits this priming response in goldenrod plants.