This review summarizes the literature related to the chemical ecology of the Cerambycidae and provides a brief overview of cerambycid biology, ecology, economic significance, and management. Beetles in the family Cerambycidae have assumed increasing prominence as pests of forest and shade trees, shrubs, and raw wood products, and as vectors of tree diseases. Exotic species associated with solid wood packing materials have been notable tree killers in North American urban and peri-urban forests. In forested ecosystems native species respond to disturbances such as fires and windstorms, and initiate the biodeterioration of woody tissue. Eggs are laid by females, on or through the bark surface of stem and branch tissue of moribund, recently killed or decomposing woody plants; larval cerambycids (roundheaded woodborers) typically feed in the phloem and later in the xylem. Females will also, in some cases, select living hosts, e.g. adult conifer and angiosperm trees, for oviposition. Research on the chemical ecology of over 70 species has revealed many examples of attractive kairomones (such as floral volatiles, smoke volatiles, trunk and leaf volatiles, and bark beetle pheromones), repellents and deterrents, oviposition stimulants, short- and long-range sex pheromones, and defensive substances. Emerging generalities are that attractants tend to be monoterpenoids and phenolic esters; oviposition stimulants are monoterpenoids and flavanoids; short-range sex pheromones are female-produced, methyl-branched cuticular hydrocarbons; and long-range sex pheromones are male-produced α-hydroxy ketones and (α,β)-diols ranging in length from 6 to 10 carbons. The latter compounds appear to originate from glands in the male thorax; putative defensive substances originate from metasternal secretory pores or mandibular glands. In one unusual case, a flightless, subterranean female that attacks sugar cane produces a sex pheromone that is derived from the amino acid isoleucine. With significantly more than 35,000 species of Cerambycidae worldwide, these generalities will be subject to change as more species are examined.

A review of the chemical ecology of the Cerambycidae (Coleoptera)

The nitrogen content of plant tissue is low relative to that of herbivores; as a consequence, dietary N can limit the growth and reproduction of herbivores and select for attributes that increase N acquisition. Bark beetles face a particularly severe challenge because the phloem that they consume is very low in nitrogen and phosphorus relative to their requirements. We quantified variation in the phloem concentrations of N and P in the host tree, Pinus taeda, and evaluated the following hypotheses regarding the role of sym- biotic fungi in nutrient budgets of the herbivore Dendroctonus frontalis: D. frontalis ex- perience variation in phloem nutrient concentrations across several spatial scales (HI); mycangial fungi enhance the diet of D. frontalis larvae by contributing to the acquisition of N and P (H2); Ophiostoma minus, an apparently antagonistic fungal symbiont, hinders D. frontalis larvae because it does not enhance nutrient concentrations of the phloem as much as mycangial fungi do (H3); and larvae of bark beetle species that lack mycangial fungi must consume more phloem to accomplish the same growth as larvae of D. frontalis (H4). In addition, we developed a general model for the N budgets of herbivorous insects that identifies the possible combinations of dietary and physiological parameters that can allow developmental success on low-nutrient diets. Spatial variation in phloem N was mostly at the level of trees within sites (a scale of meters) while P mostly varied among sites (a scale of kilometers). Trees with higher N content produced larger D. frontalis adults. Prior to infestation by beetles, phloem nutrient concentrations were very uniform within trees and very low relative to that of the bark beetles (N and P concentrations of D. frontalis adults were 28 and 8 times greater, re- spectively). During infestation, phloem nutrient concentrations increased overall and be- came highly variable within trees. Nitrogen concentrations increased from 0.40 + 0.01% (mean + 1 SE) in uninfested phloem to 0.86 + 0.03% in the phloem surrounding successfully developing D. frontalis larvae, which are typically associated with one or two species of mutualistic mycangial fungi. Nitrogen concentrations were intermediate in other micro- habitats within infested trees, including regions with no adult colonization, with failed larval development, or colonized by the antagonistic bluestain fungus 0. minus. We pa- rameterized a general nutrient-budget model for D. frontalis and a sympatric non-mycangial bark beetle, Ips grandicollis, which indicated that (1) mycangial fungi provide their benefits by concentrating dietary N for larvae; (2) 0. minus may exert its antagonistic effects on D. frontalis larvae by failing to concentrate dietary N as much as mycangial fungi do; (3) non-mycangial bark beetles meet their N budgets through high consumption of unaltered, low-N phloem; and (4) larvae should easily meet their P requirements with any combination of consumption rate and development time that allows them to meet their N requirements. Alternative strategies for N acquisition may have general consequences for the population dynamics and community interactions of bark beetles.

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Nitrogen budgets of phloem-feeding bark beetles with and without symbiotic fungi

Pine-feeding bark beetles (Coleoptera: Scolytidae) interact chemically with their host pines (Coniferales: Pinaceae) via the behavioral, physiological, and biochemical effects of one class of isoprenoids, the monoterpenes and their derivatives. Pine monoterpenes occur in the oleoresin and function as behaviorally active kairomones for pine bark beetles and their predators, presenting a classic example of tri-trophic chemical communication. The monoterpenes are also essential co-attractants for pine bark beetle aggregation pheromones. Ironically, pine monoterpenes are also toxic physiologically to bark beetles at high vapor concentrations and are considered an important component of the defense of pines. Research over the last 30 years has demonstrated that some bark beetle aggregation pheromones arise through oxygenation of monoterpenes, linking pheromone biosynthesis to the host pines. Over the last 10 years, however, several frequently occurring oxygenated monoterpene pheromone components (e.g., ipsenol, ipsdienol and frontalin) have also been shown to arise through highly regulated de novo pathways in the beetles (reviewed in Seybold and Tittiger, 2003). The most interesting nexus between these insects and their plant hosts involves the late-stage reactions in the monoterpenoid biosynthetic pathway, during which isomeric dimethylallyl diphosphate and isopentenyl diphosphate are ultimately elaborated to stereospecific monoterpenes in the trees and to hydroxylated monoterpenes or bicyclic acetals in the insects. There is signal stereospecificity in both production of and response to the monoterpenoid aggregation pheromones of bark beetles and in response to␣the monoterpenes of the pines. In the California fivespined ips, Ips paraconfusus, we have discovered a number of cytochome P450 genes that have expression patterns indicating that they may be involved in detoxifying monoterpene secondary metabolites and/or biosynthesizing pheromone components. Both processes result in the production of oxygenated monoterpenes, likely with varying degrees of stereospecificity. A behavioral analysis of the stereospecific response of I. paraconfusus to its pheromone is providing new insights into the development of an efficacious bait for the detection of this polyphagous insect in areas outside the western United States. In contrast, a Eurasian species that has arrived in California, the Mediterranean pine engraver, Orthotomicus (Ips) erosus, utilizes both a monoterpenoid (ipsdienol) and a hemiterpenoid (2-methyl-3-buten-2-ol) in its pheromone blend. The stereospecificity of the response of O. erosus to the monoterpenoid appears to be the key factor to the improved potency of the attractant bait for this invasive species.

Pine monoterpenes and pine bark beetles: a marriage of convenience for defense and chemical communication

Bark beetles (order Coleoptera: family Scolytidae) comprise a taxonomic group of species that look similar although they differ widely in their ecology and biochemical adaptations to host trees. This diversity of bark beetle biology, in which each species is adapted to only one or a few host-tree species, has probably resulted from natural selection due to the great variety of trees and their biochemicals. It also is likely that each species of tree has coevolved various chemicals to defend against the herbivorous selection pressures of bark beetles and other insects (Erlich and Raven, 1965; Feeny, 1975; Cates, 1981; Berryman et al., 1985). Host-plant chemicals can be attractive, repellent, toxic, or nutritious to bark beetles and have effects on: (1) finding and accepting the host tree (host selection and suitability); (2) feeding stimulation and deterrence; (3) host resistance; (4) pheromone/allomone biosynthesis and communication; and (5) attraction of predators, parasites, and competitors of bark beetles.

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Host-Tree Chemistry Affecting Colonization in Bark Beetles

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.

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Ethanol and ()-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

Responses of seven species of pine-infesting beetles to traps baited with either turpentine, ethanol, turpentine and ethanol released from separate dispensers, or a 1:1 solution of turpentine and ethanol released from one dispenser were assessed in three field experiments. The weevil species, Pachylobius picivorus (Germar), and the cerambycid pine sawyer, Monochamus carolinensis (Olivier), were attracted to turpentine and were unaffected by the addition of ethanol. The ambrosia beetle, Xyleborus affinis Eichhoff, responded to ethanol alone but was not attracted to turpentine, nor did the presence of turpentine significantly affect its response to ethanol. The remaining four species displayed responses to turpentine that were enhanced by the addition of ethanol, but in different ways according to the method of deployment. Hylobius pales (Herbst) weevils and M. titillator (F.) sawyers displayed greatest attraction to turpentine and ethanol whether they were released from side-by-side dispensers or as a solution from one dispenser. The black turpentine beetle, Dendroctonus terebrans (Olivier), displayed the highest response to turpentine and ethanol in solution. The ambrosia beetle, X. pubescens Zimmermann, responded in low numbers to turpentine or ethanol deployed singly, but displayed an enhanced response (20-fold increase) to turpentine and ethanol deployed side-by-side and an even greater response (60-fold increase) to a solution of turpentine and ethanol. Reasons for increased responses by some species to a solution of turpentine and ethanol over the two released separately are not clear; they may lie in different dosages or evaporation rates of volatiles in the field. Laboratory analyses of trapped headspace volatiles from dispensers containing only turpentine and those containing a solution of turpentine and ethanol revealed no differences in the amounts of four principal monoterpene hydrocarbons (α-pinene, camphene, β-pinene, and limonene) released over time. The synergistic effect of turpentine and ethanol for some species and not others may point to ecological differences between species with regard to the condition of preferred host material.

Synergism of Turpentine and Ethanol as Attractants for Certain Pine-Infesting Beetles (Coleoptera)

Controlled infestation ofDendroctonus terebrans (Olivier) on bolts of slash pine,Pinus ellionii Engelm. var.elliottii, elicited greater attraction of wild conspecifics than uninfested bolts. Secondary attraction was not apparent, however, to standing slash pines that had received volunteer attacks, when compared with attraction to unattacked but susceptible trees. Hindguts from in-flight or attacking femaleD. terebrans contained frontalin, and those from in-flight or attacking males containedexo-brevicomin.Trans-pinocarveol,cis-verbenol,trans-verbenol, myrtenal, verbenone, myrtenol, and other compounds were produced by both sexes during gallery construction in host trees. Synthetic frontalin, when deployed with a standard host odor mixture of turpentine and ethanol, was very attractive to maleD. terebrans in field-trapping experiments. The addition of eitherexo-brevicomin orendo-brevicomin to the frontalin-turpentine combination negated the attractive effect of frontalin for males.Trans-verbenol, myrtenol, and verbenone had little effect onD. terebrans behavior. Responses of females did not differ among treatments in any of the 11 field experiments.

Secondary attraction and field activity of beetle-produced volatiles inDendroctonus terebrans.

The density of eggs laid per centimeter of gallery by laboratory-reared Ips calligraphus (Germar) females was determined following introduction into thin phloem bolts cut from 25-yr-old slash pine, pinus elliotii Engelm. var. elliottii , that had been fertilized at the time of planting with a combination of nitrogen, phosphorus, and potassium, or phosphorus alone. Egg density was negatively correlated with female pronotal width (size) and positively correlated with the phloem phosphorus concentration. These two variables explained 64% of the variation in egg density. It is hypothesized that altering egg density in response to varying phloem nutrition represents a resource partitioning mechanism that reduces larval competition. These results also suggest that excessive phosphorus fertilization of slash pine on the Coastal Plain soils could contribute to a build-up in the beetle population without the added benefits of stand growth.

Effects of slash pine phloem nutrition on the reproductive performance of Ips calligraphus (Coleoptera: Scolytidae)

The black turpentine beetle, Dendroctonus terebrans (Olivier), utilizes the bicyclic ketals frontalin, produced by females, and exo -brevicomin, produced by males, as sex pheromones. The isomer endo -brevicomin also is active behaviorally and may be produced by males, but its role is unclear. Responses of D. terebrans to traps baited with synthetic enantiomers of frontalin, exo -brevicomin, and endo -brevicomin were assayed in five field experiments. Males were strongly attracted to (â)-frontalin evaporated with pine turpentine (volatile host terpenes) and to racemic frontalin with turpentine, but (+)-frontalin was at best slightly attractive. Increased doses of (+)-frontalin did not interrupt the response of males to the (â) enantiomer. Both enantiomers of exo -brevicomin and the racemic solution were attractive to females when deployed with turpentine, as were (+), (â), and racemic endo -brevicomin. However, an experiment that examined the effect of exo -brevicomin on the response of males to turpentine and frontalin found that (+)- exo -brevicomin and the racemate were attractive to females, but the (â) enantiomer was not. Neither racemic exo -brevicomin nor either of the enantiomers interrupted the response of males to frontalin, unlike results from earlier studies that used high release rates of host volatiles. Although one enantiomer of both frontalin and exo -brevicomin was most active, their antipodes were not inhibitory and racemic material elicited responses similar to those elicited by the single enantiomers. Behavioral activity of (â)-frontalin and (+)- exo -brevicomin in D. terebrans is typical of the genus. In species of Dendroctonus for which enantiomeric specificity has been studied, (â)-frontalin and (+)- exo -brevicomin are behaviorally active and are produced in greater abundance compared with their respective antipodes.

Response Specificity of Dendroctonus terebrans (Coleoptera: Scolytidae) to Enantiomers of Its Sex Pheromones

Les rondins infestes artificiellement par des mâles de O. c. attirent les mâles et les femelles, alors que les rondins non infestes ou infestes par des femelles n'attirent pas O. c. L'ajout de femelles a des rondins portant deja des mâles ne diminue pas l'attractivite, la femelle ne produit donc pas de pheromone masquante. Le systeme pheromonal est identique a celui d'autres Ipini pour lesquels le mâle initie le forage de la galerie, produit un attractif qui attire les femelles et les mâles opportunistes

Thomas W. Phillips

Papers

Synergism of Turpentine and Ethanol as Attractants for Certain Pine-Infesting Beetles (Coleoptera)

Secondary attraction and field activity of beetle-produced volatiles inDendroctonus terebrans.

Effects of slash pine phloem nutrition on the reproductive performance of Ips calligraphus (Coleoptera: Scolytidae)

Response Specificity of Dendroctonus terebrans (Coleoptera: Scolytidae) to Enantiomers of Its Sex Pheromones

Pheromone-based aggregation in orthotomicus caelatus (eichhoff) (coleoptera: scolytidae)