Host Defense Metabolites Alter the Interactions between a Bark Beetle and its Symbiotic Fungi.

Successful host plant colonization by tree-killing bark beetle-symbiotic fungal complexes depends on host suitability, which is largely determined by host defense metabolites such as monoterpenes. Studies have shown the ability of specific blends of host monoterpenes to influence bark beetles or their fungal symbionts, but how biologically relevant blends of host monoterpenes influence bark beetle-symbiotic fungal interaction is unknown. We tested how interactions between two host species (lodgepole pine or jack pine) and two fungal symbionts of mountain pine beetle (Grosmannia clavigera or Ophiostoma montium) affect the performance of adult female beetles in vitro. Beetles treated with the propagules of G. clavigera or O. montium or not treated (natural fungal load) were introduced into media amended with a blend of the entire monoterpene profile of either host species and beetle performance was compared. Overall, host blends altered beetle performance depending on the fungal species used in the beetle amendment. When beetles were amended with G. clavigera, their performance was superior over beetles amended with O. montium in either host blend. Furthermore, G. clavigera-amended beetles performed better in media amended with host blends than without a host blend; in contrast, O. montium-amended beetles performed better in media without a host blend than with a host blend. Overall, this study showed that host defense metabolites affect host suitability to bark beetles through influencing their fungal symbionts and that different species of fungal symbionts respond differentlly to host defense metabolites.

Acetophenone as an anti-attractant for the western pine beetle, Dendroctonus Brevicomis LeConte (Coleoptera: Scolytidae).

Host location and colonization by bark beetles is dependent upon the relative and absolute amounts of attractant and antiattractant compounds available. Many investigations have lead to use of antiattractants for the management of these pests and have been especially focused on verbenone. However, recent studies have identified new antiattractants for several species of bark beetles. We report results of recent investigations of the response of western pine beetle, Dendroctonus brevicomis LeConte, to two recently identified antiattractants, acetophenone, and fenchyl alcohol, with verbenone as a standard of comparison, in northern California. Release of both acetophenone and verbenone resulted in significantly lower trap catches of D. brevicomis in aggregation pheromone-baited traps, while fenchyl alcohol was inactive. Acetophenone was the only antiattractant that did not reduce numbers of the most abundant predator of D. brevicomis, Temnochila chlorodia (Mannerheim), responding to the attractant pheromone of its prey. Aggregation pheromone-baited traps with acetophenone also had the highest predator/prey ratio. Our results suggest that acetophenone may be part of the intra- and interspecific interactions among sympatric species of bark beetles and may have application in their control.

Response to host volatiles by native and introduced populations of Dendroctonus valens (Coleoptera: Curculionidae, Scolytinae) in North America and China.

Bark beetles (Coleoptera: Curculionidae, Scolytinae) have specialized feeding habits, and commonly colonize only one or a few closely related host genera in their geographical ranges. The red turpentine beetle, Dendroctonus valens LeConte, has a broad geographic distribution in North America and exploits volatile cues from a wide variety of pines in selecting hosts. Semiochemicals have been investigated for D. valens in North America and in its introduced range in China, yielding apparent regional differences in response to various host volatiles. Testing volatiles as attractants for D. valens in its native and introduced ranges provides an opportunity to determine whether geographic separation promotes local adaptation to host compounds and to explore potential behavioral divergence in native and introduced regions. Furthermore, understanding the chemical ecology of host selection facilitates development of semiochemicals for monitoring and controlling bark beetles, especially during the process of expansion into new geographic ranges. We investigated the responses of D. valens to various monoterpenes across a wide range of sites across North America and one site in China, and used the resulting information to develop an optimal lure for monitoring populations of D. valens throughout its Holarctic range. Semiochemicals were selected based on previous work with D. valens: (R)-(+)-alpha-pinene, (S)-(-)-alpha-pinene, (S)-(-)-beta-pinene, (S)-(+)-3-carene, a commercially available lure [1:1:1 ratio of (R)-(+)-alpha-pinene:(S)-(-)-beta-pinene:(S)-(+)-3-carene], and a blank control. At the release rates used, (+)-3-carene was the most attractive monoterpene tested throughout the native range in North America and introduced range in China, confirming results from Chinese studies. In addition to reporting a more effective lure for D. valens, we present a straightforward statistical procedure for analysis of insect trap count data yielding cells with zero counts, an outcome that is common but makes the estimation of the variance with a Generalized Linear Model unreliable because of the variability/mean count dependency.

Trap type, chirality of alpha-pinene, and geographic region affect sampling efficiency of root and lower stem insects in pine.

Root and lower stem insects cause significant damage to conifers, vector phytopathogenic fungi, and can predispose trees to bark beetle attacks. The development of effective sampling techniques is an important component in managing these cryptic insects. We tested the effects of trap type and stereochemistry of alpha-pinene, in combination with ethanol, on catches of the root colonizing weevils (Coleoptera: Curculionidae) Hylobius spp. [mostly Hylobius pales (Herbst)], and Pachylobius picivorus (Germar), the root colonizing bark beetle (Coleoptera: Scolytidae) Hylastes porculus Erickson, and the lower stem colonizing bark beetle Dendroctonus valens (LeConte). We tested for inter-regional differences by conducting similar field assays in the northern (Wisconsin) and southern (Louisiana) United States. The more effective trap type varied with region. Root weevils were caught primarily in pitfall traps in Wisconsin, whereas they were caught mostly in lower stem flight traps in Louisiana. In Wisconsin, root colonizing bark beetles were also caught primarily in pitfall traps, but lower stem colonizing bark beetles were caught primarily in lower stem flight traps. The root feeding weevils preferred (-) over (+)-alpha-pinene in both regions. Some exceptions relating to trap type or gender occurred in southern populations. The two root and lower stem colonizing bark beetles in Wisconsin showed no preference between (+) and (-)-alpha-pinene in combination with ethanol. No bark beetles were caught in the south. Our results suggest that modifying trap type and enantiomeric ratios of monoterpenes for different insect groups and in different regions can improve sampling efficiency for these important pests.