Nancy E. Gillette

Red turpentine beetle: innocuous native becomes invasive tree killer in China.

The red turpentine beetle (RTB), Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae), is a secondary pest of pines in its native range in North and Central America. Outbreaks and tree mortality attributed to RTB alone are rare in its native range. RTB was introduced into China in the early 1980s and spread rapidly from Shanxi Province to four adjacent provinces; it has infested over 500,000 ha of pine forest and has caused extensive tree mortality since 1999. We provide a historical background on RTB outbreaks, explanations for its invasive success, management options, and economic impacts of RTB in China. Genetic variation in RTB fungal associates, interactions between RTB and its associated fungi, behavioral differences in Chinese RTB, and other factors favoring RTB outbreaks are considered in an effort to explain the invasiveness of RTB in China. The promise of semiochemicals as a management tool is also discussed.

Complex interactions among host pines and fungi vectored by an invasive bark beetle

*Recent studies have investigated the relationships between pairs or groups of exotic species to illustrate invasive mechanisms, but most have focused on interactions at a single trophic level. *Here, we conducted pathogenicity tests, analyses of host volatiles and fungal growth tests to elucidate an intricate network of interactions between the host tree, the invasive red turpentine beetle and its fungal associates. *Seedlings inoculated with two strains of Leptographium procerum isolated from Dendroctonus valens in China had significantly longer lesions and higher mortality rates than seedlings inoculated with other fungal isolates. These two strains of L. procerum were significantly more tolerant of 3-carene than all other fungi isolated there, and the infection of Chinese pine (Pinus tabuliformis) seedlings by these two strains enhanced the production and release of 3-carene, the main attractant for D. valens, by the seedlings. *Our results raise the possibility that interactions among the fungal associates of D. valens and their pine hosts in China may confer advantages to these strains of L. procerum and, by extension, to the beetles themselves. These interactions may therefore enhance invasion by the beetle-fungal complex.

Red Turpentine Beetle, Dendroctonus valens LeConte (Coleoptera: Scolytidae), Response to Host Semiochemicals in China

Abstract The response of the introduced red turpentine beetle, Dendroctonus valens LeConte, to host semiochemicals in Shanxi Province, China, was distinctly different from that reported in previous studies conducted in the western part of the native range of D. valens in the central Sierra Nevada, CA. This finding suggests either that there is regional variation in D. valens response to host volatiles in North America or that the species underwent rapid adaptation after its introduction into Asia. In the Chinese population of D. valens, (+)-3-carene was the most attractive host monoterpene tested in studies conducted in 2002 using multiple funnel traps suspended in a Pinus tabuliformis stand. It attracted significantly more beetles than did any other single semiochemical or any of the ternary or quaternary blends tested, including the standard D. valens blend used in North America [a 1:1:1 blend of (+)-α-pinene, (−)-β-pinene, and (+)-3-carene]. (+)-α-Pinene and (−)-β-pinene, presented individually, were not significantly more attractive than controls. Adding limonene to the standard lure decreased response of D. valens but not significantly. A new type of semiochemical release vial was tested using a range of release rates of a 1:1:1 blend of (+)-α-pinene, (−)-β-pinene, and (+)-3-carene. The rates ranged from 150 to 210 mg/d, and these were compared with the standard North American lure, which releases ≈110 mg/d. The most attractive of these vials, which released ≈150 mg/d, captured significantly more beetles than did the standard release device; however, increasing the release rate beyond 150 mg/d did not further increase trap catch. The implications of our results for the phylogenetic geography of D. valens and its management as an invasive species are discussed.

Geographic Variation in Bacterial Communities Associated With the Red Turpentine Beetle (Coleoptera: Curculionidae)

ABSTRACT Bacterial communities are known to play important roles in insect life histories, yet their consistency or variation across populations is poorly understood. Bacteria associated with the bark beetle Dendroctonus valens LeConte from eight populations, ranging from Wisconsin to Oregon, were evaluated and compared. We used the culture-independent technique of denaturing gradient gel electrophoresis to visualize bacterial diversity, or individual operational taxonomic units (OTUs), from individual beetles. One-way analysis of similarities was used to test for differences of bacterial communities between sites. Analysis of community profiles showed that individual beetles on average contained 10 OTUs, with frequency of association from 2 to 100% of beetles. OTU sequences most closely matched &bgr;- and &ggr;-proteobacteria, and one each matched Bacilli and Actinobacteria. Several OTUs were particularly abundant, most notably an Actinobacterium from 100% and two Proteobacteria from 60% of beetles sampled. Some OTUs were similar to previously described bacteria with known biochemical capabilities and ecological functions, suggesting that some bacterial associates of D. valens may contribute to its ability to exploit a resource low in nutrients and high in defensive compounds. There were significant differences of bacterial communities between sites. The strength of these differences was positively correlated with distance between sites, although additional unexplained factors also contribute to the variation.

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)-(+)-α-pinene, (S)-(−)-α-pinene, (S)-(−)-β-pinene, (S)-(+)-3-carene, a commercially available lure [1:1:1 ratio of (R)-(+)-α-pinene:(S)-(−)-β-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.

Do novel genotypes drive the success of an invasive bark beetle–fungus complex? Implications for potential reinvasion

Novel genotypes often arise during biological invasions, but their role in invasion success has rarely been elucidated. Here we examined the population genetics and behavior of the fungus, Leptographium procerum, vectored by a highly invasive bark beetle, Dendroctonus valens, to determine whether genetic changes in the fungus contributed to the invasive success of the beetle-fungal complex in China. The fungus was introduced by the beetle from the United States to China, where we identified several novel genotypes using microsatellite markers. These novel genotypes were more pathogenic to Chinese host seedlings than were other genotypes and they also induced the release of higher amounts of 3-carene, the primary host attractant for the beetle vector, from inoculated seedlings. This evidence suggests a possible mechanism, based on the evolution of a novel genotype during the two or three decades since its introduction, for the success of the beetle-fungal complex in its introduced region.

Large shift in symbiont assemblage in the invasive red turpentine beetle.

Changes in symbiont assemblages can affect the success and impact of invasive species, and may provide knowledge regarding the invasion histories of their vectors. Bark beetle symbioses are ideal systems to study changes in symbiont assemblages resulting from invasions. The red turpentine beetle (Dendroctonus valens) is a bark beetle species that recently invaded China from its native range in North America. It is associated with ophiostomatalean fungi in both locations, although the fungi have previously been well-surveyed only in China. We surveyed the ophiostomatalean fungi associated with D. valens in eastern and western North America, and identified the fungal species using multi-gene phylogenies. From the 307 collected isolates (147 in eastern North America and 160 in western North America), we identified 20 species: 11 in eastern North America and 13 in western North America. Four species were shared between eastern North America and western North America, one species (Ophiostoma floccosum) was shared between western North America and China, and three species (Grosmannia koreana, Leptographium procerum, and Ophiostoma abietinum) were shared between eastern North America and China. Ophiostoma floccosum and O. abietinum have worldwide distributions, and were rarely isolated from D. valens. However, G. koreana and L. procerum are primarily limited to Asia and North America respectively. Leptographium procerum, which is thought to be native to North America, represented >45% of the symbionts of D. valens in eastern North America and China, suggesting D. valens may have been introduced to China from eastern North America. These results are surprising, as previous population genetics studies on D. valens based on the cytochrome oxidase I gene have suggested that the insect was introduced into China from western North America.

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.

The Push-Pull Tactic for Mitigation of Mountain Pine Beetle (Coleoptera: Curculionidae) Damage in Lodgepole and Whitebark Pines

ABSTRACT In an attempt to improve semiochemical-based treatments for protecting forest stands from bark beetle attack, we compared push—pull versus push-only tactics for protecting lodgepole pine (Pinus contorta Douglas ex Loudon) and whitebark pine (Pinus albicaulis Engelm.) stands from attack by mountain pine beetle (Dendroctonus ponderosae Hopkins) in two studies. The first was conducted on replicated 4.04-ha plots in lodgepole pine stands (California, 2008) and the second on 0.81-ha plots in whitebark pine stands (Washington, 2010). In both studies, D. ponderosae population levels were moderate to severe. The treatments were 1) push-only (D. ponderosae antiaggregant semiochemicals alone); 2) push—pull (D. ponderosae antiaggregants plus perimeter traps placed at regular intervals, baited with four-component D. ponderosae aggregation pheromone); and 3) untreated controls. We installed monitoring traps baited with two-component D. ponderosae lures inside each plot to assess effect of treatments on beetle flight. In California, fewer beetles were collected in push—pull treated plots than in control plots, but push-only did not have a significant effect on trap catch. Both treatments significantly reduced the rate of mass and strip attacks by D. ponderosae, but the difference in attack rates between push—pull and push-only was not significant. In Washington, both push—pull and push-only treatments significantly reduced numbers of beetles caught in traps. Differences between attack rates in treated and control plots in Washington were not significant, but the push-only treatment reduced attack rates by 30% compared with both the control and push—pull treatment. We conclude that, at these spatial scales and beetle densities, push-only may be preferable for mitigating D. ponderosae attack because it is much less expensive, simpler, and adding trap-out does not appear to improve efficacy.

Identification of Dioryctria (Lepidoptera: Pyralidae) in a Seed Orchard at Chico, California

Abstract Species of Dioryctria Zeller (Lepidoptera: Pyralidae) are important pests of conifers, particularly in seed orchards, and accurate species identification is needed for effective monitoring and control. Variable forewing morphology and lack of species-specific genitalic features hinder identification, prompting the search for additional diagnostic characters. Mitochondrial DNA (mtDNA) sequences from the cytochrome c oxidase I and II genes (COI and COII) were obtained from specimens collected at lights, pheromone traps, and host plants in the Pacific Northwest, focusing on a U.S. Forest Service seed orchard in Chico, CA. A 475-bp fragment of COI was used to identify eight distinct genetic lineages from 180 Dioryctria specimens, and these were identified as eight described species. Comparisons among mtDNA variation, adult morphology, larval host association, and pheromone attraction were used to assign individuals to species groups and to identify diagnostic characters for species identification. A 2.3-kb fragment of COI-COII was sequenced for 14 specimens to increase resolution of phylogenetic relationships. Species groups were well resolved using both the 475-bp and “DNA barcode” subsets of the 2.3-kb sequences, with the 475-bp fragment generally showing lower divergences. The zimmermani and ponderosae species groups were sister groups and had similar male genitalic morphology and larval feeding habits. The pentictonella group was sister to the zimmermani + ponderosae group clade, and all species have raised scales and a Pinus sp. larval host (where known). Combining molecular characters with morphological and behavioral characters improved identification of Dioryctria species and supported previous species group relationships.