Robert J. Rabaglia

A fungal symbiont of the redbay ambrosia beetle causes a lethal wilt in redbay and other lauraceae in the Southeastern United States

Extensive mortality of redbay has been observed in the coastal plain counties of Georgia and southeastern South Carolina since 2003 and northeastern Florida since 2005. We show that the redbay mortality is due to a vascular wilt disease caused by an undescribed Raffaelea sp. that is a fungal symbiont of Xyleborus glabratus, an exotic ambrosia beetle. Trees affected by the disease exhibit wilt symptoms that include a black discoloration of the sapwood. Redbay trees and containerized seedlings died within 5 to 12 weeks after inoculation with the Raffaelea sp. When redbay seedlings were challenged with X. glabratus, the beetles tunneled into 96% of the plants, 70% died, and the Raffaelea sp. was recovered from 91%. X. glabratus and the Raffaelea sp. have also been associated with mortality of sassafras, and the Raffaelea sp. has been isolated from wilted pondberry and pondspice. Additional inoculation studies have shown that the Raffaelea sp. is pathogenic to sassafras, spicebush, and avocado, but not to red maple. Female adults of X. glabratus have paired mycangia near the mandibles, and the Raffaelea sp. is routinely isolated from the heads of beetles. The fungus is apparently introduced into healthy redbay during beetle attacks on stems and branches. The wilt currently affecting redbay and sassafras represents a major threat to other members of the Lauraceae indigenous to the Americas, including avocado in commercial production.

Review of American Xyleborina (Coleoptera: Curculionidae: Scolytinae) Occurring North of Mexico, with an Illustrated Key

Abstract Ambrosia-feeding scolytids in the Xyleborina are the most abundant exotic bark beetles in North America. Many new species discoveries and taxonomic changes have occurred since their last review in 1982. The need for a worldwide revision of this tribe hampers the ability to identify species. To remedy this situation, an illustrated key is constructed and Xyleborus glabratus Eichhoff, Xyleborus similis Ferrari, and Euwallacea fornicatus (Eichhoff), which are new to North America, are reported and diagnosed. In addition the key is presented in electronic format with additional illustration (http://scolytid.msu.edu) to increase worldwide availability and accommodate future taxonomic revision.

Biology and host associations of redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae), exotic vector of laurel wilt killing redbay trees in the Southeastern United States

Abstract The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), and its fungal symbiont, Raffaelea sp., are new introductions to the southeastern United States responsible for the wilt of mature redbay, Persea borbonia (L.) Spreng., trees. In 2006 and 2007, we investigated the seasonal flight activity of X. glabratus, its host associations, and population levels at eight locations in South Carolina and Georgia where infestations ranged from very recent to at least several years old. Adults were active throughout the year with peak activity in early September. Brood development seems to take 50–60 d. Wood infested with beetles and infected with the Raffaelea sp. was similar in attraction to uninfested redbay wood, whereas both were more attractive than a nonhost species. Sassafras, Sassafras albidium (Nutt.) Nees, another species of Lauraceae, was not attractive to X. glabratus and very few beetle entrance holes were found in sassafras wood compared with redbay. Conversely, avocado, Persea americana Mill., was as attractive to X. glabratus as swampbay, P. palustris (Raf.) Sarg., and both were more attractive than the nonhost red maple, Acer rubrum L. However, avocado had relatively few entrance holes in the wood. In 2007, we compared X. glabratus populations in areas where all mature redbay have died to areas where infestations were very active and more recent. Trap catches of X. glabratus and numbers of entrance holes in trap bolts of redbay were correlated with the number of dead trees with leaves attached. Older infestations where mature host trees had been eliminated by the wilt had low numbers of beetles resulting in trap catches ranging from 0.04 to 0.12 beetles per trap per d compared with 4–7 beetles per trap per d in areas with numerous recently dead trees. Our results indicate beetle populations drop dramatically after suitable host material is gone and provide hope that management strategies can be developed to restore redbay trees. The lack of attraction of X. glabratus to sassafras suggests that spread of X. glabratus may slow once it is outside the range of redbay.

Exploring associations between international trade and environmental factors with establishment patterns of exotic Scolytinae

Although invasion of exotic ambrosia beetles (fungus feeders) and bark beetles (phloem feeders) (Coleoptera: Curculionidae: Scolytinae) is considered a major threat to forest health worldwide, no studies have quantitatively investigated the anthropogenic and environmental factors shaping the biogeographical patterns of invasion by these insects across large spatial scales. The primary aim of this study was to assess the relative importance of international trade and several environmental variables of the recipient region on species richness of established exotic Scolytinae. As a reference, we also evaluated the relationships between the same environmental variables and species richness of native Scolytinae. Using an information-theoretic framework for model selection and hierarchical partitioning, we evaluated the relative importance of the potential drivers of species richness of native and exotic Scolytinae in 20 European countries and the 48 contiguous continental US states. Analyses were conducted separately for ambrosia and bark beetle species. Value of imports was a strong predictor of the number of exotic Scolytinae species in both regions. In addition, in the USA, warmer and wetter climate was positively linked to increased numbers of both native and exotic ambrosia beetles. Forest heterogeneity and climatic heterogeneity and secondarily forest area were key drivers in explaining patterns of species richness for native bark beetles but not for exotic species in both regions. Our findings suggest that if current infestation levels continue on imported plants and wood packaging material, increasing international trade will likely lead to more establishments of exotic Scolytinae with concomitant negative effects on forest health in both Europe and the USA. Compared to Europe the risk of invasion appears higher in the USA, especially for ambrosia beetles in the southeastern USA where the climate appears highly suitable for exotic establishment.

Exotic bark and ambrosia beetles in the USA: potential and current invaders

Bark and ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) are among the most important insects affecting trees and forests worldwide. There are approximately 6000 scolytine species worldwide, with species found on all continents except Antarctica (Table 3.1) (Wood and Bright, 1992; Bright and Skidmore, 1997, 2002; Wood, 2007). The majority of species are found in the tropics, but many also occur in boreal forests. Undoubtedly, there are hundreds of additional species that have not yet been described. Many authorities now consider the bark and ambrosia beetles a subfamily (Scolytinae) of the weevil family (Curculionidae) (Alonso- Zarazaga and Lyal, 2009), while others continue to treat them as a distinct family (Wood, 2007). In this chapter, we will use the subfamily ranking Scolytinae, but recognize that most plant protection agencies worldwide continue to use Scolytidae.

Recovery plan for laurel wilt on redbay and other forest species caused by Raffaelea lauricola and disseminated by Xyleborus glabratus

This recovery plan is one of several disease-specific documents produced as part of the National Plant Disease Recovery System (NPDRS) called for in Homeland Security Presidential Directive Number 9 (HSPD-9). The purpose of the NPDRS is to insure that the tools, infrastructure, communication networks, and capacity required to mitigate the impact of high-consequence plant disease outbreaks are such that a reasonable level of crop production is maintained. Each disease-specific plan is intended to provide a brief primer on the disease, assess the status of critical recovery components, and identify disease management research, extension, and education needs. These documents are not intended to be stand-alone documents that address all of the many and varied aspects of plant disease outbreak and all of the decisions that must be made and actions taken to achieve effective response and recovery. They are, however, documents that will help USDA guide further efforts directed toward plant disease recovery.

Tracing the origin of a cryptic invader: phylogeography of the Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae) species complex: E. fornicatus species complex phylogeography

The ambrosia beetle morphologically identified as Euwallacea fornicatus consists of several cryptic species that exhibit large differences in the DNA sequences of several nuclear and mitochondrial gene regions. Based on these differences, we suggest that there are at least three different species each with distinct phylogeography. Members of this cryptic species complex have invaded many areas outside their native range and cause substantial damage to both agriculture (avocado in particular) and other tree species. Three of these cryptic species have invaded the USA: two species in California and a third species in both Florida and Hawaii. Identification of their native range allows directed search for their natural enemies that may be used in biological control of these tree pests.

Xyleborus seriatus Blandford (Coleoptera: Curculionidae: Scolytinae), An Asian Ambrosia Beetle New to North America

Abstract Xyleborus seriatus Blandford, an ambrosia beetle described from Japan, is reported for the first time from North America, based on specimens examined from Massachusetts. A re-description and diagnosis of the adult female, a summary of known distribution and biology, a revision to an existing key to North American xyleborine species to include this newly detected immigrant, and photographs of the adult habitus and other diagnostic morphological features are presented.

Fungal symbionts in three exotic ambrosia beetles, Xylosandrus amputatus, Xyleborinus andrewesi, and Dryoxylon onoharaense (Coleoptera: Curculionidae: Scolytinae: Xyleborini) in Florida

In nearly every forest habitat, ambrosia beetles (Coleoptera: Curculionidae: Scolytinae, Platypodinae) plant and maintain symbiotic fungus gardens inside dead or dying trees. Some non-native ambrosia beetles aggressively attack live trees and damage tree crops, lumber, and native woody plant taxa by introducing ambrosia fungi, some of which are plant pathogens. Most established exotic species, however, do not cause any economic damage, and consequently are little studied. To determine the specificity and diversity of ambrosia symbionts in under-studied non-native beetles in Florida, fungi were isolated from three species: Xylosandrus amputatus, Xyleborinus andrewesi, and Dryoxylon onoharaense. Two of the beetles sampled each yielded a fungal species isolated with 100xa0% frequency: X. amputatus: Ambrosiella beaveri or A. nakashimae, and X. andrewesi: Raffaelea sp. nov. nr. canadensis. Both of these symbionts have been isolated previously from closely related ambrosia beetles, supporting the hypothesis that some beetles can carry monocultures of fungi, but the fungi may not be specific to single beetle species. No consistent fungi were isolated from Dryoxylon onoharaense, raising questions about whether or not it truly carries its own symbionts. These results are now being used to test hypotheses and models explaining the evolution of pathogenicity within ambrosia fungi and invasion ability within exotic beetle-fungus complexes.

First records of Xyleborinus octiesdentatus (Murayama) (Coleoptera, Curculionidae, Scolytinae) from North America.

Abstract Xyleborinus octiesdentatus (Murayama), an ambrosia beetle native to Asia, is reported for the first time in North America based on specimens from Alabama and Louisiana. This is the twenty-first species of exotic Xyleborina documented in North America. A re-description of the female and a key to the four North American species of Xyleborinus are presented.