| Summary: | Increasing evidence of non-indigenous ambrosia beetles aggressively attacking hosts in their new environment in the United States has led to concern over the potential for damage to urban trees, nurseries, orchards, and forests. A novel technique of flooding host trees was devised to stimulate ambrosia beetle attacks, with ambrosia beetle attraction peaking four days following flooding. In-situ sampling identified significant differences in the composition, quantity and point of release (leaf or bole) of volatiles emitted by the flooded and non-flooded trees. Coupled gas chromatography electroantennographic detection revealed olfactory sensitivity by the ambrosia beetle Xylosandrus crassiusculus (Motschulsky) to 29 of these compounds and 12 other compounds apparently not associated with hosts. Traps baited with the combination of ethanol and eugenol showed a mean increase in catches over ethanol baits alone. During a trapping survey of Camp Beauregard, Louisiana, flight periods and biodiversity indices were collected for up to 37 species of ambrosia beetles.. Multiple regression analyses identified significant correlations between forest stand characteristics and ambrosia beetle abundances. In fungal competition and vectoring experiments, Rafaella sp., a highly pathogenic, recently discovered fungus associated with the newly-established, exotic ambrosia beetle Xyleborus glabratus (Eichhoff), did not provide significant nutritional benefits to X. crassiusculus. When Rafaella sp. was introduced into a laboratory rearing medium in advance of X. crassiusculus, fewer beetle offspring ultimately emerged. Additionally, the ambrosial associate of X. crassiusculus, Ambrosiella xylebori, demonstrated superior ability to secure and hold resources against Rafaella sp. in differential and spatial separation competition experiments. Relatively earlier addition of Rafaella sp. into beetle media decreased the likelihood of gallery construction, suggesting that X. crassiusculus could detect the presence of Rafaella sp. These three experiments support the hypothesis that these two fungi might compete for spatial and/or nutritional resources, ultimately lowering the fitness of X. crassiusculus. There was no evidence that X. crassiusculus could transport Rafaella sp. in its mycangium, hence X. crassiusculus likely cannot serve as a significant vector of Rafaella sp. in the field.
|
|---|
