Wild Bee Response to Application of the Douglas-fir Beetle Anti-Aggregation Pheromone, 3-Methylcyclohex-2-En-1-One.

Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (DFB), is the most damaging insect pest of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, in western North America. Individual high-value trees and stands can be protected during DFB outbreaks using the beetle's anti-aggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), which is available in several commercial formulations. However, other methylcyclohexanones similar in molecular structure to MCH have been shown to repel bees from agricultural areas. In forest systems, wild bees (Hymenoptera: Apiformes) provide essential pollination services to many forb and shrub species. Therefore, it is important to determine whether resident wild bee communities are affected in forests treated with MCH. To address this, the bee community was sampled within experimental sites located in Idaho and Montana, USA in 2016. At both sites, there was no significant difference in overall bee abundance, species richness, or diversity between MCH-treated plots and untreated control plots. Overall, these results indicate that treatment of Douglas-fir with MCH does not negatively impact the resident wild bee community.

Changes in the Summer Wild Bee Community Following a Bark Beetle Outbreak in a Douglas-fir Forest.

The status of wild bees has received increased interest following recent estimates of large-scale declines in their abundances across the United States. However, basic information is limited regarding the factors affecting wild bee communities in temperate coniferous forest ecosystems. To assess the early responses of bees to bark beetle disturbance, we sampled the bee community of a Douglas-fir, Pseudotsuga menziesii (Mirb.), forest in western Idaho, United States during a Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (Coleoptera: Curculionidae), outbreak beginning in summer 2016. We resampled the area in summer 2018 following reductions in forest canopy cover resulting from mortality of dominant and codominant Douglas-fir. Overall, results from rarefaction analyses indicated significant increases in bee diversity (Shannon's H) in 2018 compared to 2016. Results from ANOVA also showed significant increases in bee abundance and diversity in 2018 compared to 2016. Poisson regression analyses revealed percent tree mortality from Douglas-fir beetle was positively correlated with increases in total bee abundance and species richness, where community response variables displayed a cubic trend with percent tree mortality. Percent reduction in canopy cover from 2016 to 2018 was also correlated with bee species richness and diversity. These findings suggest that wild bee communities may benefit from changes in forest structure following bark beetle outbreaks.

Interactions between the yeast Ogataea pini and filamentous fungi associated with the western pine beetle.

Ecologically important microbes other than filamentous fungi can be housed within the fungal-transport structures (mycangia) of Dendroctonus bark beetles. The yeast Ogataea pini (Saccharomycetales: Saccharomycetaceae) was isolated from the mycangia of western pine beetle (Dendroctonus brevicomis) populations in northern Arizona (USA) with a frequency of 56%. We performed a series of in vitro assays to test whether volatile organic compounds produced by O. pini affected radial growth rates of mutualistic and antagonistic species of filamentous fungi that are commonly found in association with the beetle including Entomocorticium sp. B, Ophiostoma minus, Beauvaria bassiana, and an Aspergillus sp. We determined the compounds O. pini produced when grown on 2% malt extract agar using a gas chromatography/mass spectrometry (GC/MS) analysis of headspace volatiles. Volatiles produced by O. pini on artificial media significantly enhanced the growth of the mutualistic Entomocorticium sp. B, and inhibited growth of the entomopathogenic fungus B. bassiana. GC/MS revealed that O. pini produced ethanol, carbon disulfide (CS(2)), and Δ-3-carene in headspace. The results of these studies implicate O. pini as an important component in D. brevicomis community ecology, and we introduce multiple hypotheses for future tests of the effects of yeasts in the symbiont assemblages associated with Dendroctonus bark beetles.