Non-Native Ambrosia Beetles as Opportunistic Exploiters of Living but Weakened Trees

Abstract

Exotic Xylosandrus spp. ambrosia beetles established in non-native habitats have been associated with sudden and extensive attacks on a diverse range of living trees, but factors driving their shift from dying/dead hosts to living and healthy ones are not well understood. We sought to characterize the role of host physiological condition on preference and colonization by two invaders, Xylosandrus germanus and Xylosandrus crassiusculus. When given free-choice under field conditions among flooded and non-flooded deciduous tree species of varying intolerance to flooding, beetles attacked flood-intolerant tree species over more tolerant species within 3 days of initiating flood stress. In particular, flood-intolerant flowering dogwood (Cornus florida) sustained more attacks than flood-tolerant species, including silver maple (Acer saccharinum) and swamp white oak (Quercus bicolor). Ethanol, a key host-derived attractant, was detected at higher concentrations 3 days after initiating flooding within stems of flood intolerant species compared to tolerant and non-flooded species. A positive correlation was also detected between ethanol concentrations in stem tissue and cumulative ambrosia beetle attacks. When adult X. germanus and X. crassiusculus were confined with no-choice to stems of flood-stressed and non-flooded C. florida, more ejected sawdust resulting from tunneling activity was associated with the flood-stressed trees. Furthermore, living foundresses, eggs, larvae, and pupae were only detected within galleries created in stems of flood-stressed trees. Despite a capability to attack diverse tree genera, X. germanus and X. crassiusculus efficiently distinguished among varying host qualities and preferentially targeted trees based on their intolerance of flood stress. Non-flooded trees were not preferred or successfully colonized. This study demonstrates the host-selection strategy exhibited by X. germanus and X. crassiusculus in non-native habitats involves detection of stress-induced ethanol emission and early colonization of living but weakened trees.

First report of a sexual state in an ambrosia fungus:Ambrosiella cleistominutasp. nov. associated with the ambrosia beetleAnisandrus maiche

“…to Ranger et al (2010), but moist paper towels were placed in the lower collection bottle rather than low-toxicity antifreeze in order to maintain beetle and fungal viability (Ranger et al 2015). Female adults were stored refrigerated in parafilm-sealed Petri dishes with moist filter paper, then killed by crushing the exoskeleton and shipped overnight in glass vials with or without sterile moist filter paper.…”

“…Adult female A. maiche have been recovered from floodstressed Cornus florida L. trees attacked in Ohio, USA (Ranger et al 2015), and could present a similar risk to ornamental and horticultural trees as other invasive Xyleborini (Ranger et al 2016). Based on studies of other Anisandrus spp.…”

Plasticity of mycangia in Xylosandrus ambrosia beetles

“…An increasingly popular model for studies of the ambrosia symbiosis is the genus Xylosandrus (Harrington et al ., ; Bateman et al ., ; Kostovcik et al ., ; Mayers et al ., ; Ranger et al ., ; Frank et al ., ). Reasons for this interest include the economic impact and high abundance of some species, but also the fact that the mycangium is accessible and can be easily sampled for fungi.…”

Molecular phylogeny of bark and ambrosia beetles (Curculionidae: Scolytinae) based on 18 molecular markers

“…E-mail: bjarte.jordal@uib.no in any forests, making characteristic wood burrows deep into the wood or fine engravings just under the bark of dead trees. Only a few species are capable of attacking living trees Ranger et al, 2015), whereas most species colonize woody substrates of dead plants. Some species of bark beetles are not found in logs and branches, but instead feed and reproduce in seeds, petioles, or seedlings of trees, occasionally in woody herbs and ferns, adding to the broad range of host plant relationships in this group of beetles (Jordal & Kirkendall, 1998;.…”