What indicates the presence of Ambrosia beetles in wood?

The presence of Ambrosia beetles in wood is indicated by the staining of wood inside galleries and surrounding exit holes. Ambrosia beetles carry fungal spores into the wood they infest, which they use as a food source. When they tunnel into the wood to create their galleries, the wood becomes stained due to the interaction between the wood fibers and the fungi. This staining can manifest as dark streaks or discoloration around the areas where the beetles have entered, particularly visible around the exit holes where the beetles have exited the wood. This specific staining is a clear sign of their presence and indicates that the beetles are actively infesting the wood.

Other indicators like dark frass, visible exit holes, and sawdust accumulation can suggest wood-boring insects in general, but they are not exclusive to Ambrosia beetles. Frass (insect excrement) can come from various wood-boring pests, while visible exit holes might indicate activity from different species of beetles, and sawdust can be a sign of multiple types of infestations. Thus, the specific interaction between the beetles and the wood leading to characteristic staining is the best indication of Ambrosia beetles.