1:49 Today's topic is how to put up a no vacancy sign for the Douglas-fir beetles. Most people are aware of the destruction to large swaths of forest trees brought about by a tiny insect group called bark beetles. In addition to damaging timber resources, beetle-killed trees negatively impact campgrounds' residential sites and increase wildfire severity. Research has found that pheromones, which are chemical cues used in communication within a species, are present in bark beetles and produce two types: aggregation and anti-aggregation. Aggregation pheromones are released by female Douglas-fir beetles to serve the purpose attracting mates and large numbers of beetles to come and help them overwhelm the tree defenses.