An alternative hypothesis explains outbreaks of conifer‐feeding budworms of the genus Choristoneura (Lepidoptera: Tortricidae) in Canada

This alternative hypothesis states that forests attacked by spruce budworms are, for most of the time, nutritional deserts. During these periods, endemic populations persist in scattered “refuges” on a few stressed trees, but this situation changes once trees in a forest become over‐mature and start to senesce. Senescence causes protein in their mature needles to break down at an accelerating rate, releasing higher levels of soluble amino acids into the phloem thereby increasing the quality of food for larval budworms. Additional stress such as drought that damages or kills the trees’ feeding roots accelerates this process and further elevates the quality of the food for larvae. All the foliage in the forest then become nutritious enough to support high numbers of budworm larvae so that nearly all the young larvae of moths dispersing from refuges into the surrounding newly stressed trees survive and an outbreak ensues.