Observations of predation on spruce gall aphids within the gall

A syrphid (Cnemodon sp.) and an itonidid (Aphidoletes abietis Kieffer) were fpund in Switzerland preying on gallicolae within tightly closed galls of 3 adelgid species (Sacchiphantes abietis L.,S. viridis Ratzeburg, andAdelges laricis Vallot). The pattern for gall attack and emergence was different for the 2 predator species. The syrphid entered the gall before it closed and developed at the same rate as the gall; thus, the length of the larval period was variable depending on the type of gall. The itonidid entered the gall after it had closed and caused the gall to open prematurely when the predator reached the last larval instar. The abundance of these 2 predators suggests that the gall may be an unexploited environment for biological control agents to be used against adelgid populations throughout the world.