Presumably the trichomes make it more difficult for the aphids to feed. Witch hazel leaves covered with cone galls. Hormaphis gall opened to show the interior. The white fluff is a waxy secretion produced by the aphids. The same trees seem to get hit year after year, suggesting that there may be a genetic basis for this variation in susceptibility to attack.
Many animals store food for long periods of time to prevent starvation.
One problem these animals face is deciding what food types to store and what to eat immediately. This is complicated because often the most nutritious foods spoil the fastest. It seems likely that natural selection has equipped caching species with the ability to make the correct decision. The following paragraph is the abstract of our paper which was recently published in the American Naturalist. Consequently, when selecting food for a long-term cache an animal should consider what the value of each food item will be when it is eaten rather than when it is collected.