Lack of Short or Long Term Inducible Defenses in the Red Alder: Western Tent Caterpillar System

Abstract

We tested whether mechanical damage or caterpillar feeding induced a reduction in the quality of red alder leaves by comparing the development rate, pupal size, and survival of tent caterpillars reared on leaves adjacent to damage, and on control trees or branches that lacked insect attack. No significant effects could be found to suggest an immediate reduction in quality of foliage in the vicinity of insect attack consistent with a defensive response. In long term studies, caterpillars fed foliage from an area of prolonged high caterpillar density developed more slowly and female pupae and/or adults weighed less than those fed foliage from trees in areas of recent or no caterpillar attack. These results can be explained by lower nitrogen content of trees in the area of prolonged attack. Even though food quality in the area of prolonged attack was lower than in other areas, tent caterpillar densities there remained high from 1981 to 1985. A more drastic reduction in fecundity and survival than that caused by lower nitrogen content of the foliage, is necessary to cause a population decline.