EFFECTS OF FOOD QUANTITY AND QUALITY ON EMERGENCE TIME IN THE CINNABAR MOTH

In North America some introduced cinnabar moth [Tyria jacobaeae] populations have been dense their establishment and extensively defoliate their food plants annually. Other populations fluctuate and defoliate all the available tansy ragwort [Senecio jacobaea] only every 3-4 yr. The hypothesis that annual food limitation should select for early moth emergence was tested by comparing temperature thresholds and development times for pupae from these 2 types of populations. Data do not support this hypothesis. Introduced populations living at different climates and of different European origins have similar temperature thresholds and development times. An alternative hypothesis is that moth emergence is synchronized with the time of tansy ragwort flowering. This is supported by the observation in laboratory studies that larvae which feed on flowers produce larger pupae than those which feed only on leaves. Larvae developing early in the summer and the early emerging moths tend to be smaller; larvae developing in the middle to late part of the season apparently do better.