Patterns of Juvenile Mortality Within an Oligophagous Insect Population

A 4—yr study was performed on an oligophagous population of the nymphalid butterfly Euphydryas editha. Mortality was measured on all juvenile life stages of the insect. Separate life tables were constructed for individuals associated with each of two host plant species, Collinsia torreyi and Pedicularis semibarbata, and mortality associated with these two species was compared. On average, overall mortality was found to be higher associated with P. semibarbata, which supports previous work that has shown C. torreyi to be the more suitable host plant for E. editha at this site. Other general patterns emerged from a comparison of mortality within instars. Egg and prediapause larval mortality were generally higher associated with P. semibarbata, while pupal mortality was generally higher associated with C. torreyi. Postdiapause larval mortality was extremely variable, and closely tracked levels of parasitism associated with the two host plant species. The data demonstrated considerable variation in mortality, both among life stages and among generations. This variation raises questions about the methodologies used in many suitability studies.