Epizootiology of Massospora levispora in an Isolated Population of Okanagana rimosa1,2,3

Abstract

The Massospora pathogen occurs only in the aboveground population, i.e., adults. Cicadas become infected just prior to emergence by resting spores which then produce conidia; initial infection usually results in production of conidia. Adult cicadas infected by the conidia in turn normally produce only resting spores. Prevalence of conidia infected males remains constant, whereas a slight increase was noticed in females in 1967 but was constant in 1969. In populations of 17-yr cicadas, Magicicada septendecim, where Massospora cicadina occurs, conidial prevalence is relatively constant and equal between the sexes. The majority of individuals harboring resting spores are females indicating a higher degree of secondary transmission to them. Two major emergences of O. rimosa were studied. Mark-recapture analysis and a technique for determining age distribution were utilized to estimate absolute population density. The sex ratio of adult cicadas did not differ from a 1:1 ratio at anytime. The cicadas normally emerged in the morning but emergence was prolonged or deferred by inclement weather. Total emergence for the 20 ha study area was between 1.07 × 108 and 1.37 × 106 in 1967 and 0.96 × 106 to 1.57 × 106 in 1969 at a 90% level of confidence. Bailey's triple catch analysis gave the best estimate of absolute density from mark and recapture data. Comparison of emergence with the total population shows that even this analysis grossly underestimated the population. The age distribution analysis method gave a better estimate of absolute population density.