Insect control measures can be effective not only by increasing mortality but also by affecting development and activity. Analysis of the simultaneous effects of a treatment on death times and development times is, however, complicated by difficulties that also arise in analyzing biomedical data in which there are competing causes of death. The theory that has been developed for dealing with these problems, competing risks theory, is reviewed in this article and applied to data from a laboratory study of the effects of Nosema locustae Canning and N. cuneatum Henry on mortality and development in Locusta migratoria migratorioides (Reiche & Fairmaire). Although the distributions of observed development times are similar among application rates, the use of competing risks methods showed that slower development is associated with increasing doses of both Nosema species. Further analysis of death times showed that N. locustae and N. cuneatum have quite different effects on development and mortality. N. locustae does not retard progression to the fifth instar as much as N. cuneatum, but for N. cuneatum, the death rate of inoculated locusts is greatly reduced at the onset of the fifth instar.
