Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka.
1Current address: Department of Entomology, North Dakota State University, Fargo, ND, 58105, USA. E-mail: Saddha.ganehiarachchh@ndsu.edu.
A census of the population of Sugarcane planthopper Pyrilla perpusilla Walker in Kelaniya, Sri Lanka, was carried out to assess the main mortality factors acting on egg, nymph and adult stages from July 1993 to July 1995. Biotic as well as abiotic factors responsible for the mortality of this insect were identified and eight cohorts of this pest were constructed. Results suggest that the population of P. perpusilla suffered heavy mortality during the study period and only a small proportion of eggs survived to adulthood. Among the mortality factors, natural enemies and rainfall were most important. The most severely affected stage was first instar nymph in almost all of the eight cohorts due to a high level of predation during dry months. The severity of rainfall caused high mortality among all the nymphal instars as many nymphs and predators perished.
