Biosci osciences an international journal Volume 145 Eric P. M. Grist (Dundee, Scotland) AND WILLA S. C. GURNEY (Glasgow, Scotland) Seasonal Synchronicity and Stage-Specific Life Cycles: Topp’s Beetles Revisited NIKOLAOS I. STILIANAKIS (Los Alamos, New Mexico), KLAUS DIETZ, AND DIETER SCHENZLE (Tiibingen, Germany) Analysis of a Model for the Pathogenesis of AIDS E. M. LuNGu (Gaborone, Botswana) AND B. OKSENDAL (Oslo, Norway) Optimal Harvesting from a Population in a Stochastic Crowded Environment B. G. WILLIAMS (Johannesburg, South Africa) AND C. Dye (London, United Kingdom) Infectious Disease Persistence When Transmission Varies Seasonally HERBERT W. HETHCOTE (lowa City, lowa) An Age-Structured Model for Pertussis Transmission ZiAD TAIB (GOteborg, Sweden) A Multitype Branching Process Model for Blue-Green Algae VOLUME CONTENTS Elsevier