LIFE HISTORY OF A SEMELPAROUS ONISCID ISOPOD, SCHIZIDIUM TIBERIANUM VERHOEFF, INHABITING THE MEDITERRANEAN REGION OF NORTHERN ISRAEL

ABSTRACT

The oniscid pillbug, Schizidium tiberianum Verhoeff (Armadillidiidae), inhabits the Mediterranean region of northern Israel. Its population structure was studied in a pine forest. Since no overlap in weight (age) groups was observed, Schizidium was inferred to have an annual cycle. Males were rarely found in the natural population, and the sex ratio in the population was 1M: 6F. The sex ratio in juvenile cohorts raised in the laboratory was 1:1. This indicates a possible higher mortality among males. Indeed, the laboratory males died sooner than females. Oogenesis and subsequent vitellogenesis are short, lasting 3 months. These are reflected in increased dimensions of both ovaries and oocytes. Vitellogenesis ends when the mature ova move into the marsupium. A loss in oocytes, partly due to oosorption, was noticeable at this stage. Eggs, embryos, and mancas can be found simultaneously in the marsupium. The females die soon after having released their mancas, and the latter feed on their mother's carcass.