REPRODUCTIVE AND POPULATION BIOLOGY OF PORCELLIO SCABER (ISOPODA, ONISCIDEA) IN BENGHAZI, LIBYA

ABSTRACT

The breeding of Porcellio scaber in Benghazi, Libya, was almost continuous in the field throughout the period of study (May 1993 to May 1994) except from November 1993 till the middle of January 1994. Sexes were distinguished in animals 5 mm long on the basis of secondary sexual characters. Mature males and females were present all the year round. The total number of eggs produced was correlated with the body length of gravid females. The average incubation periods of field animals during summer/autumn and late winter/spring were 18 and 32 days, respectively. Brood mortality was 8.5%. The newly hatched stadium had a body length of 2 mm and the initial growth was rapid for those born in summer/autumn as compared with those born in late winter/spring. A bimodal size distribution in P. scaber population observed in May 1993 changed to a unimodal one during November 1993, reversing to bimodality from February till the beginning of May 1994. The disappearance of the upper mode in the size distribution was compensated for by the recruitment of young and the rapid growth of different size classes. An increase in the embryo crop and embryo production was evident during spring as compared with the summer and autumn seasons. The sex ratio showed a preponderance of females over males in most of the months and seasons studied.