Six species and subspecies of rats and mice, Arvicanthis niloticus, Rattus norvegicus, R. rattus frugivorus, R. rattus alexandrinus, R. rattus rattus, and Mus musculus, were found associated with cotton, wheat, maize, sugar-cane, vegetables, fruit and berseem in the vicinity of Alexandria, Egypt. A. niloticus comprised 42·2% of all species collected. Maize, wheat, cotton and berseem were infested most. The lowest infestation was recorded in the fruit fields. Infestation in sugar-cane and vegetables was intermediate. R. norvegicus, M. musculus, R. rattus frugivorus, R. rattus alexandrinus and it. rattus rattusformed 23·9, 16·7, 10·4, 4·2 and 2·7% of the species collected respectively. Of the seven crops investigated, only two (cotton, wheat) were not infested with R. rattus rattus, but all were plagued with some species of rodents. The abundance of these rodents in fields seemed to be positively correlated with temperature and relative humidity. Winter represents a definite off-season for all species recorded.
Six species of fleas (Xenopsylla cheopis, Nosopsyllus fasciatus, Ctenocephalides felis felis, Leptopsylla segnis, Pulex irritans and Echidnophaga gallinacea), three of sucking lice (Polyplax abyssinica, P. spinulosa and Hoplopleura capitosa), five of parasitic mites (Ornithonyssus bacoti, Laelaps echidnina, L. keegani, Androlaelaps zulu and Haemolaelaps sp.) and the tick Rhipicephalus sanguineus sanguineus were recovered from the rodents. Fleas (especially X. cheopis) and lice generally showed a certain degree of host specificity. A close relationship has been shown to exist between the abundance of fleas and lice and the abundance of some rodent hosts and climate. However, no definite host specificity or relation to climate was shown by infestation with mite species. Only B. sanguineus sanguinetie was recovered from S. rattus frugivorus during July, October and December; from R. rattus alexandrinus during November; and from R. rattus rattus during September. Its rate of infestation did not exceed one specimen per rodent host.