Dr. Kassai Tibor - Dr. Murai Éva szerk.: Parasitologia Hungarica 6. (Budapest, 1973)
more than one cysts. These values in females were 41 and 19 respectively. Considering the fully developed larvae, 43 males and 50 females were infested by one and 9 males and 9 females by more than one larvae. We found several times some lactating and at the same time gravid females with an intensive infestation. The greatest number of larvae found was 6. 4) There were important differences in the occurrence of strobilocercosis according to the seasons (Table 2 and Pig. 3). The infestation was at a minimum during summer or the period of vegetation, and at a maximum in winter populations. This is probably connected with the vole-killing activity of predators or some other factor (during the infective phase of oncosphera, resistance of voles). Aware of the reproductive cycle in the vole population, the specimens infested by strobilocercosi can be considered indicative of the whole population and their disappearance from the population until summer time indicates a relatively quick mortality of overwintered animals next spring. These data confirm the results of the seasonal changes of the structure in Microtus arvalis populations shown by MARTINET (1967), MARTINET and SPITZ (1971). (In our experimental area we found the sexually inactive - non breading - season in 1968/69 from the middle of Oct. to the middle of April, in 1969/70 from Dec. to the end of March, in 1970/71 from Oct. to the middle of Pebr. and in 1971/ 72 from the end of Sept. to the middle of March.) In autumn, the small infestations of corn cultures (Pig. 3) are probably due to the fact that these are ploughed and sown in October-November .The majority of these populations consisted of recent immigrants from other territories. The migration is probably an explanation of the fact that strobilocercosis is more frequent even in autumn in these areas than during the summer . 5) Considering the infectious sources mentioned, only the Bük vole population is really known . The area represented by col126
