S. Mahunka szerk.: Folia Entomologica Hungarica 46/2. (Budapest, 1985)

The individual number of Musca autumnalis imagos on the bodies of cattle is insignificant compared with the estimated individual number of the whole populations on pasture. In the literature there are data for the ratio of the imagos on cattle at a given moment to the whole population as 4 to 20 % (PICKENS and MILLER, 1980, etc.). On the basis of our data we have made an estimation to determine this ratio. A full-grown cow defecates dung equalling c. 50 00 g dry weight daily. Let us suppose that half of that quantity, i.e. 2500 g is dropped on pastures, the other half is trampled in the corrals, at watering places, etc. Using the results from cattle dropping samples taken in many areas of Hungary in the last 15 years from May to September, a calculation has been made: how many individuals of Musca autumnalis are developing as a mean from the amount of dung one cow produces a day. We must stress that our calculation is not from estimations but from data of concrete massweighings and rearings. So, based on samples collected near Aranyos gad any, in the July of 1969 (PAPP, 1971, Table 1: Nos 8-52): 1260 ex. of M. autumnalis were reared from 2021 g dry weight of 44 samples, that is 0.623 ex./g with a dominance of individuals of 10.03 %; Hortobágy National Park, 27-29th August 1974: 28 ex. of M. autumnalis from 178 g dry weight of four samples, i.e. 0.157 ex./g with a dominance of 10.45 %; Szentendre, 18th July 1972: 93 ex. of M. autumnalis from 84 g dry weight of two samples, i.e. 1.107 ex./g with a dominance of 27.43 %; from data published by PAPP (1976), on the basis of 11 samples taken in six areas of the country: c. 0.8 ex./g with a mean dominance of 25.74 %; from the data of present studies at Mezohék (Table 1): 0.946 ex./g with a very high dominance (56 . 97 %); from c. 400 g dry weight of eight samples taken at Izsák 189 M. autumnalis specimens were reared, i.e. 0.458 ex./g with a dominance of 7.65 %. Based on all these we can estimate that in Hungary a mean of 0.5 Musca autumnalis specimen per 1 g dry weight of cattle droppings develops on pastures from the middle or end of May to September. A calculation from data of eggs laid in or of larvae extracted from droppings would result in even higher values since we calculated from data of imagos emerged. Our calculation for the ratio of the imagos on the bodies of cattle at a given moment to the whole population of imagos Is based on the above data, on the numbers of flies caught on cattle (Table 2) and on their dominance values. As we have mentioned above, we can state that in our country the number of specimens of Musca autumnalis is 20 to 25 times higher than those of Hae matobia

, i.e. if 1250 specimens of M. autumnalis emerge from dung defecated by a cow daily,then 50 to 60 specimens of Haematobia develop In the same amount of dung (from data of Table 1 this is slightly lower than 20 but 9 samples are from corrals!). One can catch 4 to 8 times more specimens of Haematobia than those of Musca autumnalis on cattle (in some cases 40-60 times more). Let us choose a mean value of six times more (it is from data of Nos 7-28 of Table 2: M. autum nalis

: 519 ex., Haematobia

: 3215 ex.). In reality, while 100 ex. of Haematobia emerge, then 20002500 M. autumnalis emerge from the same droppings; on the bodies of cattle for 100 ex. of Haematobia we can find only 16 specimens of Musca autumnalis

. Since practically every specimen of Haematobia is remaining on the cattle (except for just egg-laying females), we can see from the above calculation that less than 1 % of the actual imago populations of Musca autumnalis are remaining at a given moment on the bodies of cattle. If the emergence ratio of Musca autumnalis is 1250 specimens per cow per day and one specimen lives 14 days as a mean and if a continuous and equal seplacement Is supposed (which is not without reason for Hungary in the summer period), one cow maintains 17, 500 specimens of Musca autumnalis imagos. Its 0.1 % is 17.5 specimens. If one-twentieth of the 1250 specimens is calculated for those of Haematobia

, supposing similar life-span also for these species, 62.5 x 14 = 875 specimens of Haematobia per cow is obtained. Well, these values, 17.5 specimens of Musca autumnalis and 875 specimens of Haematobia per cow are in a conspicuously good agreement with the number of flies we can observe on a cow of herds without chemical control in Hungary in July August; we regard this fact as a best evidence of our calculation. As we observed, though the populations of Musca autumnalis are in need of cattle droppings as substrate for their development but their imagos well thrive also in lack of cattle. The Izsák sample of Table 3 was collected on a pasture, whence cattle had been driven in the previous night. The imagos of this population were feeding on flowers, on less old cattle droppings. It was observed very frequenty that the imagos of the species Musca autumnalis, Musca tempestiva and Mus ca osiris suck fluids of saliva of cattle left on stubs of grass, besides fresh cattle dung, urine and meadow flowers. On cows of the above-mentioned herd, which was driven at a distance of about 2 kms, imagos of Musca autumnalis were found only exceptionally. All these are why we can propose that if pastures are changed at or just after sunset to a distance of at least 1-2 kms, we can