[Decrease in the milk yield in cows casued by dipterous blood-sucking insects and the protection of heifers with Oxamate, a repellent, in the area of Leningrad].

: Blood-sucking dipterous insects, milk yield losses caused by these insects to cows in the pasture and the possibilities of cattle protection against these insects were investigated in the Leningrad region of the USSR in 1982-1984. The invasion by horse-flies causes the greatest trouble to grazing cattle. Twenty-five horse-fly species were identified during the study. The nine prevailing species constituted more than 85% of the horse-flies invading the animals. The horse-flies flew for 50-55 days from the beginning of June to the beginning of August; mass flights were observed for two weeks starting in the second decade of June. A twelve-hour repelling action was recorded in the Oxamate repellent applied as 20% emulsion. A new portable motor-powered aerosol sprayer was tested during the study. The losses in milk yields caused by horse-flies in the Leningrad region were computed; in the period of the horse-fly flights the milk yields are reduced by 13%. The economic benefit of the treatment of the animals with the Oxamate repellent was 9.11 roubles per rouble invested. Manitoba-type traps attracting the horse-flies to an optical bait (a black ball or cube) were used as an additional method of reducing the occurrence of horse-flies in the pasture.