Aktivitet af mitter på græsningsarealer ved Egeløkke lung

Aktivitet af mitter på græsningsarealer ved Egeløkke lung

Summary and conclusions

The activity of biting midges (Ceratopogonidae: Culicoides) at the marsh Egeløkke Lung, Langeland, Denmark, was recorded by daily sampling from early May to mid November 1998, using two automatic light traps. One trap was placed at the edge of the marsh, which is the breeding site of several species of biting midges, some of them occurring in high densities. To elucidate the flight range of the midges another light trap was placed at a distance of about 40 m from the edge of the marsh. A total of 30,514 biting midges were collected in the two light traps. Culicoides punctatus and C. obsoletus were most abundant. The predominant species were sexed, and the reproductive status of female midges was assessed (nulliparous, gravid, parous empty). Based on the gonotrophic distribution pattern the potential number of hostseeking biting midges trapped in the two light traps was estimated. Further, the number of biting midges attacking pastured heifers was recorded. The midges were collected by means of a modified vacuum cleaner and species and reproductive status were assessed. C. punctatus and C. obsoletus were predominant cattlebiting species.

The summer of 1998 was generally extremely windy, restraining the flight activity of the biting midges. Even wind speeds as low as <3m/s hamper their flight. Due to the many windy days the distinct activity peaks, which usually indicate the emergence of new generations, were blurred. Owing to the windy weather the dispersal of midges from the breeding site into the pasture was strongly reduced. In the pasture the activity of the midges was only <20% of that recorded near the marsh, the latter being surrounded by scrub providing shelter.

In 1998 the risk of mass attacks of biting midges on pastured cattle was low even at a distance less than 40 m from the marsh. In a year with normal wind conditions a much greater distance to the breeding site is presumably required in order to protect the cattle against biting midges.

It was impossible to predict adult population maxima of the predominant species by mathematical simulation. The failure is caused by the atypic flight activity of the biting midges and the blurred sequence of generations in 1998.