The field biology of the adult sheep headfly, Hydrotaea irritans (Fallén) (Diptera: Muscidae), in south-western Scotland

Abstract

AbstractAdults of Hydrotaea irritans (Fall.) in south-western Scotland were caught in a Manitoba trap and a black suction trap baited with carbon dioxide. Trapped flies were dissected to investigate their reproductive condition, their blood feeding activity and whether they were newly emerged. Trapping of the first gravid females in August was accompanied by a sharp decline in adult activity. The proportions of females in the various ovarian categories suggested that there is a preliminary phase before host-seeking begins, attraction to animals during most of the cycle and a behavioural change at the end. Females with eggs at stages I, II and III accounted for 94% of all females caught; the only females with blood in the gut were in these categories. Some males also were obviously blood-fed. There was a single mating period lasting five weeks. Inseminated females were first trapped in the third week of July, when the numbers of males started to decline, and within five weeks all females trapped were found to have been inseminated. After this, no more males were caught. Only females with eggs in stages later than stage II of the first ovarian cycle were inseminated. H. irritans was univoltine, with two but not three complete ovarian cycles during the summer. There was no difference in feeding or reproductive development between flies from the two traps.