The biology of the sheep headfly Hydrotaea irritans (Fallen) (Diptera: Muscidae) in south west Scotland

Berlyn, Andrew David (1980) The biology of the sheep headfly Hydrotaea irritans (Fallen) (Diptera: Muscidae) in south west Scotland. PhD thesis, University of Glasgow.

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The flight activity of H. irritans was investigated in Western Scotland using an unbaited suction trap, a CO2 baited suction trap and a Manitoba trap. In addition, trapped flies were dissected to investigate their reproductive condition, their blood-feeding activity, and whether they were newly emerged. Consistently more female flies were caught than males. The seasonal activity of adults was determined from the geometric means of catches from a Manitoba trap and a suction trap baited with carbon dioxide. The activity of females was greatest in the middle of July and declined sharply in the first week of August when the first gravid females were trapped. 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. Male activity reached a peak at the same time as that of the females, then declined as an increasing number of females was found to be inseminated. Six weeks from the start of the male decline 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 quite three ovarian cycles during the summer. There was no difference in feeding or reproductive development between flies from the two traps. Females were most active between 10.00 and 15.00 h B.S.T., with a peak about 13.00 h. The sex ratio did not vary significantly through the day. Multiple regression equations of climatic and seasonal factors with log catches of flies were very similar for the two types of trap. Radiant temperature, illumination, windspeed and date were shown to influence the activity of females and, with the exception of illumination, male activity also. Seasonal activity curves were plotted for both sexes in the two traps. Modified Manitoba traps were used on a forest track to investigate the factors which attract host-seeking adult H. irritans. Carbon dioxide, coloured spheres, movement, heat, a swarm of other headflies and Haematopota pluvialis (L) were shown to be attractants. Traps with coloured spheres attracted more irritans than traps without spheres. Matt black, shiny black and shiny red spheres attracted more male and female H. irritans than did shiny green, white and yellow spheres. Significant increases in the number of headflies caught did not occur when carbon dioxide was released from a trap at rates above 2 litres/min. Results suggest that carbon dioxide acts as a long range headfly attractant with a visual factor becoming important near the host. Manitoba traps were also used with three headfly repellents in order to evaluate the trap's potential for testing repellents. The extent of adult H. irritans activity in various habitats in a spruce forest was investigated using Manitoba traps. Most H. irritans were trapped in a firebreak or on a rough track. Least flies were caught within a clearing or thicket. It is suggested that in softwood plantations H. irritans uses firebreaks and tracks as flight paths and rarely flies amongst the trees.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: A R Hill
Keywords: Entomology
Date of Award: 1980
Depositing User: Enlighten Team
Unique ID: glathesis:1980-72652
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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