Mozzie

Midge Biology: A Few Rambling Thoughts

Many, Many Thanks To Dr. Alison Blackwell For The Entire Content Of This Page, Thanks Ali !!
Classification & Distribution Life Cycle Life cycle of C. impunctatus Importance in the Ecosystem Importance to Man : Nuisance value Importance to Man : Disease transmission Importance to Man : When/Why Midges Bite	Dr Alison Blackwell (PhD) Senior Research Fellow Centre for Tropical Veterinary Medicine Royal (Dick) School of Veterinary Studies Easter Bush Veterinary Centre Roslin Midlothian, EH25 9RG Email: ablackwell @ vet.ed.ac.uk WWW : CTVM

Classification & Distribution Biting midges belong to the Insect Order Diptera, the true flies (only 1 pair of wings, unlike most other insects which have 2 pairs) and the family Ceratopogonidae. Taxonomically they are more closely related to the blackflies (Simuliids) and non-biting chironomid midges than the mosquitoes, which belong to the Dipteran family Culicidae.
Within the biting midge family there are several "genera" which feed from only plant tissue or some from the body tissues of other insects. The most advanced genus (in evolutionary terms) is Culicoides, which has adapted its mouthparts to feed on the blood of warm-blooded vertebrates (both mammals & birds). Culicoides are most important when thinking about their impact on man.	There are > 1,000 species of Culicoides biting midges worldwide, inhabiting all areas except the Poles and reportedly New Zealand & Patagonia (presumably because of geographical isolation or otherwise it’s too dry and hot there for them).
In the UK there are approx. 37 Culicoides spp., occurring from the North of Scotland to Southern England, although their numbers tend to be greatest in parts of Western Scotland and the Highlands. Of these 37 species, the most dominant species are Culicoides impunctatus in Scotland and Culicoides obsoletus in S. England. C. impunctatus is responsible for > 90% biting attacks on people in Scotland and is also the species you would encounter in the Kielder Forest etc.. C. obsoletus tends to be found around domestic gardens etc.	Midge distribution is related the larval breeding grounds. Midge larvae are usually found in semi-solid areas - soil, animal manure etc. C. impunctatus larvae thrive in damp, acidic peaty soil, which is one of the (many) reasons why this species is so successful in Scotland, due to the abundance of this sort of habitat. The reason why you don’t get midges on the East coast of Scotland (or not in the numbers as found in the West) is that the winters are milder in the West - very few ground frosts which could kill the larvae, which are the over-wintering stages (see below). Areas of suitable habitat for midges to breed in England are less abundant.
Life Cycle
Biting midges have what is called a "holometabolous" metamorphosis, which means that the adult and larval stages look very different from each other and are separated by an intermediate, pupal stage. In areas where the climate isn’t suitable for adult midges to survive all-year-around (ie. UK), the larval stage provides an important means of overwintering. This doesn’t occur in other parts of the world (eg. Southern Europe, Africa etc.), where adults can be found 12 months of the year.	Midge larvae are worm-shaped, approx. 2 mm long and move with a sinusoidal movement. They tend to live in the water films of the soil or whatever medium they are living in. In Scotland, C. impunctatus larvae can be found in the first 5 cm of the soil, with about 75% in the first 2 cm below the soil surface.
Life cycle of C. impunctatus (very similar for most British Culicoides spp.):
C. impunctatus has 2 generations per season. The first adults emerge in mid-late May, triggered by an increase in day length and temperature. Male midges emerge a few days before the females (called protandry) - this is so the males are ready to mate as soon as the females emerge.	Males form mating swarms over visual markers - protruding vegetation, dark patches on the ground etc. Females fly into these swarms and pairs form and fall to the ground, where mating is completed. Males will mate as many times as they can, whereas females are reluctant to mate more than once - they get enough sperm in one mating to fertilise all of the eggs they are likely to lay.
C. impunctatus is autogenous, in that the females do not require a bloodmeal to lay their first batch of eggs. The females emerge with 2 large fat bodies, which fill the abdomen, and the fat/protein reserves in these are used to mature the first batch of eggs (about 100). This behaviour is probably the key to the success of C. impunctatus in Scotland, since bloodmeals may be difficult to find in parts of the Highlands. Subsequent egg batches (laid at 5-7 day intervals) derive from a bloodmeal. C. impunctatus actually "prefers" to feed from deer or cattle - man is fed on only opportunistically, because he happens to be there. There are a further 4 Culicoides species that will take a bloodmeal from man, including C. maritimus, which is found on beaches and has a very painful bite. The second (and any further) batch of eggs is smaller, 30 - 40. Female midges rarely live longer than 2 weeks (depending on the weather) and thus, are unlikely to lay more than 2 egg batches. Females lay their eggs in vegetation (dominated by rushes and mosses) and the larvae find their way into the soil, where they develop through 4 larval stages or "instars". This takes approx. 4 weeks, with the larvae feeding primarily on decaying plant & animal matter. They may also be cannibalistic. Larvae from the first generation eggs pupate at about 4 weeks and emerge as the second generation of adults in about mid June and the mating/feeding cycle is repeated. The subsequent larvae, however, effectively go into a diapause state when the reach the final, 4th instar in approx. late Aug/early Sept. They remain as 4th instar larvae in the soil throughout the winter, pupating the following Spring/early Summer and forming the first generation of adults the next year.
Importance in the Ecosystem
Very little is known of this aspect. The adult midges may well form the food of some bats and small birds but there’s little proof of this.	The larvae probably form part of the "decomposer" food chain, helping to break down decaying plants and animals although again, there’s little proof and their importance in comparison with other decomposers is not known.

Importance to Man
Nuisance value	Midges in the UK, particularly in Scotland, disrupt tourism, outdoor recreation & industry through their biting attacks on man. C. impunctatus is thought to cause >90% of the biting in Scotland, resulting in a 20% loss in working man hours in the forestry industry during the summer months.
Disease transmission	elsewhere in the world biting midges are vectors of some serious livestock diseases, including African horse sickness virus and bluetongue virus of sheep. You need adult midges to be around all the year for them to act as vectors (the virus or other pathogen has a multiplication phase in the insect and so would die out in areas when the midge enters an overwintering period).
When/Why Midges Bite	Both male and female midges sugar feed (plant nectar etc.) but only females blood feed, due to the need to develop their eggs. The majority of species in the UK are most active at dawn & dusk and in still, warm conditions. One species in Scotland, Culicoides heliophilus is active in full sunlight and has a nasty bite. All species, however, will be tempted to bite during the daytime if a potential bloodmeal (i.e. man) is nearby, particularly if it is overcast, with little wind C. impunctatus tends to be worst during the hour just before sunset and the hour just after sunrise. The activity of other species varies by an hour or so but these differences are probably not significant.
The attraction of a particular individual to a midge depends on body odour etc., as previously mentioned, together with the different reactions of people to midge bites. Biting midges have about 500 olfactory receptors on their antennae (at least 4 different morphological forms), some of which respond to a small number of chemicals (specialists), with some responding to a broad range of chemicals (generalists). Biting midges are less sophisticated than mosquitoes in their blood feeding. Mosquitoes are "vessel feeders", in that they inject their mouthparts directly into a blood capillary to feed from. Midges are "pool feeders" - they use their mandibles to effectively cut a hole in the skin, creating a pool of blood from which they feed. Anticoagulant is pumped into the wound to stop the blood from clotting.