Garden pest control - Midge Larva (Description and control instructions)

Midge is a name given to numerous minute species of flying, biting insects. The one which causes most problems is the Highland Midge, Culicoides impunctatus , which is thought to cause about 90% of bites. For such a small creature (usually a few millimetres long) they cause a great deal of suffering.

Midges can carry a notifiable viral disease known as Bluetongue which affects ruminant animals such as sheep, cattle and deer. It does not affect humans. The disease causes excessive production of saliva, swelling of the face and tongue which also becomes cyanotic, making it turn blue; the joints can also become swollen. Sheep are the most affected with about 70% fatalities and the survivors can be severely debilitated. Other ruminants may not show symptoms, but are capable of transmitting it when bitten by a midge which will carry it to its next host.

It was originally found in Africa where it is endemic, but has been moving northward and has moved to Mainland Europe in the last decade where it can be transmitted by other Culicoid midge species than the one in Africa. It was thought that the English Channel and North Sea would act as barriers to its progress. However, in September 2007, some cases have been found in Suffolk, possibly caused by some midges carried in the wind. It does not usually thrive at lower temperatures, but global warming has changed the potential regions for outbreaks to manifest.

Midges are attracted by the carbon dioxide (CO2) exhaled by all animals and are thought to be able to detect it from 200 metres away. Activity is mainly at dusk or dawn, but they can also be present during daylight hours in the shade among trees and in dull weather. Could patio heaters be attracting them as they emit CO2? So as well as contributing to global warming they could be helping to put the dampers on evening entertainment al fresco, by attracting swarms of midges!

They are found in damp places where there are suitable sites for breeding. The larvae are detritovores, feeding on dead plant material in wet peat or in the silt in lakes and ponds, so they are an important part of the cycle which breaks down this debris. The adults are also an important food source for birds and bats, so unfortunately complete eradication is not an option.

The females must feed on blood to ensure that the eggs they lay will survive. In doing so they inject some saliva and this causes an allergic reaction which can vary in intensity for different individuals. They also release a pheremone to inform others that a blood source is present.

There are two batches of eggs laid in a season. The first is larger in number, but does not require the blood meal, so it is the second batch produced in late summer and autumn which leads to the biting frenzy. The first instar larvae which hatch, burrow into the moist ground and after three more instars emerge to increase the population greatly. The adult females from this generation do all the biting and the larvae they give rise to spend the winter underground to emerge as the adults of the following spring.

Treatments

Over the years there have been many potions devised to repel the onslaught of the midges.

• Farmers have used walnut leaves which are rubbed along the backs of cattle to act as a repellant.
  
  
• Other aromatic foliage such as Artemisia 'Powis Castle' or Cotton Lavender (Santolina) may work as well.
  
  
• The "Midge Eater" is a device which emits CO2 and a few other animal aromas to attract the midges and they are sucked into a collecting bag. It can catch millions of them in an evening and looks something like a patio heater. Propane gas is passed over a catalyst to produce a small flow of CO2 and a pellet of other attractants provides an irresistable lure.
  
  
• There are many liquids and gels which can be applied, they are mostly based on Citronella oil or synthetic chemicals such as di-methyl phthalate and di-ethyl toluamide.
  
  
• It has been shown that dark colours attract the midges so it is best to avoid dark clothing when they are known to be about.
  
  
• Taking two desertspoonsful of distilled vinegar a day is said to ward off biting insects as it taints the perspiration so it will have an unpleasent smell for a while.
  
  
• Try to avoid their habitats at dawn or dusk and during dull weather.