Insects such as flies, mosquitoes, midges, red mites and ticks cause major economic loss to farmers. Their bites produce skin lesions, irritations or allergic–type reactions to the animals or to the farm workers. On the other hand, insects are vectors of pathogenic bacteria and virus, like Pasteurella sp, E.coli, Salmonella sp or Avian Influenza Virus.

Insect control can only be achieved by an integrated pest management approach. However, although even when very strict control plans are implemented, it is difficult to get completely rid of insects.

Use of repellent essential oils is natural complement to other measures taken in the pest management plan.

Repellent essential oils

Repellents are substances that are applied to surfaces or sprayed into the environment to discourage insects from approaching, landing or climbing.

A large number of essential oils have been found to be insect repellents, including ginger, peppermint, rosemary, anise, cinnamon and clove. Many of these plants have been used in traditional practices to reduce the number of mosquitoes or flies.

After studying the chemical composition of the essential oils that have repellent properties, it has been concluded that most of them were rich in molecules that met two conditions:

• Contained a hydroxyl group (b-caryophyllene is an exception)
• Had a monoterpene or sesquiterpene structure

Examples of these molecules with repellent properties are:

• Monoterpenes: pinene, cineole, eugenol, limonene, terpinolene, citronellol, citronellal, camphor, thymol.
• Sesquiterpene: b-caryophyllene.

It has also been discovered that synthetic blends of the compounds listed above are much less effective as repellents than natural essential oils. As it is well known, essential oils contain complex mixtures of many molecules, often more than 200, so there may exist a synergism among the major and the minor constituents of the oil for the repellent activity.