The search for chemicals to control mosquitoes continues as resistance to existing compounds grows.Â Natural compounds offer hope. In Thailand Polsomboon and colleagues have experimented on the irritant and repellent effects of catnip (Nepeta cataria) oil on two types of disease-carrying mosquitoes (Anopheles and Aedes).
The Thai research team found that, “Catnip oil has strong irritant and repellent actions on mosquito test populations as indicated by the comparatively low escape time (from test chambers.” The authors hope that their research “will help in better understanding how catnip oils act against mosquitoes and how they might be used in the future.”
Catnip is part of the mint family which according to Wikipedia comprises about 210 genera and some 3,500 species under the family name of Lamiaceae or Labiatae.Â Wikipedia also reports that, “Mint leaves are often used by many campers to repel mosquitoes. It is also said that extracts from mint leaves have a particular mosquito-killing capability. Mint oil is also used as an environmentally-friendly insecticide for its ability to kill some common pests like wasps, hornets, ants and cockroaches.” Wikipedia explains that, “Oil isolated from catnip by steam distillation is a repellent against insects, in particular mosquitoes, cockroaches and termites.”
In the Bolivian Amazon Moore and colleagues volitilized Mentha arvensis on kerosene lamps which reduced biting by 41% inside traditional homes. Local cultural knowledge was used by Moore et al. to identify the plants they studied and provides an important guide for finding locally available plants.
In eastern Nigeria for example, villagers in focus groups explained that, “Leaves could be burned in the room to drive out mosquitoes. Participants specifically mentioned a local herb named nsigbu enwu, which would repel mosquitos if hung in the room, or burned when dry. It grows like a weed around most homes.” Onwujekwe et al. documented the same experience wherein people reported “burning or placing local leaves (osigbu) in and around the house. The leaves are good mosquito repellents because of their smell.” Among the Yoruba in Nigeria a similar plant, efinrin (Ocimum gratissimum), also from the mint family, is believed to have mosquito repellent properties among other indigenous medical uses.
More research and particularly application are needed on new potential natural plant products that can help control malaria. Time is of the essence as urbanization and climate change threaten the habitats where these plants are found.