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Mosquitoes will conquer pyrethrum

Promoting the use of pyrethrum to control malaria in East Africa (see Combating malaria and poverty with biopesticides) is not without its problems.

The article stated that pyrethrum — a non-toxic, organic pesticide — has no history of insect resistance. This may be correct for pyrethrum itself, largely because it is not very widely used. But its derivatives, the pyrethroids, are widely used and resistance to those compounds is on the increase everywhere.

In this context, it is important to note that malaria mosquitoes in Africa are fast developing resistance to permethrin (a pyrethroid), which is commonly used to treat bednets.

Large-scale treatment of bednets with pyrethrum will almost certainly lead to resistance against it in mosquitoes.

The article also states that pyrethrum is a biopesticide, but this term is usually reserved for products that contain living organisms, like viruses or fungi. It would be better to produce a true biopesticide based on a fungus that infects and kills mosquitoes, as it is much more difficult for mosquitoes to develop resistance against parasitic fungi.

Several research groups are working on the development of such a biopesticide, for example at the universities of Wageningen in the Netherlands, and Edinburgh, in the United Kingdom, and at the National Institute for Communicable Diseases in Johannesburg, South Africa.