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Mosquito nets from public health to plant health

Long life insecticidal mosquito nets are already coming into wide use by African households (VHI)
Long life insecticidal mosquito nets are already coming into wide use by African households
VHI

A new factory in Tanzania is manufacturing millions of insecticidal mosquito nets to fight the scourge of malaria. The venture, catalysed by the World Health Organization (WHO), is proving a success, but the partners are already looking beyond the public health sector to new applications: if the technology can be adapted to agricultural use, the nets might protect vegetables as well as people. The transition will depend on the ability of the partners to make the jump between the worlds of public health and agriculture - if, indeed, the two sectors are really so different.

A flexible textile

More than a simple barrier, an insecticidal mosquito net acts as a "human-baited trap", killing insects as they come looking for food in the night. Ordinary nets have to be frequently re-sprayed with chemicals to achieve this, but long-lasting insecticidal nets (LLINs) have small amounts of insecticides safely manufactured into the fabric and retain their potency for 3-5 years. The first LLIN, Olyset®, was invented by Japan's Sumitomo Chemical, and has been recommended by WHO since 2001 as a malaria-fighting technology. The original product, however, was expensive and unavailable in Africa. Taking the lead to change this, in 2003 WHO started a public-private partnership with Sumimoto and A to Z Textile Mills, Africa's largest mosquito net manufacturer. Their joint venture, Vector Health International (VHI), built a factory in Arusha, Tanzania. The millions of nets made here are distributed by a fleet of 145 vehicles to village outlets around the country, where they sell for about US$5.

With mosquito net production firmly established in Tanzania, VHI took a look across the boundaries of development sectors and recognised uses for their nets in agriculture. High value vegetable crops such as cabbage and eggplant are as susceptible as sleeping humans to insect attack, and, just as often, rely on dangerous chemical sprays for protection.

Nets in the field

The A to Z textile factory in Arusha, Tanzania can produce millions of nets every month (VHI)
The A to Z textile factory in Arusha, Tanzania can produce millions of nets every month
VHI

As with the "human-baited mosquito trap", agricultural LLINs could also take advantage of insect behaviour. One major African pest, cabbage worms, are larvae of nocturnal moths. Nets could be spread at night to keep moths away and removed by day to allow the plants sunlight. Similarly leaf-eating mites, which destroy many vegetables, migrate to the tops of plants every night, where they would encounter the insecticidal nets. Other pests such as aphids and whiteflies need lots of ultraviolet light, and these could be controlled through UV-absorbing nets during the day. In all cases, the nets are a more targeted solution than insecticide sprays, and leave no residues on the vegetables.

VHI believed that their existing technology could be applied to a variety of agricultural problems, but it was clear that a whole new set of partnerships were needed. Reaching out around the world, they first communicated with the French research centre CIRAD for help in testing the nets. They then visited vegetable producers in Kenya and Tanzania, and other research institutes such as the International Centre of Insect Physiology and Ecology (ICIPE), the World Vegetable Center (AVRDC), and the Kenya Agricultural Research Institute (KARI). All showed an immediate interest in the technology, the producers most of all.

Farmers in Benin drape an acaricidal net over an eggplant crop in the evening to test its effectiveness against mites (VHI)
Farmers in Benin drape an acaricidal net over an eggplant crop in the evening to test its effectiveness against mites
VHI

CIRAD carried out trials in Benin, in experimental plots and the fields of local farmers. The farmers were sceptical of the new approach at first, but were tempted by an alternative that was cheaper and easier than spraying. After the first harvest, producers were quickly won over and have since formed local associations to buy nets. The trials produced two journal publications: the first showing that untreated mosquito nets kept moths off cabbage plants; the second that nets treated with acaricide kept eggplants completely free of mites when draped over the plants just once every three nights.

Partners across sectors

Dr. Pierre Guillet of VHI continues to seek partners in agriculture; alternatives to traditional insecticides are technologies that need public involvement, he believes. "The issue is that pesticide companies are more interested in developing and selling formulations that have to be sprayed twice a week rather than a long-lasting product that will last for months or years." Even Olyset® was developed for other applications, until WHO convinced Sumitomo of its potential for malaria prevention. "When WHO asked other pesticide companies to develop LLINs, none responded."

With these same few multinational companies driving agricultural pest control, durable net-based solutions are not likely to appear on the market without help from the public sector. "The tendency in public health had long been to wait until industry developed products. During the last decade, a more proactive approach has been adopted where public health institutions and actors approached industry with requests to develop products with certain attributes." In agriculture, too, proactive and creative partnerships are needed, and the right technologies can come from surprising places.

Written by: T. Paul Cox

Date published: May 2010

 

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