The five most active countries, in numbers of weed species targeted and agents released, are the USA, Australia, South Africa, Canada and New Zealand, in that order, with the USA and Australia nearly twice as active as the others (See Table below). All these countries have a long history of successful weed biological control. For example, Hawaii has a success rate close to 50%, with seven out of 21 weed species targeted under 'complete' control, and significant partial control of three more (Gardner et al. 1995). Originally agricultural weeds were targeted, but there is an increased emphasis now on using biological control for weeds of natural ecosystems (here called environmental weeds), which are having a major impact on native ecosystems in Hawaii (Markin et al. 1992). Hawaii undertakes its own foreign exploration programs, and increasingly introduces pathogens as well as insects.

Continental USA is actively involved in several programs. Overseas surveys and testing are undertaken through various USDA-ARS laboratories or through the International Institute of Biological Control (IIBC) - now part of CABI Bioscience. Canada also has an active weed biological control program, and usually employs CABI Bioscience for overseas surveys. Canada and the USA work closely together in both overseas exploration and introductions.

Australia is the second most active country. Foreign exploration is usually undertaken by Australian scientists based overseas, or by employing CABI Bioscience personnel, particularly to test pathogens which are increasingly used. New Zealand has several programs underway, cooperating with Australia, undertaking their own overseas research, or contracting CABI Bioscience. New Zealand also uses exotic pathogens.

South Africa has a very active program, with an excellent success rate of 83% overall, with six weeds out of 23 targeted under complete control and a further 13 under substantial control (Hoffmann 1995). South Africa carries out its own overseas exploration and cooperates closely with Australia, both for shared weed problems and because many plants from each country have become weeds in the other.

Other countries involved in classical biological control are Malaysia, Thailand, India, Indonesia, Vietnam, Papua New Guinea and China. In Africa; Uganda, Zambia, Tanzania, Kenya, Ghana, Côte d'Ivoire and Benin have active biological control projects. FAO now promotes biological control of weeds as a preferred option, and is currently supporting programs for the biological control of water hyacinth in Latin America and Africa, itchgrass (Rottboelia spp.) in Central America and the Caribbean, Chromolaena odorata in West Africa, and the parasitic weeds Orobanche and Cuscuta species in North Africa (Labrada 1996).

International cooperation has been a feature of biological control from the start. For example, the lantana seed fly Ophiomyia lantanae, collected by Koebele and established in Hawaii, was sent to New Caledonia in 1908, in 1911 to Fiji, and in 1914 to Australia. This cooperation has continued through joint projects, supply of nucleus colonies of proven agents, and sharing of test data and information on rearing methods etc.

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Rachel McFadyen and Brian Willson