Biological control of pests is the method of controlling pests, whether of plants, animals or man, by exposing them to their natural enemies or unfavourable conditions. It includes such techniques as the introduction of exotic predators or diseases of the pest organism, manipulation of the pest's environment, the breeding of crop plants resistant to disease, releasing sterile males of a pest to interfere with reproduction, using sex attractants to trap and kill males before mating can ensue, and manipulating genes in order to render males sterile. Detailed understanding of the breeding and feeding habits of the vectors and their predators helps. Biological control is not aiming to eradicate the pest, it is to lower it to an acceptable level. In 16-18% of cases the control is a complete success, and in a further 42% there are substantial reductions, meaning of 60% of control is successful.
The use biological pest control tries to rebalance an ecological system that man has taken out of balance.
Modern biological control is regarded by many to have its roots in Adelaide, Australia in 1888 where was discovered the use of the predatory beetle Rodolia cardinalis. Exported to California, within two years it wiped out the devastating cottony cushion scale which plagued the citrus industry, and went on to attain similar results in over 50 countries.
This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends training extension agents and involving farmers and women's groups in crop health and alternative non-chemical ways of controlling pests in agriculture.
Mosquitoes are rare in urban Singapore. It is an offence, punishable by a fine or even imprisonment, to allow water to stagnate in places where it could become a mosquito breeding site. With no vectors to foster transmission, malaria and mosquito-borne arbovirus infections such as dengue and Japanese B encephalitis are a much smaller problem than they would otherwise be.
In central and southern China, the snail hosts of schistosomiasis were effectively controlled by cutting away the sloping sides of ponds and canals to create vertical walls which were a less hospitable environment than a gentle slope at the junction of land and water which the snails prefer for mating. This method of vector control is possible and successful because of the labour-intensive Chinese rural economy, and thorough understanding of the habits of the local snails.
The Light of Life project in the Philippines uses neither chemicals nor pesticides, but rather spreads paddy husk to control Japanese snails in rice fields.
The African soapberry plant (Phytolacca dodecandra), traditionally cultivated in many parts of the continent as a laundry soap and shampoo, contains a molluscicide (snail-killing agent). The berries of the plant known in Ethiopia as endod are lethal to most species of snails. The discovery offers a potentially low-cost agent in the control of snail-borne diseases like schistosomiasis, or sleeping sickness (affecting 200 million people in Africa, Asia and Latin America and causing 200,000 deaths every year), liver-fluke in animals, onchocerciasis (river blindness) and guinea worm infections. Toxicological studies have proved the plant safe for humans and other animals and plants and the WHO has given the go-ahead for extensive field tests in Africa. In 1994 a USA university was also granted a USA patent on an endod-based molluscicide with theaim of producing a product to control the zebra mussels which in the past 10 years have invaded American lakes and clogged water supply systems, causing damage estimated in hundreds of millions of dollars.
The mealybug, inadvertently introduced from South America in the early 1970s, has cut cassava yields by two-thirds by 1983. Biologists eventually found natural enemies that would control the spread of the pest. With the help of mass-rearing and distribution techniques developed at the International Institute of Tropical Agriculture in Nigeria and the International Centre for Tropical Agriculture, the natural predators are now at large in 90% of the cassava-growing region of Africa, bringing losses under control. This effort saved a crop that provides a quarter of the food energy consumed in Sub-Saharan Africa, at an estimated benefit-cost ratio of nearly 150 to 1.
In 1993, the South Pacific Commission (SPC) reared and distributed 1,274 consignments of four biological agents for the control of two major crop pests in four member nations. The biological agents included two species of leaf mining beetles and one species of leaf sucking bugs to control the weed Lantana camara in Niue and Solomon Islands, as well as a wasp for whitefly control in New Caledonia and Queensland, Australia. In the same year, a biological control programme partly run by SPC succeeded in: controlling the corn borer in Papua New Guinea through inundative release of an egg parasite (a wasp); releasing a wasp for the control of the diamond-back moth in Fiji, Papua New Guinea, and Tonga; establishment of a psyllid to control giant sensitive weed in Fiji; control of the rhinoceros beetle in Western Samoa through the distribution and spraying of a pathogenic fungus to kill beetles at breeding sites and the release of a baculovirus through infected beetles; developing control of cabbage pests using Bacillus thuringiensis as part of an integrated approach. The SPC-EC taro beetle biological control project used a virus, species of fungi, nematodes and bacteria, in controlling the taro beetle.
The ladybug beetle found in Australia saved the California citrus industry from destruction by cottony cushion scale in the 1880's.
Virtually every vine in France has been grafted onto a rooted cutting from an American vine because American vines were immune to the American phylloxera bug which was the cause of a devastating plague in European vineyards.
As of 1995, the work of the European Biological Control Laboratory (located in France and established in 1918) has found antidotes to about 25 weeds and 40 insect pests.
Biocontrol is economically feasible in that it establishes a once-for-all self-regulatory system in which natural enemies keep the pest in check below a damaging level without any further effort or expense. It utilizes no chemicals which threaten, pollute or damage the environment or serve to introduce chemical-resistant strains. Finally, biocontrol utilizes none of the fossil fuels that are required in the production of chemical products.
Strict control over the introduction of pests and diseases from abroad is also necessary to ensure the protection and productivity of crops.
Unlike the ensured control obtained from the use of chemicals, biocontrol is variable. Developmental research on such control methods is long and, upon application, may take years to be effective. In addition, an introduced 'natural enemy' may itself become an unwanted pest over time.