Biological pest control

UNESCO Courier, Oct, 1988

For 1,700 years, the Chinese have controlled insect pests by biological means, using one insect to kill another. Perhaps their most striking and important use of biological pest control was in the use of yellow citrus killer-ants to protect mandarin trees. Here is how a text of 304 AD, Records of the Plants and Trees of the Southern Regions, describes the use of the carnivorous yellow ants:

'The mandarin orange is a kind of orange with an exceptionally sweet and delicious taste.... The people of Jiaoshi [Tonkin] sell in their markets [carnivorous] ants in bags of rush matting. The nests are like silk. The bags are all attached to twigs and leaves which, with the ants inside the nests, are for sale. The ants are reddish-yellow in colour, bigger than ordinary ants. These ants do not eat the oranges, but attack and kill the insects which do. In the south, if the mandarin orange trees do not have this kind of ant, the fruits will be damaged by many harmful insects, and not a single fruit will be perfect."

This biological pest control first came to Western attention when a paper on the subject was published in the North China Herald on 4 April 1882. But it was not until a serious outbreak of citrus canker occurred in the Florida citrus groves in the 1910s that a plant physiologist was sent to China by the US Department of Agriculture in 1915 to search for canker-resistant oranges, and discovered the citrus ants. In 1958, a Chinese scientist, Chen Shou-jian, recommended a renewed study of the ants. Their use in Chinese orange groves continues to this day.