Biological pest control

Syrphus hoverfly larva (below) feed on aphids (above), making them natural biological control agents.
A parasitoid wasp ( Cotesia congregata) adult with pupal cocoons on its host, a tobacco hornworm Manduca sexta (green background). One example of a hymenopteran biological control agent.

Biological control is a method of controlling pests such as insects, mites, weeds and plant diseases using other organisms. [1] It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also involves an active human management role. It can be an important component of integrated pest management (IPM) programs.

There are three basic strategies for biological pest control: classical (importation), where a natural enemy of a pest is introduced in the hope of achieving control; inductive (augmentation), in which a large population of natural enemies are administered for quick pest control; and inoculative (conservation), in which measures are taken to maintain natural enemies through regular reestablishment. [2]

Natural enemies of insect pests, also known as biological control agents, include predators, parasitoids, pathogens, and competitors. Biological control agents of plant diseases are most often referred to as antagonists. Biological control agents of weeds include seed predators, herbivores and plant pathogens.

Biological control can have side-effects on biodiversity through attacks on non-target species by any of the same mechanisms, especially when a species is introduced without thorough understanding of the possible consequences.

History

The term "biological control" was first used by Harry Scott Smith at the 1919 meeting of the Pacific Slope Branch of the American Association of Economic Entomologists, in Riverside, California. [3] It was brought into more widespread use by the entomologist Paul H. DeBach (1914–1993) who worked on citrus crop pests throughout his life. [4] [5] However, the practice has previously been used for centuries. The first report of the use of an insect species to control an insect pest comes from " Nanfang Caomu Zhuang" (南方草木狀 Plants of the Southern Regions) (ca. 304 AD), attributed to Western Jin dynasty botanist Ji Han (嵇含, 263–307), in which it is mentioned that " Jiaozhi people sell ants and their nests attached to twigs looking like thin cotton envelopes, the reddish-yellow ant being larger than normal. Without such ants, southern citrus fruits will be severely insect-damaged". [6] The ants used are known as huang gan (huang = yellow, gan = citrus) ants ( Oecophylla smaragdina). The practice was later reported by Ling Biao Lu Yi (late Tang Dynasty or Early Five Dynasties), in Ji Le Pian by Zhuang Jisu ( Southern Song Dynasty), in the Book of Tree Planting by Yu Zhen Mu ( Ming Dynasty), in the book Guangdong Xing Yu (17th century), Lingnan by Wu Zhen Fang (Qing Dynasty), in Nanyue Miscellanies by Li Diao Yuan, and others. [6]

Biological control techniques as we know them today started to emerge in the 1870s. During this decade, in the USA, the Missouri State Entomologist C. V. Riley and the Illinois State Entomologist W. LeBaron began within-state redistribution of parasitoids to control crop pests. The first international shipment of an insect as biological control agent was made by Charles V. Riley in 1873, shipping to France the predatory mites Tyroglyphus phylloxera to help fight the grapevine phylloxera ( Daktulosphaira vitifoliae) that was destroying grapevines in France. The United States Department of Agriculture (USDA) initiated research in classical biological control following the establishment of the Division of Entomology in 1881, with C. V. Riley as Chief. The first importation of a parasitoidal wasp into the United States was that of the braconid Cotesia glomerata in 1883–1884, imported from Europe to control the invasive cabbage white butterfly, Pieris rapae. In 1888–1889 the vedalia beetle, Rodolia cardinalis, a lady beetle, was introduced from Australia to California to control the cottony cushion scale, Icerya purchasi. This had become a major problem for the newly developed citrus industry in California, but by the end of 1889 the cottony cushion scale population had already declined. This great success led to further introductions of beneficial insects into the USA. [7] [8]

In 1905 the USDA initiated its first large-scale biological control program, sending entomologists to Europe and Japan to look for natural enemies of the gypsy moth, Lymantria dispar dispar, and brown-tail moth, Euproctis chrysorrhoea, invasive pests of trees and shrubs. As a result, nine parasitoids (solitary wasps) of gypsy moth, seven of brown-tail moth, and two predators of both moths became established in the USA. Although the gypsy moth was not fully controlled by these natural enemies, the frequency, duration, and severity of its outbreaks were reduced and the program was regarded as successful. This program also led to the development of many concepts, principles, and procedures for the implementation of biological control programs. [7] [8] [9]

Cactoblastis cactorum larvae feeding on Opuntia prickly pear cacti

Prickly pear cacti were introduced into Queensland, Australia as ornamental plants, starting in 1788. They quickly spread to cover over 25 million hectares of Australia by 1920, increasing by 1 million hectares per year. Digging, burning and crushing all proved ineffective. Two control agents were introduced to help control the spread of the plant, the cactus moth Cactoblastis cactorum, and the scale insect Dactylopius. Between 1926 and 1931, tens of millions of cactus moth eggs were distributed around Queensland with great success, and by 1932, most areas of prickly pear had been destroyed. [10]

The first reported case of a classical biological control attempt in Canada involves the parasitoidal wasp Trichogramma minutum. Individuals were caught in New York State and released in Ontario gardens in 1882 by William Saunders, trained chemist and first Director of the Dominion Experimental Farms, for controlling the invasive currantworm Nematus ribesii. Between 1884 and 1908, the first Dominion Entomologist, James Fletcher, continued introductions of other parasitoids and pathogens for the control of pests in Canada. [11]

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