The Experiment Station of the Hawaiian Sugar Planters' Association was organized in 1904. On its staff were four entomologists, R. C. L. Perkins, O. H. Swezey, G. W. Kirkaldy, and F. W. Terry. Koebele and Alexander Craw, employed jointly with the Territorial Board, were consultants.

Their first problem was the sugarcane leafhopper, which then threatened to destroy the sugar industry. The early importations resulted in the establishment of four egg parasites, Paranagrus optabilis and Anagrus frequens from Australia, Ootetrastichus beatus from Fiji, and O. formosanus from Formosa. Paranagrus and Ootetrastichus gave a substantial measure of relief but not complete control. A further search for additional species of greater effectiveness in Australia and Fiji disclosed a bug, Cyrtorhinus mundulus, that was predaceous on leafhopper eggs. Its introduction in 1920 finally solved the problem. The leafhopper quickly subsided to a noninjurious level.

The conquest of the leafhopper was followed by that of the New Guinea sugarcane weevil which, while less destructive, caused losses of a million dollars or more each year because the larvae bored in the cane stalks. The search by Frederick Muir through Borneo, New Guinea, and adjoining areas revealed a parasitic fly, Microceromasia sphenophori, that attacks the grubs. Air transport was unknown in those days, and the problem of bringing the parasite alive from New Guinea to Hawaii seemed insurmountable. Muir's repeated efforts from 1907 to 1910, including finally the establishment of several relay stations en route, is one of the epics of entomological exploration. The subjugation of the beetle borer quickly followed the establishment of the fly in Hawaii.

While the leafhopper and weevil were the outstanding pests of cane, many others have caused appreciable damage and have necessitated the importation of natural enemies. The outcome has been successful with the oriental beetle, several species of army-worms, the Chinese grasshopper, a mole cricket (Gryllotalpa africana), a cane aphis (Aphis sacchari), and two species of mealybugs. Many parasites of miscellaneous pests also have been imported, some with conspicuous benefit. such as those against the fern weevil, torpedo bug, a scale on coconut (Pinnaspis buxi), the coconut mealybug on avocado, and cockroaches.

The work in Hawaii may be brought up to date by mention of the work on fruit flies, including the oriental fruit fly. First found in the Islands in 1945, it quickly demonstrated its destructive capabilities. Its habits and its large numbers in Hawaii are a serious threat to the fruit industry in California, through the possibility of entry in aircraft or by other means. The importation of natural enemies was undertaken in a cooperative effort of the Hawaii Agricultural Experiment Station, the Board of Commissioners of Agriculture and Forestry of Hawaii, the Hawaiian Sugar Planters' Association Experiment Station, the Pineapple Research Institute, the University of California, and the Bureau of Entomology and Plant Quarantine.

The first shipments of parasites were brought from Malaya and the Philippines by the Board of Commissioners of Agriculture and Forestry in 1948. Since then the exploratory work by the cooperating agencies has extended to South and East Africa, India, Thailand, China, Formosa, Australia, and several islands of the South Pacific. Between 3o and 5o species of parasites have been imported for testing. Many have been released in large numbers. The importation program was completed in 1951. Four or more parasitic species are established in Hawaii. Two of them, originally imported from Malaya, have brought about commercial control on the island of Oahu and prospects of similar control on the other islands appeared excellent.

MANY OF THE introduced parasites and predators I have mentioned have held the pest insects under control for many years and other control measures have not been required. Since 1945, however, complications have arisen because of the new insecticides, beginning with DDT and followed by a series of others, some of which are more toxic than DDT. The use of DDT in the orange orchards of California for control of the citricola scale was followed by widespread outbreaks of the cottony-cushion scale, the first since 1890. This was due to the destruction of the vedalia by the insecticide.

In other instances, the use of the new insecticides against a specific crop pest has upset the natural balance of minor pests of the same crop, likewise apparently due to elimination of their natural enemies. The application of DDT and some other chemicals to vegetable and fruit crops frequently brings heavy infestations of aphids and spider mites pests that at times become more destructive than the ones against which the insecticide was applied. This upsetting of the natural equilibrium has created a serious situation in pest control and is being investigated. The solution may be found in a combination of remedial measures involving a change in the insecticide used, its formulation, the time of application, or in some other change in current practices.

THIS ACCOUNT of biological control of insect pests has described only the more important achievements in the United States. The same method has been employed with conspicuous success in other countries, notably Australia, New Zealand, Fiji, and Canada. At least 30 major insect pests have been fully controlled in one or more countries through the use of parasites and predators and substantial reductions brought about in the infestations of a much larger number.

C. P. CLAUSEN was leader of the division of foreign parasite introduction, Bureau of Entomology and Plant Quarantine, from its establishment in 1934 until 1951, when he retired and became chairman of the division of biological control at the University of California. His training was obtained at the University of California. In 1916-17 he conducted a search for natural enemies of citrus scale insects in Japan, China, Formosa, and the Philippines for the California State Commission of Horticulture. After joining the Department of Agriculture in 1920 he spent the following 11 years in a search for natural enemies of the Japanese beetle in Japan and India and of the citrus blackfly in Malaya.