Biological Control Is the Million Natural Enemies of Many Kinds Citrophilus Mealybug Campaign in Cali- Are Released Each Year by the University Fornia
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iological control involves discover- Citroph ilus mealy bug B ing, importing, and using the most effective natural enemies of pest insects Second only to cottony cushion as a or weeds that can be found. More than 10 success story for biological control is the million natural enemies of many kinds citrophilus mealybug campaign in Cali- are released each year by the University fornia. of California (UC) through its Biological In the 1920s citrophilus mealybug Control divisions at Albany and Riverside. was a spreading scourge in citrus orchards. UC scientists estimate that the It was highly destructive, it spread rapid- importation and release of biological con- ly, and it affected other fruit trees and trol agents in California alone has saved ornamentals. The mealybug’s origin was producers and consumers of food and fiber a mystery, but UC scientists deduced it about $300 million in the last half century. must have come from a climate similar Worldwide, the importation of natural to that of southern California and from a enemies has brought about some degree place linked by steamer to England, of control of 186 species of pest insects; South Africa, and California, the three there have been 384 successful projects places where the mealybug was known. in biological control of pest insects to date. This pointed to Sydney, Australia. In this review, “biological control” Harold Compere, a UC biological (BC) refers to only one of the many non- control scientist, was dispatched to Aus- chemical insect control methods on which tralia in 1927. Within a year he found an UC scientists are working. BC is the im- infested mulberry tree on which virtually portation, colonization, and spreading of all of the mealybugs had been parasitized. natural enemies (usually from the ”old He collected two parasites, Gocrophagus country” where the pests originated) to gurneyi and Tetracnemus pretiosus, and reduce a pest’s population density to a accompanied them to California on the lower average than would otherwise steamship Tahiti. Both parasites were occur. colonized and released in 1928. In 1929 citrophilus mealybugs were already being decimated wherever the First success parasites had been liberated; by 1930 the parasites’ eggs laid inside mealybug lar- The first effective and sustained vae had resulted in complete economic success of biological control occurred in control. Since that time, no infestations 1888 against the cottony cushion scale, of any importance have occurred. Orange Zceryapurchasi. The scale attached itself County citrus growers alone saved $0.5 to leaves and twigs of citrus trees, then million to $1 million a year. The cost? sucked out the sap. Discovered in Cali- About $1,700, not including Compere’s fornia in 1872, it soon threatened to salary of $150 a month. destroy the citrus industry. Albert Koebele, a USDA ento- Conquering a weed mologist, was sent to Australia in 1888 Vcdalia, the iZustralian ladyhird beetle /Rodolia to seek a parasite that apparently was A classic example of biological con- cardinalis) feeding on cottony cushion scale trol was a joint UC-USDA campaign against lIwrl/a purrhasi). keeping the scale under control there. Koebele shipped 514 vedalia beetles (the Klamath weed (Hypericum perforaturn), Australian ladybird, Rodolia cardinalis) an accidental import from Europe. By to California, where they quickly became 1944 it occupied over 2,000,000 acres of established. rangeland in 30 California counties, By 1890 the vedalia had attacked crowding out range grasses. Livestock and almost obliterated all infestations in men suffered financial losses, because California. Cost of the vedalia program, cattle and sheep feeding on the toxic all told, was less than $5,000. Benefits? weed lost weight and because land values - Millions of dollars annually in California. decreased, making it hard to get loans Similar successes were scored with the for improvements. Chemical controls, ap- same beetle in more than 50 countries. plied against a mere trace of the total Unfortunately, DDT and other infested acreage by state and local govern- chemicals, used after World War 11, ments, cost as much as $300,000 a year. destroyed the vedalia in many areas. As early as 1922 Professor Harry Cottony cushion scale then re-emerged Scott Smith, head of biological control as a serious pest after 50 years of ab- work in California, proposed the impor- sence. The vedalia was recolonized after tation of insects that fed on the weed in the insecticide residues on tree foliage Europe. In 1944 Smith finally was author- Vedalia larva feeding on cottony cushion scale. had dissipated, and soon reasserted its ized to import four kinds of beetles and 10 times lifesize control over cottony cushion scale. a gall-forming fly from Australia and 8 CALIFORNIAAGRICULTURE OCTOBER 1977 Europe. After careful testing to ensure means has been difficult and costly. Its w a I n u t aphid. the beetles wouldn’t attack desirable thorns and seeds are picked up and spread Discovered near Fresno in 1934, plants, the four beetles - Chrysolina by tires and bare feet. the olive scale, Purlntoria oleue (Colvee), hyperici C. quadrigemina, C. varicLns, In 1961, UC and USDA bio-control soon threatened many household and and Agrilus hyperici-and the gallfly scientists imported two weed-attacking parkway plants as well as olive and de- were released. All except C. variuns be- weevils from Italy: Microlarinus lureynii ciduous fruit trees. By 1960, more than came established; C. quadrigemina was and M. lypriformis. The former infests 200 types of ornamental plants, 28,000 the most successful species. puncture vine fruits and destroys the acres of olive orchards, and Lhousands of From a single colony of 5,000 C. seeds; the latter attacks the stem and deciduous fruit trees in 26 counties in the quadrigemina beetles released in 1945- crown. The two weevils were fairly suc- Central Valley and parts of southern 46, more than three million beetles were cessful in attacking the ground-hugging California were infested. Olive scale not collected for redistribution in California weed, but they soon ran into trouble only attacks leaves, twigs, and limbs, hut in 1950. The beetles also were sent to from native American insects. Two tiny also infests olive fruits, causing heavy Washington, Oregon, Idaho, Utah, Nevada, wasps attacked and destroyed about one- losses. The olive industry spent millions and Montana, where they became es- quarter of the young weevils in test of dollars fighting the pest. tablished. plots; two other native insects destroyed In the late 1940s. UC scientists By 1955 Klamath weed virtually the weevil eggs. As a result, weevil des- introduced natural enemies of olive scale. disappeared as a pest. Chemical control truction of puncture vine was cut in half. Only an Aphytis parasite from Egypt sur- costs dropped from $300,000 to less than Seeds of puncture vine can live in the soil, vived, but in small numbers. Other enemies $300 a year. Land values went up again. where weevils can’t get at them for 20 of olive scale were sought in Spain, Pakis- As range grasses reappeared, animals years or more. Even if two-thirds of the tan, India, and the Near East. Of four stopped losing weight. UC scientists seeds are destroyed before they mature, Aphytis strains imported, the most suc- estimate that savings to the livestock in- the remaining third can present a control cessful was a “Persian” strain of Aphytis dustry plus savings in control costs have problem. rnaculicornis from Iran and Iraq. Over been $3,500,000 per year, totaling about Despite these problems, the reser- the next eight years, more than 27 mil- $80,500,000 through 1976. voir of puncture vines seeds has diminished lion parasites of that strain were colonized In California, only Siskiyou County, over the last decade. In the presence of at hundreds of olive orchard sites in 24 with its very cold winters, still has a the imported weevils, now spread through- counties. Thousands were also released Klamath weed problem. Improved con- out California, puncture vine plants pro- on deciduous fruit trees, ornament a I trol has been obtained recently by the in- duce only about one-sixth as many spiny trees, and shrubs. troduction of a more cold-resistant C. hy- burs as they otherwise would.. Olive scale densities declined perici beetle and the root borer, Agrilus In another attack on weeds, on the dram B t i ca I I y , b ti t. scientists sought a hyperici, and by an apparent adaptive Channel Islands off Santa Barbara, UC higher degree of control than could he improvement of C. quadrigemina. scientists released a mealybug that achieved with the Persian Aphytis alone. sucked the juices out of prickly pear Although the Persian parasite often at- Puncture vine effort cactus, largely ridding the islands of this tacked and killed more than 90 percent of the olive scales in a given area in spring, Attempts to control puncture vine rangeland pest. (Tribulus terrestris) have been less suc- it failed to follow up in summer hcciiuse cessful than the Klamath weed project. Two recent successes of an intolerance to hot, dry weather and The control of puncture vine (long because of the absence of host (scale) a major pest around houses, roadways, The two most successful applica- stages during the late spring. ginning mills, vacant lots, and sometimes tions of biological control in recent years Two new species of aphelinid para^ on croplands) by chemical or cultural have been against olive scale and the sites were introduced from West F’aki- Adult seed weevil (Microlarinus lareyniil on a seed pod of the Stem of puncture vine plant showing damage caused h) the stem wwvil. .Mrrrk puncture vine, nibulus ierrestris.