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COTTONY-CUSHION SCALE, Icerya purchasi Maskell -- Homoptera, Margarodidae

(Contacts)

Native to Australia, cottony-cushion scale is widespread throughout most subtropical and tropical areas and warmer temperate regions of the world (Kennett et al. 1999). It has a wide host range and has the capacity to weaken or kill mature trees. It is adapted to a wide range of climates and is a pest of numerous fruit and shade trees and shrubs, being especially important on citrus, mango and guava.

This particular project was referred to by DeBach (1974),<PHOTO>, as the one that, "... established the biological control method like a shot heard around the world." The cottony-cushion scale was discovered on Acacia in Menlo Park, central California around 1868, from which is spread rapidly. Folllowing its discovery on acacia in northern California around 1868, by 1886 its effect on the new citrus industry in southern California was devastating. Citrus growers tried washes and cyanide fumigation but these were not effective. Damage was so extensive that many growers abandoned or burned their trees and real estate values plummeted (DeBach 1974). Alarmed California horticultural officials began inquiries and enlisted the aid of Charles V. Riley <PHOTO>, Chief of the U. S. Dept. of Agriculture, Division of Entomology. Riley emerged as the dominant figure in this project but others made more important contributions.

The principal foreign explorer involved was Albert Koebele, <PHOTO>, while D. W. Coquillett <PHOTO> played the important role of receiving and colonizing the imported natural enemies. In 1885 Riley sent A. Koebele <PHOTO> to Alameda, California, at a salary of $100.00 per month to conduct an "investigation of the history and habits of insects of California." About the same Riley appointed Coquillett, a skilled amateur entomologist from Anaheim, California, as field agent to work on the control of the cottony-cushion scale around Los Angeles. In February 1886 both men were assigned to work together at Los Angeles on the scale.

Riley was trying to determine the native home of the cottony-cushion scale by correspondence in order to begin the exploration phase of the project. By 1887 officials in California were also trying to locate its source. DeBach (1974) suggests that possibly stimulated by such correspondence, Frazer Crawford, an entomologist of Adelaide, Australia, discovered in 1886 the parasitic fly Cryptochaetum (= Lestophonus) iceryae Williston, an effective natural enemy of the scale. Early in 1887 Crawford wrote to Riley that I. purchasi in Adelaide was destroyed by a dipterous parasitoid and sent drawings of the fly and also specimens which the U. S. Department of Agriculture received in February 1887. At first Riley doubted its parasitic status, because no true dipterous fly parasitoids of scale insects were then known. Later he became convinced of its importance and this became the main objective in Koebele's exploration trip to Australia. Riley also recommended in 1886 that the natural enemies of the cottony-cushion scale be investigated in Australia and introduced into California. The same year the California Fruit Growers' Convention petitioned Congress to appropriate funds for the USDA to do the work. However, Congress refused and maintained that USDA funds could not be spent in foreign travel.

The California Fruit Growers' Convention invited Riley in April 1887 to provide a remedy for the cottony-cushion scale epizootic, where he stated his belief that the scale came from Australia where it was harmless and probably not from New Zealand where it was recorded as a serious pest. He assumed that parasitoids regulated the scale at low densities in Australia and again recommended that they be investigated and imported into California. He offered to send an entomologist to do this but that the US Congress would consider the idea absurd. Thus he asked that the State of California or Los Angeles County appropriate a few thousand dollars to import the natural enemies. Although the Convention again adopted a resolution in favor of sending someone to Australia for natural enemies, no funds were generated from California.

Around that time, the California State Inspector of Fruit Pests, W. G. Klee, corresponded with W. M. Maskell <PHOTO> in Auckland, New Zealand (Maskell had described the scale as a new species from Auckland in 1978) and with Frazer Crawford in Adelaide, Australia. Maskell told Klee positively that Australia was the native home (letter was published in the Pacific Rural Press, May 7, 1887). Subsequently Riley, who meanwhile had reconsidered where the country of origin might be and was suggesting Mauritius (letter to Pacific Rural Press, June 4, 1887), agreed that Australia was probably the native home (letter in Pacific Rural Press, March 4, 1888).

As a result of Klee's correspondence, Frazer Crawford with considerable effort collected and sent some live Cryptochaetum to Klee who liberated the flies on cottony-cushion scale in San Mateo County near San Francisco in early 1888 before Koebele sailed for Australia--ostensibly to get the same flies (DeBach 1974). This probably resulted in Cryptochaetum's establishment because it eventually became common in California and there is doubt that Koebele's later shipments to Los Angeles did survive after release.

Financing for Koebele's trip to Australia was through some skillful political maneuvering. In 1888 an International Exposition was to be held in Melbourne, Australia, and a US exhibit was planned through the U.S. State Department. Through the efforts of Riley, N. J. Coleman, The California Commissioner of Agriculture and others, the U. S. Secretary of State was persuaded to allocate $2,000 to pay the travel expenses of an e4ntomologist who was to represent the U. S. State Department at the Exposition. Riley selected Albert Koebele, his assistant, who sailed from San Francisco on August 25, 1888.

Koebele experienced few of the problems in Australia that plagued some of the later foreign explorers. As an official representative of the U.S. State Department and the U. S. Department of Agriculture, he received utmost cooperation and was accompanied by knowledgeable local entomologists or growers, who often led him to known pockets of the otherwise rare cottony-cushion scale. He was also furnished with free passes by the State railways in Australia. After he arrived in Sydney on September 20, 1888, Koebele searched for four days and found only a few Icerya and no natural enemies. The local orange growers had no knowledge of the scale. Proceeding to Melbourne by train, he searched for some six days but found no Icerya. He then went to Adelaide with a letter of introduction to Frazer Crawford, and the next day in gardens in Adelaide Icerya was found, with the very first scale examined containing nine pupae of Cryptochaetum iceryae. Nearly all the scales examined in Adelaide were parasitized.

While collecting scales for shipment to California with Crawford in a North Adelaide garden on October 15th, Koebele related on July 1889 (after his return to California), "I discovered there, for the first time, feeding upon a large female Icerya, the Lady-bird, which will become famed in the United States--Vedalia cardinalis." <PHOTO>. By this time the beetle was showing its potential in California. Koebele had written to Riley about his discovery and Riley replied that he thought that Cryptochaetum was probably the most promising, but to try others as well.

Koebele then went to Mannum in the Murray River valley, where much of today's oranges are grown. There he found the scale being parasitized by Cryptochaetum, the Rodolia (= Vedalia, = Novius) cardinalis Mulsant and a predatory green lacewing. He returned within a week to Adelaide with material that was placed in a cool cellar to await shipment to California. On October 24-25 he collected more scales in North Adelaide, along with many parasitic flies and green lacewings. He described his first shipment as:

"I finished collecting for my first shipment on the 25th and estimated that I had about 6000 Icerya, which in return would produce at an average about four parasites [Lestophonus = Cryptochaetum] each. They were packed partly in wooden and partly in tin boxes. Small branches generally full of scales were cut so as to fit exactly lengthwise into the box. With these the boxes were filled and all loose scales placed in between, plenty of space remaining for any of the insects within to move about freely without danger of being crushed by loose sticks. Salicylic acid was used in small quantities in the tin boxes to prevent mold, yet these, as I have been informed by Mr. Coquillett, arrived in a more or less moldy condition, while those in wooden boxes always arrived safe. In addition, Dr. Schomburgh, director of the botanical gardens at Adelaide, kindly fitted up for me a Wardian case which was filled with living plants of orange and Pittosporum in pots. Large numbers of Icerya were placed in this, and such larvae as were found feeding upon them...The object of this was to have the Lestophonus go on breeding within the case during the voyage. No doubt many infested scales arrived in Los Angeles."

"I found [later] on examining the tree [in Los Angeles], on April 12, 1889, under which this case had been placed with a tent over it, that from several of the Iceryas the Lestophonus had issued. This case, as Mr. Coquillett informed me in a letter of November 30, arrived in good condition, except that the putty had been knocked off in several places, leaving holes large enough for the parasites to escape. Before opening the case he found two coccinellid larvae crawling on the outside, and these when placed with the Icerya attacked it at once. He further said that there were only about half a dozen living Chrysopa adults. This would show that the Lestophonus was still issuing on arrival in California and all turned out more favorably than I had anticipated on seeing the box handled in such a rough manner by the steamer hands at Sydney, to which point I accompanied this as well as all the subsequent shipments. I expected little good would come out of this method of sending and therefore concluded to send only small parcels on ice thereafter, as had been partly done at first. If once the insects could be placed in good condition in the ice-house on the steamer just before leaving, where a temperature of 38° Fah. at first and about 46° Fah. on arrival in San Francisco existed, they must arrive safely. To accomplish this, the parasites with their hosts were all collected the last three days before leaving Adelaide, and on arriving home were immediately placed in a cool cellar. On the trip from Adelaide to Sydney, which takes two days by train, y insects came generally in an ice-box on the sleeping-car."

Koebele then surveyed other areas in Victoria and New South Wales but concluded that the Adelaide area was best, so returned on November 8, 1888. After collecting about 6,000 scales in five days and making a trip to Melbourne for additional material, he left Adelaide for Sydney with the second shipment. He writes:

"On the 26th I left Adelaide on my way to Sydney, with what I considered even a better shipment than the first. Unfortunately this lot arrived in a bad condition at San Francisco, owing to a gale on the route when the parcels fell off the shelving in the ice-house, in which they had been placed, and most of them were crushed by cakes of ice falling on them."

Koebele made a third shipment in late December and then travelled to Brisbane, where he found only a few specimens of Icerya and slowly returned to Melbourne with very poor collecting along the way. At Melbourne he collected Cryptochaetum on a related scale, Monophloebus sp. He then collected Icerya with parasitoids and about 200 Rodolia cardinalis in the Sydney Town Hall garden, being now either more proficient at collecting or luckier than during his first trip to Sydney. Under instructions from Riley to study Icerya in New Zealand on his way home, he boarded ship on January 13, 1889 with his insects in the cold room, and arrived in Auckland, New Zealand on January 28th. The scales with parasitoids and Rodolia beetles were found to be in excellent condition at Auckland and were repacked in wooden boxes with fresh Icerya found in Auckland, and apparently were sent on to California. He found no natural enemies in Auckland; however at Napier he found large numbers of Rodolia cardinalis feeding on Icerya. According to Koebele this predator had arrived in Auckland by chance, where Icerya was destroying host plants five years previously, and there it cleaned nearly the whole district around Auckland within about two years. At the time of Koebele's visit the predator was dispersing into new areas, hence his big collection of about 6,000 specimens of Rodolia cardinalis at Napier. Returning to Auckland, these were placed in the ship's cool-room at 4° C (38° F). He left Auckland on February 25th and arrived in San Francisco, Saturday evening March 16th, 1889. The material could not be sent to Coquillett at Los Angeles until the following Monday and he received it on March 20th, 34 days since collection and 29 days on ice. Yet this arrived in better condition than any previous shipment. The specimens were liberated under the same caged tree in Los Angeles that had received the earlier specimens, which was on the property of F. W. Wolfskill. According to Coquillett's records, 129 living Rodolia cardinalis were liberated through January 24, 1889. On February 21, 35 Rodolia arrived and were colonized on the property of J. R. Dobbins in San Gabriel. The final shipment of 350 live Rodolia that was brought personally by Koebele on the ship was colonized on March 20, 1889. About one-third went to the Dobbin's grove and the remainder to the large A. S. Chapman grove in the San Gabriel valley.

Altogether there were about 12,000 living Cryptochaetum iceryae received from Koebele, which were all put under one caged tree. When the tree was examined on April 12, 1889 he noted that very few Cryptochaetum remained of the vast numbers of flies received.

Rodolia cardinalis had killed nearly all the Icerya at the Wolfskill tree by early April 1889. Therefore, one side of the cage was removed and the beetles were allowed to move to adjoining trees. On April 12, Coquillett began sending colonies to other parts of the State. By June 12, two months after the cage was opened, 10,555 Rodolia cardinalis had been distributed to 208 different growers and successful colonization occurred in nearly every case. Within six months of the first release of 28 beetles and with a total release of only 129, the original trees in Wolfskill's orchard were virtually Icerya-free and the beetles had spread to a distance of 3/4 mile. In his Annual Report for 1889 Riley stated that in the original orchard (Wolfskill) practically all the scales were killed before August 1889 and further that by the end of 1889 Icerya was no longer a factor to be considered in citrus growing in California. Coquillett wrote in 1889 regarding the San Gabriel colonization of February and March:

"All of these colonies have thrived exceedingly well. During a recent visit to each of these groves I found the lady-birds on trees fully one-eighth of a mile from those on which the original colonies were placed, having thus distributed themselves of their own accord. The trees I colonized them on in the grove of Dobbins were quite large and were thickly infested with the Iceryas, but at the time of my recent visit scarcely a living Icerya could be found on these and on several adjacent trees, while the dead and dry bodies of the Iceryas still clinging to the trees by the beaks, indicated how thickly the trees had been infested with these pests, and how thoroughly the industrious lady-birds had done their work."

J. R. Dobbins reported on July 1889, only four months after the first beetles were released:

"The vedalia has multiplied in numbers and spread so rapidly that every one of my 3200 orchard trees is literally swarming with them. All of my ornamental trees, shrubs, and vines which were infested with white scale, are practically cleansed by this wonderful parasite. About one month since I made a public statement that my orchard would be free from Icerya by November 1 [1889], but the work has gone on with such amazing speed and thoroughness that I am today confident that the pest will have been exterminated from my trees by the middle of August. People are coming here daily, and by placing infested branches upon the ground beneath my trees for two hours, can secure colonizes of thousands of the vedalias, which are there in countless numbers seeking food. Over 50000 have been taken away to other orchards during the past week, and there are millions still remaining, and I have distributed a total of 63000 since June 1."

The Dobbins orchard was so completely free of Icerya that on July 31 he posted a notice that he had no more beetles for distribution. The other colonized grove in San Gabriel was similarly cleaned of scale (DeBach 1974). In 1888 A. S. Chapman stated that he was being forced to abandon citrus growing on account of scales, while in October 1889 he stated that Rodolia had cleaned up the scale on 150 acres. In just one year shipments of oranges from Los Angeles County increased dramatically from 700 to 2,000 freight train car lost.

Riley in 1893 (DeBach 1974) published the following:

"Mr. William F. Channing, of Pasadena, one of the eminent Unitarian divine, wrote two years later [in 1891]: We owe to the Agricultural Department the rescue of our orange culture by the importation of the Australian lady-bird, Vedalia cardinalis."

"The white scales were incrusting our orange trees with a hideous leprosy. They spread with wonderful rapidity and would have made citrus growth on the whole North American continent impossible within a few years. It took the Vedalia, where introduced, only a few weeks absolutely to clean out the white scale. The deliverance was more like a miracle than anything I have ever seen. In the spring of 1889 I had abandoned my young Washington navel orange trees as irrecoverable. Those same trees bore from two to three boxes of oranges apiece at the end of the season (or winter and spring of 1890). The consequence of the deliverance is that many hundreds of thousands of orange trees (navels almost exclusively) have been set out in southern California this last spring."

Out of a total original stock of 514 beetles colonized from the end of November 1888 to late March 1889 the rapidity and extent of this control was nearly unbelievable (DeBach 1974). Coquillett in a letter to Riley, October 21, 1889, summarized it as follows:

"The first half of the year I devoted nearly the whole of my time to propagating and distributing the Australia Lady-bird (Vedalia cardinalis) recently introduced by this Division. At the present time it is very difficult to find a living Fluted Scale (Icerya purchasi Maskell) in the vicinity of this city [Los Angeles], so thoroughly has the Lady-bird done its work; and, indeed, the same is true of nearly the entire southern part of the state, as well as of many localities in the northern part."

DeBach (1974) reported that by 1890 all infestations in the State had been completely decimated. The cost, aside from Koebele's and Coquillett's salaries, was about $1,500.00; and all told less than $5,000.00. Benefits to the citrus industry of California have amounted to millions of dollars annually ever since and as an aftermath similar successes have been attained over the years in more than fifty countries around the world by transfer of Rodolia cardinalis and to a lesser extent of Cryptochaetum iceryae. Albert Koebele immediately became famous and continued as a foreign explorer for the USDA and later for Hawaii, although he never again achieved such a spectacular success. In California special funds were raised and Koebele was presented with a gold watch and his wife with a pair of diamond earrings.

DeBach (1974) relates that as a sequel to this story, Cryptochaetum iceryae had been increasing in California and eventually became dominant in coastal areas, which includes Los Angeles where Rodolia attained its first notoriety. Research since has shown that Cryptochaetum alone would have done just as spectacular a control in the citrus areas of 1890 as did Rodolia. However, with expansion of citrus to hotter, drier interior areas of California, Rodolia is the most important biological control factor.

Kennett et al (1999) mention the importation of another coccinellid, Rodolia koebelei (Horn), which was introduced from Australia in 1892. Although it became established and persisted for a number of years, it was eventually displaced by R. cardinalis.

Later studies in southern California by Quezada, <PHOTO>, (Quezada & DeBach 1973) revealed that Rodolia cardinalis and Cryptochaetum iceryae impacted their host in concert, with Rodolia tending to displace Cryptochaetum in arid areas, the reverse being true along coastal areas while in intermediate areas both tended to be commonly present, depending on environmental fluctuations. Greathead (1976) reported that in colder climates Rodolia is frequently eliminated during winter and recolonization is necessary to maintain control. Cryptochaetum has a more restrictive range of adaptability and has not been successfully introduced to as many areas as Rodolia.

For greater detail on the various aspects of this biological control effort please refer to the following references (Riley 1887, Coquillet 1889, Marchal 1908, Savastano 1919, Kuwana 1922, Autuori 1928, Gomez-Clemente 1929, Poutiers 1930, Thorpe 1930, Essig 1931, Leonard 1932, Bazduireva 1933, Bodenheimer 1933, Bodenheimer & Tenenbaum 1934, Wolcott & Sein 1933, Chen 1934, Stepanov 1935, Wille 1935, 1941; Ramachandra Rao & Cherian 1944, Geier & Baggiolina 1950, Pruthi 1950, Subramaniam 1954, 1955; Bartlett & Lagace 1960).

REFERENCES: [Additional references may be found at: MELVYL Library ]

Anonymous. 1917. Investigations on the coccinellid, vedalia, and the scale-insect Icerya. Dept. Agric. & Com. Plant Path. & Injur. Insects Bull. 3: 107 p. (Abs. in REv. Appl. Ent. (A), 6: 282).

Autuori, M. 1928. Syneura infraposita Borgm.-Schmitz (Diptera: Phoridae) um novo parasita da Icerya purchasi Mask. Inst. Biol., Sao Paulo, Arch 1: 193-200. [in Portuguese w/ English summary].

Balachowsky, A. 1932. Observations biologique sur l'adaptation de Novius cardinalis Muls. aux depens de Gueriniella serratulae F. (Contribution a l'etude des coccides de france; 6 note). Rev. Pathol. Veg. Ent. Agric. Fr. 19: 11-17.

Bartlett, B. R. 1978. Coccidae. In: C. P. Clausen (ed.), Introduced Parasites and Predators of Arthropod Pests and Weeds. U. S. Dept. Agric. Agric. Handbk. No. 480, Washington, D.C. 545 p.

Bartlett, B. R. & C. F. Lagace. 1960. Interference with biological control of cottony-cushion scale by insecticides and attempts to reestablish a favorable natural balance. J. Econ. Ent. 53: 1055-58.

Bazduireva, V. I. 1933. The fluted scale (Icerya purchasi Mask.) and its control. A review of literature. Plant Protect. (Leningrad) (1932) 3: 35-64. [in Russian].

Bodenheimer, F. S. 1933. Icerya purchasi Mask. and Novius cardinalis Muls. Ztschr. f. angew. Ent. 19: 514-43.

Bodenheimer, F. S. & B. Tenenbaum. 1934. Icerya purchasi Mask. and its control in Palestine. Hadar: 32-4.

Chen, F. 1934. Notes on two coccinellids of Hwang-Yeh, Chekiang. Ent. & Phytopath 2: 142-48. [in Chinese].

Clausen, C. P. 1978a. Biological control of citrus insects. Chapter 6,

Vol. IV. In: The Citrus Industry. Univ. of Calif. Div. Agric. Sci., Berkeley, Calif. 362 p.

Coquillet, D. W. 1889. The imported Australian lady-bird. Insect Life 2: 70-4.

DeBach, P. 1964. Successes, trends and future possibilities. In: P. DeBach (ed.), Biological Control of Insect Pests and Weeds. Reinhold Publ. Co., New York. 844 p.

DeBach, P. 1974. Biological Control by Natural Enemies. Cambridge Univ. Press. 323 p.

Doutt, R. L. 1958. Vice, virtue and the vedalia. Bull. Ent. Soc. Amer. 4: 119-23.

Doutt, R. L. 1964. The historical development of biological control. Chapter 2, In: P. DeBach (ed.), Biological Control of Insect Pests and Weeds. Reinhold Publ. Co., New York. 844 p.

Essig, E. O. 1931. A History of Entomology. MacMillan Co., New York. 1029 p.

Geier, P. & M. Baggiolini. 1950. Quelques observationes sur la biologie de Pericerya purchasi Mask. au Tessin (Homop., Margaroid.). Schweitz. Ent. Gesell. Mitt. 23: 104-16.

Gomez-Clemente, F. 1929. La lucha natural. Estudio acerca de la Icerya purchasi Mask. y de su parásito el Novius cardinalis Muls. Estac. Fitopatol. Agric. Valencia. 53p.

Greathead, D. J. 1976. A review of biological control in western and southern Europe. Tech. Comm. No. 7, CIBC. Commonw. Agr. Bur., Farnham Royal, Slough, England. 182 p.

Kennett, C. E., J. A. McMurtry & J. W. Beardsley. 1999. Biological control in subtropical and tropical crops. In: Bellows, T. S. & T. W. Fisher (eds.), Handbook of Biological Control: Principles and Applications. Academic Press, San Diego, New York. 1046 p

Koebele, A. 1890. Report of a trip to Australia to investigate the natural enemies of the fluted scale. U. S. Dept. Agric., Bur. Ent. Bull. 21: 1-32.

Kuwana, I. 1922. Studies on Japanese Monophelebinae. Contrib. II. the genus Icerya. Japan Dept. Agric. & Com., Imp. Plant Quart. Sta. Bull. 2. 43 p.

Leonard, M. D. 1932. The cottony cushion scale in Puerto Rico. J. Econ. Ent. 25: 1103-07.

Marchal, P. 1908. The utilization of auxiliary entomophagous insects in the struggle against insects injurious to agriculture. Pop. Sci. Monthly (Apr.): 352-419.

Poutiers, R. 1930. Sur le comportemente du Novius cardinalis (Coleoptera, Coccinellidae) vis-a-vis de certains alcaloides. Soc. de Biol. (Paris) Compt. Rend. 103, 1023-25.

Pruthi, H. S. 1950. A foreign insect menace to Indian citrus industry checked. Indian Farming 11: 5-6.

Quayle, H. J. 1938. Insects of Citrus and Other Subtropical Fruits. Comstock Publishing Co., Ithaca, New York. 583 p.

Quezada, J. R. & P. DeBach. 1973. Bioecological and population studies of the cottony-cushion scale, Icerya purchasi Mask. and its natural enemies, Rodolia cardinalis Mul. Cryptochaetum iceryae Will., in southern California. Hilgardia 41: 631-88.

Ramachandra Rao, R. S. Y. & M. C. Cherian. 1944. The fluted scale, Icerya purchasi Mask., as a pest of wattle in south India, and its control by the biological method. Madras Agric. J. 32: 20.

Riley, C. V. 1887. The Icerya or fluted scale, otherwise known as the cotton cushion scale. U. S. Dept. Agric., Div. Ent. Bull. 15. 40 p.

Riley, C. V. 1893. Parasitic and predaceous insects in applied entomology. Insect Life 6: 130-41.

Savastano, L. 1919. La ginestra etnea e la cumune, l'Iceria e il Novius. Acireale R. Staz. Sper. di agrumic. e Fruttic. 37: 1-4.

Smith, H. S. & H. Compere. 1916. Observations on the Lestophonus, a dipterous parasite of the cottony cushion scale. Bull. Calif. Dept. Agric. 5: 384-90.

Stepanov, E. M. 1935. The biological method of controlling pests of plants in Abkhazia. [Abs. in REv. Appl. Ent. (A), 24: 674).

Subramanium, T. V. 1955. Control of the fluted scale in peninsular India. Indian J. Ent. 16: 391-415.

Subramanium, T. V. 1955. Control of the fluted scale in peninsular India. Indian J. Ent. 17: 103-20.

Thorpe, W. H. 1930. The biology, post-embryonic development, and economic importance of Cryptochaetum iceryae (Diptera, Agromyzidae) parasitic on Icerya purchasi (Coccidae, Monophlebini). Zool. Soc. London Proc. 60: 929-71.

Wille, J. E. 1935. Icerya purchasi y Novius cardinalis. (Peru) Min. de Fomento, Dir. Agric. y Ganad. Informe 32. 23 p.

Wille, J. E. 1941. Resçmen de los diferences labores ejecutadas en el Peru para combatir insectos daninos por el "método biológico." 6th Pacific Sci. Cong. Proc (1939) 4: 369-71.

Wolcott, G. N. & F. Sein, Jr. 1933. A year's experience with the cottony cushion scale in Puerto Rico. Puerto Rico Dept. Agric. J. 17: 199-21.