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OLIVE SCALE, Parlatoria oleae (Colvee) -- Diaspididae

Olive scale is believed to be native to the Middle East. It became established near Fresno, California around 1934 on olives, and rapidly spread throughout the Central Valley and into southern California, becoming a major pest of many deciduous fruit crops and ornamentals in addition to olives (DeBach 1974). Losses due to damage and the cost of chemical control were >1-million $$/year. It not only caused massive plant damage due to heavy infestations but was also serious on olives because even one scale per fruit would cause discoloration and cullage. Therefore, it was evident from the start that biological control would have to be very thorough.

A biological control effort was initiated in 1949 with the importation of a strain of Aphytis maculicornis (Masi) that was found attacking olive scale in Egypt. The effort failed. In 1951, Dr. Harry Smith arranged for Dr. A. M. Boyce to search for natural enemies throughout the presumed native home of the olives scale from India through the Middle East, North Africa and the Mediterranean. Dr. Boyce was abroad about one year and made numerous consignments to California by air from India, Pakistan, Afghanistan, Iran, Iraq, Syria, Lebanon, Israel, Cyprus, Egypt, Greece and Spain. Even during the relatively modern period he experienced many adventures, including collecting in rebel areas under armed escorts. Additional shipments were made by collaborators from India and Pakistan in 1952-3 (DeBach 1974).

Several species of parasitoids were obtained and colonized in California, including four strains or sibling species of Aphytis maculicornis. These were indistinguishable morphologically but laboratory studies suggested that they had distinct biological attributes, so they were reared and liberated separately in the field. It then became obvious that the Persian strain of A. maculicornis released in 1952 was the only natural enemy showing appreciable promise in the field. Over 20 million parasitoids were colonized during 1952-60 at several hundred sites in 24 counties of California. Dramatic results soon became evident. The Persian Aphytis became readily established everywhere and increased rapidly, commonly attaining parasitization rates of >90% and generally reducing the average densities of olive scale populations by 98-99%. Plant damage was practically eliminated, but even this dramatic reduction proved to be economically unsatisfactory on olive in many cases because even one scale on a fruit may cause it to be rejected, and not more than 5% cullage was acceptable. Since a heavily infested olive tree might have over one million scales, a reduction of 99% would leave 10,000 scales, which could mean that a large number of fruit might have one or more scales. The parasitoid was prevented from being more effective because its populations were greatly reduced each summer by the hot dry weather. Otherwise, it would probably produced complete biological control everywhere as it did in a few favorable localities (DeBach 1974).

In an effort to establish additional effective natural enemies, Dr. Paul DeBach while searching for parasitoids of the California red scale in West Pakistan early in 1957 had gone with Dr. M. A. Ghani to a remote village in the Tribal Territories where citrus had been reported. It was to be a brief 3-day trip with one day at the village for collecting because of continuing travel commitments (DeBach 1974). Upon arrival there, DeBach and Ghani found that the altitude was too high and the climate too cool for citrus, so DeBach spent the day looking for other scale insect parasitoids on deciduous fruit trees and ornamentals. Olive scale was found and parasitoid activity was noticeable, especially emergence holes of internal parasitoids in dead scales. DeBach knew that no internal parasitoids were established in California, and therefore collected as much f this material as he could and then returned to Rawalpindi the next day, where he packaged it and sent it to the University of California at Berkeley by airmail. Dr. Boyce believes that he made the original discovery of Coccophagoides during his earlier collecting trip, but that successful culture in California was not obtained (A. M. Boyce, pers. commun.).

Two species of parasitoids emerged from this single shipment and both were successfully cultured. Only one, however, Coccophagoides utilis Doutt, became established. By early 1961 it showed great promise of improving the degree of biological control of olive scale in the two groves in which it was first released in 1957-8. This led to mass culture and colonization of over 4 million of the parasitoids during 1962-4 at over 170 sites in 25 counties. Widespread complete biological control resulted. Coccophagoides acted as a complementary mortality factor to Aphytis maculicornis. Although it only added ca. 4-8% additional host mortality to that which A. maculicornis could have produced by itself, this was sufficient to reduce the equilibrium level of the scale population so that no cullage of olives remained (DeBach 1974). DeBach (1974) holds this example as illustrating the futility of trying to evaluate the potential or actual effectiveness of a parasitoid on the basis of the percent parasitization of the host, and it emphasizes that all parasitoids within reason should be tried until completely satisfactory biological control is obtained (Huffaker & Kennett 1966, DeBach, Rosen & Kennett 1971, DeBach 1974).

For additional information on biological control effort, and biologies of host and natural enemies, please see the following (McKenzie 1952, Doutt 1953, 1954, 1966; Hafez & Doutt 1954, Clausen 1956, 1959; Huffaker & Kennett 1960, 1966; Applebaum & Rosen 1964, Huffaker & Doutt 1965, Broodryk & Doutt 1966, Kennett et al. 1965, 1966, Finney 1966, Kennett 1967).

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

Applebaum, S. W. & D. Rosen. 1964. Ecological studies on the olive scale, Parlatoria oleae, in Israel. J. Econ. Ent. 57: 847-50.

Broodryk, S. W. & R. L. Doutt. 1966. Studies of two parasites of olive scale, Parlatoria oleae (Colvee). II. The biology of Coccophagoides utilis Doutt (Hymenoptera: Aphelinidae). Hilgardia 37: 233-54.

Clausen, C. P. 1956. Biological control of insect pests in the continental United States. U. S. Dept. Agric. Tech. Bull. 1139. 151 p.

Clausen, C. P. 1959. Releases of recently imported insect parasites and predators in California, 1956-57. Pan-Pacific Ent. 35: 107-08.

DeBach, P. 1974. Biological Control by Natural Enemies. Cambridge University Press, London & New York. 323 p.

DeBach, P., D. Rosen & C. E. Kennett. 1971. Biological control of coccids by introduced natural enemies. In: C. B. Huffaker (ed), Biological Control. Plenum Press, New York. 511 p.

Doutt, R. L. 1953. Natural enemies of olive scale. Calif. Agric. 7: 5.

Doutt, R. L. 1954. An evaluation of some natural enemies of the olive scale. J. Econ. Ent. 47: 39-43.

Doutt, R. L. 1966. Studies of two parasites of olive scale, Parlatoria oleae (Colvee). I. A taxonomic analysis of parasitic Hymenoptera reared from Parlatoria oleae (Colvee). Hilgardia 37: 219-31.

Finney, G. L. 1966. Studies of two parasites of olive scale, Parlatoria oleae (Colvée). Hilgardia 37: 337-43.

Hafez, M. & R. L. Doutt. 1954. Biological evidence of sibling species in Aphytis maculicornis (Masi) (Hymenoptera, Aphelinidae). Canad. Ent. 86: 90-6.

Huffaker, C. B. & R. L. Doutt. 1965. Establishment of the coccinellid Chilocorus bipustulatus Linnaeus, in California olive groves. Pan-Pacific Ent. 41: 61-63.

Huffaker, C. B. & C. E. Kennett. 1966. Studies of two parasites of olive scale, Parlatoria oleae (Colvee). IV. Biological control of Parlatoria oleae (Colvee) through the compensatory action of two introduced parasites. Hilgardia 37(9): 283-335.

Huffaker, C. B., C. E. Kennett & G. L. Finney. 1962. Biological control of the olive scale Parlatoria oleae (Colvee) in California by imported Aphytis maculicornis (Masi) (Hymenoptera: Aphelinidae). Hilgardia a32: 521-636.

Kennett, C. E. 1967. Biological control of olive scale, Parlatoria oleae (Colvee), in a deciduous fruit orchard in California. Entomophaga 12: 461-74.

Kennett, C. E., C. B. Huffaker & K. W. Optiz. 1965. Biological control of olive scale. Calif. Agric. 19: 12-15.

Kennett, C. E., C. B. Huffaker & G. L. Finney. 1966. Studies of two parasites of olive scale, Parlatoria oleae (Colvee). III. The role of an autoparasitic aphelinid, Coccophagoides utilis Doutt, in the control of Parlatoria oleae (Colvee). Hilgardia 37: 255-82.

McKenzie, H. L. 1952. Scale studies. X. Distribution and biological notes on the olive Parlatoria scale, Parlatoria oleae (Colvée) in California (Homoptera: Coccoidae; Diaspididae). Calif. State Dept. Agric. Bull. 41: 127-38.