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GRAPELEAF SKELETONIZER (Western)

Harrisina brillians Barnes & McDunnough -- Lepidoptera, Zygaenidae

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The western grapeleaf skeletonizer, Harrisina brillians Barnes & McDunnough, was originally distributed throughout the southwestern United States and northern Mexico. It was first found in California in San Diego in 1941, where it severely defoliated wild grapes, Vitis girdiana Munson in the canyons. Soon it became a serious pests in commercial vineyards. The larvae are voracious feeders and can devastate a crop by defoliating an entire vineyard.

In 1950 efforts were initiated in the University of California to control grapeleaf skeletonizer biologically. Parasitoids were introduced, with two species, the braconid, Apanteles harrisinae Muesebeck and the tachinid, Ametadoria miscella (Wulp) (= Sturmia harrisinae Coquillett) predominating (Clausen 1961). A virulent granulosis virus was also accidentally introduced. Initially, Apanteles was the most abundant of the two parasitoids and contributed to the reduction of the infestations, but later it declined in importance because of heavy mortality from attack by hyperparasitoids, especially Dibrachys sp. (Clausen 1978). Although a sharp decline in the number and severity of infestations was observed in southern California, this cannot be attributed to the activities of the two parasitoids only, because a virus disease, probably brought in with the shipment of larvae from Arizona in 1950-51, became established and spread rapidly (Smith et al. 1956). The virus must be credited with a major role in control of the pest, and its rapid distribution over the infested area was undoubtedly facilitated by mechanical transmission from place to place via the parasitoids, contaminated by the diarrheic discharges of diseased caterpillars( Wehrle 1939, Lange 1944, Smith & Langston 1953, Smith et al. 1955a,b).

Surveys in San Diego County in 1982-1983 revealed that it was necessary to spray grapeleaf skeletonizer in commercial vineyards (Flaherty et al. 1985). Abandoned untreated vineyards and backyard vines were severely defoliated despite the activity of the imported parasitoids. Symptoms of virus infection were not observed in the survey. Grapeleaf skeletonizer was not found in wild grapes, V. girdiana, except where they were in close proximity to heavily infested commercial V. vinifera vineyards (Flaherty & Wilson 1992).

The skeletonizer invaded the San Joaquin Valley in 1961 (Clausen 1961), and new infestations appeared thereafter throughout the Central Valley in spite of eradication efforts. Renewed efforts to introduce natural enemies were made in the 1980's, which resulted in the translocation of parasitoids from southern California and the acquisition of new species and strains from Torreón vicinity in Mexico (E. F. Legner and B. Villegas, unpub. data). Extensive insecticide treatment during introduction, however, precluded establishment in most areas. Some success was achieved outside the principal grape production area near Redding, with the establishment of Apanteles spp. and Ametadoria spp. This insect is now regarded a serious pest of commercial vineyards and backyard vines, as well as in wild grapes, Vitis californica Bentham by Flaherty & Wilson (1992). Apanteles harrisinae and A. miscella were not successfully established in the San Joaquin Valley (Flaherty et al. 1985). Only a few parasitoid recoveries were made at release sites which may be related to heavy spray pressure during the introduction period (E. F. Legner, unpub. data). Samples of larvae taken from heavily infested and abandoned vineyards in San Diego County showed only 13% parasitism, which is below the 42-62% reported by Clausen in 1953-54 (Clausen 1961). There was also no evidence of virus present. Clausen (1961) thought that the virus must be credited with the major role in reducing grapeleaf skeletonizer populations to low levels and exterminating many small infestations. Flaherty et al. (1985) considered that at that time the virus was more widespread and had reduced grapeleaf skeletonizer populations to levels that made it more manageable by the parasitoids. This may account for the greater parasitism reported by Clausen (1961) and that found by Flaherty et al. (1985). However, the present absence of virus in abandoned vineyards in San Diego County and the absence of observable grapeleaf skeletonizer in wild grapes is considered an enigma (Flaherty & Wilson 1992). The grapeleaf skeletonizer has shown cyclic abundance, however, and the surveys conducted in San Diego County could have been during one of the cyclic outbreaks. Surveys by E. F. Legner & R. W. Warkentin (unpub. data) during other years have shown this insect to be as rare as reported by Clausen earlier. Also, widespread application of insecticides to vineyards in the south could be responsible for minimizing natural enemy activity. In the San Joaquin Valley the virus of grapeleaf skeletonizer is extremely virulent and has the potential of becoming incorporated into an areawide biological control effort, including wild grapes, backyard vines and commercial vineyards (Flaherty et al. 1985).

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

Bellows, T. S. & T. W. Fisher (eds.). 1999. Handbook of Biological Control: Principles and Applications. Academic Press, San Diego, New York. 1046 p.

Clausen, C. P. 1961. Biological control of western grape leaf skeletonizer (Harrisina brillians B. & McD.) in California. Hilgardia 31: 613-37.

Clausen, C. P. 1978. Zyagaenidae. In: C. P. Clausen, Introduced Parasites and Predators of Arthropod Pests and Weeds. U. S. Dept. Agric., Agric. Handbk. No. 480. 545 p.

Flaherty, D. L. & L. T. Wilson. 1992. Biological control of insects and mites on grapes. In: Principles and Application of Biological Control. University of California Press, Berkeley, CA. (in press).

Flaherty, D. L., L. T. Wilson, V. M. Stern & H. Kido. 1985. Biological control in San Joaquin Valley vineyards. p. 501-20. In: M. A. Hoy & D. C. Herzog (eds.), Biological Control in Agricultural IPM Systems. Academic Press. 589 p.

Lange, W. H., Jr. 1944. The western grape leaf skeletonizer, Harrisina brillians, in California. Calif. State Dept. Agric. Bull. 33: 98-104.

Smith, O. J. and R. L. Langston. 1953. Continuous laboratory propagation of western grape leaf skeletonizer and parasites by prevention of diapause. J. Econ. Ent. 46: 477-84.

Smith, O. J., A. G. Diboll & J. H. Rosenberger. 1955a. Laboratory studies of Pelecystoma harrisinae (Ashmead) an adventive braconid parasite of the western grape leaf skeletonizer. Ann. Ent. Soc. Amer. 48: 232-37.

Smith, O. J., P. H. Dunn & J. Rosenberger. 1955b. Morphology and biology of Sturmia harrisinae Coquillett (Diptera), a parasite of the western grape leaf skeletonizer. Calif. Univ. Publ. Ent. 10: 321-58.

Smith, O. J., K. M. Hughes, P. H. Dunn and I. M. Hall. 1956. A granulosis virus disease of the western grape leaf skeletonizer and its transmission. Canad. Ent. 88: 507-15.

Wehrle, L. P. 1939. Grape Insects in Arizona. Ariz. Agric. Expt. Sta. Bull. 162: 274-92.