BLUE GUM PSYLLID

BLUE GUM PSYLLID

The blue gum psyllid, Ctenarytaina eucalypti, was first discovered in Monterey County, California in January 1991. Since the original find the psyllid has spread in a very short time throughout the California coastal area and into the central valley.

The blue gum psyllid is native to Australia, where it feeds on blue gum, Eucalyptus globulus, and other Eucalyptus species that have waxy blue juvenile foliage. Eucalyptus pulverulenta, a suitable host for this pest, has been planted in plantations along the coastal counties of California. Its foliage is used by the floral industry in flower arrangements. Growers applied large amounts of pesticides to prevent damage to foliage during the two to three years after the psyllid be-came established.

Description of Pest and Damage The blue gum psyllid has 4 or more generations per year, depending on climate and plant suitability. The adult is gray with orange bands on the abdomen and is an active flyer. There are five instars, each with different patterns of orange and brown to gray markings.

The female oviposits yellow eggs in clusters at the base of the terminal leaves and axial buds. The nymphs hatch and settle to feed on the leaf or stem near the egg clusters. Feeding causes acute damage, such as inhibition of new shoot formation and distortion in the shape of new leaves. The nymphs secrete wax-coated honeydew spheres as well as copious amounts of waxy filament, which can conceal them from view. Besides unsightly foliage distortion, sooty mold growing on the honeydew ruins the aesthetic appeal of the foliage in floral arrangements.

Biological Control

A search for natural enemies of the psyllid was conducted in Australia and New Zealand in 1991-1992. A tiny wasp, Psyllaephagus pilosus, was found to be an effective natural enemy of the psyllid in these countries. The adult is small (1 mm) and black with a hint of green iridescence. The female wasp deposits a single egg inside a late-instar psyllid nymph. The hatched larva feeds inside the nymphs, pupates and emerges as a new adult in about three weeks. A round exit hole in the dorsum of the psyllid mummy (Fig. 4) is reliable evidence of successful parasitation. The female also host-feeds on the body fluids which exude from holes she makes in young psyllid nymphs with her ovipositor. These parasitoids were reared at our facilities in winter/spring 1992-1993 and a total of more than 6,400 were released at 8 sites in the counties of San Diego, San Luis Obispo, Monterey, Alameda, and Sonoma. By the end of 1993 the parasitoid was established at all release sites; at several sites parasitization rates of more than 50% were recorded. By early 1994 we recorded a 35 mile natural spread of the parasitoid from the first release site in Monterey.

During the period from 1991 to 1995 we sampled foliage of both E. globulus and E. pulverulenta for the presence of psyllids and parasitoids and compared the counts with the catches of the adults on yellow sticky traps. The monitoring system with sticky traps reliably measured population levels of both insects on foliage.

During the 1994 and 1995 growing seasons the numbers of psyllids caught in traps fell to well below the catches recorded in 1991 (after pesticide sprayings in the absence of parasitoids). Parasitoids reduced the psyllid population to a level causing insignificant economic damage. Most growers have suspended use of pesticides and are now relying on the parasitoids to control the pest. The cost savings to growers from this successful biological control program has been immense.

EDITOR: Pavel Avihra, Horticulture Advisor, University of California Cooperative Extension, 1682 Novato Blvd., Suite 150 B, Novato, C.A. 94947

Donald L. Dahlsten, David L. Rowney, Richard L. Tassan, William A. Copper, Laboratory of Biological Control, University of California, Berkeley; William E. Chaney, UCCE Monterey County; Karen L. Robb, UCCE San Diego County; Steven Tjosvold, UCCE Santa Cruz County; Mary Bianchi, UCCE San Luis Obispo County and Priscilla Lane, Sonoma County Department of Agriculture

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