Dr. Donald L. Dahlsten, University of California at Berkeley, Center for Biological Control
© The Regents of the University of California, (1996)
(for an economic analysis of this project, click here)
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.
Fig. 1. Blue gum psyllid adult and large nymph with honeydew (photo by Jack Kelly Clark).
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 the blue gum psyllid, has been planted in plantations along the coastal counties of California. Foliage from this Eucalyptus is used by the floral industry in flower arrangements. Growers used large amounts of pesticides to control the psyllid in these plantations during the two to three years after the psyllid became 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
(Fig. 1) is gray with orange bands on the abdomen; it is an active flyer. There are five instars, each with different
patterns of orange and brown to gray markings.
Fig. 2. Blue gum psyllid nymphs and honeydew (photo by Jack Kelly Clark).
Fig. 3. P. pilosis ovipositing in a psyllid nymph (photo by Jack Kelly Clark).
Clusters of yellow eggs are deposited at the base of the terminal leaves and axial buds. The nymphs settle and feed on the leaf or stem near where the eggs were deposited. The nymphs (Fig. 2) secrete wax-coated honeydew spheres as well as copious amounts of waxy filament, which can conceal them from view.
High numbers of psyllids and/or sooty mold growing on the honeydew detracts from the aesthetic appeal of the foliage in floral arrangements. Feeding by psyllids also causes acute damage, such as inhibition of new shoot formation and distortion in the shape of new leaves.
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 wasps (Fig. 3)are small (1 mm), and black with a hint of green iridescence.
The female wasp deposits a single egg inside a late-instar psyllid nymph. After about three weeks of development is complete, a new adult chews a round hole in the dorsum of the psyllid mummy (Fig. 4) and emerges. The female also host-feeds on the body fluids which exude from holes she makes in young psyllid nymphs with her ovipositor.
Fig. 4. Emergence hole in psyllid nymph (photo by Jack Kelly Clark).
These parasitoids were reared at our facilities in winter/spring 1992-1993 and a total of more than 6400 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 mid-1994 we recorded a natural spread of the parasitoid of 11 miles from the first release site in Monterey.
During the period from 1991 to 1995 we measured psyllid and parasitoid levels by sampling foliage of both E. globulus and E. pulverulenta, and developed an inexpensive monitoring system using yellow sticky traps to capture adult psyllids and parasitoids. The sticky trap system proved a simple method of reliably measuring 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 levels that were previously seen only after spraying of pesticides. Psyllids did not cause significant economic damage in most areas, so most growers have suspended use of pesticides and are now relying on the parasitoids to control the psyllid. The cost savings to growers from this successful biological control program has been immense (see our economic analysis).
Donald L. Dahlsten, David L. Rowney, Richard L. Tassan, William A. Copper, Center for Biological Control, U. C. Berkeley
William E. Chaney, University of California Cooperative Extension, Monterey County.
Karen L. Robb, University of California Cooperative Extension, San Diego County
Steven Tjosvold, University of California Cooperative Extension, Santa Cruz County.
Mary Bianchi, University of California Cooperative Extension, San Luis Obispo County
and Priscilla Lane, Sonoma County Department of Agriculture
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