Six species of overseas insects low starthistle replaces desirable veg- Yellow starthistle, one of California’s more pernicious weeds, infests this field in have been approved for release as etation, in both natural and managed Nevada County. biological control agents of yellow settings. In natural settings, it dimin- starthistle, California’s most per- ishes recreational values, and dense vasive weed. Previously, four stands of this invasive exotic can re- Mayfield 1985). Yellow starthistle’s biocontrol insects were known to duce biodiversity and help carry wild logarithmic range expansion contin- be established in California; we fires. Within California’s agricultural ues. A 1997 survey by California De- now confirm the establishment of community, yellow starthistle most se- partment of Food and Agriculture the peacock fly, as well as the ac- verely impacts ranchers. While young (CDFA) found this weed in 42% (n = 1,935) of California’s 4,638 townships cidentally introduced false pea- yellow starthistle shoots can be grazed - each 6 by 6 square miles - and in cock fly. Remarkably, the false by cattle, the sharp spines of older plants deter feeding, thereby greatly 22% (1,019 townships) the infestations peacock fly is significantly more reducing the forage value of hundreds are reported as ”high” (Pitcairn et al. widespread and more effective of thousands of acres for most of the 1998a). “High“ abundance was de- against yellow starthistle than the year. Yellow starthistle can be toxic to fined as being, at a minimum, several peacock fly - or any other horses that feed on it, causing a fatal miles of dense roadside infestation. biocontrol insect to date. How- neurological disorder called ”nigro- Widespread exotic pests, such as ever, since the false peacock fly is pallidal encephalomalacia” (Cordy yellow starthistle, are obvious targets not an approved agent, we will 1978). Starthistle removal also in- for classical biological control, in await completion of our ongoing creases herbicide and labor costs for which natural enemies of a pest are field and laboratory assessments other agricultural enterprises, such as imported from its native territory. Po- of this fly’s safety to crops and vineyards and orchards. tential biocontrol agents for weeds are native plants before recommend- Yellow starthistle is native to the carefully selected and screened in ex- ing use of this promising fly as a eastern Mediterranean region of tensive tests to ensure their safety. biological control agent. Eurasia, and was introduced into Cali- Prior to release, an array of federal fornia more than 150 years ago and state agencies review the host While California’s diverse habitats (Maddox and Mayfield 1985). It is now range tests and other information support hundreds of invasive weed the state’s most widespread weed. The about the proposed agent; formal ap- species, probably none is more wide- infested area increased from an esti- proval for release must be granted by spread nor pernicious than yellow mated 1.2 million acres in 1958 to 7.9 the U.S.Department of Agriculture’s starthistle (Centaurea solstitialis L.) Yel- million acres in 1985 (Maddox and Animal and Plant Health Inspection Service (USDA-APHIS), as well as by and at one of the Idaho sites in 1995 they were the result of natural migra- the state where the release will take (Turner et al. 1996). Establishment of tion from the long-established popula- place. this fly was not observed at any of the tions at the Merlin release site (107 This classical biological control ap- six California sites (Turner et al. 1996). miles away), rather than from our re- proach has been used against more At the three sites (in Idaho, Oregon leases earlier that year in Shasta and than 100 weed species worldwide. and Washington) where the peacock Siskiyou counties. California has benefited greatly from fly did establish, bachelor’s button, the successful biological control of in- Centaurea cyanus, was widespread. Discovery of a new fly vasive plants such as Klamath weed Bachelor’s button is another exotic an- The ease with which these flies (Hypericum perforaturn), tansy ragwort nual, closely related to yellow from Oregon established at all sites, (Seneciojacobaea), and puncture vine starthistle, that is invasive in the Pa- including those that lacked bachelor’s (Tribulus terrestris) (Julien 1992). Over- cific Northwest. It was theorized that button, along with their rapid dis- seas surveys to locate potential the early-blooming bachelor’s button persal from the release sites, was un- biocontrol agents for yellow starthistle flowers were acting as an alternate expected - especially in light of the began in Europe 40 years ago, and, to host until yellow starthistle blossomed complete failure of the earlier releases date, six insect species have been ap- some weeks later (Turner et al. 1996). in California. In 1996, we submitted proved and released in the United Buoyed by these successful estab- specimens of the flies recovered from States for control of this invasive weed lishments, we renewed the coloniza- the field in California to two experts (table 1).All six species attack the tion effort for the peacock fly in Cali- on fly taxonomy at the CDFA Plant flowers or seeds of yellow starthistle. fornia, with releases at 7 sites in 7 Pest Diagnostics Center. Neither counties in 1995, and 15 more releases thought that these California flies fit The peacock fly in 12 counties in 1996. Sites containing the published description of Ckaeto- The third seed head fly to be ap- both bachelor’s button and yellow rellia australis. The second taxonomist, proved for release was the peacock fly, starthistle were given the highest pri- Eric Fisher, identified them as Ck. Ckaetorellia australis Hering, whose lar- ority. In California, bachelor’s button succinea (Costa), a similar species from vae feed inside the seed head of yel- has naturalized primarily in higher el- Europe and Asia. We then curtailed all low starthistle, destroying most of the evation sites in the northern part of the further releases of Ckaetorellia flies in developing seeds. The mature larvae state. Second priority was given to California. After assembling Chaeto- overwinter in the old heads, with the sites with early-blooming yellow rellia specimens recovered from field adults emerging in the spring. Females starthistle. All flies released (except sites in California, Oregon and Wash- oviposit on maturing buds. Releases of one sample from bachelor’s button) ington, we shipped these, along with peacock flies, reared from yellow were those that emerged from yellow voucher Ckaetorellia specimens from starthistle heads shipped from Greece starthistle heads collected at the Mer- those originally imported and tested at to the USDA Agricultural Research lin, Ore., site. the ARS quarantine in Albany to Ian Service (ARS) quarantine facility in Al- During our surveys at the end of White at the British Museum of Natu- bany, Calif., began in 1988. By 1994, 1995, populations of Chaetorellia flies ral History, London, for confirmation. peacock fly had been released at 14 were found at multiple locations in Dr. White is an authority for the genus sites in California, Idaho, Oregon and Humboldt and Trinity counties in Ckaetorellia and had recently published Washington, but establishment was Northern California. The fly popula- a revision of this genus (White and confirmed only at two sites that year, tions in these counties were so large Marquardt 1989). He confirmed that one each in Oregon and Washington, and widespread that we surmised that the majority of Ckaetorellia specimens from California and Merlin were, in fact, Ck. succinea. White and Marquardt (1989) place the nine known species of Ckaetorellia into two groups - Ck. succinea belonging to one group, and Ck. australis to another. Ck. succinea (and the other two species in its group) has an extra ”spot” on each side of its thorax that is lacking in Ck. australis and the other five species in its group. As no other members of the first group have been recorded in North America, we use this extra “spot” as an easy way to distinguish it from all other Ckaetorellia flies found here. Since Ck. australis is widely known in California as the peacock fly, The quarantine records showed that 207 and 268 sites, respectively, in Cali- there had been 17 shipments of fornia. We revisited not only the origi- Chaetorellia-infested heads from Greece nal Ckaetorellia release sites, but also during 1986-1994. Flies emerging from searched yellow starthistle along prob- nine of these shipments of yellow able flyways, such as major river sys- starthistle heads were eventually re- tems or highways. At each site, we leased in four states. There were 43 systematically swept the yellow voucher specimens from these release starthistle heads with an insect net shipments, and our cooperators in (usually 20 sweeps), and, for at least other states also had retained a similar one site in each county, collected number. We identified the voucher heads that had recently finished flow- specimens, and had representative ering. The latter were held in emer- specimens confirmed by Ckaetorellia gence containers in the laboratory un- expert White. This allows us to put til the flies stopped emerging from C 5: forth the following probable scenario them, about 1 year later. Over the last for the introduction of the false pea- 4 years, we collected more than 700 cock fly. Ckaetorellia australis was the samples from over 450 California sites only fly present among the voucher (fig. 1).We recovered ”true” peacock Above, the false peacock fly, Chaetorellia succinea. Below, the false peacock fly specimens from all these shipments, fly at four release sites, and at 20 addi- (left), and the “true” peacock fly, Ch. aus- except for a 1991 shipment of yellow tional, scattered sites in seven corn- fralis (right).