Imported Parasitic Wasp Helps Control Red Gum Lerp Psyllid

UC Agriculture & Natural Resources California Agriculture Title Imported parasitic wasp helps control red gum lerp psyllid Permalink https://escholarship.org/uc/item/1f63j4hz Journal California Agriculture, 59(4) ISSN 0008-0845 Authors Dahlsten, Donald L. Daane, Kent M. Paine, Timothy D. et al. Publication Date 2005 Peer reviewed eScholarship.org Powered by the California Digital Library University of California RESEARCH ARTICLE ▼ Imported parasitic wasp helps control red gum lerp psyllid Donald L. Dahlsten Kent M. Daane Timothy D. Paine Karen R. Sime Andrew B. Lawson David L. Rowney William J. Roltsch John W. Andrews Jr. John N. Kabashima David A. Shaw Karen L. Robb James A. Downer* Pamela M. Geisel William E. Chaney Chuck A. Ingels The parasitoid Psyllaphaegus bliteus has Lucia G. Varela been released throughout California to Mary L. Bianchi control the red gum lerp psyllid, a pest of eucalyptus. Above, an adult P. bliteus uses Gary Taylor its ovipositor to place an egg inside the ▼ red gum lerp psyllid nymph. The parasitoid develops inside the psyllid nymph, which typically does not show any signs of parasit- years ago. Until recently, eucalyptus ism until the nymph reaches the fifth instar, The red gum lerp psyllid is an insect trees in California were relatively free when the parasitoid pupa — far left, white body, and left, dark body — can be seen native to Australia, where it feeds from damaging insect pests. Most of through the mummified psyllid. upon eucalyptus species. Since 1998 California’s native insects cannot feed on eucalyptus, which is well protected this psyllid has spread throughout Cal- from herbivores by chemicals such as ifornia, resulting in millions of dollars distasteful essential oils (which are fa- first found on river red gum in June in damage and control costs. To help miliar to anyone who has smelled the 1998 in Los Angeles County and had suppress the red gum lerp psyllid, a bi- strong odor of the leaves). The Austra- spread throughout the state by 2000, ological control program was initiated lian insects that have adapted to feed and throughout Mexico and parts of and a psyllid-specific parasitic wasp on eucalyptus were not transported to Florida by 2002. In Australia there are a was imported from Australia in 1999 California with earlier shipments of number of eucalyptus species that the and released in 2000. In most coastal plant propagation material, usually red gum lerp psyllid can feed on, but in in the form of seeds. This began to California the only favored eucalyptus regions this biological control agent change in the early 1980s and at least species present is the river red gum; has provided substantial control, but 15 eucalyptus-feeding insect species the forest red gum (E. tereticornis) and in some interior regions the psyllid from Australia were accidentally intro- flooded gum (E. rudis), both also in still remains a problem. Researchers duced and are now established in Cali- California, are less-favored trees that the are continuing their investigations to fornia (Paine and Millar 2002). While psyllid can feed on as well. determine if full statewide suppres- eucalyptus trees may be unwanted in Red gum lerp psyllid nymphs build sion will be realized eventually, or if some areas because they crowd out na- white conical shelters called lerps from tive vegetation, their extensive value in excreted honeydew and waxes, and further importation of new parasitoid many other locations led to efforts to live underneath these structures. The species is needed. control the psyllid. nymphs feed by sucking plant sap from River red gum (Eucalyptus camal- leaves. The accumulation of the sticky ucalyptus trees and shrubs, valued dulensis) is among the most com- lerps and honeydew on leaves and for their ability to flourish in arid monly planted shade and windbreak under infested trees creates a nuisance, regionsE and their varied horticultural trees in California and is also grown while heavy infestations lead to defolia- uses, have been a familiar feature of commercially for fuel wood and fi- tion, branch dieback and occasionally California’s urban and rural landscapes ber (Cockerham 2004). The red gum tree death (Paine et al. 2000). since they were first introduced from lerp psyllid (Glycaspsis brimblecombei The first attempts to control red their native Australia more than 150 Moore; Hemiptera: Psylloidea) was gum lerp psyllid focused on the use of *Author’s correction after press time. http://CaliforniaAgriculture.ucop.edu • OCTOBER–DECEMBER 2005 229 ▼ Below, life stages of the red gum lerp psyllid include, (left to right) large nymph, row of eggs, winged adult and small lerp (the protective covering produced by nymphs). Jack Kelly Clark Kelly Jack ▼ Clockwise from top left: Karen Sime, UC Berkeley postdoctorate researcher, checks a caged eucalyptus leaf for evidence of P. bliteus activity and parasitism rates; the late Don Dahlsten (first author) was a leading UC researcher (1966–2003) in biological control of urban and forest pests (shown in 1974); small discs coated with a Jack Kelly Clark Kelly Jack light oil were used to capture and sample populations of adult red gum lerp psyllid and P. bliteus; red gum lerp psyllids feed on eucalyptus leaves, building up to such high densities that the accumulation of psyllids and honeydew causes sooty molds, defoliation and even tree death; in the San Joaquin Valley (Tulare County), a dead red gum eucalyptus (left) near an undamaged and uninfested blue gum eucalyptus (right) demonstrates the psyllid’s feeding preferences. systemic insecticides, mainly to target Classical biological control appeared, ulation dynamics throughout the state. heavy infestations on particularly valu- therefore, to be the most promising We therefore investigated whether red able trees. The proper timing of treat- approach for controlling the red gum gum lerp psyllid populations could ments was difficult to determine and lerp psyllid. We report here on a large be tracked with sticky traps, which control was not always achieved (Paine collaborative effort between UC, the had been used for the blue gum and et al. 2000). The obvious impracticality California Department of Food and eugenia psyllid programs (Dahlsten et of using insecticide treatments on trees Agriculture (CDFA) and research scien- al. 1998). The traps consisted of trans- throughout the state led us to investi- tists in Australia. parent 4-inch (10-centimeter) plastic gate more sustainable options. We first disks coated with a thin layer of motor Prerelease psyllid sampling investigated whether any predators oil additive and clipped over a yellow already present in California could pro- Before the biological control program backing. At each site, 10 to 12 traps vide control. Lady beetles (Hippodamia), began, we gathered detailed information were hung in eucalyptus trees and green lacewings (Chrysoperla), minute about red gum lerp psyllid populations changed weekly. pirate bugs (Orius) and syrphid flies throughout California. Beginning in July In 1999 and 2000, we tested trap ac- feed on adult and immature red gum 1999, sample sites were established in curacy at two sites, one in Northern lerp psyllids (Erbilgin et al. 2004). Alameda, Santa Clara, Monterey, Los California (Alameda County) and However, even when present in large Angeles and San Diego counties. By July the other in Southern California (Los numbers, these predators did not pro- 2002, we had established 32 sample sites, Angeles County). Near each trap at vide adequate control. with at least one site located in every these sites, two 12-inch (30-centimeter) In Australia, red gum lerp psyllid California county in which red gum lerp foliage samples were collected every populations are held in check in large psyllid had been reported. 3 weeks (20 to 24 samples per site per part by species of parasitic wasps that Sampling psyllid populations ac- sample date). We found a good cor- specifically attack them and their close curately can be difficult. The most relation between the mean number of relatives. Other parasitoid species im- accurate way of measuring densities adult female psyllids per sticky trap ported from Australia had successfully and damage levels is to count psyllid and the mean number of psyllid eggs controlled earlier outbreaks of other nymphs on leaves. This method, how- per leaf sample (P < 0.01, r2 = 0.82; introduced Australian psyllid species ever, is time-consuming and impracti- Paine et al. [2000]), indicating that the in California, including the blue gum cal for the large number of sample sites sticky-trap counts provided a good es- psyllid (Dahlsten et al. 1998) and the and frequent sampling dates needed to timate of psyllid activity in eucalyptus. eugenia psyllid (Dahlsten et al. 1995). follow psyllid and natural-enemy pop- Thereafter, we relied exclusively on the 230 CALIFORNIA AGRICULTURE • VOLUME 59, NUMBER 4 Fig. 1. P. bliteus oviposition success in different host develop- mental stages, as indicated by the percentage egg deposition (± SEM) of parasitized red gum lerp psyllids, was significantly different (F = 12.48, df = 4,25, P < 0.001). Above each bar, Fig. 2. P. bliteus lifetime fecundity under glasshouse conditions, as means followed by different letters are significantly different estimated by egg deposition with an overabundant host supply. (Tukey’s HSD test, P < 0.05). Source: Daane et al. (2005). Source: Daane et al. (2005). sticky-trap technique to monitor the culture and was selected for release for oviposition, the parasite larvae did psyllids. In addition, we used the same after experiments showed that it specifi- not fully develop until after the host traps to monitor parasitoid populations cally attacked the red gum lerp psyllid reached the fifth (last) instar. In addi- after we began releasing them. when tested against three other psyllid tion, adult female wasps also occasion- Initially, we counted both male and species (Eugenia, blue gum and mela- ally killed psyllid nymphs by host female adult psyllids per trap by sample leuca) (Paine et al.

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