UC scientists apply IPM techniques to new eucalyptus pests

Timothy D. Paine u Donald L. Dahlsten P Jocelyn G. Millar P Mark S. Hoddle o Lawrence M. Hanks Eucalyptus trees have been im- isitors to California are struck by early introductions were made to pro- portant components of the Cali- V the abundance and variety of eu- vide timber for railroad ties and milled fornia urban landscape for almost calyptus trees throughout the state. lumber. Unfortunately, either the spe- 150 years. Until 1984, they were More than 700 species in the genus Eu- cies planted were not appropriate or free of both insect and disease calyptus are native to Australia and the growing conditions were unsuit- pests. In the last 16 years, how- New Guinea, and approximately 90 able for supporting these early com- ever, a series of herbivorous in- species have been introduced into mercial ventures. Recently, however, sect species have been intro- North America over the last 150 years there has been a renewed interest in duced into the state, probably (Doughty 2000). Some species have planting eucalyptus as an economical accidentally, causing significant not been viewed favorably because of source of biomass, hardwood veneer damage to the trees. Research their messy growth habits, and in fact and very high quality cellulose pulp one species (E. globulus) has been for the production of printer and pho- programs have provided solutions listed as a potentially invasive weed. tocopier paper. As the resource value to some of these pest problems, However, many other species have of native forests in California is reas- but more pests are continually in- great value for their form, evergreen sessed in terms that limit timber har- troduced, recently the red gum foliage, floral show and other horticul- vest, renewable plantations of trees lerp psyllid, the lemon gum lerp tural qualities. like eucalyptus may become increas- psyllid, and the eucalyptus tor- Eucalyptus trees are now found ingly important to meet the expanding toise beetle. Scientists are devel- throughout the state in areas with suit- demand for wood fiber. oping new strategies to control able climates. The trees are capable of Eucalyptus trees have been used ex- the recent invaders in concert very rapid growth and can thrive tensively in windbreak plantings in with existing pest management without supplemental irrigation in many agricultural areas statewide. programs, integrating methods many sites. Consequently they have However, the most valuable use of the across broad geographic, horti- been widely planted for a variety of trees has been their widespread plant- cultural and economic scales. purposes. It has been reported that ing in California urban landscapes.

8 CALIFORNIA AGRICULTURE, VOLUME 54, NUMBER 6 -* 8 x0 7 The river red gum tree on the left has been partly defoliated by red gum lerp psyllids.

The trees provide aesthetic value, ab- sorb sound and pollutants, and offer shade, reducing the heat load on struc- tures and decreasing cooling costs. Low water requirements and, until re- cently, the absence of insect pests and diseases, have made eucalyptus a par- ticularly important component of the The research programs supported by cones and are often covered with urban forest. the UC IPM project have quickly pro- sticky honeydew and black sooty Eucalyptus trees were first brought vided solutions to many serious pest molds. The psyllid populations can into the state around 1850 as seeds problems. However, the continuing in- reach very high densities on suscep- (Doughty 2000), ensuring that poten- troduction of new insect pests poten- tible Eucalyptus species and cause ex- tial pest insect species were not intro- tially jeopardizes the balances achieved tensive defoliation because heavily in- duced with the trees. More than a cen- in these successful IPM programs. Man- fested leaves wither and drop off the tury of relatively pest-free status agement solutions for red gum lerp trees. Branch die back and death of changed with the discovery of the eu- psyllid, tortoise beetle and a long- suppressed or weakened trees has oc- calyptus longhorned borer, Phora- homed borer are under investigation. curred in a number of the heavily in- cantha semipunctata, in Orange County Glycaspsis brimblecombei. The fested areas in the state. in 1984. Since that time, about 15 dif- red gum lerp psyllid, Glycaspsis Two approaches are being taken to ferent eucalyptus-feeding insect spe- brimblecombei, was first detected on manage lerp psyllid populations. Sys- cies have been introduced into Califor- June 17,1998, in El Monte, Los Ange- temic insecticides are under investiga- nia, putting the tree resource at risk. les County, and infestations were ob- tion as a short-term and small-scale While all of these insects are native to served in other Southern California lo- approach to reduce infestation densi- Australia, about half of them exist in cations and inNorthern California by ties and limit successive years of defo- other parts of the world, making it dif- July of that year. Like the blue gum liation on valuable trees. However, the ficult to determine their source popula- psyllid that was introduced earlier, timing of applications appears to be tion and mode of entry into California. this psyllid feeds on plant fluids that it difficult to gauge, and the materials Introductions of pest species of eu- extracts from young leaves. Although applied have produced only mixed re- calyptus have continued with unfortu- this insect feeds on a broad range of sults in the landscape. The use of in- nate regularity over the last two de- Eucalyptus species, it prefers to colo- secticides is not self-sustaining and the cades. Three recent arrivals have nize members of the red gum species materials must be applied repeatedly. triggered new research efforts, the group, particularly river red gum (E. Therefore the approach is at best only most comprehensive to date aimed at camaldulensis). Unlike the blue gum a stop-gap measure until the long- managing the red gum lerp psyllid psyllid, which feeds as exposed indi- term solution, biological control with and eucalyptus tortoise beetle. New viduals on the leaves, G. brimblecombei natural enemies, can be implemented. exotic pests are continually introduced constructs a white conical cover of In February 1999 we began seiting into the California landscape, requir- sugar, called a lerp, and feeds con- up monitoring sites for adult psyllids. ing new control efforts. Scientists must cealed under this shelter. Infested A monitoring site consists of 10 sticky

CALIFORNIA AGRICULTURE, NOVEMBER-DECEMBER2000 9 counted. There is an and a series of host specificity tests excellent relation- were conducted with three other psyl- ship between the lid species (eugenia psyllid, blue gum number of adult fe- psyllid and melaleuca psyllid). The males caught in the testing of melaleuca psyllid was of sticky traps and the particular concern because it is a immature stages on USDA candidate for the biological the foliage samples control of melaleuca in the Florida Ev- (fig. 2), and particu- erglades. It appears that P. bliteus is larly the eggs (fig. 3). specific to the red gum lerp psyllid, so This shows that the we decided to start a mass rearing pro- sticky traps are a re- gram and begin releasing. Our own in- liable method of esti- sectary and the California Department Date mating psyllid populations. of Food and Agriculture, Sacramento, Fig. 2. Number of red gum lerp psyllid are rearing parasitoids, and shortly we females per trap, foliage eggs and Populations of psyllids were very immatures, Ardenwood, Alameda County, low from January through April in will have a third insectary at the UC Plot 1,1999-2000. Ardenwood, with peaks from June to Kearney Agricultural Center in Parlier August (fig. 2). Initially we were plot- involved in the rearing. traps, although in a few areas we have ting total psyllids, but with the red We have had considerable difficulty more than 10. We are using the same gum lerp psyllid there is a seasonal with the mass rearing of this small type of sticky traps that we used for change in the percentage of females in wasp. First we had problems getting the blue gum psyllid and the eugenia the population. A graph of the total enough small red gums to establish a psyllid studies: a 4-inch-diameter plas- population would be misleading, so psyllid population, and then we dis- tic lid (10.5 cm diameter, 87 sq cm) we graph only females but still count covered that there were many more coated with motor oil additive, which males to estimate sex ratio changes. male psyllids than females for most of fits over a lid that has been painted The highest number of females occurs the year (fig. 4). Finally we found that yellow with the lip removed so that in the summer months and drops to there is a long host-feeding period for traps can be changed efficiently. By 20% to 25% the rest of the year (for ex- the female wasps and that they kill June 2000 we had established 26 moni- ample, Valley Village Park in Los An- psyllid nymphs and do not parasitize toring sites (fig. I) throughout the state, geles, fig. 4). The pattern of male bias them initially. As a result, we have including coastal and inland sites. With in the sex ratio has been consistent in made only small releases of 50 to 100 many cooperators, we are changing a to- all of our plots throughout the state. adults in 9 locations in the state (fig. 1). tal of 326 traps weekly to count and sex In August 1999, parasitoids of the The first release was made on June adult psyllids. The traps are also use- lerp psyllid were collected at several 7,2000, at Valley Village Park in North ful in monitoring adult parasitoids. locations in southern Australia. Eight Hollywood, and two other releases We also sample foliage once every 3 species of Psylluephugus (Hymenop- (one in Los Angeles and one in weeks in two locations, one in Los An- tera: Encyrtidae) were reared in the Alameda County) were made in June. geles and the other at Ardenwood, UC Berkeley quarantine facilities. One We made no releases for 2 months be- Alameda County, in Northern Califor- of the species (P. fuustus) was a hyper- cause of the rearing problems men- nia. Two 12-inch (30 cm) branches are parasite (i.e., a parasite of a parasite), tioned above. Since Aug. 21,2000, we taken in the vicinity of the 10 sticky and six of the other species did not do have released in six other areas (fig. 1). traps in each plot, and all the eggs and well in our rearings. One species, P. We made our first recovery of a nymphal stages of the psyllid are bliteus, was selected as the candidate, parasitoid on a sticky trap in our Red-

Fig. 3. Red gum lerp psyllid sampling, Ardenwood, Alameda Fig. 4. Number of red gum lerp psyllid females per trap, Valley County, Plot 1. Number of eggs versus females. Village Park, Los Angeles, 1999-2000.

10 CALIFORNIA AGRICULTURE, VOLUME 54, NUMBER 6 The Australian tortoise beetle is a pest A The first longhorned borer Phoracantha first collected in Riverside County in 1998. semipunctata (left) was detected on euca- lyptus in California in 1985. A second spe- cies, P. recurva, (right) was detected in wood City, San Mateo County plot on Southern California in 1995. a trap that was set out on Aug. 24, b The eucalyptus snout beetle defoliates 2000. This plot is 10 miles from the eucalyptus trees. Ardenwood plot where the parasitoids were released on June 14. This is a good indication that the wasps are es- had been accidentally introduced on tablished and spreading. We plan to eucalyptus several years earlier. X 8 continue monitoring the psyllid and the Wasp-rearing techniques, as well as 7 parasitic wasps for the next 2 years. methods of estimating densities of the The behavior of the egg parasitoid Trachymela sloanei. The eucalyp- beetle, have been developed, and ini- A. longoi in relation to the eggs of the tus tortoise beetle, Trachymela sloanei, tial parasitoid releases totaling more two borer species is markedly differ- was first collected in Riverside County than 1,000 individuals were made in ent, and this difference may be of criti- in March 1998. It has become estab- the summer of 2000. The releases will cal concern. Although the wasps locate lished in five Southern California continue throughout the active period egg masses of the two borers in the counties since the initial discovery. for the beetle. Population monitoring field at the same rate, in laboratory tri- The adults of this insect are cryptically for the beetles and the parasitoids will als, the wasp parasitizes a greater pro- colored, blending in with the bark of also continue, to determine the impact portion of P. semipunctata eggs than of eucalyptus trees, where they typically of the natural enemies. P. recurva eggs. The combination of es- remain hidden during the day. How- Phoracantha recurva. Approxi- cape from extensive parasitism of ever, when they open their elytra to mately 10 years after the discovery of eggs; earlier seasonal activity, which fly, the hind wings are a brilliant red the first longhorned borer on eucalyp- may permit P. recurva to colonize color and the insects are clearly vis- tus in California, a second species, available resources before emergence ible. Larvae also tend to hide under Phoracantha recurva, was detected in of P. semipunctata; and, potentially, en- loose bark on the main stem and large Southern California in 1995. The more hanced competitive ability, may help branches during the day before emerg- recently introduced borer species ap- explain the replacement of P. ing to feed on young leaves and tender pears to have very similar ecological semipunctata by P. recurva in many stems at night. Adults also feed on requirements to P. semipunctata. Al- parts of Southern California. Ecologi- leaves and young stems, but of par- though differences in host species cal interactions between the two ticular importance, adults clip off preferences have not yet been studied wood-boring species are currently un- young, tender leaf shoots as they begin in California or, for that matter, any- der investigation at UC Riverside. In to expand. This insect not only con- where in the world, there appears to addition, the existing biological con- sumes leaves, it also removes the be little difference in colonization pat- trol programs were augmented with young expanding leaves as the tree at- terns between the two beetles. Both releases in the summer of 2000 of two tempts to refoliate. species are highly attracted to stressed parasitoid species, Syngaster lepidus A biological control research pro- trees, so managing irrigation regimes and Jarra phoracantha, that attack the gram supported in part by UC IPM is critical for managing risk from both larvae of both Phoracantha species. has been implemented in an effort to species. However, it does appear that Monitoring programs are in place to provide a long-term solution to this P. recurva emerges much earlier in the determine if these larval parasites es- newly introduced pest problem. An year than P. semipunctata. Therefore tablished populations in California egg parasitoid, Enoggera reticulata, was the window of opportunity for timing and whether the parasites had an im- obtained from biological control work- cultural practices that stress eucalyp- pact on borer populations. ers in the Republic of South Africa in tus trees to periods when the beetles 1999. The parasitic wasp had been ini- are not present (or are present at very IPM successes tially collected from Australia and was low densities) may be much narrower Phoracantha semipunctata. The released in South Africa in a successful now than it was before the second eucalyptus longhorned borer was the attempt to control a tortoise beetle that borer was introduced. first major eucalyptus insect pest4n-

CALIFORNIA AGRICULTURE, NOVEMBER-DECEMBER 2000 11 Support from the UC IPM program reduction in numbers of eucalyptus facilitated the development of an effec- trees killed since the wasps became tive pest management program for established. this insect. The fundamentals of this Gonipterus scutellatus. The euca- program are detailed in Paine et al. lyptus snout beetle, Gonipferus (1995). The beetles are normally active scutellatus, was discovered defoliating f from approximately the beginning of windrow eucalyptus trees along citrus u June until the end of September. Be- groves in Ventura County in March cause the adults are attracted to 1994 (Cowles and Downer 1995). The stressed trees, recommendations to ar- adults are relatively nondescript borists were adopted to minimize risk brown beetles, but the legless larvae Anaphes nitens lays its eggs in the eggs of the eucalyptus snout beetle. The devel- to trees by scheduling potentially are bright yellowish green with black oping parasitoid consumes and kills the stressful cultural activities, such as stripes, have a slimy coating, and pro- host eggs. pruning or transplanting, during the duce long filaments of black excre- times of the year with the lowest levels ment. Female beetles deposit hard of beetle activity. Susceptible and re- brown egg capsules containing an av- sistant species of Eucalyptus were iden- erage of nine eggs on shoots and tified, and the nursery and landscape young leaves. Both the adults and the industries have incorporated that in- larvae consume young and tender formation into their planting recom- leaves, buds and shoots. Extensive mendations. Scientists identified bark feeding can completely defoliate trees moisture content as the critical mecha- and kill branches, while intermediate f u nism of tree resistance to borers; larvae levels of defoliation can retard growth -% m were successful in penetrating bark and affect tree shape. Y r with moisture content less than 50%, This insect has been introduced -Jm but were unsuccessful if the moisture from Australia into several eucalyptus- The blue gum psyllid was until recently content was greater than 55%. There- growing regions around the world, the most damaging of introduced psyllids. fore irrigation recommendations were and has caused extensive damage developed to maintain bark moisture wherever it has become established. For- above the critical threshold. tunately, it has proven relatively easy to troduced into California (Scriven et al. Sources of beetles and beetle move- control by the introduction of a specific 1986). The initial discoveries were ment in urban environments were egg parasitoid, Anaphes nifens.Female A. made in Orange County, but within a evaluated in the process of developing nitens search for the eggs of their beetle few years the beetle had become dis- sanitation programs to limit risk from hosts and lay their eggs in the eggs of tributed throughout the entire euca- insects emerging from infested host the beetle. As with A. longoi, the devel- lyptus range in the state. Male and fe- material. A set of guidelines describ- oping parasitoid consumes and kills the male beetles are attracted to volatile ing these practices was developed for host eggs. chemicals produced by stressed, dy- implementation by the landscape and A. nitens were obtained from col- ing, damaged or recently killed euca- arboriculture industries. leagues in the Republic of South Africa lyptus trees. Mating occurs on the The final step in the IPM program and were reared in large numbers at trunks of susceptible trees. Females lay was to establish effective natural en- UC Riverside for release in California. batches of 10 to 40 eggs on the trunk emies of the pest in the California Releases were made in Ventura surface under the loose, exfoliated landscape. A host-specific egg parasi- County in August 1994 and during the bark or in cracks and crevices in the toid, the wasp Avetianella longoi, was summer of 1995. The parasitoids rap- bark. Newly emerged larvae bore identified in Australia, brought to UC idly became firmly established, and through the outer bark of the tree and Riverside and reared in large num- snout beetle populations declined dra- mine through the phloem, cambium bers. More than 600,000 individuals matically. By 1997, densities of beetle and outer layers of xylem tissues. If were released at locations in Northern larvae had dropped to barely detect- the insects are colonizing a living tree, and Southern California. A. longoi is able levels. Although reduced to larval feeding can effectively girdle now distributed throughout the state. nondamaging levels, the geographic and kill the tree. At the end of the lar- The female wasps search for beetle egg distribution of the beetle has contin- val feeding period, the insects bore masses and insert their eggs into the ued to expand into adjacent counties. deep into the wood to construct a pu- eggs of the beetle. As many as five However, in all cases the parasitoid pal cell that is capped at the log sur- parasitoids develop in individual host distribution has expanded in tandem, face with a plug of wood fibers and eggs, killing them (Hanks et al. 1996). to mirror the distribution of its host. excrement. Adult beetles bore out of The parasitoid has proven to be highly Consequently, where pesticide use has their pupal cells through the plug and efficient (parasitism rates exceeding not disrupted the actions of the parasi- emerge from the tree to search for 90%), and arborists from many parts toid, there have not been further re- mates and begin a new generation. of the state have reported a dramatic ports of damage, and the bhlogical

12 CALIFORNIA AGRICULTURE, VOLUME 54, NUMBER 6 control program has provided an ef- species. Therefore future IPM programs fective and permanent solution to the must integrate approaches that target in- problem, requiring no further input. dividual pests into strategies for manag- Ctenarytaina eucalypti. The blue ing a pest complex. This approach re- gum psyllid, Ctenarytaina eucalypti, quires more detailed knowledge of the was until recently the most damaging ecologies of each insect species, and of member of a guild of Australian psyl- the interactions of each species with other lids that have been introduced into members of the community. California (Dahlsten et al. 1998b). The The fundamental information gener- psyllids remove fluids from the plant, ated from such studies will be critical for and feeding damage causes stunting, future integrative efforts. It is clear that if distorted growth and defoliation. The current patterns of pest invasion con- blue gum psyllid was first discovered tinue, other insect species that feed on eu- 0f in Monterey County in 1991, and by 5 calyptus will be introduced into Califor- the end of that year had expanded its 8 nia-and will also have to be managed as range to at least 12 other counties in part of an expanding pest complex. the state. Although found on land- The parasitoid Psyllaephagus pilosus has scape and windrow Eucalyptus significantly reduced blue gum psyllid T.D. Paine and J.G. Millar are Professors populations. globrilus, E. cinerae, E. glaucescens, E. and M.S. Hoddle is Assistant Cooperative camaldiilensis and E. viminalis, the ma- Extension Specialist, Entomology Depart- jor commercial impact was the heavy Future outlook ment, UC Riverside; D.L. Dahlsten is Pro- damage (for example, a 30% reduction Eucalyptus had virtually no insect fessor, Center for Biological Control, UC in the 1991 harvest) to E. pirlvercrlentn pests or diseases for almost a century Berkeley; L.M. Hanks is Assistant Profes- grown commercially for cut foliage. and a half in California. When the first sor, Entomology Department, University of Damage to the foliage crop included pests were detected, it was possible to Illinois at Urbana-Champaign. The authors inhibition of new shoots, distorted develop pest management strategies appreciate the assistance of William E. growth, deposits of sticky honeydew directed toward individual pest spe- Chaney, A. James Downer, John N. that supported growth of sooty molds cies, and often with a single effective Kabashima, Karen L. Robb and Steven and unsightly waxy residues depos- tactic. However, California now has Tjosvold, UC Cooperafive Extension Advi- ited by immature psyllids. accumulated a community of at least sors in Monterey, Ventura, Orange, San Supported in part by the UC IPM three feeding guilds of insects, includ- Diego, Santa Criiz and Sun Luis Obispo project, a biological control program ing borers, defoliators and sap-feeding counties, respectively, for their assistance was initiated with the collection of a insects. Individual pest species can no in conducting the various research projects nymphal parasitoid, Psyllaephagus longer be managed in isolation. In- described in this review. The research was pilosus, in Australia. The parasitoid stead, integrated pest management funded by a wide range of sources, includ- was reared in large numbers at UC strategies must take into consider- ing the UC Statewide Integrated Pest Man- Berkeley. The first releases of wasp ation the entire complex of insect agement Program. adults were made in spring 1993, with herbivores. additional releases of 6,000 adults in For example, when there were no References four counties throughout 1993. The leaf or sap-feeding pests, management Cowles RS, Downer AJ. 1995. Eucalyptus parasites quickly established in the re- of tree stress to reduce risk of infesta- snout beetle detected in California. Cal Ag lease sites, and sampling in 1994 re- tion by a single borer species was rela- 49( 1):38-40. Dahlsten DL, Hansen EP, Zuparko RL, vealed parasitism rates of 50% to tively simple. Now, there are at least Norgaard RE. 1998a. Biological control of the 100%. By 1995, the parasitoids had be- two important defoliators and two blue gum psyllid proves economically benefi- come broadly distributed throughout damaging fluid feeders that apply ad- cial. Cal Ag 52(1):35-40. many parts of the state. Reductions in ditional stress to trees, and this stress Dahlsten DL, Rowney DL, Copper WA, et al. 1998b. Parasitoid wasp controls blue gum blue gum psyllid populations as a re- cannot be mitigated simply by proper psyllid. Cal Ag 52(1):31-34. sult of the biological control program irrigation. Furthermore, management Doughty RW. 2000. The Eucalyptus: A have continued. An economic analysis options, particularly pesticide applica- Natural and Commercial History of the Gum tions or cultural practices, aimed at Tree. Baltimore, MD: The Johns Hopkins Uni- of the benefit to the cut-foliage indus- versity Press. 237 p. try alone indicated that the biological one pest species may exacerbate prob- Hanks LM, Paine TD, Millar JG. 1996. Tiny control program generated a benefit- lems with another species. For ex- wasp helps protect eucalypts from eucalyptus cost ratio ranging from a minimum of ample, fertilization may improve tree longhorned borer. Cal Ag 50(3):14-6. Paine TD, Millar JG, Hanks LM. 1995. Biol- 9:l to a maximum of 24:1, based solely vigor, but it may also improve the ogy of the eucalyptus longhorned borer in Cali- on elimination of pesticide treatments quality of the tree as a food source for fornia and development of an integrated man- (Dahlsten et al. 1998a). These calcu- the leaf- and fluid-feeding insects. In agement program for the urban forest. Cal Ag lated benefits are very conservative contrast, biological control efforts di- 49( 1):34-7. Scriven GT, Reeves EL, Luck RF. 1986. and do not include increased crop rected toward controlling one pest Beetle from Australia threatens eucalyptus. yields or environmental impacts. may have limited impact on other pest Cal Ag 40(4):4-6.

CALIFORNIA AGRICULTURE, NOVEMBER-DECEMBER 2000 13