LONGHORNED BORERS

Integrated Pest Management for Professional Landscapers and Home Gardeners

trees suffering from stress, especially drought stress. The problem is exac- erbated in California because many eucalyptus trees are growing in unmanaged or minimally managed environments with no supplemental irrigation. Both the and euca- lyptus trees are native to Australia. (actual Eucalyptus species that naturally (actual size) grow in wetter areas of Australia have size) been planted in California where they Figure 1. Adult semi- experience prolonged dry periods, Figure 2. Adult . punctata. which makes them susceptible to attack by these beetles. hatching. If conditions are less than Two closely related species of IDENTIFICATION ideal, the small larvae feed outward longhorned borers (family Ceramby- Adult eucalyptus longhorned borers from the egg mass, leaving a distinct cidae) attack eucalyptus in California. have shiny, dark brown and yellow to dark trail 1/4 inch to several inches long Phoracantha semipunctata (Fig. 1) was cream-colored areas on their wing that scores the bark surface before they introduced into southern California in covers. The antennae are as long as bore into the cambial tissue on the in- the 1980s and rapidly became a pest. or longer than the body, and the an- ner surface of the bark. Once the larvae It currently occurs throughout Califor- tennae of males have prominent have bored into the inner bark, the nia wherever eucalyptus trees grow. spines. The mature larvae may be galleries they form beneath the wood This readily attacks and kills large (more than 1 inch long) and are surface can extend several feet. large numbers of eucalyptus trees. cream colored and legless. Natural enemies of the eucalyptus In trees with heavy infestations, the borer were introduced from Australia, Females lay eggs under loose bark or scraping sounds made by the develop- and biological control in combination in crevices on bark surfaces. If condi- ing larvae chewing into the cambium with improved cultural care of euca- tions are ideal, larvae will bore di- are clearly audible from a distance of lyptus dramatically reduced the num- rectly into the inner bark after several feet. ber of trees killed each year by the borer. In 1995, a second species of borer, Phoracantha recurva (Fig. 2), TABLE 1. Differences between Two Eucalyptus Longhorned Borers in was discovered in southern California California. in Los Angeles, Riverside, Orange, and San Bernardino counties. Like P. semi- Characteristic Phoracantha semipunctata Phoracantha recurva punctata, this beetle is expected to color of wing mostly dark brown; zigzag mostly cream to yellowish; eventually spread throughout Califor- covers (elytra) line bisecting cream-colored dark brown areas primarily nia wherever eucalyptus grows. Not area in middle of elytra limited to rear third of elytra all of the previously introduced natu- ral enemies are effective against this golden hairs on none to sparse long, dense new borer, and P. recurva together underside of each with several other new pests is caus- segment ing increased stress and mortality of Sources: Gill, R. J. 1997. An Australian eucalyptus beetle. California Plant Pest and Dis- eucalyptus. ease Report 16(1-2):12; Hanks, L. M., T. D. Paine, J. G. Millar, and C. Campbell. Another tree-killing pest of eucalyptus invades California. California Plant Pest and Disease Report Longhorned borers are attracted to 16(1-2):19-21 freshly cut wood, dying limbs, and

PEST NOTES Publication 7425 University of California Division of Agriculture and Natural Resources Revised January 2000 January 2000 Eucalyptus Longhorned Borers

These two Phoracantha species re- sustain beetle larvae; old dry logs are packed with larval excrement. In- semble each other but differ some- too hard for larvae to feed on and fested trees are often killed in a mat- what in biology. Distinguishing then successfully develop. ter of a few weeks. Resprouting may between P. semipunctata and P. occur from the tree base. recurva can be useful in predicting the Following pupation, adult beetles importance of biological control emerge from the same holes by chew- MANAGEMENT based on whether one or both borer ing through the plugs of frass. During The same methods are used to man- species are present in that area. Dif- spring and summer, the beetle re- age both Phoracantha species. Control ferences in wing color and hairs and quires 3 to 4 months to complete its eucalyptus longhorned borers by spines on antennae help to distin- life cycle, but starting in fall and win- reducing tree stress, properly han- guish between P. semipunctata and P. ter it may require up to 9 months. dling eucalyptus wood, planting resis- recurva (Table 1). For example, dark There are two and possibly three tant species, and avoiding activities brown predominates on the wing cov- poorly synchronized generations a that disrupt biological control. Pesti- ers of P. semipunctata, while yellow to year; adults can emerge anytime from cide applications generally are not cream color predominates on wing April through October. effective in managing these pests. covers of P. recurva. The life cycle of P. recurva differs Eucalyptus are also attacked by sev- LIFE CYCLE somewhat from that of P. semi- eral other introduced . Pest Several nights after emerging and punctata, and it is currently in the managers should learn how their ef- mating, the female beetles of P. process of being documented. forts, such as choosing a tree species semipunctata begin laying eggs in Phoracantha recurva may have a to plant, may affect the control of groups of 3 to 30 under loose bark of longer period of activity each year, these other pests. Eucalyptus pests eucalyptus trees. Females may live with adults emerging as early as include leaf-feeding beetles, eucalyp- one or more months and lay up to 300 February. tus gall wasp, and at least six species eggs, which hatch in about 1 to 2 of psyllids (see UC IPM Pest Notes Pub- weeks depending on temperature. In their native Australia, eucalyptus lication 7423, Psyllids and UC IPM Pest First-instar larvae may bore directly longhorned borers develop in broken Notes Publication 7460, Eucalyptus into the inner bark or they may mine limbs, pruned limbs, fallen trees, and Redgum Lerp Psyllid). Certain of these short distances in the outer bark lay- highly stressed trees. They rarely kill insects are now under effective bio- ers before turning inward to mine at healthy trees. Eucalyptus naturally logical control, including the blue the bark-cambium- interface, growing in areas to which they are gum psyllid (Ctenarytaina eucalypti) leaving a dark stain on the wood sur- adapted appear more resistant to and eucalyptus snout beetle or the face. At the end of the feeding period, beetle attack, and beetles in Australia gumtree weevil (Gonipterus larvae excavate pupal chambers in are preyed upon by many natural scutellatus). Several parasites are be- the wood. They enter the chambers, enemies. ing introduced to control other pests, packing the holes behind them with such as the leaf-feeding Australian wood shavings and frass (Fig. 3). Lar- DAMAGE tortoise beetle (Trachymela sloanei). vae require about 70 days to develop Holes in the bark and stains or oozing Inappropriate actions such as spray- in fresh wood or logs during hot sum- liquid on limbs or trunks are common ing persistent broad-spectrum insecti- mer months, and up to 180 days in longhorned borer damage symptoms. cides can harm natural enemies and drier logs. Only relatively fresh logs Foliage may discolor and wilt, and might cause outbreaks of these other limbs may die back. Longhorned bor- pests. Conversely, uncontrolled popu- ers mostly attack stressed or dam- lations of pests such as eucalyptus aged plants; vigorous, well-watered redgum lerp psyllid (Glycaspis trees are rarely attacked. However, in brimblecombei) can seriously stress California many eucalyptus trees are trees, increasing eucalyptus suscepti- seasonally water-stressed during hot bility to longhorned borers. summer months, rendering a signifi- cant proportion of them susceptible Cultural Management to the beetle. Choose eucalyptus species that are well adapted to each location and Extensive larval feeding at the inner provide them with proper cultural (actual size bark-cambium-xylem interface can care. Certain species of eucalyptus of ) effectively girdle the tree. Trees at are more resistant to longhorned bor- this stage of infestation are character- ers (Table 2). Most eucalyptus spe- ized by a thin canopy with wilted or cies that are adapted to wetter Figure 3. Mature larva exposed in wood. dry leaves; the bark is cracked and growing conditions are more suscep-

◆ 2 ◆ January 2000 Eucalyptus Longhorned Borers

Biological Control TABLE 2. Relative Susceptibility of Eucalyptus spp. to Phoracantha semipunctata. Biological control with natural en- More susceptible More resistant emies may provide the best long-term solution to longhorned borer prob- blue gum, E. globulus hybrid, E. trabutii lems. If beetle populations are re- flooded gum, E. grandis lemon gum, E. citriodora duced to low levels, natural enemies Karri gum, E. diversicolor mountain gum, E. dalrympleana are better able to keep populations in manna gum, E. viminalis red ironbark, E. sideroxylon check, and vigorous trees can survive shining gum, E. nitens river red gum, E. camaldulensis a few attacks. At least one native Cali- Sydney blue gum, E. saligna sugargum, E. cladocalyx fornia wasp that parasitizes beetles, swamp mahogany, E. robusta Helcostizus rufiscutum (Ichneumon- idae) attacks P. semipunctata, but the Adapted from Hanks, L. M., T. D. Paine, J. G. Millar, and J. L. Hom. 1995. Variation among most effective parasites are those that Eucalyptus species in resistance to eucalyptus longhorned borer in southern California. have been imported from Australia. Entomologia Experimentalis et Applicata 74:185-194. The most important parasitic wasp from Australia is Avetianella longoi, a tible to longhorned borers, while the December and January when adult 1/16-inch-long, host-specific encyrtid more resistant eucalyptus often are beetles are inactive. When extensive that lays its eggs within the eggs of species adapted to drier conditions. limb removal is planned for reasons the beetles. Avetianella longoi dis- However, most eucalyptus can be other than dead wood removal or to perses rapidly and efficiently finds attacked if they are heavily stressed, eliminate hazardous trees, space the borer eggs. This wasp has widely es- for example by being planted in poor trimming over several years. Other- tablished in northern and southern soils or deprived of sufficient water. A wise, the tree may not have adequate California, typically attacking and well-maintained tree of a susceptible foliage to produce the food it needs to killing over 90% of P. semipunctata species may be at less risk of infesta- maintain good health. Also, extensive eggs in the field. Preliminary re- tion than a neglected tree of a resis- pruning suddenly exposes previously search, however, suggests that it may tant species. Trees with some shaded bark to direct sunlight, which be less effective against P. recurva. resistance to these wood borers may can result in sun scald cankers that produce copious amounts of resin in are susceptible to borer attack. Four species of braconid wasp para- response to an attack. sites have also been introduced Eucalyptus logs used for firewood and (Syngaster lepidus, Callibracon Consider providing supplemental dead or dying branches and trees are limbatus, Jarra maculipennis, and J. water on a regular schedule during the primary beetle-breeding sites. phoracantha). At least one, S. lepidus, prolonged dry periods, particularly if Sanitation is critical for reducing may be established at several sites. seasonal rainfall has been below nor- beetle numbers. Until the wood dries These wasps are attracted to infested mal. It is particularly important not to below a critical level, it remains suit- eucalyptus trees and use long egg- suddenly cut off irrigation to trees able and highly attractive to oviposit- laying structures to drill through the that have been receiving water regu- ing beetles. Anything that can be done bark and locate feeding beetle larvae. larly. These trees will become water to speed the drying process, such as The female wasps paralyze the devel- stressed and susceptible to heavy cutting and splitting wood, helps to oping larvae and lay one or more eggs attack. Irrigate around the outer reduce the length of time the wood on each one. These eggs hatch and canopy, not near the trunk. Trees can support beetle development. If the developing parasite larvae feed on should receive proper amounts of the wood is already infested, it should the borer larvae, eventually killing water to maintain tree vigor; however, be treated or destroyed. Bury, burn them. These species of wasps are frequency and duration of irrigation (where permitted), or chip infested highly specialized parasites attacking depends on the site, use, and species eucalyptus wood. Chipped eucalyptus only certain beetles; they represent of eucalyptus. The watering schedule makes an excellent mulch. Alterna- no threat to humans, pets, or live- used for lawns is too frequent, and its tively, remove the bark from felled stock. All were originally introduced duration is inadequate to maintain logs or solarize the wood by placing it to control P. semipunctata; additional good tree health. Such a watering in a sunny location for 10 to 12 weeks parasite species may be introduced to schedule is likely to promote tree root and covering it with ultraviolet- better control P. recurva. disease. resistant plastic. This prevents new beetles from attacking and resident Chemical Control Protect trees from injuries. Remove beetles from emerging and flying to Early work from both California and infested trees and branches immedi- nearby living eucalyptus. Solarized other regions where beetles have ately, but do all other pruning during wood can be stored for firewood. become established demonstrates

◆ 3 ◆ January 2000 Eucalyptus Longhorned Borers

that insecticides are not suitable for ronmental conditions that favor the agement Guide. Oakland: Univ. Calif. management of eucalyptus tree to the disadvantage of the Div. Agric. Nat. Res., Publication longhorned borer populations. Con- beetle. Because natural enemy intro- 3359. tact and systemic insecticides are ductions by government agencies ineffective, costly, or environmentally and university scientists are funded Paine, T. D., J. G. Millar, and L. M. inappropriate because of the poten- through taxes, public and profes- Hanks. 1995. Integrated program tial for drift, effects on beneficial or sional support is critical to the ongo- protects trees from eucalyptus nontarget insects, and risk of expo- ing success of biological control. longhorned borer. Calif. Agric. 49(1): sure to human populations in urban 34-37. environments. COMPILED FROM: Dreistadt, S. H., J. K. Clark, and M. L. Borer management must focus on Flint. 1994. Pests of Landscape Trees providing cultural practices and envi- and Shrubs: An Integrated Pest Man-

For more information contact the University of California Cooperative Extension or agri- cultural commissioner’s office in your coun- ty. See your phone book for addresses and phone numbers. AUTHORS: T. D. Paine, J. G. Millar, and S. H. Dreistadt EDITORS: P. Gouveia and B. Ohlendorf ILLUSTRATIONS: V. Winemiller TECHNICAL EDITOR: M. L. Flint DESIGN AND PRODUCTION: M. Brush WARNING ON THE USE OF CHEMICALS PRODUCED BY IPM Education and Publica- Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations given tions, UC Statewide IPM Project, University on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed, away of California, Davis, CA 95616-8620 from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits and/or vegetables ready to be picked. Dispose of empty containers carefully. Follow label instructions for disposal. Never reuse the containers. Make sure empty containers are not accessible to children or . Never dispose of containers where they may contaminate water supplies or natural waterways. Do not pour down sink or toilet. Consult your county This Pest Note is available on the World agricultural commissioner for correct ways of disposing of excess pesticides. Never burn pesticide containers. Wide Web (http://www.ipm.ucdavis.edu) The University of California prohibits discrimination against or harassment of any person employed by or To simplify information, trade names of products seeking employment with the University on the basis of race, color, national origin, religion, sex, physical or have been used. No endorsement of named products mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status, age, is intended, nor is criticism implied of similar prod- sexual orientation, citizenship, or status as a covered veteran (special disabled veteran, Vietnam era veteran, ucts that are not mentioned. or any other veteran who served on active duty during a war or in a campaign or expedition for which a This material is partially based upon work supported campaign badge has been authorized). University Policy is intended to be consistent with the provisions of by the Extension Service, U.S. Department of Agricul- applicable State and Federal laws. Inquiries regarding the University’s nondiscrimination policies may be ture, under special project Section 3(d), Integrated directed to the Affirmative Action/Staff Personnel Services Director, University of California, Agriculture and Pest Management. Natural Resources, 1111 Franklin, 6th Floor, Oakland, CA 94607-5200; (510) 987-0096.

◆ 4 ◆