Viewing Document
Title UC scientists apply IPM techniques to new eucalyptus pests
File Options PDF | Additional Information
Quick Link Repository View:
Direct to File:
Abstract Eucalyptus trees have been important components of the California urban landscape for almost 150 years. Until 1984, they were free of both insect and disease pests. In the last 16 years, however, a series of herbivorous insect species have been introduced into the state, probably accidentally, causing significant damage to the trees. Research programs have provided solutions to some of these pest problems, but more pests are continually introduced, recently the red gum lerp psyllid, the lemon gum lerp psyllid, and the eucalyptus tortoise beetle. Scientists are developing new strategies to control the recent invaders in concert with existing pest management programs, integrating methods across broad geographic, horticultural and economic scales.

Author s
Dahlsten, Donald L.: J.G. Millar is Professors
Hanks, Lawrence M.: L.M. Hanks is Assistant Professor, Entomology Department, University of Illinois at Urbana-Champaign. The authors appreciate the assistance of William E. Chaney, A. James Downer, John N. Kabashima, Karen L. Robb and Steven Tjosvold, UC Cooperative Extension Advisors in Monterey, Ventura, Orange, San Diego, Santa Cruz and San Luis Obispo counties, respectively, for their assistance in conducting the various research projects described in this review. The research was funded by a wide range of sources, including the UC Statewide Integrated Pest Management Program, Entomology Department, University of Illinois at Urbana-Champaign
Hoddle, Mark
Entomologist   CE Entomology Specialist
Biological control of ornamental and agricultural pests. Pest and natural enemy biology and behavior. Assessing impact of natural enemies on pest population growth
Millar, Jocelyn G
Entomologist   Professor
Insect behavior; identification, synthesis, and testing of insect kairomones and pheromones; insect acoustic signaling
Paine, Timothy D
Entomologist and Professor
Integrated pest management of insects affecting nursery stock, woody ornamental or landscape plants, and trees in urban or recreational forests; ecological interactions between environmental stress on plants and insect herbivores; chemical ecology; insect-microorganism-plant interactions; biological control
Publication Date Nov 1, 2000
Date Added May 11, 2009
Copyright © The Regents of the University of California
Copyright Year 2000

IPM strategies combat the recently intro- duced eucalyptus pests red gum lerp psyl lid and eucalyptus tortoise beetle.

OCR Text
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 early introductions were made to pro - Eucalyptus trees have been im - isitors to California are struck by vide timber for railroad ties and milled Vthe abundance and variety of eu - portant components of the Cali - lumber . Unfortunately , either the spe - calyptus trees throughout the state . fornia urban landscape for almost cies planted were not appropriate or More than 700 species in the genus Eu - 150years . Until 1984 , they were the growing conditions were unsuit - calyptus are native to Australia and free of both insect and disease able for supporting these early com - New Guinea , and approximately 90 pests . In the last 16years , how - mercial ventures . Recently , however , species have been introduced into ever , a series of herbivorous in - there has been a renewed interest in North America over the last 150 years sect species have been intro - planting eucalyptus as an economical ( Doughty 2000 ) . Some species have duced into the state , probably source of biomass , hardwood veneer not been viewed favorably because of accidentally , causing significant and very high quality cellulosepulp their messy growth habits , and in fact damage to the trees . Research for the production of printer and pho - one species ( E.globulus ) has been programs haveprovided solutions tocopier paper . As the resource value listed as a potentially invasive weed . to some of thesepest problems , of native forests in California is reas - However , many other species have but more pests are continually in - sessed in terms that limit timber har - great value for their form , evergreen troduced , recently the red gum vest , renewable plantations of trees foliage , floral show and other horticul - lerp psyllid , the lemon gum lerp like eucalyptus may become increas - tural qualities . psyllid , and the eucalyptus tor - ingly important to meet the expanding Eucalyptus trees are now found toise beetle . Scientists are devel - demand for wood fiber . throughout the state in areas with suit - oping new strategies to control Eucalyptus trees have been used ex - able climates . The trees are capable of the recent invaders in concert tensively in windbreak plantings in very rapid growth and can thrive with existing pest management many agricultural areas statewide . without supplemental irrigation in programs , integrating methods However , the most valuable use of the many sites . Consequently they have across broad geographic , horti - been widely planted for a variety of trees has been their widespread plant - ing in California urban landscapes . cultural and economic scales . purposes . It has been reported that 8 CALIFORNIA AGRICULTURE , VOLUME 54 , NUMBER 6 * - 8 x0 7 The river red gum tree on the left has been gum lerp psyllids . partly defoliatedby red 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 - cones and are often covered with The research programs supported by ticularly important component of the sticky honeydew and black sooty the UC IPM project have quickly pro - urban forest . molds . The psyllid populations can vided solutionsto many serious pest Eucalyptus trees were first brought reach very high densities on suscep - problems . However , the continuing in - into the state around 1850 as seeds tible Eucalyptus species and cause ex - troduction of new insect pests poten - ( Doughty 2000 ) , ensuring that poten - tensive defoliation because heavily in - tiallyjeopardizes the balancesachieved tial pest insect species were not intro - fested leaves wither and drop off the in these successfulIPM programs.Man - duced with the trees . More than a cen - trees . Branch die back and death of agementsolutions for red gum lerp tury of relatively pest - free status suppressed or weakened trees has oc - psyllid , tortoisebeetle and a long - changed with the discovery of the eu - curred in a number of the heavily in - homed borer are under investigation . calyptus longhorned borer , Phora - fested areas in the state . Glycaspsisbrimblecombei.The in Orange County cantha semipunctata , Two approaches are being taken to red gum lerp psyllid , Glycaspsis in 1984 . Since that time , about 15dif - manage lerp psyllid populations . Sys - was first detected on brimblecombei , ferent eucalyptus - feeding insect spe - temic insecticidesare under investiga - June 17,1998 , in El Monte , Los Ange - cies have been introduced into Califor - tion as a short - term and small - scale les County , and infestations were ob - nia , putting the tree resource at risk . approach to reduce infestation densi - served in other Southern California lo - While all of these insects are native to ties and limit successiveyears of defo - cations and inNorthern California by Australia , about half of them exist in liation on valuable trees . However , the July of that year . Like the blue gum other parts of the world , making it dif - timing of applications appears to be psyllid that was introduced earlier , ficultto determinetheir source popula - difficult to gauge , and the materials this psyllid feeds on plant fluids that it tion and mode of entry into California . applied have produced only mixed re - extracts from young leaves . Although Introductions of pest species of eu - sults in the landscape . The use of in - this insect feeds on a broad range of calyptus have continued with unfortu - secticidesis not self - sustainingand the Eucalyptus species , it prefers to colo - nate regularity over the last two de - materials must be applied repeatedly . nize members of the red gum species cades . Three recent arrivals have Therefore the approach is at best only group , particularly river red gum ( E . triggered new research efforts , the a stop - gap measure until the long - camaldulensis ) . Unlike the blue gum most comprehensive to date aimed at term solution , biological control with psyllid , which feeds as exposed indi - managing the red gum lerp psyllid natural enemies , can be implemented . viduals on the leaves , G . brimblecombei and eucalyptus tortoise beetle . New In February 1999 we began seiting constructs a white conical cover of exotic pests are continually introduced up monitoring sites for adult psyllids . sugar , called a lerp , and feeds con - into the California landscape , requir - A monitoring site consists of 10sticky cealed under this shelter . Infested ing new control efforts.Scientistsmust CALIFORNIA AGRICULTURE , NOVEMBER - DECEMBER2000 9 and a series of host specificitytests counted . There is an were conducted with three other psyl - excellent relation - lid species ( eugenia psyllid , blue gum ship between the psyllid and melaleuca psyllid ) . The number of adult fe - testing of melaleuca psyllid was of males caught in the particular concern because it is a sticky traps and the USDA candidate for the biological immature stages on control of melaleuca in the Florida Ev - the foliagesamples erglades . It appears that P . bliteus is ( fig . 2 ) , and particu - specificto the red gum lerp psyllid , so larly the eggs ( fig . 3 ) . we decided to start a mass rearing pro - This shows that the gram and begin releasing . Our own in - sticky traps are a re - sectary and the California Department liable method of esti - Date of Food and Agriculture , Sacramento , mating psyllid populations . Fig . 2 . Number of red gum lerp psyllid are rearing parasitoids , and shortly we Populations of psyllids were very females per trap , foliage eggs and will have a third insectary at the UC low from January through April in immatures , Ardenwood , Alameda County , Kearney Agricultural Center in Parlier Plot 1,1999 - 2000 . Ardenwood , with peaks from June to involved in the rearing . August ( fig . 2 ) . Initially we were plot - traps , although in a few areas we have We have had considerable difficulty ting total psyllids , but with the red more than 10 . We are using the same with the mass rearing of this small gum lerp psyllid there is a seasonal type of sticky traps that we used for wasp . First we had problems getting change in the percentage of females in the blue gum psyllid and the eugenia enough small red gums to establish a the population . A graph of the total psyllid studies : a 4 - inch - diameterplas - psyllid population , and then we dis - population would be misleading , so tic lid ( 10.5cm diameter , 87 sq cm ) covered that there were many more we graph only females but still count coated with motor oil additive , which male psyllids than females for most of males to estimate sex ratio changes . fits over a lid that has been painted the year ( fig . 4 ) . Finally we found that The highest number of females occurs yellow with the lip removed so that there is a long host - feeding period for in the summer months and drops to traps can be changed efficiently . By the female wasps and that they kill 20 % to 25 % the rest of the year ( for ex - June2000 we had established 26 moni - psyllid nymphs and do not parasitize ample , Valley Village Park in Los An - toring sites ( fig.I ) throughout the state , them initially . As a result , we have geles , fig . 4 ) . The pattern of male bias includingcoastal and inland sites.With made only small releases of 50 to 100 in the sex ratio has been consistent in many cooperators , we are changinga to - adults in 9 locations in the state ( fig . 1 ) . all of our plots throughout the state . tal of 326 traps weekly to count and sex The first release was made on June In August 1999 , parasitoids of the adult psyllids . The traps are also use - 7,2000 , at Valley Village Park in North lerp psyllid were collected at several ful in monitoring adult parasitoids . Hollywood , and two other releases locations in southern Australia . Eight We also sample foliageonce every 3 ( one in Los Angeles and one in species of Psylluephugus ( Hymenop - weeks in two locations , one in Los An - Alameda County ) were made in June . tera : Encyrtidae ) were reared in the geles and the other at Ardenwood , We made no releases for 2 months be - UC Berkeley quarantine facilities . One Alameda County , in Northern Califor - cause of the rearing problems men - of the species ( P.fuustus ) was a hyper - nia . Two 12 - inch ( 30cm ) branches are tioned above . Since Aug . 21,2000 , we parasite ( i.e . , a parasite of a parasite ) , taken in the vicinity of the 10sticky have released in six other areas ( fig . 1 ) . and six of the other species did not do traps in each plot , and all the eggs and We made our first recovery of a well in our rearings . One species , P . nymphal stages of the psyllid are parasitoid on a sticky trap in our Red - bliteus , was selected as the candidate , Fig . 4 . Number of red gum lerp psyllidfemales per trap , Valley Fig . 3 . Red gum lerp psyllidsampling , Ardenwood , Alameda Los Angeles , 1999 - 2000 . Village Park , County , Plot 1 . Number of eggs versus females . 10 CALIFORNIA AGRICULTURE , VOLUME 54 , NUMBER 6 The Australian tortoise beetle is a pest A The first longhornedborer Phoracantha first collectedin RiversideCounty in 1998 . was detected on euca - semipunctata ( left ) lyptus in California in 1985 . A second spe - cies , P . recurva , ( right ) was detected in Southern Californiain 1995 . wood City , San Mateo County plot on a trap that was set out on Aug . 24 , b The eucalyptussnout beetle defoliates eucalyptustrees . 2000 . This plot is 10miles from the 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 X tablished and spreading.We plan to eucalyptus several years earlier . 8 7 continuemonitoringthe psyllid and the Wasp - rearing techniques , as well as parasitic wasps for the next 2 years . methods of estimating densities of the The behavior of the egg parasitoid Trachymelasloanei.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 RiversideCounty 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 egg masses of the two borers in the continue throughout the active period counties since the initial discovery . field at the same rate , in laboratory tri - for the beetle . Population monitoring The adults of this insect are cryptically als , the wasp parasitizes a greater pro - for the beetles and the parasitoids will colored , blending in with the bark of portion of also continue , to determine the impact 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 - cape from extensive parasitism of Phoracantharecurva.Approxi - ever , when they open their elytra to eggs ; earlier seasonal activity , which mately 10 years after the discovery of fly , the hind wings are a brilliant red may permit the first longhorned borer on eucalyp - 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 - explain the replacement of recently introduced borer species ap - P . ing to feed on young leaves and tender pears to have very similar ecological semipunctata by P . recurva in many stemsat night . Adults also feed on requirements to parts of Southern California.Ecologi - P . semipunctata . Al - leaves and young stems , but of par - cal interactions between the two though differencesin host species ticular importance , adults clip off wood - boring species are currently un - preferences have not yet been studied young , tender leaf shoots as they begin der investigation at UC Riverside.In in California or , for that matter , any - 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 Jarraphoracantha , that attack the gram supported in part by UC IPM larvae of both Phoracantha species . is critical for managing risk from both has been implemented in an effort to Monitoring programs are in place to species . However , it does appear that provide a long - term solution to this determine if these larval parasites es - P . recurva emerges much earlier in the newly introduced pest problem . An year than P . semipunctata . Therefore tablished populations in California egg parasitoid , Enoggera reticulata , was and whether the parasites had an im - the window of opportunity for timing 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 IPM successes 1999 . The parasitic wasp had been ini - are not present ( or are present at very tially collected from Australia and was low densities ) may be much narrower Phoracanthasemipunctata.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 reduction in numbers of eucalyptus Support from the UC IPM program trees killed since the wasps became facilitated the development of an effec - established . tive pest management program for Gonipterusscutellatus.The euca - this insect . The fundamentals of this lyptus snout beetle , Gonipferus program are detailed in Paine et al . scutellatus , was discovered defoliating ( 1995 ) . The beetles are normally active windrow eucalyptus trees along citrus from approximately the beginning of f u groves in Ventura County in March Juneuntil the end of September . Be - 1994 ( Cowles and Downer 1995 ) . The cause the adults are attracted to adults are relatively nondescript stressed trees , recommendations to ar - brown beetles , but the legless larvae borists were adopted to minimize risk Anaphes nitens lays its eggs in the eggs are bright yellowish green with black to trees by scheduling potentially of the eucalyptus snout beetle . The devel - stripes , have a slimy coating , and pro - stressful cultural activities , such as oping parasitoidconsumes and kills the host eggs . duce long filaments of black excre - pruning or transplanting , during the ment . Female beetles deposit hard times of the year with the lowest levels brown egg capsules containing an av - of beetle activity . Susceptible and re - erage of nine eggs on shoots and sistant species of Eucalyptus were iden - young leaves . Both the adults and the tified , and the nursery and landscape larvae consume young and tender industries have incorporated that in - leaves , buds and shoots . Extensive formation into their planting recom - feeding can completely defoliate trees mendations . Scientists identified bark and kill branches , while intermediate moisture content as the critical mecha - f levels of defoliation can retard growth nism of tree resistance to borers ; larvae u % - and affect tree shape . were successful in penetrating bark m Y This insect has been introduced with moisture content less than 50 % , r - mJ from Australia into severaleucalyptus - but were unsuccessful if the moisture The blue gum psyllid was until recently growing regions around the world , content was greater than 55 % . There - of introducedpsyllids . the most damaging and has caused extensive damage fore irrigation recommendations were wherever it has become established . For - developed to maintain bark moisture tunately , it has proven relatively easy to above the critical threshold . control by the introduction of a specific Sources of beetles and beetle move - troduced into California ( Scriven et al . egg parasitoid , Anaphes nifens.FemaleA . ment in urban environments were 1986 ) . The initial discoveries were search for the eggs of their beetle nitens evaluated in the process of developing made in Orange County , but within a sanitation programs to limit risk from hosts and lay their eggs in the eggs of few years the beetle had become dis - the beetle . As with A . longoi , the devel - insects emerging from infested host tributed throughout the entire euca - oping parasitoid consumes and kills the material . A set of guidelines describ - lyptus range in the state . Male and fe - host eggs . ing these practices was developed for male beetles are attracted to volatile A . nitens were obtained from col - implementation by the landscape and chemicals produced by stressed , dy - leagues in the Republic of South Africa arboriculture industries . ing , damaged or recently killed euca - The final step in the IPM program and were reared in large numbers at lyptus trees . Mating occurs on the UC Riverside for release in California . was to establish effective natural en - trunks of susceptible trees . Females lay emies of the pest in the California Releases were made in Ventura batches of 10 to 40 eggs on the trunk County in August 1994and during the landscape . A host - specific egg parasi - surface under the loose , exfoliated summer of 1995 . The parasitoids rap - toid , the wasp bark or in cracks and crevices in the Avetianella longoi , was idly became firmly established , and bark . Newly emerged larvae bore identified in Australia , brought to UC snout beetle populations declined dra - through the outer bark of the tree and Riverside and reared in large num - matically . By 1997 , densities of beetle mine through the phloem , cambium bers . More than 600,000 individuals larvae had dropped to barely detect - and outer layers of xylem tissues . were released at locations in Northern If able levels . Although reduced to and Southern California . the insects are colonizing a living tree , A . longoi is nondamaging levels , the geographic larval feeding can effectively girdle now distributed throughout the state . distribution of the beetle has contin - and kill the tree . At the end of the lar - The female wasps search for beetle egg ued to expand into adjacent counties . val feeding period , the insects bore masses and insert their eggs into the However , in all cases the parasitoid deep into the wood to construct a pu - eggs of the beetle . As many as five distribution has expanded in tandem , pal cell that parasitoids develop in individual host is capped at the log sur - to mirror the distribution of its host . eggs , killing them ( Hankset al . 1996 ) . face with a plug of wood fibers and Consequently , where pesticide use has The parasitoid has proven to be highly excrement . Adult beetles bore out of not disrupted the actions of the parasi - efficient ( parasitism rates exceeding their pupal cells through the plug and toid , there have not been further re - 90 % ) , and arborists from many parts emerge from the tree to search for ports of damage , and the bhlogical of the state have reported a dramatic mates and begin a new generation . 12 CALIFORNIA AGRICULTURE , VOLUME 54 , NUMBER 6 species.Therefore future IPM programs control program has provided an ef - must integrate approaches that target fective and permanent solution to the in - problem , requiring no further input . dividual pests into strategies for manag - ing a pest complex.This Ctenarytainaeucalypti.The blue approach re - gum psyllid , quires more detailed knowledge of the Ctenarytaina eucalypti , ecologies of each insect species , and of was until recently the most damaging the interactions of each specieswith other member of a guild of Australian psyl - members lids that have been introduced into 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 f tinue , other insect species that feed on eu - 0 in Monterey County in 1991 , and by 5 calyptus will be introduced into Califor - 8 the end of that year had expanded its nia - and will also have to be managed as range to at least 12 other counties in part of an expanding pest complex . The parasitoid Psyllaephaguspilosus has the state . Although found on land - significantly reduced blue gum psyllid scape and windrow Eucalyptus T.D . Paine and J.G . Millar are Professors populations . E . cinerae , E . glaucescens , E . globrilus , and M.S . Hoddle is Assistant Cooperative Extension Specialist , Entomology Depart - camaldiilensis and E . viminalis , the ma - Futureoutlook ment , UC Riverside ; D.L . Dahlsten is Pro - jor commercial impact was the heavy fessor , Centerfor Biological Control , UC damage ( for example , a 30 % reduction Eucalyptus had virtually no insect in the 1991harvest ) to pests or diseases for almost a century Berkeley ; L.M . Hanks is Assistant Profes - E . pirlvercrlentn and a half in California . When the first grown commercially for cut foliage . sor , Entomology Department , University of Illinois at Urbana - Champaign . The authors pests were detected , it was possible to Damage to the foliage crop included develop pest management strategies inhibition of new shoots , distorted appreciate the assistance of William E . directed toward individual pest spe - growth , deposits of sticky honeydew Chaney , A . James Downer , John N . cies , and often with a single effective that supported growth of sooty molds Kabashima , Karen L . Robb and Steven tactic . However , California now has and unsightly waxy residues depos - Tjosvold , UC CooperafiveExtension Advi - sors in Monterey , Ventura , Orange , San accumulated a community of at least ited by immature psyllids . Diego , Santa Criiz and Sun Luis Obispo three feeding guilds of insects , includ - Supported in part by the UC IPM ing borers , defoliators and sap - feeding project , a biological control program counties , respectively , for their assistance insects . Individual pest species can no was initiated with the collection of a in conducting the various research projects longer be managed in isolation . In - nymphal parasitoid , Psyllaephagus described in this review . The research was stead , integrated pest management pilosus , in Australia . The parasitoid funded by a wide range of sources , includ - strategies must take into consider - ing the UC Statewide Integrated Pest Man - was reared in large numbers at UC ation the entire complex of insect Berkeley.The first releases of wasp agement Program . herbivores . adults were made in spring 1993 , with For example , when there were no References additional releases of 6,000 adults in leaf or sap - feeding pests , management four counties throughout 1993 . The Cowles RS , Downer AJ . 1995 . Eucalyptus of tree stress to reduce risk of infesta - snout beetle detected in California . Cal Ag parasites quickly established in the re - 49 ( 1 ) : 38 - 40 . tion by a single borer species was rela - lease sites , and sampling in 1994re - Dahlsten DL , Hansen EP , Zuparko RL , tively simple . Now , there are at least vealed parasitism rates of 50 % to Norgaard RE . 1998a . Biologicalcontrol of the two important defoliators and two 100 % . By 1995 , the parasitoids had be - blue gum psyllid proves economically benefi - cial . Cal Ag 52 ( 1 ) : 35 - 40 . damaging fluid feeders that apply ad - come broadly distributed throughout Dahlsten DL , Rowney DL , Copper WA , et ditional stress to trees , and this stress many parts of the state . Reductions in al . 1998b . Parasitoidwasp controls blue gum cannot be mitigated simply by proper blue gum psyllid populations as a re - psyllid . Cal Ag 52 ( 1 ) : 31 - 34 . irrigation . Furthermore , management sult of the biological control program A Doughty RW . 2000 . The Eucalyptus : Natural and CommercialHistory of the Gum options , particularly pesticide applica - have continued . An economic analysis Tree . Baltimore , MD : The Johns Hopkins Uni - tions or cultural practices , aimed at of the benefit to the cut - foliage indus - versity Press . 237 p . one pest species may exacerbate prob - try alone indicated that the biological Hanks LM , Paine TD , Millar JG . 1996 . Tiny wasp helps protect eucalypts from eucalyptus lems with another species . For ex - control program generated a benefit - longhorned borer . Cal Ag 50 ( 3 ) : 14 - 6 . ample , fertilization may improve tree cost ratio ranging from a minimum of Paine TD , Millar JG , Hanks LM . 1995 . Biol - vigor , but it may also improve the 9 : l to a maximum of 24 : 1 , based solely of the eucalyptus longhorned borer in Cali - ogy quality of the tree as a food source for on elimination of pesticide treatments of an integratedman - fornia and development agement programfor the urbanforest . Cal Ag the leaf - and fluid - feeding insects . In ( Dahlsten et al . 1998a ) . These calcu - 49 ( 1 ) : 34 - 7 . contrast , biological control efforts di - lated benefits are very conservative Scriven GT , Reeves EL , Luck RF . 1986 . rected toward controlling one pest and do not include increased crop Beetlefrom Australia threatens eucalyptus . Cal Ag 40 ( 4 ) : 4 - 6 . may have limited impact on other pest yields or environmental impacts . CALIFORNIA AGRICULTURE , NOVEMBER - DECEMBER2000 13
Posted By