Biological Control 23, 27–34 (2002)doi:10.1006/bcon.2001.0983, available online at http://www.idealibrary.com on

Status of Charidotis pygmaea (Coleoptera: Chrysomelidae)as a Biological Control Agent of Lantana montevidensis

(Verbenaceae) in AustraliaM. D. Day and T. D. McAndrew

Alan Fletcher Research Station, P.O. Box 36, Sherwood, Queensland 4075, Australia

Received December 29, 2000; accepted July 24, 2001; published online October 23, 2001

The establishment of the leaf-feeding beetle Chari-dotis pygmaea Klug and its potential to control Lan-tana montevidensis (Sprengel) Briquet, a serious pas-ture weed of central and southern Queensland, Aus-tralia, were assessed. C. pygmaea was collected inBrazil from Lantana fucata Lindley, a plant morpho-logically similar to L. montevidensis. Over 40,000 bee-tles were released over 3 years by use of caged anduncaged techniques at 25 sites throughout southeastand central Queensland. At 6 of the sites where de-tailed and frequent monitoring occurred, no adultswere found 6 months after the release. At another 2sites, adults were present for only 12 months. Only asmall number of eggs were laid at any single site andfew larvae completed development to the adult stage.No signs of insect activity were found at any site after24 months. Comparative laboratory and experimentalfield plot trials with both the weedy (field host) and theornamental (glasshouse host) forms of L. monteviden-sis did not show significant differences in insect per-formance. Assessment of nitrogen, phosphorous, po-tassium, and water contents, leaf hairiness, and leaftoughness of both the weedy and the ornamentalforms of L. montevidensis grown under glasshouse andfield plot conditions did not show differences betweenthe two plant forms. There were, however, differencesin the percentage of adults that developed in the glass-house trials compared to the field plot trials (55% vs5%). Field observations in Brazil showed that C. pyg-maea was found only on L. fucata and L. tiliifoliaChamisso and was not seen on L. montevidensis grow-ing in the same region. Climate matching withCLIMEX showed that most areas in Australia where L.montevidensis is a major problem are not climaticallysimilar to the collection sites of C. pygmaea in Brazil.Whereas populations of C. pygmaea can be maintainedon L. montevidensis under glasshouse conditions, itperforms poorly on that species under field conditions.Unsuitable climatic conditions and an incompatibletarget plant are the most likely factors affecting thepoor performance of C. pygmaea. Consequently, field

27

releases of the agent in Australia have ceased and C.pygmaea is not recommended as a biological controlagent for L. montevidensis in Australia. © 2001 Elsevier

Science

Key Words: Charidotis pygmaea; Lantana fucata; bi-ological control; horticultural varieties; field assess-ment; host plant; environmental factors.

INTRODUCTION

The chrysomelid beetle Charidotis pygmaea Klug(Coleoptera: Chrysomelidae) was the first agent re-leased in Australia for the biological control of creepinglantana, Lantana montevidensis (Sprengel) Briquet, aweed affecting tens of thousands of hectares of pas-tures in central and southeast Queensland. L. montevi-densis is a low sprawling herbaceous plant that flowersprolifically in summer or after rain (Day et al., 1999).Seeds are produced in drupes and are spread mainly bybirds and occasionally by kangaroos.

C. pygmaea was first observed on L. tiliifoliaChamisso, a close relative of L. camara L., in surveysconducted by Winder and Harley (1983) in Brazil andwas later reported on a plant then identified as L.montevidensis. Consequently, C. pygmaea was col-lected from this plant and imported into Australia in1993, to control both L. camara and L. montevidensis,and was approved for field release in 1995. Subsequentsurveys near Curitiba, Brazil in 1997 found that C.pygmaea was in fact collected from L. fucata Lindley, aplant morphologically similar to L. montevidensis (C.Garcia, Department of Natural Resources and Mines[DNR&M], Queensland, Australia, personal communi-cation). C. pygmaea adults feed and oviposit on theunderside of leaves. Larvae feed initially on the under-side and then move to feed on the upper surface ofleaves. In large populations, the insect can severelydefoliate the plant, thereby reducing plant vigor andflowering. Pupation can occur on the leaves or on thestems, and the life cycle is completed in about 6 weeks.

1049-9644/01 $35.00© 2001 Elsevier Science

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28 DAY AND MCANDREW

A complete life history of C. pygmaea is given in Day etal. (1999).

A colony of C. pygmaea was maintained on potted L.montevidensis plants in screened aluminum cages inglasshouses at the Alan Fletcher Research Station(AFRS), Brisbane, Queensland, Australia after labora-tory host preference trials showed that it performedbetter on this plant than on L. camara (Day et al.,1999). Insect cultures were maintained on a predomi-nantly sterile ornamental form of L. montevidensis be-cause of its ready availability and to reduce the furtherspread of the weed. A complete rearing method is out-lined in Day et al. (1999). From 1996 to 1998, over40,000 adults were released at 25 sites (mean 620adults/field site/release) throughout the infested areasfrom central to southeast Queensland by use of bothcage and open field releases. Whereas adults persistedfor several months in the field, very few eggs were laid.Adult numbers declined after release and no adults orother stages were present at any site after 24 months.

The failure of biological control agents to establish inthe field has been the subject of much discussion(Sands and Harley, 1980; Wapshere, 1985; Grevstad,1996). The appropriateness of the host plant, environ-mental conditions, parasitism/predation, and releasemethods used have all been proposed as possible rea-sons that some agents have not established (Memmottet al., 1996; Day and Neser, 1999; Broughton, 2000). Inaddition, inappropriate sampling methods or low pop-ulations of agents may result in the perception thatagents have failed to establish (McClay et al., 1990;McFadyen, 1992; Dhileepan et al., 1996). This paperdescribes glasshouse, laboratory, and field investiga-tions undertaken with both the weedy form and theornamental form of L. montevidensis to determine whyC. pygmaea has performed poorly in the field. Resultsfrom these investigations are then used to determinethe potential of C. pygmaea as a biocontrol agent inAustralia.

MATERIALS AND METHODS

Field Release and Monitoring

Adults were released into the open in batches of atleast 500 adults, or into cages in batches of at least 250adults, on healthy shaded stands of L. montevidensis.The release cages consisted of 2-cm-diameter galva-nized pipes supporting 50% green shadecloth material.The corners were sewn and the posts were placed in theground, such that the edge of the material could besecured to the ground to minimize the escape of adults.Cages were left in position for up to 4 weeks to ensurethat sufficient numbers of eggs were laid in one loca-tion, prior to being removed to allow the remainingadults to disperse. The use of cages facilitated thecounting of eggs and larvae by limiting the search area.

In the open releases, adults were held in cages in thelaboratory until they were sexually mature and re-leased over an area not larger than 5 m2 to minimizeadult dispersal and to maximize the chance of adultsfinding a mate. Release sites ranged from Monto (25°S,151°E) in central Queensland to Canungra (28°S,152°E) in southeast Queensland. Release sites wereselected near creeks or gullies, so that plants wouldtend not to dry out in winter, or beneath trees thatoffered shade in summer.

Five caged and open field release sites in southeastQueensland (Beenleigh, Mt. Cotton, Narangba, PeakCrossing, and Wivenhoe Dam) were monitoredmonthly during the active growing season of the plantfor the presence of adults, eggs, and larvae for up to 3months following the release of the adults. Detailedmonitoring of two separate releases at Mt. Gravatt inBrisbane was conducted weekly. On each visit, allstages of C. pygmaea were counted and stems contain-ing eggs and larvae were tagged for ease of futureobservations of subsequent larval development. To tryto quantify and standardize results, searching was con-ducted systematically over 1 h in concentric circlesradiating out from the center of the release area, con-centrating on plants with feeding scars. By the con-ducting of monitoring in this fashion, a larger time isspent in the area in which adults were released andwhere feeding scars were present and less time is spentin areas farther from the release area where fewer orno feeding scars were present. The presence of spidersand predatory insects was also recorded. Additionalobservations at all sites were made 6, 12, and 24months after the adults were released.

Laboratory Trials

Ten pairs of sexually mature adults from the glass-house culture were confined for 7 days in each of threecages, containing both the weedy and ornamentalforms of L. montevidensis, to test whether the form ofL. montevidensis influenced insect performance. Afterthe adults were removed, the number of feeding scarsand eggs on each plant were recorded. The plants werethen caged individually and examined weekly, and thenumber of individuals that completed development toadulthood was recorded. Newly emerged adults thatdeveloped from the same plant form were pooled andplaced in new cages with fresh plants of both weedyand ornamental forms of L. montevidensis for 7 days todetermine whether previous host experience influ-enced performance of the next generation. Three rep-licates with adults that had developed from each plantform were set up. The number of feeding scars, eggs,and individuals that completed development on eachplant were recorded. Results were analyzed with asingle-factor ANOVA.

29C. pygmaea FOR BIOCONTROL OF L. montevidensis

Caged Field Trials

Experimental plots were set up at AFRS to assessthe performance of insects in the field. Ten pairs ofsexually mature adults from the glasshouse culturewere confined in each of three gauze bags tied tobranches on each plant of the two forms of L. montevi-densis and allowed to feed and oviposit for 7 days inirrigated and nonirrigated no-choice field plot trials.There were four plants of each form in each treatment,with a total of 30 pairs of adults on each plant and 120pairs of adults per plant form and treatment. Thesetrials aimed to simulate field conditions while allowingmore intensive monitoring of insect numbers and de-velopment. Adults were removed after 7 days and thenumber of adult feeding scars and eggs present wererecorded. The gauze bags were left on the plants toprevent predation or parasitism of eggs and larvae asspiders and predatory ants have been observed to feedon larvae under field conditions. The plants were ex-amined weekly and the number of individuals thatcompleted development to adulthood was recorded. Re-sults were analyzed with a two-factor-with-replicationANOVA, following arcsine transformation for percent-ages (i.e., the percentage of eggs from which adultsdeveloped).

Plant Analysis

Leaf toughness, leaf hairiness, and percentage ofnitrogen, phosphorous, potassium, and water contentwere measured for both the ornamental and the weedyforms of L. montevidensis grown under field and glass-house conditions to determine differences in the mor-phology or nutrients of the leaves due to plant form orgrowing conditions.

Leaf toughness was measured with a modified por-table leaf penetrometer as described by Sands andBrancatini (1991). One leaf from the second pair ofleaves of a stem was tested. Three measurements weretaken from each leaf and leaves were taken from 20stems of each form grown in both the field and theglasshouse.

The number of hairs on a 2-mm2 section of the secondleaf of each of 30 stems, of each form and cultivationmethod, were counted with a dissecting microscope andan ocular micrometer. Care was taken to ensure thatleaf sections did not contain major veins to minimizevariation in the number of hairs present.

The percentage N, P, and K in leaves of each plantform grown under different conditions was measuredwith 10 g of the second pair of leaves dried in an ovenat 70°C for 24 h. The material was then ground with arotary grinder fitted with a 1.0-mm mesh and digestedby the Kjeldahl method. N and P were measured withan autoanalyzer, and K was measured by flame pho-tometry. The percentage water content of each plantform grown under different conditions was measured

with 10 g of the second pair of leaves immediatelyweighed on a top-pan balance. The leaves were thendried in an oven at 70°C for 24 h and reweighed, andthe percentage water was calculated.

Data on leaf toughness and leaf hairiness were ana-lyzed with a single-factor ANOVA.

Field Surveys in Brazil

Additional field observations were conducted aroundCuritiba, Brazil, where C. pygmaea was originally col-lected, to determine the species of Lantana that arehosts to C. pygmaea in its native range. Plants weresearched visually and the presence or absence of C.pygmaea was recorded. Pressed specimens of each spe-cies of Lantana were taken to the Curitiba Herbariumfor identification by Gert Hatschbach, a taxonomistspecializing in the genus Lantana.

Climate Matching

Comparisons of climates were conducted with theclimate modeling program CLIMEX (Sutherst et al.,1999) to predict the areas in Australia that are likely tobe more climatically suitable for C. pygmaea. The com-parisons were made by the determination of variationsin mean maximum and minimum monthly tempera-tures, relative humidity, and rainfall quantity and pat-tern. Towns in Australia having a 60% Match Indexwith Curitiba, Brazil were identified. Match Indicesgreater or less than 60% gave results either that weretoo restrictive or that included areas that were quiteclimatically dissimilar to the sites in Brazil (R. W.Sutherst, CSIRO, personal communication).

RESULTS

Field Release and Monitoring

C. pygmaea was not present in any stage at any ofthe eight monitored sites 24 months after the insectwas released. At six sites, Beenleigh (1720 adults re-leased), Canungra (4500 adults), Mt. Cotton (534adults), Narangba (1400 adults), Peak Crossing (1700adults), and Wivenhoe Dam (840 adults), no insectswere present after 6 months. Subsequent visits after12 and 24 months also failed to find any adults or signsof feeding damage. At the remaining two sites, Mt.Gravatt (1700 adults and 500 adults released on sep-arate occasions) and Monto (8500 adults released over2 years), only a few insects were present after 6 monthsand no insects were seen after 12 and 24 months. Atmost sites, some eggs and larvae were observed a fewweeks after release, but, invariably, no larvae com-pleted development. At Mt. Gravatt, where detailedmonitoring of two separate releases occurred, femalesinitially laid eggs and some larvae completed develop-ment (Fig. 1a and 1b). These adults soon died and no

30 DAY AND MCANDREW

adults were present 6 months after either release. Afew spiders were seen on plants containing eggs andlarvae but their impact on insect numbers was difficultto determine.

Laboratory Trials

In first generation choice trials in a glasshouse,adults reared on the ornamental form preferred to feedon the ornamental form over the weedy form (F 1,5 556.4, P , 0.002) (Fig. 2). However, the number of eggslaid (F 1,5 5 0.18, P , 0.7) or the percentage of eggsfrom which adults developed (F 1,5 5 0.02, P , 0.9) oneach form were not significantly different (Fig. 3). Inthe second generation, there was no significant differ-ence in the number of feeding scars on each form whenadults were reared on the ornamental form (F 1,5 50.004, P , 1.0). However, adults reared on the weedyform preferred to feed on the ornamental form (F 1,5 516.9, P , 0.02) (Fig. 2). Females of the second gener-

FIG. 1. The number of adults, eggs, larvae, and pupae present onL. montevidensis at Mt. Gravatt (Brisbane) following the release of1200 mature C. pygmaea in January 1997 (a) and 500 adults inFebruary 1999 (b). No pupae were found following the 1999 release.

ation reared on either the ornamental form or theweedy form preferred to lay on the ornamental form.However, these values were not significantly different(F 1,5 5 0.8, P , 0.5 and F 1,5 5 3.5, P , 0.2, respec-tively). There was no significant difference in the sub-sequent percentage development to adult stage of in-sects whose parents had been reared on the ornamen-tal form (F 1,5 5 1.7, P , 0.3) or on the weedy form(F 1,5 5 1.5, P , 0.3) (Fig. 3).

Caged Field Trials

There were no significant differences, due to eitherplant form or watering regime, in the number of feed-ing scars present (F 9,47 5 1.37, P , 0.3) (Fig. 2) oroviposition (F 9,47 5 0.57, P , 0.9) (Fig. 3). A signifi-cantly higher percentage of insects completed develop-ment on the ornamental form grown under irrigationthan in the other three treatments (F 9,47 5 2.87, P ,0.02). Generally, eggs laid and subsequent develop-ment to adult stage, were much lower in the field trialsthan in the laboratory trials (Fig. 3).

Plant Analysis

There was little difference in the percentage of watercontent and N and K in leaves of the two forms of L.montevidensis grown under different conditions (Table1). However, there was a substantial difference in thepercentage of P, with leaves of the weedy form at Mt.Gravatt having 25% of the P contained in weedy-formplants grown in the glasshouse. The toughness ofleaves varied significantly between the two formsgrown under different conditions. The weedy formgrown at the Mt. Gravatt field site and under thenonirrigated cage site had tougher leaves (F 6,139 57.25, P , 0.0001). The ornamental form grown underglasshouse conditions had tougher leaves than leavesof the weedy form grown under glasshouse conditions.

FIG. 2. The number of adult C. pygmaea feeding scars presentafter 7 days on the weedy and ornamental forms of L. montevidensisin first (F1) and second (F2) generation laboratory choice trials andno-choice irrigated and nonirrigated field plot trials.

31C. pygmaea FOR BIOCONTROL OF L. montevidensis

However, there was no correlation between leaf tough-ness and the number of eggs laid on the plants (linearregression: F 1,5 5 0.036, P . 0.86, r 2 5 0.009) orbetween leaf toughness and percentage development oflarvae (linear regression: F 1,5 5 0.53, P , 0.51, r 2 50.12). Leaves of the ornamental form grown in theglasshouse had significantly more hairs per 2 mm2

(200) than leaves of the weedy form grown in the glass-house (103) or leaves of the weedy form growing at Mt.Gravatt (97) (F 2,89 5 843.5, P , 0.0001) (Table 1).

Field Surveys in Brazil

During the additional field surveys around Curitiba,Brazil, C. pygmaea was found on L. fucata and L.tiliifolia but was not seen on L. montevidensis. L. mon-tevidensis occurs mainly as a low scrambling plant inrocky and dry areas, whereas L. fucata is found alongthe flats and beside roads. Both species have similarmorphologies and habits, being low-growing sprawlingplants.

TAB

Percentage N, P, K, and Water Content, Leaf ToughneGrown in the Glas

Perc

N P

Ornamental form—glasshouse 2.97 0.67Weedy form—glasshouse 4.48 1.11Ornamental form—nonirrigated field plot 4.02 0.40Weedy form—nonirrigated field plot 3.66 0.32Ornamental form—irrigated field plot 3.43 0.52Weedy form—irrigated field plot 2.96 0.60Weedy form—Mt. Gravatt release site 3.01 0.28

FIG. 3. The number of eggs laid by C. pygmaea after 7 days andthe subsequent number of adults that completed development on theweedy and the ornamental forms of L. montevidensis in first (F1) andsecond (F2) generation laboratory choice trials and no-choice irri-gated and nonirrigated field plot trials.

Climate Matching

Climatic data could be obtained for only two siteswhere C. pygmaea was found (Curitiba in the ParanaState, Brazil and Porto Alegre in the Rio Grande State,Brazil). Two sites are insufficient to develop an ecocli-matic model capable of predicting areas climaticallyfavorable for C. pygmaea. However, by climate match-ing with a Match Index of 60%, the regions in Australiamost climatically similar to those sites where C. pyg-maea was found in its native range were identified.These regions ranged from Brisbane to southern NewSouth Wales. The only region in Australia where L.montevidensis occurs as a weed that also had a 60%similarity with the climate of Curitiba was in south-east Queensland, which included Brisbane and Ca-nungra. Sites at Monto, where many earlier releaseswere made, Peak Crossing, and Wivenhoe Dam hadhigher summer temperatures and lower humidity thanCuritiba. Beenleigh, Mt. Cotton, Mt. Gravatt, andNarangba are all locations within the greater Brisbanearea and so were also considered to have a 60% simi-larity in climate.

DISCUSSION

Numerous reasons have been cited for biological con-trol agents failing to establish in the field. The speciesfrom which the agent has been collected in its nativerange, plant variety, climate, parasitism, and releasemethods have all been proposed to influence establish-ment and performance of agents (Sands and Harley,1980; Grevstad, 1996; Day and Neser, 1999; Brough-ton, 2000). In addition, agents have been known topersist in the field for many years in such low numbersthat establishment was thought not to have occurred(McFadyen, 1992; Dhileepan et al., 1996).

Adult C. pygmaea can live and reproduce on L. mon-tevidensis in the glasshouse for up to 12 months (Day etal., 1999). However, adults in the field appeared topersist for only 6 months and laid only a few eggs.Subsequent development to adult was also very low,

1

and Leaf Hairiness of Two Forms of L. montevidensisuse and the Field

age Leaf toughness Leaf hairiness

K Water Mean S.E. Mean S.E.

2.20 73.63 1.85 0.06 200.9 2.82.90 78.82 1.40 0.06 103.1 1.43.00 73.20 1.62 0.062.60 73.19 1.90 0.073.00 73.56 1.52 0.082.40 74.11 1.75 0.061.90 65.27 1.87 0.05 96.8 1.5

LE

ss,sho

ent

32 DAY AND MCANDREW

with very few first generation adults being found in thefield at only one site. Newly emerged adults can easilybe distinguished from field-released adults, in thatthey are bright red, becoming a dull yellow and then aniridescent yellow on maturity (Day et al., 1999). Al-though spiders and predatory ants were seen in thefield on L. montevidensis containing eggs and larvae,their impact was difficult to assess.

Laboratory and caged field trials showed that thereis little difference in the performance of the insect onthe two forms of L. montevidensis growing under thesame conditions. The analysis of percentage water andN, P, and K content showed little difference betweenthe two plant forms, and there was no correlation be-tween leaf toughness and number of eggs laid. How-ever, there were differences in the performance of C.pygmaea on L. montevidensis in the glasshouse and inthe field. Very few eggs were laid in the field comparedto the laboratory, and survival to adult stage in thefield was very poor. Parasitism and/or predation werenot viewed as contributing factors for the poor devel-opment as branches and stems with eggs and larvaewere bagged and other insects were never observedwithin the bags.

The results of the field and laboratory trials sug-gested that the plant species and/or the environmentdo not allow the insect to persist in areas in which itwas released and are probably the main reasons for theinsect not establishing. Although predation may be acontributing factor, the low numbers of eggs observedin both bagged and unbagged field trials suggest thatother factors are more influential. Field surveys inBrazil indicated that L. montevidensis may not be anatural host for C. pygmaea, as this insect has beenfound only on L. fucata and L. tiliifolia. Althoughhealthy populations of C. pygmaea can be maintainedon L. montevidensis under glasshouse conditions, theinsect did not maintain populations on this plant underfield conditions in Queensland.

There have been several examples in which potentialbiocontrol agents collected from a congener in the na-tive range have been maintained on the target weed inthe glasshouse and have failed to establish on the weedunder field conditions, e.g., Lioplacis elliptica Stål andAnacassis fuscata Klug released on Baccharis halimi-folia L. (McFadyen, 1987a,b), Cactoblastis spp. re-leased to control Opuntia spp. (McFadyen, 1985), andseveral species released to control L. camara (Day andNeser, 1999).

The effectiveness of the collection of potential agentsfrom plant species other than the target species hasbeen debated (Hokkanen and Pimentel, 1984; Wap-shere, 1985; Goeden and Kok, 1986). Hokkanen andPimentel (1984) argue that collection of potentialagents from plant species other than the target speciesis advantageous, as the plant and the insect have notevolved together and so the plant would not have de-

veloped any specific defence strategies against thatinsect. They cite, as an example, the success of Cacto-blastis cactorum (Bergroth) in controlling prickly pearin Australia. However, Goeden and Kok (1986) arguethat most successful biological control agents havebeen collected from the same species that they wereintended to control. They add that the number of suc-cesses cited by Hokkanen and Pimentel (1984) is in factmuch lower and that the success of agents collectedfrom another species is the exception rather than therule.

Myers et al. (1989) proposed that plants do not evolvedefences against insects per se but respond by produc-ing more shoots or vegetative material. Potentialagents should be collected from the identical species asthey are better adapted to the plant. Other plant spe-cies may not have all the necessary nutrients for in-sects to complete development and produce viable eggs.In addition, other plant species may have an unsuit-able morphology or may contain compounds that deterfeeding and/or oviposition of the potential agent (Cor-bet, 1985).

Apart from host suitability, climate also determinesthe establishment and range of many biocontrol agents(Sands and Harley, 1980). These authors state thatpotential agents should be collected from climatic areassimilar to those in which the agents are likely to bereleased. C. cactorum controls Opuntia spp. in Queens-land but does not control the same weed in New SouthWales, where temperatures prevent the insect fromcompleting two generations per year (Hosking et al.,1988).

Other agents have also controlled a weed in somelocations but not others. A survey of biological controlagents attacking L. camara in Australia has found thatonly two species, Lantanophaga pusillidactyla(Walker) and Ophiomyia lantanae Froggatt, are foundthroughout the range of L. camara, whereas the re-maining 15 species that have established have morelimited distributions. In addition, Octotoma scabripen-nis Guerin-Melville and Teleonemia scrupulosa Stålcan be quite damaging to L. camara during the warmmonths and in tropical and subtropical areas but haverelatively little impact on L. camara during the coolerwinter months or in southern New South Wales (Dayand Neser, 1999).

The use of CLIMEX has helped with the releasestrategies of several agents, including A. compressa onL. camara (Palmer et al., 1996) and Chiasmia assimilis(Warren) and C. inconspicua (Warren) on Acacia nil-otica indica (Bentham) Brenan (W. A. Palmer,DNR&M, Queensland, Australia, personal communi-cation). A major limitation with the use of CLIMEX canbe the low numbers of locations in the native range forwhich climatic data can be obtained. The more loca-tions where the insect occurs in its native range, themore robust the model of a likely distribution of the

33C. pygmaea FOR BIOCONTROL OF L. montevidensis

insect in a new country. Because climatic data could beobtained only for two sites at which C. pygmaea wasfound, a model could not be developed and the climatematching facility of CLIMEX was used instead.

Many releases of C. pygmaea were conducted in cen-tral Queensland where the most serious infestations ofL. montevidensis occur. However, the release sites atMonto, Wivenhoe Dam, and Peak Crossing were prob-ably unsuitable for C. pygmaea, as these centers havehigher summer temperatures and much lower humid-ity and rainfall than Curitiba. As a result, further fieldreleases at Wivenhoe Dam and Peak Crossing ceasedwhile sites around Monto with more suitable microcli-mates were sought. In addition, more C. pygmaea werereleased in sites around Brisbane (Beenleigh, Mt. Gra-vatt, Mt. Cotton, and Narangba) and Canungra to thesouth, as these centers appeared to be more climati-cally similar to the areas in Brazil from which C. pyg-maea was collected. However, C. pygmaea was not seenat any of these sites after 24 months, suggesting thatthese sites may also be unacceptable for C. pygmaea.

The final consideration in the determination of whyC. pygmaea has not been observed in the field iswhether release numbers were sufficient. If the sizes ofthe releases are too small, establishment may not oc-cur, as dispersion of adults result in females not beingmated or populations becoming so dispersed that indi-viduals cannot be found. Grevstad (1999) had 100%establishment of the chrysomelid beetle Galerucellapusilla (Duftschmidt) when adults were released inbatches of 540. Populations also established when only60 adults were released but with a much lower proba-bility. In the present study, at least 250 adults werereleased in cages for 4 weeks to prevent dispersion andto give the adults a chance to mate and lay eggs in arestricted area, and at least 500 mated adults werereleased at any one time when cages were not used.The low numbers of eggs seen after adults were con-fined to cages and the low subsequent survival to theadult stage suggests that it is unlikely that releasenumbers of C. pygmaea were insufficient for establish-ment to occur. A more likely explanation is that envi-ronmental conditions and/or host plant were not con-ducive to insect survival and oviposition.

Although monitoring of field and experimental trialshave shown that the performance of C. pygmaea in thefield is poor, it would be premature to state that theinsect has definitely not established in the field. Thereare several examples in which biocontrol agents havesurvived in low numbers for many years without beingdetected before populations have grown into largenumbers. The now widely established biocontrolagents Bucculatrix parthenica Bradley and Smicronyxlutuentus Dietz, introduced to control Parthenium hys-terophorus L., were undetected in the field for severalyears and thought not to have established (McClay et

al., 1990; McFadyen, 1992). However, the combinedresults of the field and laboratory trials, the climatematching, and the collection of C. pygmaea from a hostother than the target weed suggest that the agent isunlikely to do well as a biocontrol agent of L. montevi-densis in Australia. As a result of the agent’s initialpoor performance, the mass breeding program andfield releases have ceased.

ACKNOWLEDGMENTS

The authors thank Martin Hannan-Jones and Wilmot Senaratnefor their assistance with the CLIMEX models, the Department ofNatural Resources, Natural Resource Science for conducting thechemical analysis of the plant material, Don Sands, CSIRO for hisadvice and use of the leaf penetrometer, John Winder for conductingadditional surveys in Brazil, Gert Hatschbach for identifying theLantana spp., and the staff at AFRS for their helpful comments onthe manuscript.

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