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Annotated bibliography

Post-release studies

Weed biological control agents


Andreas J.E., Schwarzlander M. and Clerck-Floate R.d (2008). The occurrence and potential relevance of post-release, nontarget attack by Mogulones cruciger, a biocontrol agent for Cynoglossum officinale in Canada. Biological Control 46: 304-311
The root-mining weevil Mogulones cruciger, was approved and released in Canada, but was not approved for release in the United States, to control Cynoglossum officinale. Confamilial species co-occurring with C. officinale at six M. cruciger release sites in Alberta and British Columbia were assessed over a two year period. All four co-occurring species were attacked by the weevil to varying degrees, although attack was inconsistent between years and sites and nontarget species were attacked to a lesser degree than C. officinale. There was a positive relationship between the probability of nontarget attack and C. officinale attack rate by M. cruciger suggesting that the immigration of M. cruciger into the US may expose certain Boraginaceae to nontarget attack, but the risk to native species is unknown.

Balciunas J.K. and Villegas B. (2007). Laboratory and realized host ranges of Chaetorellia succinea (Diptera : Tephritidae), an unintentionally introduced natural enemy of yellow starthistle. Environmental Entomology 36: 849-857
In 1999, Chaetorellia succinea (Costa) (Diptera: Tephritidae), an unintentional introduction from Greece, was considered for biocontrol of yellow starthistle, Centaurea solstitialis L., one of the worst weeds in the western United States. However, the host range of C. succinea had not been studied, and so the physiological host range was determined in the laboratory by exposing it under no-choice conditions to 14 potential Cardueae hosts. Two introduced weed species and the native American basketflower (Centaurea americana Nuttall) were found to be laboratory hosts, although yellow starthistle was highly preferred. Because Ch. succinea is already widespread throughout California, flower heads were collected from 24 potential host plant species in the field to determine the realized host range. Ch. succinea emerged only from the other two known hosts: Ce. melitensis and Ce. sulfurea. Our results suggest that American basketflower growing in the southwestern United States may also be at risk if Ch. succinea expands its range into that region.

Balciunas J.K., Burrows D.W. and Purcell M.F. (1996). Comparison of the physiological and realized host-ranges of a biological control agent from Australia for the control of the aquatic weed, Hydrilla verticillata. Biological Control 7: 148-158.

Carvalheiro L.G., Buckley Y.M., Ventim R., Fowler S.V. and Memmott J. (2008). Apparent competition can compromise the safety of highly specific biocontrol agents. Ecology Letters 11: 690-700
Using food webs, the authors demonstrate that the use of a highly host-plant specific weed biocontrol agent, recently introduced into Australia, is associated with declines of local insect communities via indirect effects, most likely apparent competition. Both species richness and abundance in insect communities (seed herbivores and their parasitoids) were negatively correlated with the abundance of the biocontrol agent, Mesoclanis polana (Diptera: Tephritidae), a seed herbivore of Chrysanthemoides monilifera ssp. rotundata (Bitou). More investment is required in pre-release studies on the effectiveness of biocontrol agents, as well as in post-release studies assessing indirect impacts, to avoid or minimize the release of potentially damaging species.

Cristofaro M.De Biase A. and Smith . (2013). Field release of a prospective biological control agent of weeds, Ceratapion basicorne, to evaluate potential risk to a nontarget crop. Biological Control 64: 305-314.

Denslow J.S. and D'Antonio C.M. (2005). After biocontrol: Assessing indirect effects of insect releases. Biological Control 35: 307-318.
Weeds in conservation land have become a focus of biological control projects where desired outcomes include both reduction of the target and indirect effects of increased diversity and abundance of native species and restoration of ecosystem services. Few quantitative assessments of the impacts of pest plant reduction on community composition or ecosystem processes were found and there was variation in the impacts of agent(s) across the invasive range of the target plant as well as variation in impacts on the invaded ecosystem. Most successful weed management programs integrated the use of biocontrol agents with other weed management strategies, especially modifications of disturbance and competing vegetation.

DePrenger-Levin M.E., Grant TA., Dawson C. (2010). Impacts of the introduced biocontrol agent, Rhinocyllus conicus (Coleoptera: Curculionidae), on the seed production and population dynamics of Cirsium ownbeyi (Asteraceae), a rare, native thistle. Biological Control 55(2): 79-84.
This study evaluated non-target effects of Rhinocyllus conicus Frolich, on Cirsium ownbeyi S.L. Welsh, a rare, native and short-lived perennial thistle in northwestern Colorado, northeastern Utah, and southwestern Wyoming. C. ownbeyi is one of 22 known native hosts on which this introduced weevil has naturalized. The study population remained stable over the eight years of the study despite damage by thebeetle. The growth rate from was 1.03; however, large inter-year variation indicates this rare species is still vulnerable to local extirpation. The target species, Carduus nutans L. (musk thistle) is generally absent near the study plots, which may limit the population levels of R. conicus that can be sustained in this area. Although R. conicus utilizes C. ownbeyi as a host plant, the late flowering and the small size of the flower heads may limit the impact of R. conicus on C. ownbeyi.

Dhileepan K., Trevino M. and Raghu S. (2006). Temporal patterns in incidence and abundance of Aconophora compressa (Hemiptera: Membracidae), a biological control agent for Lantana camara, on target and nontarget plants. Environmental Entomology 34: 1001-1012
The membracid Aconophora compressa Walker, released in 1995 to control Lantana camara (Verbenaceae) in Australia, has since been collected on several nontarget plant species. A survey suggested that sustained populations of A. compressa were found only on the introduced nontarget ornamental Citharexylum spinosum (Verbenaceae) and the target weed L. camara. However, it was found on other nontarget plant species when populations on C. spinosum and L. camara were high, suggesting a spill-over effect. Some attack on nontarget plants could have been anticipated from host specificity studies done on this agent before release. This raises important issues about predicting risks posed by weed biological control agents and the need for long-term postintroduction monitoring on nontarget species.

Fowler S.V., Gourlay A.H., Hill R.L. and Withers T. (2003). Safety in New Zealand weed biocontrol: a retrospective analysis of host-specificity testing and the predictability of impacts on non-target plants. Pp. 265270 in Proceedings of the XI International Symposium on Biological Control of Weeds, Canberra, Australia, 2003, J.M. Cullen, D.T. Briese, D.J. Kriticos, W.M. Lonsdale, L. Morin and J.K. Scott (Ed.).
A retrospective analysis showed that all weed biocontrol agents released in New Zealand were subjected to generally appropriate host-range tests, although there were several examples where significant plant species were not tested. The results have been used to focus field surveys on the most likely non-target plant species to be attacked by biocontrol agents in New Zealand. For example, Tyria jacobaeae (cinnabar moth) did feed on some Senecio species in the original host-range tests, so the occasional field attack on native New Zealand fireweeds such as S. minimus was predictable. To date, this is the only weed biocontrol agent in New Zealand (of the total of 32 established in the field since 1929) that has been recorded attacking a native non-target plant species in the field. There were two cases where test results did not predict potentially substantial non-target impacts: Bruchidius villosus (broom seed beetle) and Cydia succedana (gorse pod moth), attacking seed of nontarget, exotic Fabaceae. Limited replication and duration of tests, were among possible explanations for the failure to predict these impacts.

Fowler S.V., Syrett P. and Hill R.L. (2000). Success and safety in the biological control of environmental weeds in New Zealand. Austral Ecology 25: 553-562.
Weed biological control agents have been recorded attacking non-target plants in NZ and elsewhere, but the effects are usually minor and/or transitory. Probably only two cases, worldwide, will result in significant damage to non-target plants both of which predictable from host range testing. For NZ programmes a full/partial success rate of 83% was calculated. Costs of biocontrol programmes against some NZ weeds can be reduced by using Australian research.

Frye, M.J., Lake, E.C. and Hough-Goldstein, J. (2010). Field host-specificity of the mile-a-minute weevil, Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae). Biological Control 55: 234-240
The authors hypothesized that Rhinoncomimus latipes (Coleoptera: Curculionidae), the biological control agent released against mile-a-minute weed, Persicaria perfoliata (Polygonaceae), would not feed or oviposit on nontarget plants in a two-phase, open field setting. Whereas prerelease studies showed feeding at low levels on 9 of the 13 plant species tested here, under open field conditions R. latipes did not feed on any nontarget plant species and dispersed from these plants. In an open field setting, where the weevil was able to use its full range of host-selection behaviors, there was no observed risk of nontarget effects for any species tested

Gassman A. and Louda S.M. (2001). Rhinocyllus conicus: initial evaluation and subsequent ecological impacts in North America. Pp. 147-183 In: Evaluating indirect ecological effects of biological control, E. Wajnberg, J.K. Scott and P.C. Quimby (Ed.) CABI Publishing, Wallingford, Oxon., UK.

Groenteman, R., Fowler, S.V. and Sullivan, J.J. (2011). St. John's wort beetles would not have been introduced to New Zealand now: A retrospective host range test of New Zealand's most successful weed biocontrol agents. Biological Control 57: 50-58
St. John's wort, Hypericum perforatum, was a serious weed in New Zealand (NZ) pastures in the 1930s. Chrysolina hyperici and C. quadrigemina, were introduced to NZ in 1943 and 1965, respectively. Earlier host specificity testing in Australia was deemed sufficient for approval for release in NZ. A review of worldwide reports suggested that St. John's wort beetles will attack a range of Hypericum species in the field. After a series of laboratory tests conducted to simulate modern host-range-testing protocols the authors concluded that the two Chrysolina species would not have been approved for introduction to NZ under current risk assessment protocols, and that NZ would have missed out on one of its greatest biocontrol success stories. No evidence for impacts on the populations of indigenous congeners has been recorded. Better procedures are required to predict the realized host-range of an agent from the potential range in contained host-range testing.

Haines M.L., Martin J.-F., Emberson R.M., Syrett P., Withers T.M. and Worner S.P. (2007). Can sibling species explain the broadening of the host range of the broom seed beetle, Bruchidius villosus (F.) (Coleoptera : Chrysomelidae) in New Zealand? New Zealand Entomologist 30: 5-11
Following introduction into New Zealand for biological control of Scotch broom, Cytisus scoparius, the broom seed beetle, Bruchidius villosus, was found utilising tagasaste, Chamaecytisus palmensis, which was not predicted by host range testing. One possible explanation for these inconsistencies is that more than one species is included within the current concept of B. villosus. However, sequence data from the mitochrondrial gene COI showed a low level of sequence polymorphism (0.8%) between individuals of B. villosus suggesting that B. villosus is a single species with a broader host range than was predicted by host range tests.

Haines M.L., Syrett P., Emberson R.M., Withers T.M., Fowler S.V. and Worner S.P. (2004). Ruling out a host-range expansion as the cause of the unpredicted non-target attack on tagasaste (Chamaecytisus proliferus) by Bruchidius villosus. Proceedings of the XI International Symposium on Biological Control of Weeds: 271-276
This paper describes an investigation of the original host-testing procedures. Despite showing a strong preference for Scotch broom, the beetles tested in this study accepted Chamaecytisus proliferus for oviposition allowing us to rule out the possibility that a host range expansion has occurred.

Hill M.P. and Hulley P.E. (1995). Host-range extension by native parasitoids to weed biocontrol agents introduced to South Africa. Biological Control 5: 297-302.
Host range extension by native parasitoids to insect biocontrol agents of weeds in South Africa were examined. All host range extensions were from native herbivores and occurred within 3 years of release. Poorly concealed endophytic agents were most susceptible to attack, whereas exposed feeders were relatively free from attack.

Kaufman L.V. and Wright M.G. (2009). The impact of exotic parasitoids on populations of a native Hawaiian moth assessed using life table studies. Oecologia 159: 295-304
This study investigated the impact of introduced Hymenoptera parasitoids on the Hawaiian moth Udea stellata (Butler) which has seven alien parasitoids associated with it. The study determined the relative contribution of the seven parasitoid species to the population dynamics of U. stellata. The factors found to contributed to total mortality were: disappearance (42.1%), death due to unknown reasons during rearing (16.5%) and parasitism (4.9%). Adventive parasitoids inflicted greater total larval mortality attributable to parasitism (97.0%) than purposely introduced species (3.0%).

Lesica P. and Hanna D. (2004). Indirect effects of biological control on plant diversity vary across sites in Montana grasslands. Conservation Biology 18: 444-454.
The hypothesis that biological control agents reduce the dominance of the target weed, increasing the native plant diversity was tested. Aphthona nigriscutis was released into grassland sites infested with Euphorbia esula L. on a nature reserve in Montana (U.S.A.) and compared with herbicide treatment. After 5 years, Aphthona release caused a 33-39% decline in Euphorbia aboveground biomass compared with controls at all sites. Other effects of the biocontrol depended on the site. Results suggested that biocontrol reductions in weed dominance was not always associated with increased species diversity. Monitoring of community-level effects should accompany biocontrol introductions on nature reserves.

Louda S.M. (1998). Population growth of Rhinocyllus conicus (Coleoptera: Curculionidae) on two species of native thistles in Prairie. Environmental Entomology 27: 834-841.
Rhinocyllus conicus is a flowerhead weevil deliberately introduced into the USA for the biological control of invasive exotic thistles in the genus Carduus. This study documents the course and magnitude of the weevil population expansion onto nontarget host plants Platte thistle and wavyleaf thistle, a later flowering native species. There is greater phenological synchrony of Platte thistle than wavyleaf thistle flowerhead development with R. conicus oviposition activity. The results suggest that pre-release studies should account for ecological characteristics, such as phenology.

Louda S.M. (1999). Negative ecological effects of the musk thistle biological control agent, Rhinocyllus conicus. Pp. 213-243 In: Nontarget effects of biological control introductions, P.A. Follett and J.J. Duan (Ed.) Kluwer Academic Publishers, Norwell, Massachusetts, USA.

Louda S.M. (2000). Rhinocyllus conicus - insights to improve predictability and minimize risk of biological control of weeds. Proceedings of the X International Symposium on Biological Control of Weeds: 187-193
This paper reviews information on the release of Rhinocyllus conicus to control Carduus spp. thistles in North America and suggests 8 lessons for future biological control efforts: (1) better a priori quantification of the occurrence and ecological effects of the weed; (2) improved ecological criteria to supplement the phylogenetic information used to select plants for pre-release testing; (3) increased assessment of potential direct and indirect effects when an agent looks promising but feeding tests suggest it is not strictly monophagous, (4) quantitative evaluation of the efficacy of the proposed biological agent (5) more evidence on alternative control methods; (6) expanded review, both prior to release and periodically afterward; (7) addition of post-release evaluations and redistribution control; and, finally, (8) a rethinking of the situations that qualify for the use of biological control releases.

Louda S.M. and Arnett A.E. (2000). Predicting non-target ecological effects of biological control agents: evidence from Rhinocyllus conicus. Proceedings of the X International Symposium on Biological Control of Weeds: 551-567
The significant non-target ecological effects of Rhinocyllus conicus on native species in the northcentral USA provides the opportunity to evaluate factors that might help predict direct non-target effects, and indirect effects mediated by trophic interactions. The relevance for biocontrol risk assessment of at least four important ecological relationships has emerged from these studies so far: (1) ecological and phylogenetic similarity of potential host plants; (2) synchrony of critical stages between insect and potential host plant(s), as well as acceptability; (3) population limiting processes of potential host plants; and, (4) overlap of feeding niche within the native guild of species dependent upon the host plants. In the selection of biocontrol agents, knowledge of the ecological relationships should help to quantify the risks inherent in deliberate introductions of new species.

Louda S.M. and O'Brien C.W. (2002). Unexpected ecological effects of distributing the exotic weevil, Larinus planus (F.), for the biological control of Canada thistle. Conservation Biology 16: 717-727.

Louda S.M., Kendall D., Connor J. and Simberloff D. (1997). Ecological effects of an insect introduced for the biological control of weeds. Science 277: 1088-1090.
The weevil Rhinocyllus conicus, introduced to control exotic thistles, has exhibited an increase in host range as well as continuing geographic expansion, in the USA and Canada. Weevils significantly reduce seed production of native thistles, and density of native tephritid flies was lower at high weevil density.

Louda S.M., Pemberton R.W., Johnson M.T. and Follett P.A. (2003). Nontarget effects - the Achilles' heel of biological control? Retrospective analyses to reduce risk associated with biocontrol introductions. Annual Review of Entomology 48: 365-396.
Ten projects with quantitative data on nontarget effects were reviewed and the patterns which emerged were discussed. The review lead to six recommendations: avoid using generalists or adventive species; expand host-specificity testing; incorporate more ecological information; consider ecological risk in target selection; prioritize agents; and pursue genetic data on adaptation.

Louda S.M., Rand T.A., Arnett A.E., McClay A.S., Shea K. and McEacherne A.K. (2005). Evaluation of ecological risk to populations of a threatened plant from an invasive biocontrol insect. Ecological Applications 15: 234-249.
The risk to the rare, Pitcher's thistle (Cirsium pitcheri) in North America from Rhinocyllus conicus, a biological control weevil now feeding on many native thistles, was evaluated. It was hypothesized that quantification of host specificity and potential phenological overlap between insect and plant would improve assessment of the magnitude of risk. In laboratory host specificity tests, we found no significant difference in R. conicus feeding or oviposition preference between the rare C. pitcheri and the targeted exotic weed (Carduus nutans) or between C. pitcheri and Platte thistle (C. canescens), a native North American species also known to be affected by R. conicus. Results of the study indicated that the weevil poses a serious risk to the threatened C. pitcheri, supporting the suggestion that ecological data can be used to improve the quantification of risk to native nontarget plant populations within the potential physiological host range of a biological control insect.

Louda S.M., Rand T.A., Russell F.L. and Arnett A.E. (2005). Assessment of ecological risks in weed biocontrol: Input from retrospective ecological analyses. Biological Control 35: 253-264.
Quantitative retrospective analyses of ongoing biocontrol projects provide a systematic strategy to evaluate and further develop ecological risk assessment. Analyses showed that host range and preference from host specificity tests are not sufficient to predict ecological impact if the introduced natural enemy is not strictly monophagous. The studies demonstrate that the environment influences and can alter host use and population growth, leading to higher than expected direct impacts on the less preferred native host species at several spatial scales, and that easily anticipated indirect effects can be both widespread and significant. It was concluded that intensive retrospective ecological studies provide some guidance for the prospective studies which are needed to assess candidate biological control agent dynamics and impacts

Louda S.M., Simberloff D., Boettner G., Connor J. and Kendall D. (1998). Insights from data on the nontarget effects of the flowerhead weevil. Biocontrol News and Information 19: 70N-71N.

Mafokoane L.D., Zimmermann H.G. and Hill M.P. (2007). Development of Cactoblastis cactorum (Berg) (Lepidoptera : pyralidae) on six north American Opuntia species. African Entomology 15: 295-299
The recent arrival and spread of Cactoblastis cactorum in North America has raised concerns for the native Opuntia species. The host range of the moths was examined in South Africa. Results showed that although O. ficusindica is the preferred host for C. cactorum in South Africa, the moth is nevertheless able to utilize several other species of Opuntia as hosts.

McEvoy P.B. and Coombs E.M. (1999). Why things bite back: unintended consequences of biological weed control. Pp. 167-194 In: Nontarget effects of biological control introductions, P.A. Follett and J.J. Duan (Ed.) Kluwer Academic Publishers, Norwell, Massachusetts, USA.

McEvoy P.B., Karacetin E. and Bruck D.J. (2008). Can a pathogen provide insurance against host shifts by a biological control organism? Pp. 37-42 In: Proceedings of the XII International Symposium on Biological Control of Weeds, (Ed.) La Grande Motte, France, 22-27 April, 2007.
The cinnabar moth, Tyria jacobaeae (L.) (Lepidoptera: Arctiidae is less effective than alternatives (such as the ragwort flea beetle Longitarsus jacobaeae (Waterhouse) Coleoptera: Chrysomelidae) for controlling ragwort, Senecio jacobaea L. (Asteraceae), and it attacks non-target plant species. It also carries a disease (a host-specific microsporidian Nosema tyriae). We used a life table response experiment to estimate the independent and interacting effects of Old World and New World host plant species (first trophic level) and the entomopathogen (third trophic level) on the life cycle and population growth of the cinnabar moth (second trophic level). We found the population growth rate of the cinnabar moth is sharply reduced on novel compared with conventional host plants by interacting effects of disease and malnutrition. Paradoxically, a pathogen of the cinnabar moth may enhance weed biological control by providing insurance against host shifts.

Palmer W.A., Day M.D., Kunjithapatham D., Snow E.L. and Mackey A.P. (2004). Analysis of the non-target attack by the lantana sap-sucking bug, Aconophora compressa , and its implications for biological control in Australia. Pp. 341-344 In: 14th Australian Weeds Conference. Weed management: balancing people, planet, profit, B. M. Sindel and S. B. Johnson (Eds.) Wagga Wagga, New South Wales, Australia, 6-9 September 2004

Paynter Q., Martin N., Berry J., Hona S., Peterson P., Gourlay A.H., Wilson-Davey J., Smith L., Winks C. and Fowler S.V. (2008). Non-target impacts of Phytomyza vitalbae a biological control agent of the European weed Clematis vitalba in New Zealand. Biological Control 44: 248-258
The agromyzid leaf-mining fly Phytomyza vitalbae, which was introduced into New Zealand as a biological control agent of the invasive vine Clematis vitalba L. (old man's beard; Ranunculaceae) has been recorded attacking two native Clematis species in New Zealand, particularly C. foetida but at lower incidence and levels of attack than the target. No-choice starvation tests indicated that non-target attack was a "spillover" effect that is unlikely to have a major detrimental impact on the non-target plants. Our results show that the prevalence of spillover onto non-target species was underestimated in pre-release testing and we discuss how host-range testing might be improved in the light of these findings.

Pearson D.E. and Callaway R.M. (2005). Indirect nontarget effects of host-specific biological control agents: Implications for biological control. Biological Control 35: 288-298.
Recent case studies of indirect nontarget effects of biological control agents were evaluated in the context of theoretical work in community ecology. Although difficult to predict, all indirect nontarget effects of host specific biological control agents derived from the nature and strength of the interaction between the biological control agent and the pest. It was concluded that safeguarding against indirect nontarget effects of host-specific biological control agents depends on host specific and efficacious biological control agents.

Pratt P.D., Rayamajhi M.B., Center T.D., Tipping P.W. and Wheeler G.S. (2009). The ecological host range of an intentionally introduced herbivore: A comparison of predicted versus actual host use. Biological Control 49: 146-153.

Rand T.A. and Louda S.M. (2006). Invasive insect abundance varies across the biogeographic distribution of a native host plant. Ecological Applications 16: 877-890
The authors quantified the abundance of the introduced and now invasive biocontrol weevil, Rhinocyllus conicus, on a newly adopted native host plant, Cirsium canescens (Platte thistle), across the plant's distributional range using regression and structural equation analyses. R. conicus now occurs throughout the-majority of the range of C. canescens, and were highest in the center of the native plant's distribution where its coevolved, targeted weed host (Carduus nutans, musk thistle) is absent. In addition to biogeographic position, the only other consistent predictor of weevil densities across sites was the number of flower heads per C. canescens plant. The results were consistent with the hypothesis that exotic weevil abundance on C. canescens is related to the local availability of native floral resources. Results suggest that isolated, peripheral populations of C. canescens are likely to be critical for persistence of Platte thistle.

Seymour, C.L. and Veldtman, R. (2010). Ecological role of control agent, and not just host-specificity, determine risks of biological control. Austral Ecology 35: 704-711
Gall-formers are popular as biological control agents because they are host-specific and therefore considered low risk. However, galls can also be considered to be ecological engineers, because they provide nutritional resources for native invertebrates. The Authors tested whether native invertebrates had formed associations with the gall-forming fungus Uromycladium tepperianum, introduced into South Africa to control the Australian invasive alien tree Acacia saligna, by collecting U. tepperianum galls and monitoring emergence. A number of invertebrates had formed associations with the biological control agent, including the citrus pest, Thaumatotibia leucotreta (false codling moth). The study illustrated a case of a host-specific classical biological control agent providing resources for an economically significant crop pest. The authors concuded that although biological control agents are strictly vetted to ensure host-specificity, those that become abundant and can act as ecological engineers pose risks when native biota form associations with them, resulting in a number of possible cascading ecosystem effects. There could also be economic consequences when these associated species include agricultural pests. Potential ecological effects of biological control agents, should be considered in their selection.

Shea K., Kelly D., Sheppard A.W. and Woodburn T.L. (2005). Context-dependent biological control of an invasive thistle. Ecology 86: 3174-3181.
Success of biological control of Carduus nutans using insects that attack rosettes or developing seed heads, has varied in different parts of its invaded range. Here a demographic matrix models is used to compare populations in Australia and New Zealand, to explain differences. In a New Zealand population, rapid population growth of C. nutans is driven by early life history transitions. In an Australian population, fecundity of C. nutans is of reduced importance, and survivorship of rosettes plays an increased role. These differences suggest how biocontrol agents that are successful at providing control in one situation but may fail in another.

Taylor D.B.J., Heard T.A., Paynter Q. and Spafford H. (2007). Nontarget effects of a weed biological control agent on a native plant in Northern Australia. Biological Control 42: 25-33
Pre-release laboratory tests predicted that Neurostrota gunniella, an agent released in Australia against Mimosa pigra, may occasionally use Neptunia spp. as hosts. However, it was not expected to persist on Neptunia spp., nor have a significant effect. N. gunniella has established widely and is now abundant on the target weed, which grows sympatrically with at least one species of Neptunia. Nontarget attack of Neptunia major in the field has been investigated, and although an average of 61% of N. major plants growing adjacent to M. pigra thickets had evidence of attack, this was relatively low. Where M. pigra was not present, use of N. major plants by N. gunniella was noticeably reduced or absent. Post-release results support the predictions made during prerelease studies of N. gunniella.

Thomas H.Q., Zalom F.G. and Roush R.T. (2010). Laboratory and field evidence of post-release changes to the ecological host range of Diorhabda elongata: Has this improved biological control efficacy? Biological Control 53 (3): 353-359

Watson M.C., Withers T.M. and Hill R.L. (2009). Two-phase open-field test to confirm host range of a biocontrol agent Cleopus japonicus. New Zealand Plant Protection 62: 184-190.
The buddleia leaf weevil, Cleopus japonicus, was released in New Zealand in 2006 as a biological control agent for the weed Buddleja davidii. A field study investigated any impacts on six non-target plant species since release. C. japonicus strongly preferred B. davidii, but larvae were recorded on Verbascum virgatum and Scrophularia auriculata during the choice stage of the trial. Removing B. davidii plants resulted in adults feeding on the same two exotic species. Minor exploratory feeding was recorded on the natives Hebe speciosa and Myoporum laetum. These results confirm that laboratory tests have accurately predicted field host range.

Willis A.J. and Memmott J. (2005). The potential for indirect effects between a weed, one of its biocontrol agents and native herbivores: A food web approach. Biological Control 35: 299-306.
Constructing and analyzing food webs may be a valuable for assessing the post-release safety of control agents. How food webs can be used to generate testable hypotheses regarding indirect interactions between introduced agents and non-target species is shown using an exotic weed, bitou bush, Chrysanthemoides monilifera ssp. rotundata, and a key biocontrol agent for this weed in Australia, the tephritid fly, Mesoclanis polana. Food webs showed the interactions between plants, seed-feeding insects and their parasitoids.

Withers T.M., Hill R.L., Paynter Q., Fowler S.V. and Gourlay A.H. (2008). Post-release investigations into the field host range of the gorse pod moth Cydia succedana Denis & Schiffermuller (Lepidoptera : Tortricidae) in New Zealand. New Zealand Entomologist 31: 67-76
The gorse pod moth Cydia succedana was released in New Zealand as a biological control agent against gorse Ulex europaeus L. in 1992 and is now widely established. Post-release evaluations of host range were undertaken using both laboratory assays and field collections on native and exotic plants related to gorse. Field surveys detected no attack on native New Zealand plant species. However, contrary to predictions based on pre-release host-range testing, several species of exotic Genisteae were shown to be hosts of C. succedana. Hypotheses to explain this unexpected non-target attack include a seasonal asynchrony between C. succedana and gorse flowering phenology, or that the original biocontrol introduction accidentally consisted of either two cryptic species or two populations with different physiological host range.