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The broom leaf beetle (Gonioctena olivacea) and the Honshu white admiral butterfly (Limenitis glorifica) have been introduced into New Zealand as biocontrol agents of the weeds Scotch broom (Cytisus scoparius) and Japanese honeysuckle (Lonicera japonica) respectively. However, neither agent has been successful yet. Larval predation of these species could be a factor affecting their success, and this hypothesis was tested using various predator-exclusion treatments. Survival of broom leaf beetle larvae increased c. five-fold by sleeving Scotch broom seedlings in fine mesh. In contrast, survival was unaffected by excluding either crawling predators using sticky barriers or larger predators using chicken wire. Survival of Honshu white admiral butterfly larvae increased c. ten-fold by excluding either crawling predators using sticky barriers or flying predators using a fine-mesh sleeve. Simultaneously excluding both crawling and flying predators resulted in a c. 23-fold increase in survival. These results suggest that larval predation could be limiting the populations of both broom leaf beetle and Honshu white admiral. Future biocontrol programmes could prioritise candidate agents accordingly.

The bacterium, Candidatus Liberibacter europaeus (Leu) was reported in New Zealand (NZ) in 2011 in Scotch broom, Cytisus scoparius Link, and its biocontrol agent, Arytainilla spartiophila Forster (Hemiptera: Psyllidae). The aim of the study was to investigate the pathway by which Leu arrived in NZ using a retrospective risk assessment of Leu being accidentally imported with the broom psyllids in the 1990s. We developed species-specific primers for Leu detection and carried out end-point and real-time PCR analyses for Leu in potential host plants and broom psyllids throughout NZ to test two hypotheses: 1) Leu was accidentally released in NZ in broom psyllids in 1993; or 2) Leu was present in NZ pre-1993, and maintained in cultivated plants via cuttings/grafting, or in wild Scotch broom populations via shared parasitic plants. There was strong evidence to support the arrival of Leu with broom psyllids in NZ. Firstly, methods used to import broom psyllids from the UK provided a likely pathway for inadvertent release of Leu, which at the time was unknown to science, into NZ. Secondly, Leu in NZ Scotch broom plants was significantly associated with the presence of broom psyllids, with Leu absent from plants at sites without psyllids. In contrast, there was no evidence suggesting Leu was present in NZ before the release of broom psyllids: Leu was not found in ornamental brooms or pears, Pyrus communis L. (a Leu host in Europe), and parasitic plants were too uncommon to maintain Leu in wild Scotch broom. In addition, Leu in UK Scotch broom and broom psyllids has a matching partial 16S sequence to NZ Leu. It remains uncertain whether Leu is pathogenic in Scotch broom, or symptomless as in pears. Unpredictable impacts of Ca. Liberibacter spp. in different plant species probably implies that psyllids considered as future weed biocontrol agents will need to be free of these potential plant pathogens. This accidental introduction of Candidatus Liberibacter europaeus into NZ via a weed biocontrol agent happened because detection methods for unculturable organisms were not developed at the time. Molecular characterisation of insect microbiomes could become an essential procedure for pre-release safety screening of biocontrol agents that are potential vectors of plant pathogens.

We investigated the influence of biological control agent rearing success on weed biocontrol programs in New Zealand. Difficulties have been experienced in rearing approximately one third of all arthropod species imported into New Zealand containment as candidate weed biocontrol agents, and 16% of species could not be reared at all. Rearing success did not prevent agents from being approved for release because host-range testing of difficult to rear species was often completed in the native range using field-collected material. In the past, agents that could not be easily reared were directly released using field-collected material, often in large numbers. Since 1984, this approach has become harder due to the regulatory requirement for agents to be screened for the presence of pathogenic organisms, and so direct releases have been limited to very small numbers (

We tested the hypothesis that quantifying the relative performance of candidate weed biocontrol agents on test and target plants during laboratory host-range testing can predict the probability of test plants being attacked in the field. For arthropod weed biocontrol agents established in New Zealand between 1929 and 2010, the probability of host use was positively correlated with relative performance for both no-choice starvation tests and no-choice oviposition tests. Moreover, multiplying together the relative performance scores for no-choice starvation and oviposition tests to create a combined risk score for no-choice tests resulted in a clear-cut threshold indicating that for scores between 0.21 and 0.33 the probability of host use (including minor spillover attack) occurring rose from close to zero to a virtual certainty. Choice oviposition test data showed a similar pattern to no-choice data, except there were two cases where host use occurred in the field on plant species that had very low relative performance scores in the choice tests. Both of these cases were associated with asynchrony between seed-feeding biocontrol agent activity and the reproductive phenology of the target plant, indicating that choice tests may be inappropriate for certain guilds of biocontrol agent that attack ephemeral plant structures. We conclude that quantitative laboratory testing data can help predict risk of non-target attack. The ability to refer to threshold relative performance scores when deciding whether an agent is safe to release has the potential to ensure fewer environmentally safe candidate biocontrol agents are erroneously rejected, thereby enhancing efficiency in the selection and approval of new agents.

The boneseed leafroller moth Tortrix s.l. sp. ‘chyrsanthemoides’ (BSLR), originating from Western Cape Province, South African was introduced into New Zealand for the biological control (biocontrol) of a South African shrub boneseed Chrysanthemoides monilifera ssp. monilifera but has established only patchily. We investigated factors hypothesized to influence its establishment success. Field surveys and manipulative experiments ruled out climate as a factor and indicated that establishment failure was associated with predation, mainly by invasive ants of South American (Linepithema humile), and Australian (Doleromyrma darwiniana; Nylanderia sp.) origin that were attracted to invasive honeydew-secreting scale insects (Parasaissetia nigra and Saissetia oleae) found on boneseed. An exclusion experiment showed that unless invertebrate predators (mainly invasive ants and Vespula and Polistes wasps) were excluded, BSLR larvae did not survive to maturity on boneseed plants infested with scale insects. This study supports the notion that insect agents that feed externally on the host-plant are susceptible to predation in the presence of ant-tended Homoptera and that if ant-tended Homoptera are present, candidate agents should be prioritized accordingly.

The direct and indirect interactions of invasive ants with plants, insect herbivores, and Hemiptera are complex. While ant and Hemiptera interactions with native plants have been well studied, the effects of invasive ant–scale insect mutualisms on the reproductive output of invasive weeds have not. The study system consisted of Argentine ants (Linepithema humile), boneseed (Chrysanthemoides monilifera monilifera), and sap-sucking scale insects (Hemiptera: Saissetia oleae and Parasaissetia nigra), all of which are invasive in New Zealand. We examined the direct and indirect effects of Argentine ants on scale insects and other invertebrates (especially herbivores) and on plant reproductive output. Argentine ants spent one-third of their time specifically associated with scale insects in tending behaviours. The invertebrate community was significantly different between uninfested and infested plants, with fewer predators and herbivores on ant-infested plants. Herbivore damage was significantly reduced on plants with Argentine ants, but sooty mould colonisation was greater where ants were present. Herbivore damage increased when ants were excluded from plants. Boneseed plants infested with Argentine ants produced significantly more fruits than plants without ants. The increase in reproductive output in the presence of ants may be due to increased pollination as the result of pollinators being forced to relocate frequently to avoid attack by ants, resulting in an increase in pollen transfer and higher fruit/seed set. The consequences of Argentine ant invasion can be varied; not only does their invasion have consequences for maintaining biodiversity, ant invasion may also affect weed and pest management strategies.

Summary 1. Natural enemies may reduce the effectiveness of weed biocontrol agents and can also cause environmental damage, for example to a shared native insect host through apparent competition. Indeed, successful biocontrol may rely on enemy-free space and avoidance of apparent competition in the area where the biocontrol agent is introduced. 2. We surveyed parasitism in 28 insects released for weed biocontrol in New Zealand (NZ). We reviewed the global literature and databases to complement this survey, and to collate records of these insects being parasitized in their area of origin. We also collated records of native insects that feed on weeds targeted for biocontrol in NZ to test Lawton’s (1985) hypothesis that, to find enemyfree space, selected agents should ‘feed in a way that is different’ and ‘be taxonomically distinct’ from native herbivores in the introduced range. 3. We found that 19, mostly native, parasitoid species attack 10 weed biocontrol agents in NZ, of which 15 were confined to five agents that possessed ‘ecological analogues’, defined as a native NZ insect that belongs to the same superfamily as the agent and occupies a similar niche on the target weed. Parasitoid species richness in NZ was positively correlated to richness in the area of origin. However, only agents with ecological analogues contributed significantly to this pattern. 4. A review of NZ weed biocontrol programmes indicated that parasitism is significantly associated with the failure of agents to suppress weed populations. 5. Synthesis and applications. Although our conclusions are based on an unavoidably limited data set, we conclude that biocontrol agents that escape attack from parasitoids are more likely to suppress weed populations and should be less likely to have significant indirect non-target effects in food webs. Biocontrol practitioners can reduce the chance of weed biocontrol agents attracting species-rich parasitoid faunas after introduction by (i) selecting agents that have species-poor parasitoid faunas in their area of origin, and ⁄ or (ii) avoiding agents that have ‘ecological analogues’ awaiting them in the introduced range.

Lantana camara is an environmental weed in the northern North Island of New Zealand It is an increasingly observed problem in forest margins coastal scrublands dunes plantations and island habitats and its rapid uncontrolled growth can create dense impenetrable thickets suppressing vegetation and bush regeneration Biological control options are being considered for its management A strain of the Brazilian rust Prospodium tuberculatum was released against lantana in Australia in 2001 This rust was screened against invasive forms of the weed that occur in New Zealand and was found to be pathogenic under glasshouse conditions A survey found no evidence that the rust occurs in New Zealand It is concluded that P tuberculatum is potentially a suitable agent for the biocontrol of lantana in New Zealand and further research should be carried out prior to importation of the organism

The agromyzid leaf-mining fly Phytomyza vitalbae , which was introduced into New Zealand as a biological control agent of the invasive deciduous European vine Clematis vitalba L. (old man’s beard; Ranunculaceae) in 1996, was recorded attacking native non-target Clematis forsteri and Clematis foetida in New Zealand, with C. foetida being most commonly attacked. Both the incidence and levels of P. vitalbae attack were significantly lower on the non-target species, compared to on the target plant and populations of non-target plants that were growing within 4 km of the nearest known patch of C. vitalba were most commonly attacked. No-choice starvation tests indicated that survival of P. vitalbae was low and oviposition did not occur on C. foetida unless flies had previously fed on C. vitalba until they began ovipositing, indicating that non-target attack was a “spillover” effect that is unlikely to have a major detrimental impact on the non-target plants. Parasitoid rearing indicated that P. vitalbae shares parasitoids with a closely related native-leaf-miner Phytomyza clematadi . Therefore, P. vitalbae and P. clematadi potentially compete with each other, mediated through shared parasitoids. However, we found no evidence for increasing levels of parasitism of P. clematadi mines, or for a reduction in P. clematadi abundance on C. foetida with increasing proximity to C. vitalba infestations. Both the direct and indirect non-target impacts of P. vitalbae attack, therefore, appear to be minor. Host-range testing performed prior to the release of P. vitalbae in New Zealand predicted the plant species that were most at risk of non-target attack. Our results show that the prevalence of spillover onto non-target species was underestimated and we discuss how host-range testing might be improved in the light of these findings.

Japanese honeysuckle is rapidly increasing as a weed throughout most of the North Island and northern South Island of New Zealand A classical biological control programme was initiated in 20042005 with a survey of the natural invertebrate fauna and pathogens associated with the weed in New Zealand The honeysuckle was being attacked by a diverse range of native and introduced invertebrates But overall the damage was minimal and none of the herbivore niches on the weed were well utilised implying that exotic agents may have a chance of inflicting additional damage that might be sufficient to control the species Most damage was caused by foliage feeders such as lepidopterous larvae and thrips but this affected less than 5 of total plant biomass Primary and secondary foliar pathogens such as Pseudocercospora lonicerae Colletotrichum gloeosporioides Insolibasidium deformans and Phoma spp were frequently recorded Potential use of these natural enemies for weed biocontrol is discussed

The white smut fungus (Entyloma ageratinae) and the gall Xy (Procecidochares alani) were released in New Zealand in 1998 and 2001 respectively to suppress mist Xower (Ageratina riparia). The fungus established and spread rapidly, crossing 80 km of sea to Great Barrier Island within 2 years. The mean number of P. alani galls increased exponentially to 1.96/stem at release sites, but dispersal was slow. The impact of the biocontrol agents was monitored once annually from 1998/99 to 2003/04, at up to 51 sites in the North Island. The mean percentage of live leaves infected with fungus rapidly reached nearly 60%. Maximum plant height declined signiWcantly. In heavy infestations, mean percentage cover of mist Xower declined from 81 to 1.5%. Galls were only recorded towards the end of the impact study, and at low mean numbers. As mist Xower declined, the species richness and mean percentage cover of native plants increased. In contrast, the species richness and mean percentage cover of exotic plants (excluding mist Xower) did not change signiWcantly. Many plant species colonizing the plots were important native mid- or late-successional shrubs or trees. With few exceptions, the exotic plant species common in the plots were not weeds that appeared to threaten native forest habitats. There was only a weak “replacement weed eVect” from the potentially serious invader African club moss (Selaginella kraussiana). These data, together with reports of reduced threats to rare endemic plants from mist Xower, suggest this rapid, well-monitored weed biocontrol program was very successful.

Moth plant, Araujia sericifera, is an environmental weed in northern regions of New Zealand. Due to its rapid spread, its ability to cause substantial damage to natural ecosystems and the increasing cost of conventional control methods, a biological control programme was initiated. A survey of the plant in New Zealand found that damage attributed to either disease or insect herbivory was minimal with little biocontrol potential. Botanical, pathogen and insect surveys were subsequently initiated in the native South American range to locate and identify potential agents for classical biocontrol. Potential agents associated with plant damage were collected. Damage was mostly due to pathogenic attack with 90% of moth plant populations showing disease symptoms. To date, eight fungal pathogens have been associated with plant die back, leaf necroses and a severe fruit rot. At least two mosaic (virus) diseases were also found, frequently associated with colonies of the aphid, Aphis nerii.

The Mercury Islands tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae), occurs naturally only on Middle Island, a 13 ha island in the Mercury Island group, New Zealand. Growth and development were studied to support a conservation programme to establish them on two other islands and thereby reduce chances of accidental extinction. The egg incubation period was determined from 784 eggs laid by eight weta (range 6-275 eggs per female) exposed to varying temperature similar to Middle Island. Most eggs (240) hatched after 12-39 weeks but 17 eggs laid in late winter hatched after 48-63 weeks. Overall, 87% hatched between October and December, and all hatched between August and February. Egg mortality was 67% (range 50-100% for individual females). Growth and postembryonic development was observed in the laboratory at 16-18°C, and a 14 : 8 h (light : dark) photoperiod. Males and females became adult at either the 10th or 11th instar. Lengths of the head, head with jaws, pronotum, protibia, tympanal me...

Boneseed, Chrysanthemoides monilifera ssp. monilifera, is a serious invasive weed in New Zealand, particularly in coastal habitats throughout the North Island, northern parts of the South Island, and in the Port Hills near Christchurch. The invertebrate fauna associated with boneseed in New Zealand was surveyed in 1999-2000 as part of a biological control programme for the weed. Boneseed is attacked by a wide range of native and exotic insects but damage is usually not severe. Potential biological control agents that feed on foliage or seeds are unlikely to meet with significant competition from species already resident in this country. However, the combined effect of generalist predators, such as Argentine ants and spiders, and parasitoids could inhibit the effectiveness of some of the invertebrates that would be potential biological control agents. In New Zealand, most (if not all) herbivore niches on boneseed are under-utilised, and there is considerable scope for the introduction of specialised invert...

The safety record of weed biocontrol was questioned recently when examples of damage to non-target plants were reported overseas. Until now, systematic investigations of non-target feeding have not been performed in New Zealand. Results of surveys looking for evidence of non-target damage caused by 20 biological control agents released against weeds in New Zealand are presented. Most agents (16) are apparently host-specific. However, two species (Tyria jacobaeae and Phytomyza vitalbae) were recorded attacking native plants, although their attack was very minor and predictable from host-range testing performed prior to release. For two other species, Bruchidius villosus and Cydia succedana, non-target attack was not predicted from host-range testing. Larval feeding by these species was confined to mainly weedy, exotic plants that are closely related to their target plants. The reliability of host-specificity testing and overall safety record of weed biological control in New Zealand are discussed.

In the native range of Tradescantia fluminensis in SE Brazil surveys revealed a natural enemy biota attacking the plant that was rich in potential biocontrol agents for New Zealand (NZ), including nine fungi and 10 herbivorous insect species. Similar surveys in NZ, where T. fluminensis is an invasive exotic weed, revealed no specialist insect herbivores or pathogens. The Brazilian insect herbivores included leafmining, stemboring and gall-forming feeding guilds that were absent in NZ. Mean foliar damage levels per site on T. fluminensis were 7.8× higher for folivores in Brazil cf. NZ, and 21.2× higher for pathogens. The presence of rust pustules, or ‘brown lesions’, on leaves in Brazil was negatively associated with damage by folivores, perhaps indicating an antagonistic interaction. In contrast, damage by the white smut fungus, Kordyana sp., was not negatively associated with folivore damage. Mean dry biomass of T. fluminensis was significantly lower in Brazil (164 g m−2) cf. NZ (455 g m−2). In NZ, 85% of sites had biomass measures >200 g m−2 (the previously determined threshold above which native forest regeneration fails). In Brazil, only 27% of sites had biomass measures >200 g m−2. Among the insect herbivores, three chrysomelid beetles, Neolema ogloblini, Neolema abbreviata and Lema basicostata were prioritised as potential biocontrol agents. Their larvae cause potentially complementary damage to leaves, shoot-tips and mature stems, respectively. Several pathogens, including a rust, were rejected before we selected the Kordyana species. Host range testing of all four agents showed sufficient host-specificity for consideration for release in NZ. Neolema ogloblini and L. basicostata were field-released in NZ in 2011 and 2012, with the field-release of N. abbreviata due late 2012. An application to release Kordyana sp. in NZ has been made.

Puccinia myrsiphylli is reported for the first time on weed infestations of Asparagus asparagoides in New Zealand, where it is concluded to have been introduced either accidentally or autonomously by way of wind-dispersed spores. A detailed description, illustration and genetic sequence of the specimen are provided.

We explored the spatial structure of seed size variation and tested whether seed size differed between native and exotic populations in two invasive species. Seed of Cytisus scoparius (Scotch broom) is significantly heavier in its exotic range, whereas seed of Ulex europaeus (European gorse) is no different between ranges. This result suggests that seed size in C. scoparius is either adaptively or phenotypically responsive to conditions in its exotic range or that plants with large seeds were preferentially introduced. We found that modern ornamental broom seed was no bigger than seed from natural or naturalized populations, suggesting that large seed size in the exotic range is not due to preferential introduction of ornamental varieties with large seeds. Most previous studies of trait differences between native and exotic ranges in invasive species have not taken variation throughout the ranges into account. This is the most comprehensive survey of seed size variation in any species, and the first time that variation in a trait of an invasive species has been studied from individual plant level up to global ranges. Demographic rates can be affected by seed attributes making this study an important first step in understanding how population processes may differ between native and exotic ranges.