Host specificity, establishment and dispersal of the gorse thrips, Sericothrips staphylinus Haliday (Thysanoptera: Thripidae), a biological control agent for gorse, Ulex europaeus L. (Fabaceae), in Australia

Sericothrips staphylinus was released as a biological control agent for Ulex europaeus in New Zealand and Hawaii following tests on ca. 80 plant species which showed it was narrowly oligophagous. To determine the suitability of S. staphylinus for release in Australia, further host specificity tests were conducted on 38 species and cultivars of Australian plants. These tests confirmed that S. staphylinus would feed only on U. europaeus in Australia and, following formal approval, was released in Tasmania during January 2001. To develop an optimal release strategy for S. staphylinus under Australian conditions, a field trial based on an earlier New Zealand study was conducted by replicating releases of 10, 30, 90, 270 and 810 adults. Results showed that population growth, reproduction rate and the number of S. staphylinus recovered 14 months after release can be non-linear functions of release size and establishment could be achieved with as few as 10 thrips. As S. staphylinus is easily cultured ca. 250 thrips were chosen as the minimum number for release because, based on a negative binomial model, this release size produced close to the maximum population growth. Surveys in early 2007 recovered S. staphylinus from 80% of 30 sites in Tasmania, the post release period ranging from 1 to 6 years. However, densities were low (<1 thrips/cm of tip growth) with no evidence of visible plant damage. The maximum dispersal range was 180–250 m after 38 months. At all the other sites, dispersal was estimated at less than 120 m. It is possible that S. staphylinus populations are still in the lag phase of their establishment before starting to increase rapidly and disperse. However, the survey results support a recent Tasmanian study which indicated that S. staphylinus is a sedentary, latent species characterised by steady densities and low levels of damage to its host plant. Its efficacy as a biological control agent on gorse may be restricted primarily by ‘bottom up’ effects of plant quality limiting its rate of natural increase and an inability of the thrips to reach large, damaging populations under field conditions.     

The influence of host plant genotype on variation in population densities of the gorse thrips,Sericothrips staphylinus (Thysanoptera: Thripidae), and its consideration in relation to release strategies

Large variations in population densities of Sericothrips staphylinus were observed between gorse bushes at a field site in an earlier Tasmanian study. A replicated potted plant experiment was conducted to assess whether genetic variation between gorse bushes could affect densities of S. staphylinus. There were significant differences in the number of S. staphylinus recovered from the individual bushes sampled within sites and individual bushes across all sites. This provides evidence that genetic variation between gorse bushes is at least partly responsible for the observed variability in field populations. The result validates the current release strategy used for the field establishment of S. staphylinus in south-eastern Australia. This strategy involves making multiple small releases (ca. 250 adults per bush per site) instead of a small number of large releases (ca. 1000 per bush per site), thereby reducing variation in numbers due to genetic affects. Genetic variation between individual plants of the same species and associated effects on herbivore densities should be considered when devising release strategies for biological control agents.     

Suitability of Agonopterix ulicetella (Lepidoptera: Oecophoridae) as a Control for Ulex europaeus (Fabaceae: Genisteae) in New Zealand

The larvae of Agonopterix ulicetella (Stainton) (Lepidoptera: Oecophoridae) feed on the green foliage of gorse, Ulex europaeus L., and this insect is a potential biological control agent of this weed in New Zealand. The biology of the insect is described and its known parasitoids are listed. In experiments to measure oviposition preference, 46 plant species from 11 families were exposed to adult moths. Gorse was highly preferred over other plants, and there was no oviposition on 33 species tested. Eggs were found on Spartium junceum, Chamaecytisus palmensis, Lupinus arboreus, L. polyphyllus, Genista tinctoria and occasionally on eight other species. In experiments to measure the ability of first instar larvae to feed on 70 test plant species, 59 did not support development beyond the first instar and only seven species supported development to the pupal stage. These results show that under laboratory conditions this moth can lay its eggs and complete development on five members of the tribe Genisteae other than gorse. A. ulicetella was released in New Zealand in 1990 but has not yet established.     

Reproductive isolation betweenTetranychus lintearius and two related mites,T. urticae andT. turkestani (Acarina: Tetranychidae)

Gorse,Ulex europaeus L. (Leguminosae), is a serious weed in New Zealand and some other temperate parts of the world.Tetranychus lintearius Dufour (Tetranychidae) has been released in New Zealand as a biological control agent for the weed. Before it could be introduced from Europe, it was necessary to show thatT. lintearius is reproductively isolated from closely related pest mites.Crosses and reciprocal crosses were made betweenT. lintearius and four populations ofT. urticae Koch, and betweenT. lintearius and one population ofT. turkestani (Ugarov and Nikolski). In a second experiment, males of a second population ofT. lintearius were crossed with females of fiveT. urticae populations. The sex-ratio of F₁ progeny in both experiments suggested thatT. lintearius was reproductively isolated from the other species, and could therefore be used as a biological control agent for gorse.     

Bone-seed (

Bone-seed, Chrysanthemoides monilifera ssp. monilifera (L.), is an environmental weed of coastal vegetation communities scattered throughout New Zealand. To assess the long-term implications for native forest regeneration in sites where bone-seed is present, we selected four study sites around Wellington, New Zealand, where bone-seed was abundant. We compared seed bank composition in bone-seed-invaded sites with nearby native forest patches, and monitored bone-seed and native seedling recruitment with and without control of mature bone-seed plants. We also tested the potential effects of fire on bone-seed recruitment in these communities by heating seeds prior to germination. Bone-seed, gorse (Ulex europaeus), and native species emerged from seed bank samples taken from bone-seed-invaded sites, but only native species and (less) gorse emerged from seed bank samples taken from native forest patches. Gorse germination was strongly promoted by heat but bone-seed germination was less affected by heat. Bone-seed seedling abundance increased dramatically following canopy removal, whereas native seedling abundance decreased dramatically. This suggests that disturbance of any form is likely to favour recruitment of bone-seed (and gorse) over native species, although in the long term, native seedlings can establish beneath the canopy of mature bone-seed plants. It is not yet known if, in the absence of further disturbance, regenerating native vegetation will eventually replace bone-seed in New Zealand.     

Sex Attractant-based Monitoring of a Biological Control Agent of Gorse

Cydia succedana (Denis & Schiffermuller) has been introduced into New Zealand for the biological control of gorse seeds (Ulex europaeus). Traps baited with a sex attractant were developed for monitoring the flight timing and number of adult male moths, and were used as a new tool for monitoring the establishment, phenology and efficacy of the agent. The best lure tested was (E,E)-8,10-dodecadien-1-yl acetate, although high catches were also made with the E,Z isomer. There was no difference in the total catch across a range of doses from 1 to 300 mug/lure (7151 insects caught). Male flight was recorded at the bottom, middle and top of a hillside between 280 and 370 m altitude, along with the percentages of plants at each site bearing flowers and seed pods. There was an initial seasonal linkage between the catch of males and plant phenology, but a lack of synchrony was evident between the insect and the plant in the second generation, indicating a potentially important limitation for biological control at this site. The prospects for using sex attractants in traps as an aid for monitoring populations of weed biological control agents are excellent. Other potential applications include the costeffective detection of establishment and the determination of the optimal size of founding populations to ensure establishment of control agents.     

Favourable Conditions for the Bioherbicide Candidate Fusarium tumidum to Infect and Cause Severe Disease on Gorse (Ulex europaeus) in a Controlled Environment

The development of the pathogenic fungus Fusarium tumidum on gorse ( Ulex europaeus ), a major weed of pastures and plantation forests in New Zealand, was studied under controlled conditions. F. tumidum , like most other foliar fungal pathogens, requires moisture to infect plants. Long, continuous dew periods ( 24 h) after inoculation of plants provided favourable conditions for infection. The fungus, however, also caused severe disease on young plants (2 months old) exposed to two or three 12-h dew periods interrupted by 12-h dry periods. A delay of 24 h before inoculated plants were exposed to dew did not affect the severity of the disease. F. tumidum infected plants over a wide range of temperatures (5-27IC), but more plants were killed as temperatures increased during the initial infection phase. All gorse plants tested (up to 4 months old) were susceptible to the fungus, but younger plants were more easily killed. Nevertheless, the biomass of older plants that were severely diseased but not killed by the fungus was significantly reduced. The effectiveness of F. tumidum in killing plants increased with the density of inoculum sprayed. The fungus applied at a density of 1 106 conidia/ml killed more than 95% of 1.5-month-old plants. This basic knowledge of the F. tumidum -gorse system will assist in the development of a pilot bioherbicide to control gorse and broom ( Cytisus scoparius ), another economically important weed in New Zealand which is also susceptible to the fungus.     

Minimum threshold for establishment and dispersal of Lilioceris cheni (Coleoptera: Chrysomelidae): a biological control agent of Dioscorea bulbifera

The successful establishment or failure of a new population is often attributed to propagule pressure, the combination of the number of independent introduction events, and the number of individuals released at each event. The design of optimal release strategies for biological control agents benefits from an understanding of the impact of propagule pressure on the species being released. The dispersal rate of individuals from nascent population foci can also affect establishment success. We assessed the minimum threshold for establishment and measured dispersal of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent for Dioscorea bulbifera (Dioscoreales), air potato. Replicated releases of 10, 50, and 100 adults of L. cheni were conducted on the east and west coasts of south Florida. Dispersal was measured from 19 of these sites plus 19 additional release locations in south and central Florida. Lilioceris cheni established populations from all three release sizes with no apparent influence of site location. Releases of 10, 50, and 100 adults resulted in 50%, 67%, and 85% establishment, respectively. Beetles dispersed an average of 1.41?±?0.515?km/yr. Dispersal distance was significantly affected by the time since release but not the number of individuals released. Our results suggest that future releases of 100 individuals could be spaced several kilometres apart on the landscape to facilitate rapid colonisation of D. bulbifera infestations.     

The host range ofTetranychus lintearius (Acarina: Tetranychidae)

The host range ofTetranychus lintearius was examined experimentally to determine if the mite could be safely introduced into New Zealand for the biological control of gorse,Ulex europaeus (Leguminosae: Genisteae). The rationale for choosing test plants was the same as that employed for testing insect species as biological control agents. Outdoors, mite colonies could be transferred successfully from gorse plant to gorse plant, but could not re-establish on any of 39 other plant species progeny to develop, was measured on 58 plant species other than gorse. Apart fromUlex europaeus andU. minor, development was completed only onPhaseolus vulgaris andGlycine max. Further experiments using 22 bean cultivars showed that mites could not complete a second generation on detached leaf cultures, could not form permanent colonies on potted plants in the glasshouse, and remanned only a short time when transferred to bean plants in the field. Tetranychus lintearius has never been recorded from any plant butUlex species. This fact, coupled with the results of host-range testing, suggests that the mite is sufficiently host-specific to be safely used as a biological control agent for gorse in New Zealand.     

Foods of the Dartford warbler Sylvia undata on southern English heathland (Aves: Sylviidae)

This paper describes the invertebrates of Callunetum and gorse on lowland heaths in Dorset and relates how these were exploited by the Dartford warbler Sylvia undata , a scarce bird of interest to nature conservation and one of the small number of wholly insectivorous resident passerines in Britain. Gorse had a denser invertebrate fauna than Callunetum and was used for feeding at a frequency out of proportion to its abundance. Diets of adult birds closely reflected the taxonomic composition of the gorse and Callunetum faunas exploited in the observed proportions, though some noxious taxa were avoided and below a certain limit, creatures of above average size were selected. Major foods were beetles, spiders, lepidopteran larvae and bugs. Nestling birds received a diet differing in taxonomic composition and size from that of the adults, and variations between habitats were found which accorded with observations on the habitat preferences of the Dartford warbler. An experimental investigation showed the importance of gorse as a source of food for young and the adults flew considerable distances ignoring extensive deep stands of heather nearer to the nest. The possible influence of competing insectivorous vertebrates on Dartford warblers is discussed. Various mammals and reptiles appeared to be the major vertebrate predators in Callunetum, but little competition was anticipated in gorse. Scarcity of gorse on the heaths and low densities of invertebrates in heather explained the low densities at which Dartford warblers occur.     

Early establishment and dispersal of the weevil, Mogulones cruciger (Coleoptera: Curculionidae) for biological control of houndstongue (Cynoglossum officinale) in British Columbia, Canada

First released in Canada in 1997 to control the invasive rangeland weed, houndstongue (Cynoglossum officinale), the European root weevil, Mogulones cruciger, is showing early potential as a successful biocontrol agent. Out of 22 experimental releases in southeastern British Columbia, Canada, 100% established, regardless of initial release size (range 100-400). These founding populations persisted beyond 2 years, and quickly dispersed through a treed and variable landscape to colonise new houndstongue patches surrounding the original release patches. Within 3 years, the weevil had moved 1.42 km. Both initial, within-patch and later, between-patch dispersal followed a similar pattern, with M. cruciger adults and/or their feeding/oviposition damage being more concentrated nearest the original points of release and declining with distance. Within-patch, this pattern of distribution and also the rate of spread of weevils were similar regardless of initial release size; suggesting density-independence in dispersal behaviour at this scale. Closer investigation of the sequence of invasion at a larger spatial scale suggested that the weevil arrived at, colonized and increased in number on the closest host patches first. Three years post release, both distance from release patch and the number of M. cruciger released, were significant predictors of the amount of feeding/oviposition damage, and presumably weevil population size, within newly colonized houndstongue patches surrounding the original releases. These data, and the finding that more weevils were retrieved from patches where higher numbers of weevils were released in the previous year (i.e., 300 or 400 vs 100 or 200), suggest that release number and placement of releases within a landscape can be manipulated for effective houndstongue control.     

The foraging ecology of feral goats

Feral goats (Capra hircus) were studied in the Mahoenui giant weta reserve, southern King Country, New Zealand, from March 1992 to February 1993. The reserve supports the main population of the undescribed Mahoenui giant weta (Deinacrida sp.). Gorse (Ulex europaeus) is the dominant woody browse plant in the reserve and provides protection, shelter and food for weta. The activities, foraging behaviour and diet of feral goats within the reserve were measured by direct observation and analysis of rumen contents. Measures of nutrient levels indicate that gorse is adequate for goat growth only during late spring/summer, and becomes a maintenance food at other times of the year. Feeding (grazing and browsing) was the dominant activity of adult feral goats in the reserve. Females spent more time feeding than males. Grazing and browsing changed seasonally for both sexes, with grazing generally decreasing from autumn to summer, and browsing increasing from summer to spring. In every season females spent more time grazing than males, but males browsed more than females. Greater use of browse by males may be an effect of the presence of females. Browsing of gorse by goats may not be an important influence on weta survival.     

Factors affecting the cost of weed biocontrol programs in New Zealand

Many national schemes for setting priorities for invasive weed management have emphasized the current or future impacts of the weed more than the cost or feasibility of control, perhaps because the latter may be difficult to estimate. As part of a project to improve prioritization of weed biocontrol targets in New Zealand, we investigated factors that were hypothesized to influence the cost of conducting weed biological control, using data from New Zealand programs. Taxonomic isolation of the target weed, relative to commercially important plants and native flora was not a significant influence on program cost, although we present evidence that disease, which to date has only affected agents released against taxonomically isolated weed targets, has masked the importance of taxonomic isolation in New Zealand. Opposition to biocontrol has caused delays, but has not had a major influence on the cost of biocontrol in New Zealand, probably because weed species with the greatest potential for opposition were identified during feasibility studies and avoided, or because conflicts were resolved by conducting cost-benefit analyses that were minor components of the total program costs. Only two factors explained virtually all the variance in program cost: program type (repeat programs were cheaper than novel/pioneering programs); and the number of agent species released. The predicted cost of future weed biocontrol programs can now be incorporated into decision-making tools ranking New Zealand weed biocontrol targets. Efficiencies in future programs are most likely to be gained by better agent selection so that fewer agents are released. For repeat programs this could be achieved by waiting until monitoring has been conducted overseas, so that the best agents or combination of agents can be selected for any particular weed. This reiterates the need for better post-release evaluation of weed biocontrol agent effectiveness worldwide.     

Saved from extinction? Establishment and dispersal of Mercury Islands tusked weta,Motuweta isolata,following translocation onto mammal-free islands

The Mercury Islands tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae), survived only on 13 ha Ahu or Middle Island, a mammal-free island in the Mercury Group, New Zealand. Between 2000 and 2009, 567 individuals were translocated in nine releases to six nearby islands from which mammals had been removed. These translocations occurred to reduce the chance of accidental extinction of the Middle Island population of only a few hundred adults and to contribute to the restoration of the other islands. All translocated insects originated from the captive-bred progeny of one male and two females collected from Middle Island between 1998 and 2001. Their establishment on Double and Red Mercury Islands, after their releases in 2000 and 2001 respectively, was confirmed by searching plots, and by using footprint tracking tunnels on Red Mercury Island between 2008 and 2012. Tracking tunnels provided better data and proved more cost effective than searching plots for detecting large tusked weta. Tracking tunnels demonstrated that the population on Red Mercury expanded outwards from the release sites by 50–100 m each year between 2009 and 2012. These weta are now estimated to be present over more than half the Island. Tusked weta have also survived on Stanley, Korapuki and Ohinau Islands after releases in 2007, but they remain within 100 m of the release sites. No confirmed progeny of the weta released on Cuvier Island in 2008 and 2011 were detected. No tusked weta were detected on Middle Island using tracking tunnels on eight occasions between 2009 and 2012, suggesting this species is likely to be locally extinct. Despite possible failure on one island, these translocations have resulted in a significant conservation success outcome.     

Isolation and characterization of microsatellite loci from Lochmaea suturalis, the heather beetle (Coleoptera: Chrysomelidae), a pest in Europe and a biocontrol agent in New Zealand

The heather beetle Lochmaea suturalis which is native to northwest Europe has been released as a biocontrol agent for heather in New Zealand. We have isolated and optimized eight microsatellite loci from New Zealand beetles. These loci provide markers with high polymorphism ranging from four to 20 alleles per locus. Observed heterozygosity averaged 0.631 per locus. These results suggest the markers are useful for population studies that will contribute to assessment of L. suturalis as a biocontrol agent.     

Making weed biological control predictable,safer and more effective: perspectives from New Zealand

A persistent problem in weed biocontrol is how to reliably predict whether a plant that supports development in laboratory host-specificity testing will be utilized in field conditions, and this is undoubtedly preventing releases of safe and effective agents. Moreover, the potential for unanticipated undesirable indirect effects of weed biocontrol on ecological networks has raised concerns by policy-makers and the general public. The key to minimizing risks of non-target impacts is prioritizing candidate agents that are both host-specific and effective, such that the number of agents required to bring the weed under control is minimized. As a consequence both the weed and its biocontrol agents become minor components of the local biota. Here we review recent attempts in New Zealand to improve the predictive ability of host-range testing, to avoid potentially safe and effective agents being rejected. Research in New Zealand aimed at predicting whether an agent is likely to experience enemy-release (i.e. reduced parasitism and predation) could assist agent prioritization, potentially making biocontrol both environmentally safer and more effective.     

Insect assemblages in a native (kanuka –

In New Zealand, the European shrub gorse (Ulex europaeus) is becoming the initial post-disturbance shrub, replacing the native myrtaceous manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) scrub in this role. Change in the dominant vegetation is likely to affect the native invertebrate community. To quantify these changes, we compared the assemblages of four selected insect taxa (Coleoptera, Lepidoptera, and two groups of Diptera, the Tachinidae and the fungus gnats, represented in New Zealand by the families Ditomyiidae, Keroplatidae and Mycetophilidae) in neighboring stands of kanuka and gorse using Malaise and pitfall traps set during December. We sorted 34 387 specimens into 564 recognisable taxonomic units. Ordinations showed that insect assemblages associated with each habitat were distinct for all four insect groups. The gorse habitat was species rich compared with kanuka for tachinids, fungus gnats and Malaise-trapped beetles, and both habitats contained few adventive species. Many species were unique to each habitat. Some species loss might occur if the kanuka-dominated community continues to be replaced by gorse, but gorse is nevertheless considered to be valuable as a habitat for native invertebrates.     

Predicting the Impact of the Biocontrol Agent Aulacidea subterminalis (Cynipidae) on Growth of Hieracium pilosella (Asteraceae) under Differing Environmental Conditions in New Zealand

A gall wasp, Aulacidea subterminalis, was released into the field in New Zealand in 1999 for biocontrol of the grassland weed Hieracium pilosella. To predict its likely impact in the field, the effect of the gall wasp on plant growth was measured under stress-free conditions in a shade house trial with potted plants. Plants with galls showed a reduction in stolon length of 75%. They had slightly lower total dry matter and reduced root weight. In a glasshouse experiment to measure the impact of water stress, nutrient stress, and plant competition on growth of H. pilosella and performance of the gall wasp, the number and mean diameter of gall clusters were not significantly different between treatment and control plants. However, galled plants produced more, but shorter, stolons in all stress treatments, and stolons that were more branched in nutrient- and water-stressed plants, than ungalled plants. Under the plant competition treatment, total stolon length relative to biomass was greater with, than without, wasps, indicating that stolons were thinner. Galling by A. subterminalis is likely to reduce vegetative reproduction of H. pilosella whether or not the plants are stressed, indicating that the wasp may be a successful biocontrol agent.     

Evaluation of Dicyphus hersperus (Heteroptera: Miridae) for biological control of Frankliniella occidentalis (Thysanoptera: Thripidae) on greenhouse tomato

The effectiveness of inoculative releases of the mirid predator Dicyphus hesperus Knight for control of Frankliniella occidentalis (Pergande) on greenhouse tomatoes was evaluated in terms of suppression of the population densities of F. occidentalis and associated fruit damage in the presence of the predator over two seasonal trials. An inoculative release of one D. hesperus per plant (approximately 0.1:10 predator:prey ratio) at a high F. occidentalis population density (140 thrips per plant) suppressed the thrips population density to a significantly lower level, compared with the nonrelease greenhouse, but not below a thrips level that caused economic fruit damage. As the predator:prey ratio increased to approximately 0.5:10 D. hesperus:F. occidentalis, the mean percentage of the thrips-damaged fruit in the D. hesperus release greenhouse decreased to 1.6%. However, the amount of fruit feeding by D. hesperus was highly correlated to the availability of prey (or predator:prey ratio) under greenhouse conditions. D. hesperus-induced fruit damage occurred when the predator:prey ratio was >1:10 D. hesperus:F. occidentalis. Considering the potential risk of fruit damage by D. hesperus and the need for effective control of F. occidentalis, a 0.5-1:10 D. hesperus:F. occidentalis ratio is recommended when the thrips population density is in the range of 60-150 thrips per plant.     

Dispersal behavior of the parasitic wasp Cotesia urabae (Hymenoptera: Braconidae): A recently introduced biocontrol agent for the control of Uraba lugens (Lepidoptera: Nolidae) in New Zealand

Estimates of the dispersal range of a recently introduced biocontrol agent in its new environment are vital to understanding its relative searching capacity, and to foresee the maximum area that could be covered in a release event. In New Zealand, the solitary endoparasitoid Cotesia urabae Austin and Allen (Hymenoptera: Braconidae) was first released in January 2011 as a biological control agent for the gum leaf skeletoniser, Uraba lugens Walker (Lepidoptera: Nolidae). The objective of this study was to utilize an experimental approach to quantify the dispersal behavior of one generation of C. urabae. In our experiment, which used sentinel larvae as target hosts, parasitoids dispersed up to 20 m away from the release point but parasitism was highest within 5 m of the release site. A high level of parasitism was observed at the release tree (87.6%) which suggests that most of the females released may have stayed there. According to the dispersal model developed from the data collected, Cotesia would be able to disperse up to 53 m in one release event. In addition, significant differences were found between the different directions tested for dispersal, showing a clear downwind effect on dispersal suggesting that wind has a direct effect on the dispersal behavior of C. urabae in the field.