Predicting the host range of Nystalea ebalea: Secondary plant chemistry and host selection by a surrogate biological control agent of Schinus terebinthifolia

The safety of weed biological control depends upon the selection and utilization of the target weed by the agent while causing minimal harm to non-target species. Selection of weed species by biological control agents is determined by the presence of behavioral cues, generally host secondary plant compounds that elicit oviposition and feeding responses. Non-target species that possess the same behavioral cues as found in the target weed may be at risk of damage by classical biological control agents. Here we conducted host range tests and examined secondary plant compounds of several test plant species. We studied the specialist herbivore Nystalea ebalea (Lepidoptera: Notodontidae) a Neotropical species, present in Florida as a surrogate biological control agent of the weed, Brazilian peppertree Schinus terebinthifolia, invasive in Florida and Hawaii. We found that the larvae had the greatest survival when fed the target weed, the Neotropical species Spondias purpurea, the Florida native species Rhus copallinum, and the ornamental Pistacia chinensis. Reduced survival and general larval performance were found on the native species Metopium toxiferum and Toxicodendron radicans. Both the volatiles and the allergen urushiols were chemically characterized for all species but urushiol diversity and concentration best predicted host range of this herbivore species. These results provide insight into host selection and utilization by one oligophagous Schinus herbivore. Other potential biological control agents may also be sensitive to plants that contain urushiols and if so, they may pose minimal risk to these native species.     

Host range tests reveal Paectes longiformis is not a suitable biological control agent for the invasive plant Schinus terebinthifolia

The most critical step during a weed biological control program is determination of a candidate agent’s host range. Despite rigorous protocols and extensive testing, there are still concerns over potential non-target effects following field releases. With the objective to improve risk assessment in biological control, no-choice and choice testing followed by a multiple generation study were conducted on the leaf-defoliator, Paectes longiformis Pogue (Lepidoptera: Euteliidae). This moth is being investigated as a biological control agent of Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae), which is one of the worst invasive plant species in Florida, USA. Results from no-choice testing showed higher larval survival on S. terebinthifolia (48 %) and its close relative Schinus molle L. (47 %), whereas lower survival was obtained on six non-target species (<25 %). When given a choice, P. longiformis females preferred to lay eggs on the target weed, but oviposition also occurred on four non-target species. An improved performance on the native Rhus aromatica Aiton was found when insects were reared exclusively on this non-target species for one or two generations. Results from host range testing suggest that this moth is oligophagous, but has a preference for the target weed. Non-target effects found during multiple generation studies indicate that P. longiformis should not be considered as a biological control agent of S. terebinthifolia.     

Pathogenicity of Pleistophora schubergi to larvae of the orange-striped oakworm and other lepidopterous insects

First- to fourth-instar larvae of the orange-striped oakworm, Anisota senatoria, are highly susceptible to infection by Pleistophora schubergi. Death of the oakworm usually occurs in the next instar following spore ingestion. P. schubergi infects a number of other forest lepidopterous insects.     

Evaluation of intraguild interactions between two species of insect herbivores on Pistia stratiotes

Pistia stratiotes L. (Araceae) is an important weed in many waterways around the world. The South American weevil Neohydronomus affinis Hustache (Coleoptera: Curculionidae) is a successful biocontrol agent for this weed but additional agents are needed for some areas. The planthopper Lepidelphax pistiae Remes Lenicov (Hemiptera: Delphacidae) is a specific herbivore of P. stratiotes and is highly damaging in laboratory conditions. A field experiment was designed to evaluate the damage potential of L. pistiae compared to N. affinis and to assess the potential for competition between the two herbivores. Both herbivore species were reared inside floating cages on a P. stratiotes-infested lake. Plant growth indices assessed were clonation levels, biomass and plant diameter. The growth indices of plants exposed to the herbivores, individually and combined, were comparable, and significantly lower than in the control treatments. Population levels of N. affinis inside the cages were not significantly different when alone or together with L. pistae. Conversely, the density of L. pistiae was significantly lower in combination with the weevil. This suggests that L. pistiae is a damaging herbivore that will not reduce the biological control effectiveness of N. affinis.     

Host specificity ofPareuchaetes insulata (Lep.: Arctiidae), a biological control agent forChromolaena odorata (Compositae)

Larvae of the arctiid moth,Pareuchaetes insulata, from Florida fed on the leaves ofChromolaena odorata, a serious composite, alien weed in Natal, South Africa. In starvation test trials using 48 plant species,P. insulata completed its development onC. odorata andAgeratum houstonianum. Subsequent attempts to cultureP. insulata on these two plants was only successful onC. odorata. The biology ofP. insulata is similar to that of two other well studiedPareuchaetes species namelyP. pseudoinsulata andP. aurata aurata. Repeated defoliation ofC. odorata byP. insulata could contribute to its control as has been found withP. pseudoinsulata in Guam.Pareuchaetes insulata has been approved for release as a biological control agent ofC. odorata in South Africa.     

Impact of herbivory on mile-a-minute weed (Persicaria perfoliata) seed production and viability

The monophagous weevil Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) has been introduced into North America as a biological control agent for the invasive vine mile-a-minute weed, Persicaria perfoliata (L.) H. Gross. This weevil has been shown to reduce the percent cover of mile-a-minute and the number of seed clusters produced, as well as altering the phenology of seed production. However, prior work has not examined the potential impact of the weevil on seed viability and numbers of seeds per cluster. When both adult and larval weevils fed on whole plants in the greenhouse, seed production and fruit maturation were delayed and both the total number of seeds and number of seeds per cluster were reduced. Overall, weevils in greenhouse cages reduced the reproductive potential of P. perfoliata by 35%. When adult weevils were confined on developing seed clusters in the field, the number of seeds produced per cluster, the weight of seeds produced, and seed viability all decreased. Overall, the number of viable seeds per cluster was reduced by 37% in the presence of adult weevils. Taken together, these findings demonstrate that this biological control agent can have important impacts on the reproductive potential of its target weed through mechanisms that have not previously been shown.     

Biology and host specificity ofPlatphalonidia mystica (Lep.: Cochylidae) introduced into queensland to biologically controlParthenium hysterophorus (Asteraceae)

Platphalonidia mystica (Razowski &; Becker) has been studied as a potential biological control agent against parthenium weed (Parthenium hysterophorus L.). During host specificity testing, larval feeding damage occurred on sunflower (Helianthus annuus L.) and to a lesser extent onDahlia sp., but risk of damage to sunflower crops under field conditions is considered negligible. In view of the very great problem thatP. hysterophorus is causing, and the threat of its continued southward spread into Southern Queensland, New South Wales and Victoria, field release ofP. mystica was authorised and commenced in Queensland in late 1992.     

Field observations on the biology and behaviour of Dasiops caustonae Norrbom and McAlpine (Dipt., Lonchaeidae), as a candidate biocontrol agent of Passiflora mollissima in Hawaii

A newly described lonchaeid from Venezuela, Dasiops caustonae Norrbom and McAlpine, has been recommended as a biological control agent of Passiflora mollissima (H.B.K) Bailey, an aggressive exotic weed of Hawaiian rainforests. In this study, elementary biological information was collected in the field in order to determine the appropriateness of using D. caustonae as a biological control agent against this important weed. Field observations suggested that the host range of D. caustonae is limited to species of the subgenus Tacsonia. Female flies appear to mark flowers with an oviposition deterrent pheromone. This is possibly the first report of marking behaviour outside Tephritidae. The geographical range of this species is wide and comparable with that of the target weed. Life‐cycle studies demonstrated that D. caustonae is multivoltine with an estimated life‐cycle length of 3 to 4 months. Survival to adult was limited by premature flower fall, drought and interspecific competition by a bud and flower feeding Lepidoptera, Pyrausta perelegans Hampson. Additional ecological studies and host range testing of D. caustonae are recommended to determine its impact on the target weed and its safety as a biological control agent.     

Biological control of water lettuce,Pistia stratiotes [Araceae] byNeohydronomus affinis [Coleoptera: Curculionidae]

Neohydronomus affinis was imported into Australia as a potential biological control agent for the floating aquatic weedPistia stratiotes. Quarantine studies demonstrated that this weevil was host specific toP. stratiotes and it was released into the field in 1982. Subsequently it was released as a control agent for this weed in several other countries. In AustraliaN. affinis reduced infestations ofP. stratiotes by 40% or more within 12–18 months. The results are discussed in relation to its effectiveness in other parts of the world. We concluded thatN. affinis effectively controlsP. stratiotes in tropical regions (to lat. 22°), but in cooler regions its effectiveness fluctuates with seasonal conditions.      

Effect of the microsporidian Pleistophora schubergi on Anaitis efformata (Lepidoptera: Geometridae) and its elimination from a laboratory colony

Infection by the microsporidian Pleistophora schubergi was lethal to most larvae of Anaitis efformata, while sublethal infection retarded development and led to reduced longevity, weight, fecundity, and mating success in adults. Fumagillin had no effect on the level of P. schubergi infection. Benomyl suppressed infection for as long as treatment was given, but the microsporidian resurged during the nonfeeding pupal stage. P. schubergi was not transmitted transovarially and this facilitated its elimination from the colony of A. efformata in one generation through selective individual mating and rearing of the moth.     

Evaluation of the rust fungus Puccinia rapipes for biological control of Lycium ferocissimum (African boxthorn) in Australia: Life cycle,taxonomy and pathogenicity

Fungal plant pathogens are increasingly recognised as being among the most effective and safe agents in classical weed biological control programs worldwide. Suitability of the rust fungus P. rapipes as a classical biological control agent for Lycium ferocissimum (African boxthorn) in Australia was assessed using a streamlined agent selection framework. Studies with P. rapipes were undertaken to elucidate its life cycle, confirm its taxonomic placement and determine its pathogenicity to L. ferocissimum and seven closely-related Solanaceae species that occur in Australia. Field surveys in the native range of South Africa, experiments in a containment facility in Australia and DNA sequencing confirmed that P. rapipes is macrocyclic and autoecious, producing all five spore stages on L. ferocissimum. The stages not previously encountered, spermogonia and aecia, are described. Sequencing also confirmed that P. rapipes is sister to Puccinia afra, in the ‘Old World Lineage’ of Puccinia species on Lycieae. Two purified isolates of the fungus, representing the Eastern and Western Cape distributions of P. rapipes in South Africa, were cultured in the containment facility for use in pathogenicity testing. L. ferocissimum and all of the Lycium species of Eurasian origin tested ‒ Lycium barbarum (goji berry), Lycium chinense (goji berry ‘chinense’) and Lycium ruthenicum (black goji berry) – were susceptible to both isolates of P. rapipes. The Australian native L. australe and three more distantly related species in different genera tested were resistant to both isolates. The isolate from the Western Cape was significantly more pathogenic on L. ferocissimum from Australia, than the Eastern Cape isolate. Our results indicate that P. rapipes may be sufficiently host specific to pursue as a biological control agent in an Australian context, should regulators be willing to accept damage to the Eurasian goji berries being grown, albeit to a limited extent, in Australia.     

Control of Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) with acephate to exclude a biological control agent of Schinus terebinthifolia

Post-release monitoring of biological control agents to determine impact on the target weed has recently received increased priority. Several methods are available to measure the impact of a biological control agent by manipulating the agent population while measuring fitness of the weed. Brazilian peppertree, Schinus terebinthifolia is one of the most damaging weeds in subtropical areas of Florida and Hawaii. A biological control agent, the thrips, Pseudophilothrips ichini is a sap-feeder that shows high levels of specificity and causes severe distortion of leaf tips of the weed. Thrips populations of this species and a generalist thrips, the red banded thrips Selenothrips rubrocinctus were experimentally manipulated by applications of the systemic insecticide acephate by both foliar applications and by an inserted encapsulated formulation. Foliar applications protected plants against red banded thrips for 29 days and against the biological control thrips, P. ichini for 22 days after treatment. Control with inserts were initially low but was achieved after 60 days and this control continued for 182 days after treatment. Manipulation of these biological control thrips populations with foliar or inserted formulations will assist in the determination of biological control agent impact.     

Pre-release evaluation of the efficacy of the leaf-sucking bug Carvalhotingis visenda (Heteroptera: Tingidae) as a biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae)

In classical weed biological control, assessing weed response to simulated herbivory is one option to assist in the prioritization of available agents and prediction of their potential efficacy. Previously reported simulated herbivory studies suggested that a specialist herbivore in the leaf-feeding guild is desirable as an effective biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae), an environmental weed that is currently a target for biological control. In this study, we tested (i) whether the results from glasshouse-based simulated herbivory can be used to prioritise potential biological control agents by evaluating the impact of a leaf-sucking tingid bug Carvalhotingis visenda (Drake & Hambleton) (Hemiptera: Tingidae) in quarantine; and (ii) the likely effectiveness of low- and high-densities of the leaf-sucking tingid after its release in the field. The results suggest that a single generation of C. visenda has the potential to reduce leaf chlorophyll content significantly, resulting in reduced plant height and leaf biomass. However, the impact of one generation of tingid herbivory on below-ground plant components, including the roots and tuber size and biomass, were not significant. These findings are consistent with results obtained from a simulated herbivory trial, highlighting the potential role of simulated herbivory studies in agent prioritisation.     

Review of the biology and ecology of a ragweed leaf beetle,Ophraella communa (Coleoptera: Chrysomelidae), which is a biological control agent of an invasive common ragweed,Ambrosia artemisiifolia (Asterales: Asteraceae)

A ragweed leaf beetle, Ophraella communa (Coleoptera: Chrysomelidae), has been highlighted as a potential biological control agent of Ambrosia artemisiifolia. O. communa and A. artemisiifolia are native in North America and alien species in East Asia and Europe. As an invasive weed, A. artemisiifolia causes severe economic losses as reducing agricultural production as well as producing severe allergenic pollen. As an herbivore insect, O. communa has strong host preference on A. artemisiifolia. All the developmental stages of O. communa can be found on A. artemisiifolia and it attacks a single plant in repeated and extended manners. With few individuals on A. artemisiifolia, O. communa can completely defoliate before pollen production. Therefore, O. communa had been focused as a biological control of this invasive weed, but its introduction was denied because of possible damage on an important crop, Helianthus annuus. O. communa was accidentally introduced in East Asia and Europe in 1990s and 2010s, respectively. Fortunately, O. communa population was well established to suppress A. artemisiifolia in the introduced areas. Following detailed field surveys and host specificity tests of O. communa were conducted and proved a strong potential of O. communa as a biological control agent of A. artemisiifolia. Moreover, O. communa has been investigated in physiological and evolutionary studies. In this study, the potential of O. communa as a biological control agent and a study organism are reviewed.     

Insect herbivores associated with the introduced weed Bidens frondosa L. (Asteraceae) in Korea,and their potential role as augmentative biological control agents

The annual herb Bidens frondosa L., native to North America, is an invasive weed. Currently no information is available on the insect herbivores associated with this weed in Korea. A survey was carried out at two‐weekly intervals from May to October 2008 at two sites, and the incidence and abundance of various insect herbivores studied. A total nine species of insects was recorded and among them the defoliating caterpillar Hadjina chinensis (Wallengren) (Lepidoptera) was the only species known to have host plants restricted to genus Bidens. Further host specificity studies are required to evaluate the potential of this insect as a candidate for augmentative biological control agent for B. frondosa in Korea. All other insect species are either polyphagous or known crop pests.     

A microsporidium,Nosema pilicornis sp. n., of the purslane sawfly,Schizocerella pilicornis

A new microsporidian species, Nosema pilicornis, which infects the purslane sawfly, Schizocerella pilicornis, is described. This microsporidium infects most body tissues of the host. N. pilicornis was compared to other microsporidian species infecting Hymenoptera and to a group of similar microsporidia infecting Lepidoptera. N. pilicornis could be distinguished from all other microsporidian species on the basis of host range and ultrastructural characteristics of the spore. Spores were oval, containing 11 to 12 polar filament coils, and the polar filament had an angle of tilt of about 80°. N. pilicornis infected lepidopteran larvae, but only when heavy spore dosages were fed to early larval instars. S. pilicornis is a good but sporadic biological control agent of common purslane, Portulaca oleracea, a pernicious weed of vegetable, ornamental, and orchard crops. N. pilicornis, which is transovarially transmitted and causes high mortality in infected larvae, affects the performance of S. pilicornis as a biological control agent.     

Pseudomonas putida NBRIC19 provides protection to neighboring plant diversity from invasive weed Parthenium hysterophorus L. by altering soil microbial community

Parthenium hysterophorus L. (Parthenium) is an invasive weed species which is spreading worldwide affecting natural ecological systems, biodiversity, crop production and human health. The present study was conducted to evaluate the potential of plant growth promoting Pseudomonas putida NBRIC19 in detoxifying the phytotoxic effect of Parthenium. Significant increase in C/N ratio, macronutrients, and micronutrients was observed in P. putida NBRIC19-treated soil. P. putida NBRIC19 treatment of the soil provided protection to plant communities in Parthenium invaded area, as the species diversity had increased in the treatment as compared to non-bacterized soil. P. putida NBRIC19 treatment besides Parthenium, also succeeded in controlling other weed species like Commelina benghalensis and Cynodon dactylon. In addition to this, the impact of Parthenium was also studied on functional microbial diversity based on carbon source utilization pattern. It was observed that P. putida NBRIC19 treatment of soil had shifted the microflora in such a manner that utilization of toxic allelochemicals increased to lessen their phytotoxic effect. Taken together, these results suggest that soil treatment with P. putida NBRIC19 may be used as a promising biological control measure for controlling the phytotoxic effect of Parthenium and in protecting ecosystem integrity of neighboring plants in Parthenium invaded areas.     

Review of Pasteuria penetrans: Biology,Ecology, and Biological Control Potential

Pasteuria penetrans is a mycelial, endospore-forming, bacterial parasite that has shown great potential as a biological control agent of root-knot nematodes. Considerable progress has been made during the last 10 years in understanding its biology and importance as an agent capable of effectively suppressing root-knot nematodes in field soil. The objective of this review is to summarize the current knowledge of the biology, ecology, and biological control potential of P. penetrans and other Pasteuria members. Pasteuria spp. are distributed worldwide and have been reported from 323 nematode species belonging to 116 genera of free-living, predatory, plant-parasitic, and entomopathogenic nematodes. Artificial cultivation of P. penetrans has met with limited success; large-scale production of endospores depends on in vivo cultivation. Temperature affects endospore attachment, germination, pathogenesis, and completion of the life cycle in the nematode pseudocoelom. The biological control potential of Pasteuria spp. have been demonstrated on 20 crops; host nematodes include Belonolaimus longicaudatus, Heterodera spp., Meloidogyne spp., and Xiphinema diversicaudatum. Pasteuria penetrans plays an important role in some suppressive soils. The efficacy of the bacterium as a biological control agent has been examined. Approximately 100,000 endospores/g of soil provided immediate control of the peanut root-knot nematode, whereas 1,000 and 5,000 endospores/g of soil each amplified in the host nematode and became suppressive after 3 years.     

Testing biological control agent compatibility: Cyphocleonus achates and Larinus minutus on diffuse knapweed

While weed biological control success is typically achieved with one agent, multiple agents are invariably introduced. Biological control agents that share a host–plant may interact either directly or indirectly through changes in host–plant quality. Negative interactions could reduce the impacts of the agents on the density of their host–plant while positive interactions (facilitation) could improve biological control success.In the Okanagan Valley of British Columbia, Canada, initial declines in the invasive rangeland weed, diffuse knapweed (Centaurea diffusa) were attributed to the introduction of the weevil Larinus minutus. A second weevil, Cyphocleonus achates has recently become common on diffuse knapweed. We sought to determine if the recent increase of C. achates could threaten the success of L. minutus. We considered whether L. minutus colonisation or performance remained the same when C. achates was present, and whether the two agents acted independently to reduce plant performance.Neither changes in colonisation rates nor competitive interactions were apparent between C. achates and L. minutus. Both insects reduced plant performance and, for all metrics, the reduction in plant performance by one species was independent of the second. The two agents appear to be compatible and both should contribute to the control of diffuse knapweed. To assess how biological control agents interact requires understanding both their competitive interactions and their joint effects on the shared host.     

Life cycle and host specificity of the heliotrope weevil,Pachycerus cordiger (=Madidus auct.) [Col.: Curculionidae]

Pachycerus cordiger Germar (Curculionidae: Cleonini) is a potential agent for the biological control ofHeliotropium europaeum L. (Boraginaceae) in Australia. Adults feed on the leaves and larvae feed on the main roots of the weed within an earthen cell. These is one generation per year. Adults overwinter in the cells before emerging in late spring when they begin to feed, mate and oviposit on their host plants from late May until late July. Seven Boraginaceae and 31 economically important crop species were tested using adults and 1^st instar larvae.P. cordiger was found to be specific to the Boraginaceae. Field observations strongly suggested that the weevil is restricted to summer-annualHeliotropium species. A widespread egg parasite,Caenocrepis? bothynoderi Gromakov [Hymenoptera: Pteromalidae], caused up to 18% mortality.