Suppression of growth and reproductive capacity of the weed Lantana camara (Verbenaceae) by Ophiomyia camarae (Diptera: Agromyzidae) and Teleonemia scrupulosa (Heteroptera: Tingidae)

An 8-month study was conducted to determine the effect of herbivory by the herringbone leafminer Ophiomyia camarae Spencer (Diptera: Agromyzidae) and the lace bug Teleonemia scrupulosa Stål (Heteroptera: Tingidae) on growth and reproductive capacity of their host plant, Lantana camara L. (Verbenaceae). Ophiomyia camarae adults were released into field cages at two population densities while T. scrupulosa, a widespread and naturalised biocontrol agent in South Africa, colonised and attacked uncaged plants of similar size grown under similar field conditions. At lower initial density, O. camarae reduced stem height, stem diameter, leaf density, flower density and above-ground biomass by 5, 22, 54, 100 and 41%, respectively. At higher initial density of O. camarae, stem height, stem diameter, leaf density, flower density and above-ground biomass were substantially reduced by 19, 28, 73, 99 and 49%, respectively. Teleonemia scrupulosa also reduced stem height, stem diameter, leaf density, flower density and above-ground biomass by 37, 34, 75, 100 and 50%, respectively. The root development was less affected by both O. camarae and T. scrupulosa. Whilst higher densities of O. camarae exerted noticeable herbivore pressure, T. scrupulosa herbivory substantially hampered plant growth and reproductive capacity even at lower population levels. These findings suggest that O. camarae, released in 2001 for the control of lantana, would be effective as part of a complementary guild of biological control agents. The profound effect of herbivory by T. scrupulosa on plant growth and reproductive capacity suggests that it is making a much greater contribution to the biological control of lantana in South Africa than was previously thought.     

The impact of carbofuran soil application on growth and mycorrhizal colonization by Glomus clarum of groundnut

The influence of soil application of carbofuran on the growth response of groundnut, and both mycorrhizal colonization and sporulation of Glomus clarum was studied in a pot culture experiment. Carbofuran application with or without mycorrhizal inoculation increased the height of the potted plants measured 8 weeks after sowing. Mycorrhizal plants were significantly taller than nonmycorrhizal plants at the final harvest time (14 weeks). Carbofuran, at the recommmended field dose of up to 2 kg/ha, greatly increased shoot dry matter and pod yield in mycorrhizal groundnut. Colonization and sporulation by this VAM fungus were also enhanced significantly at these dose levels. The application of carbofuran at 5 kg/ha inhibited both growth and mycorrhizal status of groundnut.     

Effects in s.e. Queensland during 1967–72 of insects introduced to controlLantana camara

Seasonal fluctuations in populations of the introduced speciesTeleonemia scrupulosa Stål and damage by this insect to common taxa ofLantana camara, were observed at several field sites and experimental plots. At 2 plots effects ofT. scrupulosa populations on untreated plants were compared with plants protected by application of insecticides. On untreated plants damage varied seasonally and between taxa ofL. camara. In general attack byT. scrupulosa reduced fruiting and caused severe short term foliage damage. Combined with severe stress from some other cause heavy attack may result in long term damage or death to plants. However Common PinkL. camara was more resistant to damage than were the other taxa studied. At the time of these experiments other insect species were at very low population levels and did not have observable effects onL. camara.     

Effect of herbivory by Teleonemia scrupulosa on the performance of Longitarsus bethae on their shared host, Lantana camara

Herbivory by insects may change the characteristics of nutrients and secondary plant chemicals of the foliage, thereby altering the acceptability and suitability of the plant for oviposition, feeding and development for subsequent herbivores. In the current study, the effect of herbivory by the sap-sucking lace bug, Teleonemia scrupulosa Stäl (Heteroptera: Tingidae), on the suitability of Lantana camara L. (Verbenaceae) for the root-feeding flea beetle, Longitarsus bethae Savini & Escalona (Chrysomelidae: Alticinae), was investigated under laboratory conditions. Preference of adult L. bethae was not influenced by the intensity of feeding damage caused by T. scrupulosa adults. However, high densities of T. scrupulosa nymphs and their feeding damage caused L. bethae adults to emigrate and colonize less infested or uninfested plants. Oviposition by L. bethae was significantly reduced at high densities of T. scrupulosa nymphs. While low infestation of T. scrupulosa had no effect the survival of L. bethae, moderate and high infestations caused significant reduction in percentage survival of L. bethae. The number of T. scrupulosa nymphs was negatively correlated with the percentage survival of L. bethae. Neither the duration of development nor the body size of L. bethae was influenced by the intensity of T. scrupulosa infestation. Overall, undamaged or slightly damaged plants that allowed better survival of L. bethae were often chosen as oviposition sites in preference to those that were highly infested, and on which survival was poor. Although the present study indicates the likelihood of inter-specific competition between L. bethae larvae and T. scrupulosa, this is likely to be mitigated by female flea beetles choosing to oviposit on less infested or uninfested plants in the field.     

Host range of Lepidelphax pistiae (Hemiptera: Delphacidae) and its potential impact on Pistia stratiotes L. (Araceae)

Pistia stratiotes L. (Araceae) is a floating aquatic plant that has become invasive in Florida. It is primarily controlled with herbicides, but two biocontrol agents have previously been released to assist in management of this species. A new potential biocontrol agent from Argentina, Lepidelphax pistiae Remes Lenicov (Hemiptera: Delphacidae), has been evaluated comprehensively for specificity after initial host range studies done in its native range indicated that it is likely specific to P. stratiotes. Host range studies indicated that this insect is specific to P. stratiotes, with no survival or reproduction occurring on any of the 42 other plant species tested. Impact studies indicated that this insect can significantly damage P. stratiotes at medium and high population densities, which were comparable to those seen in its native range. Lepidelphax pistiae is sufficiently specific enough to warrant release and has a high probability of aiding management of P. stratiotes populations in Florida.     

Soil invertebrate and plant responses to mowing and carbofuran application in a North American tallgrass prairie

Relationships between soil invertebrate populations and primary production of a tallgrass prairie were investigated using the insecticide-nematicide carbofuran and a range of mowing intensities to manipulate invertebrate densities and resource quantity and quality. The trophic composition of nematode populations was monitored through each of two growing seasons. Earthworm and macroarthropod densities and primary production were assessed at the end of the second season. Invertebrate densities were generally reduced in carbofuran-treated plots, although individual weights of surviving macroarth-ropod herbivores increased significantly (p<0.05). Carbofuran failed to affect estimates of above- or belowground plant biomass after two years of treatment. Changes in resource quantity and quality resulted in rapid responses by dominant invertebrate consumer populations. A 28% reduction in live root mass and a 24% increase in root detritus following two years of mowing was associated with a 54% decrease in herbivorous nematode densities, a 47% increase in microbivorous nematode densities, and a 41% increase in native earthworm biomass.     

Influence of organic additives on the incidence of root-knot nematode,Meloidogyne javanica in roots of tomato plants

Glasshouse experiment was conducted to assess the impact of green chopped leaves of four test plants (Lantana camara, Ficus virens, Kigelia pinnata and Ficus bengalensis) and two nematicides (Phorate and Carbofuran) on the plant growth parameters of tomato cv. K25 and on the root-knot development. Results revealed that all the tested treatments significantly (p = 0.05) improved plant growth parameters and reduced root-knot development compared to control. Among the tested organic additives, chopped green leaves of Lantana camara added to soil gave the highest enhancement in plant growth parameters, including plant height, fresh and dry weight, number of fruits and fruit weight with the values of 94.2 cm, 106.8 g, 31.6 g, 7.2 and 153.3 g respectively, as well as a greater reduction of Meloidogyne javanica reproduction and development but exhibiting a lower response compared to nematicides. There was also significant reduction in root-knot development in tomato plants growing in other organic additive amended soil.     

Native isolate of <Emphasis Type="Italic">Trichoderma</Emphasis>: a biocontrol agent with unique stress tolerance properties

Species of Trichoderma are widely recognized for their biocontrol abilities, but seldom studied collectively, for their plant growth promotion, abiotic stress tolerance and bioremediation properties. Our study is a concentrated effort to establish the potential of native isolate Trichoderma harzianum KSNM (T103) to tolerate biotic (root pathogens) and abiotic stresses [high salt (100–1000 mM); heavy metal (chromium, nickel and zinc: 1–10 mM); pesticides: malathion (100–600 ppm), carbofuran (100–600 ppb)], along with its ability to support plant growth. In vitro growth promotion assays with T103 treated Vigna radiata, Vigna mungo and Hordeum vulgare confirmed ‘non-species specific’ growth promotion effects of T103. At lower metal concentration, T103 treatment was found to completely negate the impact of metal stress [60 % increase in radicle length (RL) with no significant decrease in %germination (%G)]. Even at 10 mM metal, T103 inoculation gave 80 % increase in %G and >50 % increase in RL. In vitro experiments confirmed high metal reduction capacity (47 %-Cr, 35 %-Ni and 42 %-Zn) of T103 at concentrations as high as 4 mM. At maximum residual concentrations of malathion (440 ppm) and carbofuran (100 ppb) reported in agricultural soils, T103 maintained 80 and 100 % survivability, respectively. T103 treatment has improved %G and RL in all three hosts challenged with pesticide. Isolate T103 was found to effectively suppress growth of three major root pathogens: Macrophomina phaseolina (65.83 %) followed by Sclerotium rolfsii (19.33 %) and Fusarium oxysporum (19.18 %). In the light of these observations, native T. harzianum (T103) seems to be a competent biocontrol agent for tropical agricultural soils contaminated with residual pesticides and heavy metals.     

The applicability of the plant vigor and resource regulation hypotheses in explaining Epiblema gall moth–Parthenium weed interactions

A basic question in insect–plant interactions is whether the insects respond to, or regulate plant traits, or a complex mixture of the two. The relative importance of the directions of the influence in insect–plant interactions has therefore been articulated through both the plant vigor hypothesis (PVH) and the resource regulation hypothesis (RRH). This study tested the applicability of these hypotheses in explaining the interactions between Parthenium hysterophorus L. (Asteraceae) and its stem‐galling moth, Epiblema strenuana Walker (Lepidoptera: Tortricidae). Parthenium plants exposed to galling were sampled at three sites in north Queensland, Australia, over a 2‐year period, and the relationship between gall abundance and plant vigor (plant height, biomass, flowers per plant, and branches per plant) was studied. To test the predictions of PVH and RRH, the vigor of parthenium plants protected from galling using insecticides was compared to galled plants and plants that escaped from galling. The vigor of ungalled plants was less than the vigor of galled plants. The higher plant vigor in galled plants was not due to galling, as was evident from insecticide exclusion trials. The insect seemed to preferentially gall the more vigorous plants. These findings support the predictions of the PVH and are contrary to those of RRH. Since gall abundance is linked to plant vigor, galling may have only a limited impact on the vigor of parthenium. This has implications for weed biological control. If the objective of biological control is to regulate the population of a plant by a galling insect, a preference for more vigorous plants by the insect is likely to limit its ability to regulate plant populations. This may explain the paucity of successes against biocontrol of annual weeds using gall insects.     

Phenology of Tick weed (Cleome viscosa L.) and its interaction with okra (Abelmoschus esculentus (L.) Moench) and Melodoigyne incognita

Cleome viscosa is an emerging weed with the potential of interfering with okra and influencing pests of okra. Screen house studies were conducted on the phenology of C. viscosa, its interference with okra and its interaction with root-knot nematode-infected okra. Seedlings of C. viscosa were monitored in pots for growth, yield and dry matter accumulation for 14 weeks. C. viscosa was planted with okra at densities 0, 2, 4, 6, 8 and 10 weeds per okra plant and observed for 11 weeks. Data were collected on growth, yield and dry matter of okra. Plants were inoculated with 2,500 M. incognita eggs per pot while control plants were not inoculated. C. viscosa attained 91.7 cm height and accumulated 7.8 g/plant biomass at 14 weeks after planting. The percentage reduction in okra plant height, plant dry weight and fruit yield due to interference at lowest cleome density (2 plants/pot) was 33.7, 83.6 and 82.1%, respectively. Nematode reproductive factor was significantly lower for okra alone (4.9) compared to okra with cleome (7.6). This study shows that C. viscosa is a fast-growing weed that suppressed the performance of okra even at low density, is a good host to M. incognita and increased the population of the nematode in soil.     

Effect of herbivory by Teleonemia scrupulosa on the performance of Longitarsus bethae on their shared host,Lantana camara

Herbivory by insects may change the characteristics of nutrients and secondary plant chemicals of the foliage, thereby altering the acceptability and suitability of the plant for oviposition, feeding and development for subsequent herbivores. In the current study, the effect of herbivory by the sap-sucking lace bug, Teleonemia scrupulosa Stäl (Heteroptera: Tingidae), on the suitability of Lantana camara L. (Verbenaceae) for the root-feeding flea beetle, Longitarsus bethae Savini & Escalona (Chrysomelidae: Alticinae), was investigated under laboratory conditions. Preference of adult L. bethae was not influenced by the intensity of feeding damage caused by T. scrupulosa adults. However, high densities of T. scrupulosa nymphs and their feeding damage caused L. bethae adults to emigrate and colonize less infested or uninfested plants. Oviposition by L. bethae was significantly reduced at high densities of T. scrupulosa nymphs. While low infestation of T. scrupulosa had no effect the survival of L. bethae, moderate and high infestations caused significant reduction in percentage survival of L. bethae. The number of T. scrupulosa nymphs was negatively correlated with the percentage survival of L. bethae. Neither the duration of development nor the body size of L. bethae was influenced by the intensity of T. scrupulosa infestation. Overall, undamaged or slightly damaged plants that allowed better survival of L. bethae were often chosen as oviposition sites in preference to those that were highly infested, and on which survival was poor. Although the present study indicates the likelihood of inter-specific competition between L. bethae larvae and T. scrupulosa, this is likely to be mitigated by female flea beetles choosing to oviposit on less infested or uninfested plants in the field.     

Paenibacillus terrae AY-38 resistance against Botrytis cinerea in Solanum lycopersicum L. plants through defence hormones regulation

This study aims to investigate the role of Paenibacillus terrae AY-38 to produce bioactive metabolites and to counteract pathogenic infections caused by B. cinerea. The pure culture of P. terrae (AY-38) showed the secretion of significant amount of IAA (indole-3-acetic acid) (109.57?±?3.2?µg?mL^?1). The AY-38 strain also produced siderophore and glucanase, while in the in vitro test, it showed significant antagonism to Botrytis cinerea. In the in vivo plant experiment, the sole application of AY-38 significantly improved plant growth (plant height and leaf area), while in B. cinerea infected plants, AY-38 inoculation not only decreased the disease incidence on leaves and fruits but also reprogramed the plants for higher growth. AY-38 treatments promoted and rescued plant growth by modulating the defence responses of endogenous hormones, such as jasmonic and salicylic acids. Our findings concluded that P. terrae possesses great potential as a possible biocontrol agent against B. cinerea-induced pathogenic infections.     

Influence of arbuscular mycorrhizal fungi on growth and selenium uptake by garlic plants

The aim of this study is to investigate the effects of arbuscular mycorrhizal fungi (AMF) on garlic plants growth and the uptake of selenium (Se). Garlic plants were grown in the pots inoculated with Glomus fasciculatum and G. mosseae and maintained in a greenhouse. Three weeks after planting, the pots had received different concentrations of Se (5, 10, 15, 20, 25 mg kg^?1 of soil) in the form of selenium dioxide (SeO₂) at 3 weeks intervals up to 12 weeks. For physiological and biochemical analysis, the samples were randomly collected from five plants of each experiment. Maximum AM infection, spore population and plant biomass were observed in the roots of mycorrhizal-mediated plants without Se, and they were gradually declined in both mycorrhizal and non-mycorrhizal (NM) plants with increasing concentrations of Se. Among the two Glomus species tested, G. fasciculatum-mediated plants showed higher AM infection, spore population and plant biomass than G. mosseae. No differences were observed for the uptake of Se in mycorrhizal plants and NM plants. However, NM plants uptake more Se than mycorrhizal plants. Higher contents of total chlorophyll and sugars were observed in plants inoculated with G. fasciculatum without Se and they were decreased in the presence of Se. In contrast, increased amount of glutathione peroxidase was observed at increasing concentrations of Se up to 20 mg kg^?1. High-performance liquid chromatography data revealed that SeO₂ converted to organic form of Se as γ-glutamyl-Se-methylselenocysteine. These results are basis for further investigations on the role of AMF on plant growth and uptake of Se in crop plants.     

Effectiveness of different release rates of Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae) against Tuta absoluta (Lepidoptera: Gelechiidae) in protected and open field tomato crops in Tunisia

Tuta absoluta (Meyrick) is a key insect pest of tomato crop causing major economic losses worldwide. Biological control using Trichogramma parasitoids is considered a promising, eco-friendly management tactic of this pest. We performed inundative releases of Trichogramma cacoeciae (Marchal) (Hymenoptera: Trichogrammatidae) against T. absoluta in Takelsa (northeastern Tunisia). Three weekly releases of either (i) 10, 20 or 30 Trichogramma per plant in protected (greenhouse) tomato crops or (ii) 20 or 40 Trichogramma per plant in open field tomatoes were evaluated for their effectiveness. Results indicated that 20 Trichogramma per plant was the most effective release rate in significantly decreasing the pest’s life stage densities. Parasitism rates were significantly higher on apical tomato leaves (estimated at 58.6% for the rate 20 Trichogramma per plant in greenhouses and at about 56% for the rate 40 Trichogramma per plant in open field) compared to those observed on middle leaves (24.6% and 45.26% for rate 2 respectively under greenhouse and open field conditions). Furthermore, the overall number of T. absolua eggs and larvae was significantly reduced after releases of Trichogramma parasitoids. These results clearly indicate that T. cacoeciae could be a promising biocontrol agent of T. absoluta in the largest tomato-producing area in Tunisia.     

The effects of flooding,plant traits,and predation on purple loosestrife leaf‐beetles

Classical biological weed control is based on the premise that introducing specialized natural enemies from the native range re‐establishes herbivore control of plant invaders, ultimately leading to negative population growth rates. Evidence from past biocontrol programs suggests that herbivores are not solely responsible for shaping plant demography. Diverse environmental conditions in the introduced range may not only affect demography, but also influence top‐down control of target plants. We investigated how flooding affects impacts of predators (top‐down) and plant quality (bottom‐up) on performance of two leaf‐beetles, Galerucella calmariensis L. and Galerucella pusilla Duftschmid (Coleoptera: Chrysomelidae: Galerucini), released in North America as biocontrol agents of purple loosestrife, Lythrum salicaria L. (Lythraceae). Predation and flooding regime have been linked to low leaf‐beetle recruitment at sites where insects failed to attain outbreak populations. Predator exclusion experiments at adjacent flooded and non‐flooded sites indicated a positive effect of flooding on leaf‐beetle survival for all developmental stages, whereas predator exposure had little effect. There was no difference in predation rates at sites with successful or failed purple loosestrife control, questioning the importance of predation in limiting growth and impact of these biocontrol agents’ populations. Effect of flooding on purple loosestrife quality was evaluated in a common garden study where plants were grown under different flooding treatments. Plants grown in flooded soil had higher water content and lower tannic acid concentration than plants grown in well‐drained soil. Consistent with field observations, leaf‐beetle oviposition rate and survival were higher on flooded plants. Results indicate that both bottom‐up and top‐down forces operate on Galerucella populations, yet their relative strength is mediated by flooding regime. Ignoring intricacies of plant‐herbivore and trophic interactions in the introduced range appears to be a major handicap for the improvement of weed biocontrol programs.     

Entomopathogenic fungus Clonostachys rosea as a biocontrol agent against whitefly (Bemisia tabaci)

Whitefly (Bemisia tabaci) is a notorious insect pest of many economic important crop plants including cotton, tomato, etc. The main objective of the study was to evaluate the efficacy of new biological control agent to replace toxic chemical pesticides from agro-ecosystem. Clonostachys rosea associated with whitefly and aphid (Aphis gossypii) on cotton plants was isolated and characterised on a morphological and molecular basis. Phylogenetic analysis was also performed based on the internal transcribed spacer (ITS) region. Pathogenicity of C. rosea was evaluated in two concentrations against fourth instar nymphal and adult stages of B. tabaci. The study revealed that C. rosea was highly parasitic against fourth instar nymphs than adults at different spore concentrations. Two isolates of C. rosea were identified in this study, and both were morphologically similar. However, differences were observed in the ITS region of the C. rosea isolates. Our results showed that C. rosea has the prospects to serve as a potential biocontrol agent against economically important insect pests.     

Trichoderma asperelloides antagonism to nine Sclerotinia sclerotiorum strains and biological control of white mold disease in soybean plants

Sclerotinia sclerotiorum is an important plant pathogen with worldwide distribution that causes severe economic losses of various agricultural crops such as soybean. This fungus is normally controlled with synthetic chemical fungicides that pose risks to the environment, and can be harmful to human health, and they can also induce resistance in pests. The aim of this study was to investigate the potential of Trichoderma asperelloides as a biocontrol agent towards white mold disease on soybeans crops. The antagonism of two strains of T. asperelloides (T25 and T42) isolated from soil samples was determined in-vitro by dual-culture confrontation testing on nine S. sclerotiorum strains obtained from sclerotia collected on diseased soybean plants. The mycelial growth and inhibition of carpogenic and ascospore germination by T. asperelloides extracts, as well as the efficacy of these on white mold control in soybeans were evaluated. Both strains of T. asperelloides exhibited high potential of antagonism. Methanolic and ethyl acetate extracts of the two T. asperelloides strains showed excellent growth inhibition (60–100%) on all of the pathogens tested. The ethyl acetate extracts of both T. asperelloides strains exhibited the highest efficacy against carpogenic germination, decreasing by 20–30% the number of ascospores per apothecium. Strains of T. asperelloides tested were more efficient in controlling white mold than two commercial products made from Trichoderma harzianum. The new strains of T. asperelloides have potential for successful biological control of white mold disease of soybean crops in the field.     

Efficiency of Rumex dentatus L. Leaves Extract for Enhancing Phytoremediation of Plantago major L. in Soil Contaminated by Carbosulfan

Carbosulfan and carbofuran induce water pollution and health issues. Such issues may be solved by phytoremediation. Here we tested the potential of adding Rumex dentatus L. leaves extract to Plantago major L. for enhancing phytoremediation of carbosulfan-contaminated soil. The phytoremediation efficiency of P. major L. amended with R. dentatus L. leaves extract was significantly greater than that of P. major only and R. dentatus with respect to the removal of carbosulfan from contaminated soil. The contribution of R. dentatus leaves extract to the degradation of carbosulfan in the soil were 20.95%, 18.85%, 5.2% and 1.85% after 2, 4, 8 and 16 days of treatments, respectively. The presence of P. major amended with R. dentatus leaves extract showed significant effect on uptake of carbosulfan into roots at 2 and 4 days, the uptake ratio was about 2.39 and 1.31 times higher compared to P. major alone, respectively. Carbofuran appeared in the P. major roots amended with R. dentatus leaves extract within 2 days of treatment (5.49 mg/kg) and reached the maximum over 8 days (10.19 mg/kg), while carbofuran appeared in the P. major over 4 days of treatment (4.09 mg/kg) and reached the maximum (6.92 mg/kg) over 8 days of exposure. Carbosulfan taken up into P. major leaves reached 4.36 mg/kg over 4 days, while it reached 2.75 mg/kg in P. major leaves amended with R. dentatus leaves extract over the same time. Carbofuran translocated into the P. major leaves amended with R. dentatus leaves extract and reached the maximum over 16 days of exposure (10.43 mg/kg), followed by P. major (9.47 mg/kg) and R. dentatus leaves (9.5 mg/kg), respectively. This study indicates that R. dentatus leaves extract can improve the efficiency of phytoremediation of carbosulfan.     

Phytoremediation of lead by a wild,non-edible Pb accumulator Coronopus didymus (L.) Brassicaceae

Coronopus didymus was examined in terms of its ability to remediate Pb-contaminated soils. Pot experiments were conducted for 4 and 6 weeks to compare the growth, biomass, photosynthetic efficiency, lead (Pb) uptake, and accumulation by C. didymus plants. The plants grew well having no visible toxic symptoms and 100% survivability, exposed to different Pb-spiked soils 100, 350, 1500, and 2500 mg kg^?1, supplied as lead nitrate. After 4 weeks, root and shoot concentrations reached 1652 and 502 mg Pb kg^?1 DW, while after 6 weeks they increased up to 3091 and 527 mg Pb kg^?1 DW, respectively, at highest Pb concentration. As compared to the 4 week experiments, the plant growth and biomass yield were higher after 6 weeks of Pb exposure. However, the chlorophyll content of leaves decreased but only a slight decline in photosynthetic efficiency was observed on exposure to Pb at both 4 and 6 weeks. The Pb accumulation was higher in roots than in the shoots. The bioconcentration factor of Pb was > 1 in all the plant samples, but the translocation factor was < 1. This suggested C. didymus as a good candidate for phytoremediation of Pb-contaminated soils and can be used for future remediation purposes.     

Influence of insects and fungal pathogens on individual and population parameters of <Emphasis Type="Italic">Cirsium arvense</Emphasis> in its native and introduced ranges

Introduced weeds are hypothesized to be invasive in their exotic ranges due to release from natural enemies. Cirsium arvense (Californian, Canada, or creeping thistle) is a weed of Eurasian origin that was inadvertently introduced to New Zealand (NZ), where it is presently one of the worst invasive weeds. We tested the ‘enemy release hypothesis’ (ERH) by establishing natural enemy exclusion plots in both the native (Europe) and introduced (NZ) ranges of C. arvense. We followed the development and fate of individually labelled shoots and recorded recruitment of new shoots into the population over two years. Natural enemy exclusion had minimal impact on shoot height and relative growth rate in either range. However, natural enemies did have a significant effect on shoot population growth and development in the native range, supporting the ERH. In year one, exclusion of insect herbivores increased mean population growth by 2.1–3.6 shoots m⁻², and in year two exclusion of pathogens increased mean population growth by 2.7–4.1 shoots m⁻². Exclusion of insect herbivores in the native range also increased the probability of shoots developing from the budding to the reproductive growth stage by 4.0× in the first year, and 13.4× in the second year; but exclusion of pathogens had no effect on shoot development in either year. In accordance with the ERH, exclusion of insect herbivores and pathogens did not benefit shoot development or population growth in the introduced range. In either range, we found no evidence for an additive benefit of dual exclusion of insects and pathogens, and in no case was there an interaction between insect and pathogen exclusion. This study further demonstrates the value of conducting manipulative experiments in the native and introduced ranges of an invasive plant to elucidate invasion mechanisms.