The host range and biology of <Emphasis Type="Italic">Cometaster pyrula</Emphasis>; a biocontrol agent for <Emphasis Type="Italic">Acacia nilotica</Emphasis> subsp. <Emphasis Type="Italic">indica</Emphasis> in Australia

Prickly acacia, Acacia nilotica subsp. indica (Benth.) Brenan, a major weed of the Mitchell Grass Downs of northern Queensland, Australia, has been the target of biological control projects since the 1980s. The leaf-feeding caterpillar Cometaster pyrula (Hopffer) was collected from Acacia nilotica subsp. kraussiana (Benth.) Brenan during surveys in South Africa to find suitable biological control agents, recognised as a potential agent, and shipped into a quarantine facility in Australia. Cometaster pyrula has a life cycle of approximately 2 months during which time the larvae feed voraciously and reach 6 cm in length. Female moths oviposit a mean of 339 eggs. When presented with cut foliage of 77 plant species, unfed neonates survived for 7 days on only Acacia nilotica subsp. indica and Acacia nilotica subsp. kraussiana. When unfed neonates were placed on potted plants of 14 plant species, all larvae except those on Acacia nilotica subsp. indica and Acacia nilotica subsp. kraussiana died within 10 days of placement. Cometaster pyrula was considered to be highly host specific and safe to release in Australia. Permission to release C. pyrula in Australia was obtained and the insect was first released in north Queensland in October 2004. The ecoclimatic model CLIMEX indicated that coastal Queensland was climatically suitable for this insect but that inland areas were only marginally suitable.     

Interactions of root and leaf herbivores on purple loosestrife (<Emphasis Type="Italic">Lythrum salicaria</Emphasis>)

Interspecific interactions of herbivores sharing a host plant may be important in structuring herbivore communities. We investigated host plant-mediated interactions of root (Hylobius transversovittatus) and leaf herbivores (Galerucella calmariensis), released to control purple loosestrife (Lythrum salicaria) in North America, in field and potted plant experiments. In the potted plant experiments, leaf herbivory by G. calmariensis reduced H. transversovittatus larval survival (but not larval development) but did not affect oviposition preference. Root herbivory by H. transversovittatus did not affect either G. calmariensis fitness or oviposition preference. In field cage experiments, we found no evidence of interspecific competition between root and leaf herbivores over a 4-year period. Our data suggest that large populations of leaf beetles can negatively affect root-feeding larvae when high intensity of leaf damage results in partial or complete death of belowground tissue. Such events may be rare occurrences (or affected by experimental venue) since field data differed from data obtained from potted plant experiments, particularly at high leaf beetle densities. Interspecific interactions between G. calmariensis and H. transversovittatus are possible and may negatively affect either species, but this is unlikely to occur unless heavy feeding damage results in partial or complete plant death.     

Differences in interactions of aboveground and belowground herbivores on the invasive plant <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> and native host <Emphasis Type="Italic">A. sessilis</Emphasis>

Plant invasions may result in novel plant-herbivore interactions. However, we know little about whether and how invasive plants can mediate native above- and belowground herbivore interactions. In this study, we conducted greenhouse experiments to examine the interaction between a native defoliating beetle, Cassida piperata, and a native root-knot nematode, Meloidogyne incognita, on the invasive alligator weed, Alternanthera philoxeroides. We also included their native host A. sessilis in the experiments to examine whether the patterns of above- and belowground herbivore interaction vary with host plants (invasive vs. native). We analyzed total carbon and nitrogen in leaves and roots attacked by M. incognita and C. piperata. M. incognita slightly negatively affected feeding by C. piperata on A. philoxeroides, and the leaf area damaged decreased as the number of M. incognita increased. M. incognita had a negative impact on total leaf nitrogen, but had no impact on total leaf carbon. M. incognita egg production on A. philoxeroides roots decreased as the amount of damage caused by C. piperata increased. Herbivory by C. piperata did not affect total root carbon or nitrogen. M. incognita and C. piperata did not affect each other on the native plant A. sessilis. These results suggest that invasive plants can mediate native above- and belowground herbivore interactions. The knowledge of how invasive plants affect those interactions is crucial for better understanding the impacts of biological invasions on native above- and belowground organisms.     

Herbivory and population dynamics of invasive and native <Emphasis Type="Italic">Lespedeza</Emphasis>

Some exotic plants are able to invade habitats and attain higher fitness than native species, even when the native species are closely related. One explanation for successful plant invasion is that exotic invasive plant species receive less herbivory or other enemy damage than native species, and this allows them to achieve rapid population growth. Despite many studies comparing herbivory and fitness of native and invasive congeners, none have quantified population growth rates. Here, we examined the contribution of herbivory to the population dynamics of the invasive species, Lespedeza cuneata, and its native congener, L. virginica, using an herbivory reduction experiment. We found that invasive L. cuneata experienced less herbivory than L. virginica. Further, in ambient conditions, the population growth rate of L. cuneata (λ = 20.4) was dramatically larger than L. virginica (λ = 1.7). Reducing herbivory significantly increased fitness of only the largest L. virginica plants, and this resulted in a small but significant increase in its population growth rate. Elasticity analysis showed that the growth rate of these species is most sensitive to changes in the seed production of small plants, a vital rate that is relatively unaffected by herbivory. In all, these species show dramatic differences in their population growth rates, and only 2% of that difference can be explained by their differences in herbivory incidence. Our results demonstrate that to understand the importance of consumers in explaining the relative success of invasive and native species, studies must determine how consumer effects on fitness components translate into population-level consequences. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The potential impact of the trimorphic flea-beetle, <Emphasis Type="Italic">Alagoasa extrema</Emphasis>, on a selected weedy variety of <Emphasis Type="Italic">Lantana camara</Emphasis>

The potential impact of the larval feeding by Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae: Alticinae) on potted plants of its host Lantana camara L. (Verbenaceae), a weed of major importance in South Africa, was examined. Under quarantine laboratory conditions, 2-month old plants of L. camara variety 029 White Pink were exposed to different larval feeding densities for a period of 18 days (completion of the larval stage). The above-ground dry mass of plants was significantly reduced following attack by larvae at densities of 5 larvae per plant (20% reduction) and 10 larvae per plant (28% reduction), when compared to unattacked plants. Attack by larvae over this short period had no significant impact on root growth. This demonstrates that A. extrema, once established in climatically favourable areas, could well augment other established agents in defoliating L. camara stands, reducing the accumulation of reserves and the competitiveness of the weed.     

Fitness consequences of infection of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> with its natural bacterial pathogen <Emphasis Type="Italic">Pseudomonas viridiflava</Emphasis>

Variation in plant resistance to pathogen infection is commonly observed in interactions between wild plants and their foliar pathogens. Models of host–pathogen interactions indicate that a large cost of infection is generally necessary to maintain this variation, yet there is limited evidence that foliar pathogens cause detectable fitness reductions in wild host plants. Most published work has focused on fungal pathogens. Pseudomonas viridiflava, a common bacterial pathogen of the annual weed Arabidopsis thaliana across its range, comprises two distinct genetic clades that cause disease symptoms of different severity. Here we measured the extent of infection of wild A. thaliana populations in the Midwest, USA, and examined the effect on seed production, in field and growth-chamber experiments, of experimental inoculation with isolates from the two clades. We found infection with P. viridiflava varied from 0 to 56% in Midwest A. thaliana populations, with the possibility of several leaves per plant infected later in the growing season. In the growth chambers, experimental inoculation reduced seed set by averages of 15 and 11% for clades A and B, respectively. In the field experiment, only clade A affected plant fitness significantly, reducing seed set by an average of 38%. Underlying these average effects we observed both negative and positive effects of infection, and variation in both fitness among plant genotypes and sensitivity to environmental conditions.     

<Emphasis Type="Italic">In vitro</Emphasis> selection and regeneration of chrysanthemum (<Emphasis Type="Italic">Dendranthema grandiflorum</Emphasis> Tzelev) plants resistant to culture filtrate of <Emphasis Type="Italic">Septoria obesa</Emphasis> Syd

Callus cultures derived from leaf segments of chrysanthemum cultivar ‘Snow Ball’ which was susceptible to Septoria obesa were successfully used for in vitro selection for resistance to this pathogenic fungus. Resistant cell lines were selected by culturing callus on growth medium containing various concentrations of S. obesa filtrate. Resistant calluses obtained after two cycles (30 d each cycle) of selection were used for plant regeneration. About 30% of the plants regenerated from the resistant calluses and 70–80% of the plants raised from cuttings had acquired considerable resistance against the pathogen in the field. No phenotypic variation was observed in the selected regenerates.     

Exotic grass invasion impacts fitness of an endangered prairie butterfly, <Emphasis Type="Italic">Icaricia icarioides fenderi</Emphasis>

Fender’s blue butterfly is an endangered species restricted to fragmented, grassland remnants that are becoming increasingly dominated by tall, invasive grasses in western Oregon, USA. I performed a removal experiment to assess the impacts of structural degradation accompanying the invasion of Arrhenatherum elatius, tall oat grass, on butterfly fitness and fitness related behaviors. Clipping of A. elatius to native grass sward height resulted in 2.5–5 times as many eggs laid per leaf of host plant. Both male and female butterflies basked more frequently in areas removed of A. elatius inflorescences and upon encountering the treatment edge butterflies had a high rate of return into a large area removed of the grass inflorescences. Although butterfly behavior appeared to be affected by the change in sward height on the treatment edge, there was no evidence for the edge causing a disproportionate egg load. Invasion and dominance by A. elatius appeared to diminish host plant apparency which may result in overloading of eggs on conspicuous host plants, increased incidence of emigration, and a decrease in the likelihood of colonization because female butterflies appeared indifferent to larval resources beneath A. elatius inflorescences. Dominance of natural shortgrass prairies by tall stature grasses like A. elatius may be an insidious form of habitat degradation for grassland Lepidoptera worldwide, but it may go largely unnoticed because larval and adult resources can persist under the unnaturally tall grass canopy.     

Ectopic expression of two MADS box genes from orchid (<Emphasis Type="Italic">Oncidium</Emphasis> Gower Ramsey) and lily (<Emphasis Type="Italic">Lilium longiflorum)</Emphasis> alters flower transition and formation in <Emphasis Type="Italic">Eustoma grandiflorum</Emphasis>

Lisianthus [Eustoma grandiflorum (Raf.) Shinn] is a popular cut flower crop throughout the world, and the demand for this plant for cut flowers and potted plants has been increasing worldwide. Recent advances in genetic engineering have enabled the transformation and regeneration of plants to become a powerful tool for improvement of lisianthus. We have established a highly efficient plant regeneration system and Agrobacterium-mediated genetic transformation of E. grandiflorum. The greatest shoot regeneration frequency and number of shoot buds per explant are observed on media supplemented with 6-Benzylaminopurine (BAP) and α-Naphthalene acetic acid (NAA). We report an efficient plant regeneration system using leaf explants via organogenesis with high efficiency of transgenic plants (15%) in culture of 11 weeks’ duration. Further ectopic expression of two MADS box genes, LMADS1-M from lily (Lilium longiflorum) and OMADS1 from orchid (Oncidium Gower Ramsey), was performed in E. grandiflorum. Conversion of second whorl petals into sepal-like structures and alteration of third whorl stamen formation were observed in the transgenic E. grandiflorum plants ectopically expressing 35S::LMADS1-M. 35S::OMADS1 transgenic E. grandiflorum plants flowered significantly earlier than non-transgenic plants. This is the first report on the ectopic expression of two MADS box genes in E. grandiflorum using a simple and highly efficient gene transfer protocol. Our results reveal the potential for floral modification in E. grandiflorum through genetic transformation.     

Inbreeding depression in <Emphasis Type="Italic">Solanum carolinense</Emphasis> (Solanaceae), a species with a plastic self-incompatibility response

Background  

Solanum carolinense (horsenettle) is a highly successful weed with a gametophytic self-incompatibility (SI) system. Previous studies reveal that the strength of SI in S. carolinense is a plastic trait, associated with particular S -alleles. The importance of this variation in self-fertility on the ability of horsenettle to found and establish new populations will depend, to a large extent, on the magnitude of inbreeding depression. We performed a series of greenhouse and field experiments to determine the magnitude of inbreeding depression in S. carolinense, whether inbreeding depression varies by family, and whether the estimates of inbreeding depression vary under field and greenhouse conditions. We performed a series of controlled self- and cross-pollinations on 16 genets collected from a large population in Pennsylvania to obtain progeny with different levels of inbreeding. We grew the selfed and outcrossed progeny in the greenhouse and under field conditions and recorded various measures of growth and reproductive output.     

<Emphasis Type="Italic">CbLEA</Emphasis>, a Novel<Emphasis Type="Italic">LEA</Emphasis> Gene from<Emphasis Type="Italic">Chorispora bungeana</Emphasis>, Confers Cold Tolerance in Transgenic Tobacco

A novel late embryogenesis abundant (LEA) gene (AY804193), namedCbLEA, has now been isolated fromChorispora bungeana. This rare alpine subnival plant can survive sudden snowstorms and low temperatures. The full-lengthCbLEA is 842 bp, with an open reading frame encoding 169 ami no acids. The putative molecular weight ofCbLEA protein is 17.9 kDa, with an estimatedpl of 6.45. To investigate the functioning of thisCbLEA protein in cold-stress tolerance,CbLEA was introduced into tobacco under the control of the CaMV35S promoter. Second-generation (R₁) transgenic tobacco plants exhibited significantly increased tolerance to cold. These transgenics maintained lower malondialdehyde (MDA) contents and electrolyte leakage (EL) but their relative water content (RWC) was significantly higher compared with non-transgenic plants under chilling stress. Further experimental results showed that non-transgenic plants had severe freezing damage after exposure to -2°C for 1 h, whereas the transgenics suffered only slight injury under the same conditions. Moreover, survival was longer in the latter genotype at that temperature. The extent of increased cold tolerance was positive correlated with the level ofCbLEA protein accumulation, and was also reflected by the delayed development of damage symptoms. This indicates thatCbLEA is an excellent stress tolerance gene, and holds considerable potential as a new molecular tool for engineering improved plant genetics.     

Detecting spatial interactions in the ragweed (<Emphasis Type="Italic">Ambrosia artemissifolia</Emphasis> L.) and the ragweed beetle (<Emphasis Type="Italic">Ophraella communa</Emphasis> LeSage) populations

We observed a weed (Ambrosia artemissifolia)–beetle herbivore (Ophraella communa) system for three years in a spatially continuous field (≈200 ha). We analyzed our field data in the light of two contrasting theories: the resource-concentration hypothesis and reaction–diffusion theory. For the resource-concentration hypothesis, we calculated the correlation coefficients between weed and beetle abundances for every season in each year. Although we found weak support for resource concentration in some seasons, we could not find any clear relationships in other seasons. We discuss a dispersal-based mechanism to explain the differences observed among seasons in lieu of the resource-concentration hypothesis. For the reaction–diffusion theory, we estimated the nonparametric spatial covariance functions for the spatial autocorrelation of weeds and beetles. Although we could not find any strong spatial structure for the individual species, we found evidence of spatial interactions between weeds and beetles using time lagged cross-correlation functions. Weed abundance enhanced local beetle abundance. Through time, there was evidence of beetle spillover to adjacent locations at roughly the one beetle-generation time scale. Sites with large number of beetles did not seem to reduce subsequent weed abundance.     

Habitat,density, and spatial distribution of <Emphasis Type="Italic">Rivulus giarettai</Emphasis> (<Emphasis Type="Italic">Actinopterygii</Emphasis>, <Emphasis Type="Italic">Cyprinodontiformes</Emphasis>) in southeastern Brazil

We present data on the habitat, density, and spatial distribution of Rivulus giarettai, and discuss some biotic and abiotic variables related to its abundance in Free Flowing Waters (FFW) and Dam Reservoirs (DR) in palm grove (Mauritia flexuosa) marshes (Veredas) in Uberlandia, Minas Gerais, southeastern Brazil. The mean density (individuals/plot) of R. giarettai was about 13 times higher in FFW than in DR. In FFW, the density of R. giarettai was highest at intermediate amounts of substrate (plant mass) and it was positively rank-correlated with the depth, and the number of arthropods. Individuals occurred in an aggregated distribution. The aggregated pattern could be related to a concentration of individuals in microhabitats neither too much exposed nor completely saturated by plants. R. giarettai was relatively abundant and tolerant to slight man-made habitat modifications. Damming appeared to be especially problematic by negatively affecting its density.     

Fitness aspects of transgenic <Emphasis Type="Italic">Aedes fluviatilis</Emphasis> mosquitoes expressing a <Emphasis Type="Italic">Plasmodium</Emphasis>-blocking molecule

Vector-born diseases cause millions of deaths every year globally. Alternatives for the control of diseases such as malaria and dengue fever are urgently needed and the use of transgenic mosquitoes that block parasite/virus is a sound strategy to be used within control programs. However, prior to use transgenic mosquitoes as control tools, it is important to study their fitness since different biological aspects might influence their ability to disseminate and compete with wild populations. We previously reported the construction of four transgenic Aedes fluviatilis mosquito lines expressing a Plasmodium- blocking molecule (mutated bee venom phospholipase A₂–mPLA₂). Presently we studied two aspects of their fitness: body size, that has been used as a fitness-related status, and the expression of major enzymes classes involved in the metabolism of xenobiotics, including insecticides. Body size analysis (recorded by geometric wing morphometrics) indicated that both male and female mosquitoes were larger than the non-transgenic counterparts, suggesting that this characteristic might have an impact on their overall fitness. By contrast, no significant difference in the activity of enzymes related to metabolic insecticide resistance was detected in transgenic mosquitoes. The implication on fitness advantage of these features, towards the implementation of this strategy, is further discussed.     

Host specificity of <Emphasis Type="Italic">Euops chinesis</Emphasis>, a potential biological control agent of <Emphasis Type="Italic">Fallopia japonica</Emphasis>, an invasive plant in Europe and North America

Fallopia japonica (Houttuyn) Ronse Decraene (Polygonaceae) is a serious invasive weed in North American and Europe. In its native China, a leaf-rolling weevil, Euops chinesis (Coleoptera: Attelabidae) was found attacking F. japonica in the field. No-choice tests, multiple-choice tests, open field tests and field surveys were conducted as a measure of its host specificity. Forty-six plant species were selected from 17 families for host range testing, among which, six species, F. multiflora, F. japonica, Persicaria perfoliata, Rumex acetosa, R. japonicus and R. aquaticus, were exposed to adults in no-choice tests. However, larvae could only develop successfully on F. japonica, and this plant appeared to be the only host in the field, suggesting the weevil is host-specific. As larval development appears to depend on a fungus in the leaf rolls, the insect–fungus mutualism and risks including host specificity of the fungus should be evaluated before the insect’s introduction.     

Seed production of cut-leaved teasel (<Emphasis Type="Italic">Dipsacus laciniatus</Emphasis>) in central Missouri

Cut-leaved teasel is an invasive weed in Missouri that reduces the diversification of native species along roadsides and impairs traffic visibility. Teasel is a biennial and grows as a rosette in the first year and flowers the second year. Reproduction is only by seed. Field studies were conducted in 2004 and 2005 at two locations to assess the seed production of cut-leaved teasel. From a natural stand, fifteen plants were tagged at the onset of flowering. Selected plants included those considered growing in a group and those growing alone; a plant was considered alone when no other plant was adjacent for at least 60 cm. Whenever a seedhead completed flowering, it was covered with a cellophane bag and harvested one month later. Linear regression was used to correlate the weight of seeds from a single seedhead and number of seeds to estimate the total seed production per seedhead. The number of seedheads per plant varied from 3 to 56. On average, plants growing alone had 64% more seedheads per plant than plants occurring in a group. Seed numbers in the primary seedhead ranged from 511 to 1,487. Total seed production per plant ranged from 1,309 to 33,527. Seed production was 61% greater for plants growing alone versus those growing in a group and was more prolific in 2005 than in 2004. In addition, seed production per plant varied between locations for plants growing alone, but seed yield per plant was similar for plants growing in groups. Colonization of teasel in new areas is facilitated by higher seedhead numbers per plant and total seed production compared to reproduction of plants in areas of intraspecific competition.     

Costs of induced defenses for the invasive plant houndstongue (<Emphasis Type="Italic">Cynoglossum officinale</Emphasis> L.) and the potential importance for weed biocontrol

Inducible plant defenses—those produced in response to herbivore feeding—are thought to have evolved as a cost-saving tactic that allows plants to enact defenses only when needed. The costs of defense can be significant, and loss of plant fitness due to commitment of resources to induced defenses could affect plant populations and play a role in determining the success or failure of weed biocontrol. We used methyl jasmonate (MeJA) to experimentally induce defenses without herbivores in invasive houndstongue plants (Cynoglossum officinale L.) in the field and measured resulting growth and fitness (plant size, seed number, and seed weight). MeJA-treated plants emitted large amounts of plant volatiles and produced leaves with twice as many trichomes as untreated plants. Plants with activated defenses had fewer leaves, were smaller, and produced nutlets that weighed less than plants not investing in defenses. These data indicate that herbivore-induced defenses are costly for houndstongue plants in their invaded range and represent significant indirect costs of herbivory beyond direct feeding damage (e.g., loss of photosynthetic tissue). Notably, the magnitude of defenses elicited upon feeding varies greatly by herbivore species and a better understanding of the costs of defense could help us predict which potential biocontrol herbivores are most likely to be effective.     

Methylglyoxal destroys <Emphasis Type="Italic">Agrobacterium tumefaciens</Emphasis> crown gall tumours in <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> without any adverse effect on the host plant

Methylglyoxal (MG) is a highly reactive α-oxoaldehyde, demonstrating anticancer effect on plant neoplastic tumours. In in vivo studies it was observed that MG destroyed crown gall tumours in Nicotiana tabacum produced by Agrobacterium tumefaciens, without any adverse effect on the host. The efficacy of MG in comparison to other anticancer drugs viz. cisplatin and ellagic acid in the treatment of crown gall was investigated. A slight degeneration of galls was noted in plants treated with cisplatin and ellagic acid but the plants died subsequently. With MG however, crown galls were completely cured and the plants completed their usual life cycle by flowering and producing seeds. MG inhibited the respiration of crown gall calluses suggesting that energy depletion resulted in tumour destruction.     

Diffuse interactions between two herbivores and constraints on the evolution of resistance in horsenettle (<Emphasis Type="Italic">Solanum carolinense</Emphasis>)

Interactions between plants and herbivores are considered “diffuse” if the ecological interactions between two species, or their evolutionary responses, differ depending on the presence of a third species. I looked for evidence of diffuse interactions among horsenettle (Solanum carolinense) and two common herbivores. Plants experimentally protected from lace bugs (Gargaphia solani) were twice as susceptible to attack from flea beetles (Epitrix fuscula) once transplanted into the field. Thus, the selective benefit to horsenettle of resistance against lace bugs in nature would likely be diminished by increased attack from flea beetles. Moreover, the relative rank among horsenettle genotypes for resistance against flea beetles was changed by prior exposure to lace bugs. Thus, the genetic expression of resistance to flea beetles would depend on the “lace bug environment.” By affecting selective pressures or response to selection, these sorts of diffuse interactions in a plant-herbivore community can slow the host plant’s evolution of resistance to its herbivores.