Distribution of Nothanguina phyllobia and Its Potential as a Biological Control Agent for Silver-leaf Nightshade

The nematode Nothanguina phyllobia Thorne was found within large foliar galls on the perennial weed Solanum elaeagnifolium Cav. in west Texas. A two-year survey of a 6400 sq-km area in west Texas showed extensive distribution of the nematode. No hosts other than S. elaeagnifolium were observed. Densities of juvenile nematodes in the soil were high. N. phyllobia spread rapidly after small numbers of infective juveniles were applied in a foliar spray to an S. elaeagnifolium population. The host plant declined in vigor and frequently died. Artificial inoculation of an S. elaeagnifolium population with large numbers of the nematodes by broadcasting infected plant tissue resulted in high infection incidence.     

Histopathogenesis of the Galls Induced by Nothanguina phyllobia in Solanum elaeagnifolium

The histopathogenesis of the foliar galls induced by Nothanguina phyllobia Thorne in Solanum elaeagnilolium Cav. was examined via serial sections prepared from plant shoots at 11 time intervals (0.5-30 days) following inoculation. Nematodes infected the blades and petioles of young leaves surrounding the shoot apex. Hypertrophy and hyperplasia of the palisade, pith, cortical, and vascular parenchyma resulted in the formation of confluent leaf, petiole, and stem galls up to 25 cm³ in volume. Externally, leaf galls were irregular, light-green, convoluted spheroid bulges distending the abaxial surface. Mature galls contained a cavity lined with parenchymogenous nutritive tissue comprising intercellular spaces and actively dividing hypertrophied cells. These cells contained granular cytoplasm, hypertrophied nuclei, and brightly stained large nucleoli. Vascular tissues were not discernibly affected during the early stages of gall development. As gall development progressed, however, vascular elements were often displaced and disoriented. The histopathology of this nematode indicates that N. phyllobia is a highly specialized parasite and, for that reason, is suitable as a biological control agent.     

Response of the invasive pompom weed,Campuloclinium macrocephalum (Asteraceae), to feeding by the foliage-deforming thrips Liothrips tractabilis (Phlaeothripidae) under outdoor conditions in South Africa

The foliage-deforming thrips Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae) was recently released in South Africa as the first classical biological control agent against the invasive South American herb, Campuloclinium macrocephalum (Less.) DC. (Asteraceae). The impact of the thrips on young plants and regrowth of C. macrocephalum was assessed under outdoor conditions, and the results were compared to those of earlier laboratory trials that were conducted while the agent was still under investigation in quarantine. The outdoor trials revealed that feeding by L. tractabilis reduced the growth and biomass accumulation of C. macrocephalum, particularly in young plants and to a lesser extent in regrowth, which was largely consistent with the results of the earlier laboratory trials. Thrips-infested young plants were significantly shorter, produced fewer leaves and displayed significantly lower wet root masses and lower below- and above-ground dry masses, compared to the control plants. Although thrips-infested regrowth were significantly shorter, produced fewer leaves and displayed significantly lower above-ground dry masses than the control plants, the differences in wet root masses and below-ground dry masses were not significant. Although laboratory-based impact assessments are not necessarily an accurate reflection of field impact, in this instance the results were largely validated by the outdoor assessments. The results suggest that L. tractabilis will have a negative impact on C. macrocephalum populations in the field and thus contribute towards the weed’s biological control. The establishment of L. tractabilis has recently been confirmed in South Africa, providing the opportunity to verify these predictions.     

Diversity and impact of herbivorous insects on Brazilian peppertree in Florida prior to release of exotic biological control agents

Brazilian peppertree, Schinus terebinthifolia Raddi (Anacardiaceae), is a South American plant that is highly invasive in Florida. The impact of insect herbivores on the performance of Brazilian peppertree was evaluated at two locations in Florida using an insecticide exclusion method. Although 38 species of insect herbivores were collected on the invasive tree, there were no differences in growth or reproductive output of insecticide protected and unprotected trees, providing evidence that insect feeding had no measurable impact on tree performance. The majority of insects collected on Brazilian peppertree were generalists, and several were serious agricultural pests.     

A note on the role of Kachuga tectum gray (Reptilia: Chelonia) in controlling aquatic weeds

The herbivorous turtle Kachuga tectum consumes on wide variety of aquatic weeds and has potential as a biological agent against obnoxious weed growths.     

Morphometric Analysis of Anguina amsinckiae from Three Host Species

Amsinckia species (fiddleneck) in the South Coast Ranges of California were surveyed to determine if any of the 12 different California species of Amsinckia are hosts of the nematode, Anguina amsinckiae (Steiner and Scott, 1935) Thorne, 1961. Previously only Amsinckia intermedia Fischer and Meyer was reported as a host of Anguina amsinckiae. The survey established that there are at least two additional hosts of Anguina amsinckiae: Amsinckia lycopsoides Lehmann and Amsinckia gloriosa Suksdorf. Seven sites containing nematode-infected Amsinckia plants were discovered. Every site contained two or more species of Amsinckia; however, only one site contained more than one species of Amsinckia that was galled. Nematode specimens from A. intermedia, A. lycopsoides, and A. gloriosa were used in a morphometric analysis of 14 morphological variables. Stepwise discriminant analysis of the variables to separate the populations by host were successful for females, and the pairwise F-tests showed all three populations to have different group means (P < 0.05). Males from the three hosts were not always separable, however, as only the nematodes from Amsinckia gloriosa had a different group mean (P < 0.05).     

A Method for Assessing the Migratory Response of Naegleria fowleri Utilizing [3H]Uridine-Labeled Amoebae

ABSTRACT. A new procedure is described to assay the migratory response of Naegleria fowleri (ATCC 30894) amoebae to potential chemoattractants. The method utilizes a blind-well Boyden chemotaxis chamber, two micropore filters of different construction, and amoebae-labeled with [³H]uridine. The technique was standardized by determining the influence of incubation time, filter construction, filter pore size and geometry, amoebae to filter pore ratio, and chemoattractant concentration. Radiolabeled amoebae were placed in Boyden chambers that contained the combination of an upper polycarbonate filter with distinct pores with a diameter of 8 μm and a lower filter of nitrocellulose with a 150-μm depth to separate the wells. A ratio of two amoebae to one filter pore and a 2-h incubation period were chosen to obtain optimal migration conditions. Nerve cell extract was used as the chemoattractant. The migratory responses of both highly pathogenic and weakly pathogenic strains of N. fowleri to nerve cell extract were compared using either the radiolabel procedure or the conventional single filter, leading-front method. Using either method, a highly pathogenic cloned strain of N. fowleri amoebae moved in a directiona manner (chemotactically)in vitro to B103 rat neuroblastoma cell extract. In contrast, a weakly pathogenic strain of amoebae responded in a nondirectional manner (chemokinetically) to nerve cell extract. While both the leading-front assay and the radiolabel assay give accurate results, the measurement of radiolabeled cells allows one to test a greater number of attractants in one assay and the procedure eliminates observer bias.     

A scientific approach to agent selection

Abstract  The prioritisation of potential agents on the basis of likely efficacy is an important step in biological control because it can increase the probability of a successful biocontrol program, and reduce risks and costs. In this introductory paper we define success in biological control, review how agent selection has been approached historically, and outline the approach to agent selection that underpins the structure of this special issue on agent selection. Developing criteria by which to judge the success of a biocontrol agent (or program) provides the basis for agent selection decisions. Criteria will depend on the weed, on the ecological and management context in which that weed occurs, and on the negative impacts that biocontrol is seeking to redress. Predicting which potential agents are most likely to be successful poses enormous scientific challenges. 'Rules of thumb', 'scoring systems' and various conceptual and quantitative modelling approaches have been proposed to aid agent selection. However, most attempts have met with limited success due to the diversity and complexity of the systems in question. This special issue presents a series of papers that deconstruct the question of agent choice with the aim of progressively improving the success rate of biological control. Specifically they ask: (i) what potential agents are available and what should we know about them? (ii) what type, timing and degree of damage is required to achieve success? and (iii) which potential agent will reach the necessary density, at the right time, to exert the required damage in the target environment?     

Preference and Performance of the Polymorphic Flea-beetle, Alagoasa extrema, on Selected, Weedy Lantana camara Varieties

The possible preference that the leaf-feeding flea-beetle, Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae: Alticinae), might have for different South African naturalized varieties of its host plant, Lantana camara L. (Verbenaceae), was studied under quarantine laboratory conditions. Studies included adult choice trials, larval no-choice trials and multi-generation no-choice trials using five L. camara varieties. Results indicated that A. extrema exhibited a degree of varietal preference under laboratory conditions. Variety 029 White Pink proved to be the most suitable host, although the other four tested varieties were able to support viable populations of A. extrema for three consecutive generations. Should A. extrema be released as biocontrol agent for L. camara in South Africa, all five of the tested varieties should be able to support viable populations of A. extrema in the field.     

Involvement of Reactive Oxygen Species in Plant Mitochondrial Response to Low-Temperature Stress

The review presents data for the generation of the reactive oxygen species (ROS) in mitochondria during low-temperature stress. The relation of lipid peroxidation processes in membranes to the induction of low-temperature stress is demonstrated. The data for the involvement of the mitochondrial uncoupling proteins and the processes of uncoupling oxidation and phosphorylation in the regulation of mitochondrial ROS formation during low-temperature stress are considered.     

Morphological and Morphometrical Variations of Selected Rotifer Species in Response to Predation: a Seasonal Study of Selected Brachionid Species from Lake Xochimilco (Mexico)

Allelopathy of filamentous green algae (FGA) has been less studied than that of macrophytes. Little Budworth Pool, Cheshire, UK is a small, shallow, clear-water lake with high TP concentrations, very high NO_3-N concentrations, only moderate phytoplankton density, high FGA growth (mainly Spirogyra sp.) and no submerged plants. Experiments were carried out to test the possible allelopathic effects of Spirogyra on the phytoplankton of this lake and on a submerged plant Elodea nuttallii. Changes in phytoplankton growth, phytoplankton species dynamics and species composition were apparently not influenced by allelopathy of live or decaying Spirogyra. A shift from diatom (Cyclotella sp) – cryptomonad (Chroomonas acuta and Cryptomonas erosa) dominance to Chlorococcales (Micractinium pusillum, Monoraphidium contortum and Scenedesmus opoliensis) – Volvocales (Chlorogonium elongatum and Pandorina morum) dominance was recorded in both control and FGA treatments, suggesting an effect of nutrient enrichment. Nutrient concentrations and differences in competitiveness among phytoplankton species can also explain differences in their growth rates in Spirogyra filtrate. Spirogyra also did not influence apex number per plant, shoot length or growth rate of E. nuttallii. This FGA species probably cannot control phytoplankton or E. nuttallii growth in nutrient rich conditions through allelopathy.     

Is oviposition and larval damage by the leaf-mining fly Calycomyza eupatorivora (Agromyzidae) on its target weed,Chromolaena odorata (Asteraceae), restricted by leaf-quality preferences?

The leaf-mining fly Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) was released in the eastern coastal regions of South Africa for the biological control of the invasive shrub Chromolaena odorata (L.) King and Robinson. Despite widespread establishment, its ability to inflict sufficient foliar damage has been questioned. This laboratory study was initiated to provide some insight into how increasing fly populations (represented by 1, 5 and 10 mating pairs per plant) are likely to influence leaf-mining intensity and the levels of damage. On average, individual plants exposed to five mating pairs displayed significantly more larval mines (248) than those exposed to single pairs (69), while plants exposed to 10 mating pairs were intermediate (125). Similarly, at densities of five mating pairs per plant, the percentages of available leaves that were exploited peaked at 36%, while the percentages of available leaf area that were removed by larval leaf mining peaked at 22%. The non-linear relationship between leaf mining and fly density and the high percentages of unexploited leaves suggest that leaf mining may be influenced by leaf quality, the nature of which is currently unconfirmed. These results also suggest that the levels of leaf exploitation by C. eupatorivora will be too low to have any meaningful impact in the field. Field evaluations, to be reported in a later contribution, have indeed confirmed that the impact of C. eupatorivora on mature populations of C. odorata is negligible.     

Biological Control as a Tool for Ecosystem Management

Biological control is proposed as a tool useful for ecosystem management and compatible with the goals of often competing interests regarding the restoration and maintenance of ecosystems. We summarize the effects of introduced species on ecosystems in three broad groups: insects, vertebrates, and weeds. We then discuss the role of biological control for each of these groups in the context of ecosystem management and realistic outcomes. Of the three groups, we show that biological control of weeds appears to have the best chance for success in ecosystem management. We provide two case studies to support our ideas and finally discuss future needs and trends including fiscal considerations, cost/benefits associated with biological weed control, and potential funding sources.     

Effect of environmental factors on disease development caused by the fungal pathogen Plectosporium alismatis on the floating-leaf stage of starfruit (Damasonium minus), a weed of rice

Starfruit, Damasonium minus (R. Br.) Buch, is a herbicide-resistant, aquatic-weed occurring in Australian rice fields. The fungal pathogen Plectosporium alismatis (Oudem) W.M. Pitt, W. Gams & U. Braun is a potential mycoherbicide for the control of this weed. Previous work showed that the fungus can suppress the growth of starfruit juvenile plants. This paper reports the effect of environmental factors on the disease development on starfruit at the floating-leaf stage. Fungal inoculation of plants in advanced phases of floating leaf stage reduced significantly (P<0.05) the green leaf area, but only when the percentages of diseased areas were deducted. However, inoculation when the first floating leaf was emerging reduced significantly (P<0.001) both, plant dry above-ground biomass and leaf area.     

Response of Three Semi-Arid Plant Species to Fluoride; Consequences for Chlorophyll Florescence

The study was done to investigate the ability of three semi-arid plant species viz. Acacia tortilis, Cassia fistula and Prosopis juliflora to adapt to fluoride (F) stress. Here we examined the changes in activities of chlorophyll a fluorescence and photosynthetic pigment concentration during early growth of these plants. One month old plants were treated with 10, 20, and 50 mg kg^?1 F in soilrite. We did not observe any major change in photosynthetic performance of these plants during early growth. This was revealed by ETR, ETRmax, PPFD-sat and ΔF/Fm′-sat values which were higher in these plants. The decrease in chl a, chl b and total chl concentrations were significant only at 5 days. For most of the parameters, C. fistula was found to be more sensitive to F stress and P. juliflora showed least damage from F. The lesser inhibition in the parameters reflected the F tolerant nature of these plants with respect to photosynthesis. This opens the possibility of potential use of these species for treatment of F contaminated soil and water.     

The Specific Mineral Metabolism of Selected Plant Species and its Ecological Implications

In order to assess and compare the species-specific mineral metabolism of various plants, we raised eight selected species from different families under identical nutritional conditions. Five different nutrient solutions with varying Ca/K ratios were used. After two months of growth, the leaves were harvested, arranged according to age, and analyzed with respect to their K, Ca, and Mg contents. The ion ratios, the changes of ion contents with increasing age, the differences in water- and acid-soluble Ca (calcium oxalate), and the dependence of ion uptake on variations of ion concentrations in the solutions revealed a species-specific (“physiotypic”) feature of mineral metabolism. These features are discussed taking into consideration the ecological demands of the investigated species, and assuming that the physiological peculiarities of a species should affect its ecological behavior.