Studies on ciliated protozoa in eutrophic lakes: 2. Field and laboratory studies on the effects of oxygen and other chemical gradients on ciliate distribution

An investigation into the spatial distribution of hypolimnetic ciliates in three small eutrophic lakes during the period of summer stratification was carried out. Peak ciliate densities were found to occur at the oxic/anoxic boundary, ciliate numbers declining with increasing depth within the hypolimnion. The ciliates only occurred in aerobic water where oxygen levels were less than about 0.5 mgl^–1 Laboratory experiments demonstrated that the ciliates swim upwards under anaerobic conditions but swim rapidly downwards under aerobic conditions. Further laboratory experiments showed that although the bulk of the population occured within anaerobic water, the hypolimnetic ciliates are aerobes and cannot survive indefinite anoxia. Despite the demonstrable toxicity of high levels of ammonia and sulphide, it was probably excesive distance from an available source of oxygen that excluded the ciliates from the lowest levels of the hypolimnion. Possible mechanisms which allowed these aerobic ciliates to colonise anaerobic water are considered.     

Piping Plover Chick Foraging,Growth, and Survival in the Great Plains

Abstract: We tested the hypothesis that piping plover (Charadrius melodus) habitat quality and chick survival on the Missouri River, USA, were lower on a cold-water reservoir and downstream from a hypolimnetic (cold-water) release dam with diel water fluctuations (Garrison Dam) than downstream from an epilimnetic dam (Gavins Point Dam). Plovers in adjacent alkali wetlands provided an index to the maximum reproductive potential in the region. Chicks gained weight more rapidly in the alkali wetlands than on epilimnetic and hypolimnetic river reaches. Invertebrate numbers and biomass were higher in the wetlands and epilimnetic reach, but chick survival was lower on the epilimnetic reach. Thus, piping plovers adapted to a variety of prey densities, and other factors, likely predation, reduced survival rates in the epilimnetic reach. Temporal and spatial variability in site quality indices suggests the need for a regional management strategy with different strategies at each site. Managers can minimize effects of local fluctuations in resource abundance and predators by ensuring protection of or creating geographically dispersed habitat. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):682–687; 2008)     

Parasitism of non-target lepidoptera by mass released Trichogramma brassicae and its implication for the larval parasitoid Lydella thompsoni

The release of high numbers of the eggparasitoid Trichogramma brassicae Bezd.(Hym. Trichogrammatidae) to control theEuropean corn borer (ECB), Ostrinianubilalis Hb. (Lep.: Crambidae) in maize hasraised concerns about potential negativeeffects on native natural enemies. The nativelarval parasitoid Lydella thompsoniHerting (Dipt.: Tachinidae) is the mostfrequent and important ECB parasitoid insouthern Switzerland and can achieve highparasitism rates. Its first generation emergestoo early to find ECB larvae and must rely onalternative hosts living in natural habitatsclose to maize fields. Inundative releases ofT. brassicae coincide with theoviposition period of the alternative hosts ofthe tachinid. T. brassicae moving out ofrelease fields may attack and diminish thepopulation of these hosts, creating abottleneck situation for L. thompsoni inthe subsequent spring. Laboratory hostspecificity tests showed that the tachinid'stwo most abundant spring hosts Archanarageminipuncta Haworth (1809) (Lep.: Noctuidae)and Chilo phragmitellus Hübner (1805)(Lep.: Crambidae) are successfully parasitisedby T. brassicae females in no-choicesituations. Our extensive field surveys,however, showed that the two tested springhosts escape parasitism since their eggs arewell hidden or not attractive. Negativeeffects of inundative releases of T.brassicae on the native tachinid fly L. thompsoni, such as population densityreduction, displacement, or local extinction,are very unlikely.     

Behavioural variations among strains of Trichogramma spp.: Adaptability to field-temperature conditions

In order to select a candidate strain of Trichogramma sp. for inundative releases against lepidopteran pests in cabbage field-crops in the Netherlands, the parasitization activity of a collection of 60 different Trichogramma spp. strains was studied during 2 h and 24 h exposures at 12°C. Activity and parasitism varied significantly among strains and the two characteristics were not correlated, suggesting the action of two differentially temperature-dependent mechanisms influencing both characteristics. Native strains were characterized by a low activity at 12°C, making their usefulness for inundative releases doubtful. In three strains tested at 12, 17, 20, 25 and 30°C, activity increased linearly with temperature, until nearly all females parasitized at 20 or 25°C. Parasitism increased with increasing temperature to a maximum at 20–25°C and declined at 30°C. Handling time decreased asymptotically with increasing temperature. The results of this study suggest that Trichogramma strains vary in adaptability to low temperature, making this characteristic a useful criterion for evaluation of candidate strains.

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Résumé Afin de sélectionner une souche de Trichogramma sp. (Hymenoptera, Trichogrammatidae) candidate pour des lâchés inondatifs contre les Lépidoptères pestes de chou aux Pays-Bas, l'activité de parasitisation d'une collection de 60 souches différentes de Trichogramma spp. a été étudiée à 12°C pendant des durées d'exposition de 2 h et 24 h. L'activité proportionnelle et le degré de parasitisation des femelles varient significativement selon des souches et ne sont par corrélés. Ceci suggère l'action des deux mécanismes distincts, dépendant de la température et contrôlant independamment chacun de ces processus. Les souches indigènes sont caractérisées par une faible activité à 12°C, mettant en doute leur utilisation pour les lâchés inondatifs. Dans 3 souches testées à 12, 17, 20, 25 et 30°C, l'activité augmente linéairement avec la température, jusqu'a ce que quasi toutes les femelles parasitent les oeufs hôtes à 20°C et 25°C. Le taux de parasitisation augmente avec la température atteignant un maximum à 20–25°C puis diminue à 30°C. Le temps de manipulation d'un oeuf hôte diminue asymptotiquement lorsque la température croît. Les résultats de cette étude suggèrent que la capacité d'adaptation aux températures basses varie selon les souches de Trichogramma. Cette caractéristique constitue un critère utile pour l'évaluation de souches candidates potentielles.

     

Field dispersal of the parasitoid wasp Habrobracon hebetor (Hymenoptera: Braconidae) following augmentative release against the millet head miner Heliocheilus albipunctella (Lepidoptera: Noctuidae) in the Sahel

Pearl millet is one of the major staple food crops in Sub-Sahelian Africa, and the millet head miner (MHM) [Heliocheilus albipunctella] is its major pest, causing serious economic damage in the maturity period. We studied the dispersion patterns of the endogenous ectoparasitoid, Habrobracon hebetor (Hymenoptera: Braconidae), after augmentative releases in pearl millet fields for biological control of the MHM, in 2010 and 2011 in Burkina Faso and Niger. The parasitoids were released using 15 jute bags per release site. Parasitoid dispersion was indirectly monitored through weekly assessments of MHM parasitism by H. hebetor at different distances from release points (0, 3 and 5?km) and in control villages (15?km). Our findings indicate that the jute bags released approximately 900–1000 parasitoids per site over a period of three weeks. This initial parasitoid population led to higher parasitism of MHM larvae at the site of dissemination compared to farms at distances of 3 and 5?km. However, usually after five weeks, successive generations of H. hebetor dispersed up to 3?km, causing high levels of MHM larval mortality, which sometimes is similar to those of the release points. Based on these results, we recommend the release of parasitoids at sites spaced 3?km for timely and more efficient control of MHM populations.     

Controlling the Growth of Microcystis Using Surged Artificial Aeration

This paper investigates the effect of lake mixing, due to artificial hypolimnetic aeration, on the succession and ecological composition of selected phytoplankton species in Tegeler See, Berlin. Special attention is given to Microcystis, a nuisance bloom-forming blue-green algae and its competitor (in this lake) Ceratium, a dinoflagellate. Due to the installation configuration, the aerators frequently destratified the lake, especially when the stratification was weak. Five years representing three different operating schemes of the 15 aerators (continuous aeration, non-aeration and surge aeration) in this lake were used to determine possible aeration strategies in controlling Microsystis. In order to ease correlation of the mixing status in the lake with its yearly successions of phytoplankton growth a non-dimensional parameter called the Lake number was utilised. This parameter represents a balance between: i) forcing due to wind and aerator discharge and ii) potential energy acquired from the stratification of the lake. The results indicate that surged operation of the aerators is effective in suppressing massive growth of Microcystis. Due to their ability to adapt to the mixing/stability state of the water column, prolonged aeration or prolonged stable stratified conditions have little effect in controlling this algae.     

Biological Control of Anastrepha spp. (Diptera: Tephritidae) in Mango Orchards through Augmentative Releases of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae)

Diachasmimorpha longicaudata (Ashmead) parasitoids were released by air on a weekly basis over 1600 ha of commercial mango orchards, backyard orchards, and patches of native vegetation, at a density of ca. 940 parasitoids/ha. Releases were made during 2 consecutive years, beginning at flower onset and lasting until the end of the production cycle. Two areas, 7 km apart, were compared. In one area parasitoids were released, whereas the other area was used as a control. During the 2nd year treatments were reversed. Fruit was sampled in commercial mango orchards and in backyard orchards to assess levels of parasitism in fruit fly larvae. Highly significant differences in percentage parasitism were found in release and control zones in backyard orchards. Furthermore, trapping results indicated that D. longicaudata releases were associated with ca. 2.7-fold suppression of Anastrepha spp. populations in backyard orchards. Results suggest that suppression might be affected by environmental conditions and by the parasitoid:fly ratio achieved. Anastrepha obliqua McQuart populations were suppressed more effectively by use of parasitoids than those of Anastrepha ludens Loew, perhaps due to the type of host fruits used by each species. Augmentative parasitoid releases in marginal areas surrounding commercial orchards (backyard orchards, wild vegetation) can substantially suppress fly populations. Through this approach, the number of flies that later move into commercial orchards can be significantly reduced. Such a strategy, when combined with sound orchard management schemes, can allow growers to produce clean fruit without the need to resort to the widespread use of insecticides.     

The release of genetically engineered micro-organisms and viruses into the environment

This review considers the reasons for, and research governing, the regulation and monitoring of genetically engineered micro-organisms and viruses (GEMs) released into the environment. The hazards associated with releasing GEMs into the environment are the creation and evolution of new pests and diseases, and damage to the ecosystem and non target species. The similarities and differences between GEMs and conventional micro-organisms are discussed in relation to risk assessment. Other issues covered include the persistence of micro-organisms in the environment, transgene dispersal to non-engineered microbes and other organisms, the effects of transgenes and transformation on fitness, and the evolution of pests and pathogens that are given or acquire transgenes. Areas requiring further research are identified and recommendations for risk assessment made.     

Global distribution and status of introduced Siberian chipmunks Eutamias sibiricus

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Does the implementation of environmental flows improve wetland ecosystem services and biodiversity? A literature review

Environmental flow releases are a tool for wetland restoration, but there has been no systematic evaluation of their success. We systematically assessed 102 published studies from a wide range of wetland ecosystems across the globe to determine whether releasing environmental flows could maintain or promote biodiversity and increase ecosystem services, and which strategies were most effective. We found that environmental flow releases remarkably increased regulating services (sediment regulation and water purification) and supporting services (primary production and habitat maintenance), and maintained biodiversity and provisioning services. Biodiversity responses were positive only in river wetlands, and were negative in coastal, lake, and marsh wetlands; the overall delivery of ecosystem services responded positively in all ecosystem types except artificial wetlands. The effects were positive for ecosystem services under all environmental flow regimes, and seasonal minimum flow releases could maintain biodiversity and improve ecosystem services. We also found that long‐term environmental flow releases (years to decades) maintained biodiversity. Values of a change‐in‐flow parameter (D) ranging from 0 to 10% improved both biodiversity and ecosystem services. In summary, long‐term implementation, a high‐flow regime, and D ranging from 0 to 10% for the environmental flows promoted biodiversity and improved ecosystem services around the world, particularly in river wetlands. Regional‐level conclusions might be applicable to guide the implementation of environmental flow releases, but small sample sizes reduce their reliability. We also found that the effect sizes of environmental flow release projects for biodiversity and ecosystem services were significantly and positively correlated in rivers, but not in other wetlands.