Density-Dependent Response of the Pea Aphid (Hemiptera : Aphididae) to Imidacloprid

A study was conducted to determine the influence of initial population density on the effects of pesticides on pea aphid, Acyrthosiphon pisum (Harris), populations. Three initial starting densities of pea aphids (147, 295 and 590 aphids per m(2)) were exposed to no pesticide or imidacloprid at rates of 1 or 5 g ai/ha on broad bean plants, Vicia faba L., in a greenhouse. Ten days later, population size was assessed. In general, higher initial aphid population density resulted in a higher final population density for all imidacloprid concentrations. However, population growth rates for populations started with the highest density (590 aphids per m(2)) were significantly lower than those with initial densities of 147 and 295 aphids per m(2). This was due to a relative reduction in population number. Populations begun with 147 aphids per m(2) were 50% lower after exposure to the highest concentration of imidacloprid, whereas the populations begun with 295 and 590 aphids per m(2) were 42 and 25% of the starting population size, respectively. Therefore, the pesticide actually had a greater impact on the population started with the highest density. This can be explained by a synergistic effect of the pesticide and crowding. The lower growth rate observed in the population started with the highest density was probably due to crowding, whereby aphids approached the carrying capacity and were stressed. Even though these populations were reduced, final density was still sufficiently high to limit resources. These results indicate that the response of organisms to stress is influenced by population density at the start of a stressful event, such as a pesticide exposure. Therefore, different experimental designs may result in different outcomes and starting population densities must be carefully considered when designing population-level toxicological experiments

Studying the effect of exposure of the snail Helix aspersa to the purified Bt toxin, Cry1Ab

International audienceThe present study was intended to assess the effect of the Bt toxin, Cry1Ab, on the snail, Helix aspersa.We studied hatchability of eggs as well as growth and survival of the juvenile snails. The eggs were exposed to purified Bacillus thuringiensis Cry1Ab toxin mixed in with soil in 0, 11, 22, 44 or 88 mg Bt kg1. To check the growth and survival of the juvenile snails, we conducted two different sets of experiments. In the first experiment, the snails were exposed to soil mixed with Bt toxin in 0, 5.5, 11, 22 or 44 mg Bt kg1 concentrations. In the second experiment, the snails were fed a diet with pure Bt toxin at 0, 11, 44 or 88 mg Bt kg1 dry weight. We found that Bt toxin has no negative effect on H. aspersa during the observed life stages

Increased response to cadmium and Bacillus thuringiensis maize toxicity in the snail Helix aspersa infected by the nematode Phasmarhabditis hermaphrodita.

International audienceTo determine the effect of nematode infection on the response of snails to selected toxins, we infected Helix aspersa with 0-, 0.25-, 1-, or 4-fold the recommended field dose of a commercial nematode application for agricultural use. In the first experiment, the snails also were exposed to cadmium via food and soil at concentrations of 0, 30, 60, 120, or 240 mg/kg in a full-factorial design. In the second experiment, snails were infected with nematodes and also fed either Bt (expressing Bacillus thuringiensis toxin) maize or non-Bt maize. The snails were weighed at the beginning and end (after four weeks) of the experiments, and mortality was checked daily. Neither exposure of snails to nematodes nor exposure of snails to cadmium or Bt toxin affected the survival rates of snails. The number of dead snails was highest for combinations of nematode treatments with cadmium concentrations of 120 and 240 mg/kg. In both experiments (Bt and cadmium), the growth rate decreased with increasing nematode dose. The Bt maize was not harmful to the snails in the absence of nematodes, but infected snails grew faster when fed non-Bt maize. The growth rate of snails exposed to cadmium decreased with exposure to increasing Cd concentrations and differed significantly between the no-nematode treatment and the treatments with nematode doses of one- and fourfold the recommended field dose. Snails treated with the highest dose of nematodes accumulated the highest cadmium concentrations

Interactions between toxic chemicals and natural environmental factors - a meta-analysis and case studies

The paper addresses problems arising from effects of natural environmental factors on toxicity of pollutants to organisms. Most studies on interactions between toxicants and natural factors, including those completed in the EU project NoMiracle (Novel Methods for Integrated Risk Assessment of Cumulative Stressors in Europe) described herein, showed that effects of toxic chemicals on organisms can differ vastly depending purely on external conditions. We compiled data from 61 studies on effects of temperature, moisture and dissolved oxygen on toxicity of a range of chemicals representing pesticides, polycyclic aromatic hydrocarbons, plant protection products of bacterial origin and trace metals. In 62.3% cases significant interactions (p< or =0.05 or less) between natural factors and chemicals were found, reaching 100% for the effect of dissolved oxygen on toxicity of waterborne chemicals. The meta-analysis of the 61 studies showed that the null hypothesis assuming no interactions between toxic chemicals and natural environmental factors should be rejected at p=2.7 x 10(-82) (truncated product method probability). In a few cases of more complex experimental designs, also second-order interactions were found, indicating that natural factors can modify interactions among chemicals. Such data emphasize the necessity of including information on natural factors and their variation in time and across geographic regions in ecological risk assessment. This can be done only if appropriate ecotoxicological test designs are used, in which test organisms are exposed to toxicants at a range of environmental conditions. We advocate designing such tests for the second-tier ecological risk assessment procedures.publishe

Exposure and effects assessments of Bt-maize on non-target organisms (gastropods, microarthropods, mycorrhizal fungi) in microcosms

Potential differences between Bt-maize (MEB307 expressing the insecticidal Cry1Ab protein) and a near-isogenic non-Bt variety (Monumental) in their influence on the garden snail (Helix aspersa), soil microarthropods (Collembola, Actinedida, Acaridida, Gamasida and Oribatida) and mycorrhizal fungi were studied. Growing snails were caged in microcosms allowing the development of Bt or non-Bt-maize (Zea mays L.) on a sandy loam soil. After 3 months exposure, survival and growth of snails were similar in both treatments. Cry1Ab protein was detected in the Bt-maize leaves (22–42.2 μg Bt protein g−1 dry wt), in the snail tissues (0.04–0.11 μg Bt-protein g−1 dry wt) and in their faeces (0.034–5 μg Bt-protein g−1 dry wt). Total soil microarthropod abundance and diversity were similar between control (non-Bt-maize) and the genetically modified (GM) Bt-maize microcosms. The mycorrhizal colonization of roots did not differ between Bt and non-Bt-maize (frequency of mycorrhizal roots was 88.7% and 83.3% respectively). The mycorrhizal infectivity of soils, expressed as MI50 (minimum soil dry weight required to colonize 50% of plants) was measured using red clover. MI50 was similar for soils where Bt or non-Bt-maize was cultivated for 4 months. The detection of Cry1Ab protein in the viscera and faeces of H. aspersa exposed to Bt-maize indicates that snails contribute to the transfer of the Bt-protein from plant to soil or snail predators. This may constitute an alternative route of exposure for Bt-protein in soil, but this was without a negative influence on mycorrhizal fungi or microarthropods. Results showed that Bt-maize was not toxic for the selected non-target species exposed for 3 or 4 months. The microcosms and analyses used in this study represent new methods for assessing effects of chronic exposure to GM plants of several diverse, yet ecologically and temporally associated species. As the soil organisms we studied can also be used in standardized ecotoxicological tests (XP X31-205-2 for mycorrhizal fungi, ISO 11267 for Collembola and ISO 15952 for snails), microcosm exposures represent a way to link laboratory and field methods for the ecotoxicological evaluation of GM plants

Interactions between effects of environmental chemicals and natural stressors: a review.

Ecotoxicological effect studies often expose test organisms under optimal environmental conditions. However, organisms in their natural settings rarely experience optimal conditions. On the contrary, during most of their lifetime they are forced to cope with sub-optimal conditions and occasionally with severe environmental stress. Interactions between the effects of a natural stressor and a toxicant can sometimes result in greater effects than expected from either of the stress types alone. The aim of the present review is to provide a synthesis of existing knowledge on the interactions between effects of “natural” and chemical (anthropogenic) stressors. More than 150 studies were evaluated covering stressors including heat, cold, desiccation, oxygen depletion, pathogens and immunomodulatory factors combined with a variety of environmental pollutants. This evaluation revealed that synergistic interactions between the effects of various natural stressors and toxicants are not uncommon phenomena. Thus, synergistic interactions were reported in more than 50% of the available studies on these interactions. Antagonistic interactions were also detected, but in fewer cases. Interestingly, about 70% of the tested chemicals were found to compromise the immune system of humans as judged from studies on human cell lines. The challenge for future studies will therefore be to include aspects of combined stressors in effect and risk assessment of chemicals in the environmen