Algal-bacterial interactions in metal contaminated floodplain sediments

The aim of the present study was to investigate algal-bacterial interactions in a gradient of metal contaminated natural sediments. By means of multivariate techniques, we related the genetic structure (denaturing gradient gel electrophoresis, DGGE) and the physiological structure (community-level physiological profiling, CLPP) of the bacterial communities to the species composition of the algal communities and to the abiotic environmental variables, including metal contamination. The results revealed that genetic and physiological structure of the bacterial communities correlated with the species composition of the algal community, but hardly to the level of metal pollution. This must be interpreted as an indication for a strong and species-specific linkage of algal and bacterial species in floodplain sediments. Metals were, however, not proven to affect either the algal or the bacterial communities of the Dutch river floodplains.     

Intraspecific hyperparasitism in a primary hymenopteran parasitoid

In solitary parasitoids, in which only one individual can emerge per host, the adaptive value of conspecific superparasitism is a function of the survival probability of the egg laid by the superparasitizing female. In the few cases which these probabilities are compared, the oldest immature has an advantage over the other individuals. We measured the acceptance rate of parasitized hosts and survival rate of supernumerary larvae in Anaphes victus (Hymenoptera: Mymaridae) in relation to the interval between ovipositions. When this interval was 5–7 days, the first immature was at the prepupa and pupa stage respectively, and female Anaphes victus changed their oviposition behavior markedly. They killed the developing parasitoid of their own species before ovipositing in it. The progeny of these females, which are normally primary parasitoids, developed thereafter as hyperparasitoids. Indeed, in contrast with other species, the survival of the second female's progeny increased with the time interval between ovipositions. This type of facultative intraspecific hyperparasitism is different from autoparasitism in Aphelinidae and has never been mentioned in other parasitoids; it would be adaptive if females of this short-lived species encounter low-quality patches.     

Insecticide resistance may enhance the response to a host-plant volatile kairomone for the codling moth, <Emphasis Type="Italic">Cydia pomonella</Emphasis> (L.)

The behavioral and electroantennographic responses of Cydia pomonella (L.) to the ripe pear volatile ethyl (2E,4Z)-2,4-decadienoate (Et-E,Z-DD), were compared in insecticide-susceptible and -resistant populations originating from southern France. A dose–response relationship to this kairomonal attractant was established for antennal activity and did not reveal differences between susceptible and resistant strains. Conversely, males of the laboratory strains expressing metabolic [cytochrome P450-dependent mixed-function oxidases (mfo)] or physiological (kdr-type mutation of the sodium-channel gene) resistance mechanisms exhibited a significantly higher response to Et-E,Z-DD than those of the susceptible strain in a wind tunnel experiment. No response of the females to this kairomone could be obtained in our wind-tunnel conditions. In apple orchards, mfo-resistant male moths were captured at significantly higher rates in kairomone-baited traps than in traps baited with the sex pheromone of C. pomonella. Such a differential phenomenon was not verified for the kdr-resistant insects, which exhibited a similar response to both the sex pheromone and the kairomonal attractant in apple orchards. Considering the widespread distribution of metabolic resistance in European populations of C. pomonella and the enhanced behavioral response to Et-E,Z-DD in resistant moths, the development of control measures based on this kairomonal compound would be of great interest for the management of insecticide resistance in this species.     

Travel time affects optimal diets in depleting patches

Models of prey choice in depleting patches predict an expanding specialist strategy: Animals should start as specialists on the most profitable prey and then at some point during patch exploitation switch to a generalist foraging strategy. When patch residence time is long, the switch to a generalist diet is predicted to occur earlier than when patch residence time is short. We tested these predictions under laboratory conditions using female parasitoids (Aphidius colemani) exploiting patches of mixed instars aphid hosts (Myzus persicae, L1 and L4). The duration of patch exploitation was manipulated by changing travel time between patches. As predicted, patch residence times increase with travel time between patches. Our results provide empirical support for the expanding specialist prediction: Parasitoid females specialized initially on the more profitable hosts (L4), and as the patch depleted, they switched to a generalist diet by accepting more frequently the less profitable hosts (L1). The point at which they switched from specialist to generalist occurred later when travel times and hence patch residence times were short. By affecting the patch exploitation strategy, travel time also determines the composition of hosts left behind, the “giving up composition.” The change in the relative density of remaining host types alters aphid populations’ age structure.     

Dioxin reservoirs in southern Viet Nam--a legacy of Agent Orange

In the isolated Aluoi Valley of central Viet Nam, very high levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were measured in soil, fish fat, duck fat, pooled human blood and breast milk samples collected from A So village between 1996 and 1999. The village was situated on a former military base occupied by US Special Forces between 1963 and 1966. TCDD was a contaminant of the herbicide "Agent Orange", aerially sprayed in the valley between 1965 and 1970, and stored at the A So base. Measured levels were lower near the sites of two other former US bases in the valley which had been occupied for shorter periods of time. In areas where Agent Orange had been applied by low-flying aircraft, levels of TCDD in soil, food and human samples were elevated, but lower than those near the three former US bases. We confirm the apparent food chain transfer of TCDD from contaminated soil to cultured fish pond sediments to fish and duck tissues, then to humans as measured in whole blood and breast milk. We theorize that the Aluoi Valley is a microcosm of southern Viet Nam, where numerous reservoirs of TCDD exist in the soil of former military installations south of the former demilitarized zone. Large quantities of Agent Orange were stored at many sites, used in ground and aerial applications, and spilled. TCDD, through various forms of soil disturbance, can be mobilized from these reservoirs after decades below the surface, and subsequently, introduced into the human food chain.     

Documentation of the endotoxins present in the ambient air of cotton fiber textile mills in Québec

Cotton workers are recognized as being at risk of developing occupational lung diseases. Some researchers have identified endotoxins as being a potential etiologic agent for some of the respiratory problems. This study wants to document the concentration of endotoxins found in the ambient air of textile mills where cotton fibers are handled and to identify the processing steps where the highest endotoxins concentrations in the air were found and the one where the relative limit values (RLVs) are exceeded. The 4 mills studied process cotton fibers. All the air samples were analyzed using the chromogenic Limulus Amoebocytes lysate LAL method using a kinetic detection principle based on the IRSST's standard method. In this study, a large variability in the concentrations of endotoxins in the air was observed, depending on the mill, the processing step, and the time. Despite these variations, some processes can be identified as being major generators of endotoxins in the ambient air of the mills. The highest concentrations were measured in the weaving and drawing processes and reached 10,000 EU m(-3) of air. The opening, cleaning, carding, spinning and drawing processes are the other major endotoxins generating processes with concentrations from 24 to 8,700 EU m(-3) of air. The endotoxins concentrations exceeded the RLVs for 55% of the workstations in this project. This study demonstrated that endotoxins levels in the cotton industry are high and appropriate control measures are needed.     

Type of disturbance and ecological history determine structural stability.

This study aims to reveal whether complexity, namely, community and trophic structure, of chronically stressed soil systems is at increased risk or remains stable when confronted with a subsequent disturbance. Therefore, we focused on a grassland with a history of four centuries of patchy contamination. Nematodes were used as model organisms because they are an abundant and trophically diverse group and representative of the soil food web and ecosystem complexity. In a field survey, a relationship between contaminants and community structures was established. Following, two groups of soil mesocosms from the field that differed in contamination level were exposed to different disturbance regimes, namely, to the contaminant zinc and a heat shock. The zinc treatment revealed that community structure is stable, irrespective of soil contamination levels. This implies that centuries of exposure to contamination led to adaptation of the soil nematode community irrespective of the patchy distribution of contaminants. In contrast, the heat shock had adverse effects on species richness in the highly contaminated soils only. The total nematode biomass was lower in the highly contaminated field samples; however, the biomass was not affected by zinc and heat treatments of the mesocosms. This means that density compensation occurred rapidly, i.e., tolerant species quickly replaced sensitive species. Our results support the hypothesis that the history of contamination and the type of disturbance determine the response of communities. Despite that ecosystems may be exposed for centuries to contamination and communities show adaptation, biodiversity in highly contaminated sites is at increased risk when exposed to a different disturbance regime. We discuss how the loss of higher trophic levels from the entire system, such as represented by carnivorous nematodes after the heat shock, accompanied by local biodiversity loss at highly contaminated sites, may result in detrimental effects on ecosystem functions.     

Development and application of a sediment toxicity test using the benthic cladoceran Chydorus sphaericus

This study reports on the development and application of a whole sediment toxicity test using a benthic cladoceran Chydorus sphaericus, as an alternative for the use of pelagic daphnids. A C. sphaericus laboratory culture was started and its performance under control conditions was optimised. The test was firstly validated by determining dose-response relationships for aqueous cadmium and copper and ammonia, showing a sensitivity of C. sphaericus (96 h LC(50) values of 594 microg Cd/L, 191 microg Cu/L and 46 mg ammonia/L at pH 8) similar to that of daphnids. Next, sediment was introduced into the test system and a series of contaminated sediments from polluted locations were tested. A significant negative correlation between survival and toxicant concentrations was observed. It is concluded that the test developed in the present study using the benthic cladoceran C. sphaericus is suitable for routine laboratory sediment toxicity testing.     

Learning affects host discrimination behavior in a parasitoid wasp

Learning is generally predicted not to be important in host discrimination by parasitoids, because the stimuli involved are less variable than those used in habitat location. However, Anaphes victus (Hymenoptera: Mymaridae), an egg parasitoid of Listronotus oregonensis (Coleoptera: Curculionidae) apparently learns to associate external pheromones with the presence of a conspecific in a host. In this species, females can reject a parasitized host either after antennal drumming (antennal rejection) or after the insertion of their ovipositor (sting rejection). When they encountered a series of parasitized hosts, females A. victus learned to associate the presence of the external pheromone with the presence of the internal one. Learning lasted less than 4 h and occurred earlier in a series when the female marking the egg and the one detecting that mark were close relatives. This behavior could be adaptive because antennal rejection is faster than sting rejection. Received: 11 March 1997 / Accepted after revision: 30 August 1997