Spinosad and neem seed kernel extract as bio-controlling agents for malarial vector, Anopheles stephensi and non-biting midge, Chironomus circumdatus.

OBJECTIVE: Midge egg masses are reported to support non-pathogenic strains of the cholera pathogen, Vibrio cholera (V. cholera). Mosquito born diseases have been reported to cause millions of death worldwide. The present research reveals the toxicity effect of spinosad and neem seed kernel extract (NSKE) against different larval stages of Anopheles stephensi (An. stephensi) and Chironomus circumdatus (Ch. circumdatus). METHODS: The neem seeds were collected from Marudamalai hills, Bharathiar University, Coimbatore, India. Neem seed kernels were powdered, extracted and diluted for different concentrations (2 ppm to 10 ppm). Spinosad was purchased from Kalpatharu pesticide Limited, Coimbatore, Tamil Nadu, India and thoroughly mixed with distilled water to prepare various concentrations (0.01 to 0.08 ppm) and used for bioassay. RESULTS: The results depict that spinosad is more toxic in lower concentrations when compared to NSKE and mosquitoes are more susceptible than chironomids. Lethal concentrations were evaluated using the observed mortality. The lowest LC(50) value obtained from spinosad against An. stephensi and Ch. circumdatus were 0.002 05 ppm and 0.008 91 ppm. This study investigated on effect of Spinosad and NSKE on the biology of mosquito. The immature stages of both species were susceptible to Spinosad and NSKE. Spinosad and NSKE in individual as well as combined treatment provided additional days in development for mosquitoes. CONCLUSIONS: The results conclude that Spinosad and NSKE are potential larvicides against An. stephensi and Ch. circumdatus.

Anhydrobiosis-associated nuclear DNA damage and repair in the sleeping chironomid: linkage with radioresistance.

Anhydrobiotic chironomid larvae can withstand prolonged complete desiccation as well as other external stresses including ionizing radiation. To understand the cross-tolerance mechanism, we have analyzed the structural changes in the nuclear DNA using transmission electron microscopy and DNA comet assays in relation to anhydrobiosis and radiation. We found that dehydration causes alterations in chromatin structure and a severe fragmentation of nuclear DNA in the cells of the larvae despite successful anhydrobiosis. Furthermore, while the larvae had restored physiological activity within an hour following rehydration, nuclear DNA restoration typically took 72 to 96 h. The DNA fragmentation level and the recovery of DNA integrity in the rehydrated larvae after anhydrobiosis were similar to those of hydrated larvae irradiated with 70 Gy of high-linear energy transfer (LET) ions ((4)He). In contrast, low-LET radiation (gamma-rays) of the same dose caused less initial damage to the larvae, and DNA was completely repaired within within 24 h. The expression of genes encoding the DNA repair enzymes occurred upon entering anhydrobiosis and exposure to high- and low-LET radiations, indicative of DNA damage that includes double-strand breaks and their subsequent repair. The expression of antioxidant enzymes-coding genes was also elevated in the anhydrobiotic and the gamma-ray-irradiated larvae that probably functions to reduce the negative effect of reactive oxygen species upon exposure to these stresses. Indeed the mature antioxidant proteins accumulated in the dry larvae and the total activity of antioxidants increased by a 3-4 fold in association with anhydrobiosis. We conclude that one of the factors explaining the relationship between radioresistance and the ability to undergo anhydrobiosis in the sleeping chironomid could be an adaptation to desiccation-inflicted nuclear DNA damage. There were also similarities in the molecular response of the larvae to damage caused by desiccation and ionizing radiation.

Effects of uranium-contaminated sediments on the bioturbation activity of Chironomus riparius larvae (Insecta, Diptera) and Tubifex tubifex worms (Annelida, Tubificidae).

Freshwater sediments represent a compartment for accumulation of toxic substances, notably of metallic pollutants such as uranium. However, they also constitute a privileged habitat for many benthic macro-invertebrate species with important roles in the functioning of these ecosystems, particularly through their bioturbation activities. Uranium accumulation in sediments can thus have harmful effects on these organisms (e.g., developmental delay, malformations, mortality). The present study aimed to evaluate the consequences of these effects on the bioturbation activity of Chironomus riparius larvae and Tubifex tubifex worms. These two species, which are widespread in freshwater ecosystems, are characteristic of two different modes of bioturbation: bioirrigation and upward bioconveying, respectively. By quantifying the burial and redistribution of fluorescent particulate tracers (microspheres), sediment reworking induced by these macro-invertebrates was measured after 12d of exposure. Biodiffusion D(b) and bioadvection W rates, as well as several other parameters, were estimated to assess and compare the bioturbation activity of the two species, separately and in combination, between uncontaminated and uranium-spiked sediments. The results reveal that C. riparius larvae were more sensitive to uranium, but their bioturbation activity, even under uncontaminated conditions, had little effect on sediment reworking. Particle mixing was mainly induced by T. tubifex worms, which were only affected by uranium at high concentrations in the sediment. Finally, bioturbation by T. tubifex led to a high degree of uranium release from sediment to the overlying water, which highlights the crucial role of this mostly dominant species on uranium biogeochemical cycles at concentrations existing in naturally contaminated sites.

Influence of Chironomus riparius (Diptera, Chironomidae) and Tubifex tubifex (Annelida, Oligochaeta) on oxygen uptake by sediments. Consequences of uranium contamination.

The diffusive oxygen uptake (DOU) of sediments inhabited by Chironomus riparius and Tubifex tubifex was investigated using a planar oxygen optode device, and complemented by measurements of bioturbation activity. Additional experiments were performed within contaminated sediments to assess the impact of uranium on these processes. After 72h, the two invertebrate species significantly increased the DOU of sediments (13-14%), and no temporal variation occurred afterwards. Within contaminated sediments, it was already 24% higher before the introduction of the organisms, suggesting that uranium modified the sediment biogeochemistry. Although the two species firstly reacted by avoidance of contaminated sediment, they finally colonized it. Their bioturbation activity was reduced but, for T. tubifex, it remained sufficient to induce a release of uranium to the water column and an increase of the DOU (53%). These results highlight the necessity of further investigations to take into account the interactions between bioturbation, microbial metabolism and pollutants.

Mechanistic models to perform population risk assessment with the midge Chironomus riparius: application to heavy metals.

Mechanistic models can substantially contribute to population risk assessment to assess effects on population and to increase the relevance of the toxicity parameters estimated at an individual level. We use four mechanistic models to change the scale from concentration to effects on individuals and from individuals to population with the midge Chironomus riparius: a kinetics model; an energy-based effects model, linking effects on the life cycle and compound body residues; a matrix approach to derive population growth rate; and an energy-based population model to derive carrying capacity. The whole "model battery" was applied to cadmium and copper. The data came from growth, survival, and reproduction tests. We also incorporated information about compounds physiological mode of action and kinetics. Thresholds at population level were derived through comparisons with our control database. We showed that our two population endpoints (carrying capacity and population growth rate) provide complementary information about toxicity risks, even if, in our study, population growth rate appeared to be slightly more sensitive than carrying capacity. We found population no effect concentration of, respectively, 0.42 and 9.3 mg/kg for cadmium and copper. We also showed that information about physiological mode of action was relevant, whereas a kinetics test was unnecessary.

The relationship of Chironomus riparius larval Se body burden and body concentration to larval dry mass and effects on sensitivity to selenium.

Selenium as selenite was added to laboratory cultures of Chironomus riparius. In two sets of cultures, substrate-bound Se concentrations were typically 10(3) times dissolved Se concentrations, while in the other set dissolved Se concentrations were about 10 to 50 times substrate-bound Se concentrations. Body burdens of individual second-, third-, and fourth-instar larvae and eviscerated fourth-instar larvae were measured. Regressions of Se body burden on larval dry mass found evidence for separate intercepts but common slopes for each instar, and Se body concentrations were diluted by growth. The derivation of body concentration from body burden as a function of larval dry mass was used to derive a model of body burden and body concentration as a function of instar. Toxicity tests were performed to check for a change in sensitivity to Se as a function of culture Se concentration. Larval Se concentrations were highly correlated with dissolved Se concentrations but not with substrate-bound Se concentrations. Increases in Se in substrate caused no sensitization, while increases in dissolved Se caused desensitization. We concluded that covariates such as larval dry mass should be incorporated when deriving water quality criteria.

Molecular cloning and characterization of a metal responsive Chironomus tentans alpha-tubulin cDNA.

Metal pollution of aquatic ecosystems is a problem of economic and health importance. Sensitive molecular biomarkers of metal exposure are sorely needed. We have isolated a cDNA from the midge Chironomus tentans that is transcribed in all organs and developmental stages. The cDNA encodes a protein, designated Chironomus tentans alpha-tubulin 1 (CTTUB1), which has significant similarities with invertebrate and vertebrate alpha-tubulins. CTTUB1 is abundantly transcribed in embryos and to a lesser extent in adults and larvae. CTTUB1 RNA and protein abundances are increased in larvae exposed to copper or cadmium. The pattern of cellular distribution of CTTUB1 protein in the midgut epithelial cells was radically affected by cadmium. In the midgut cells of unexposed larvae, CTTUB1 was found evenly distributed throughout the cytoplasm, while in cadmium-exposed larvae, CTTUB1 was mostly concentrated along the basolateral plasma membrane. A mechanism for the regulation of alpha-tubulin synthesis by cadmium is proposed. This is the first report on the isolation of a metal responsive gene from a neartic aquatic insect.