Risk assessment of etofenprox (Vectron) on non-target aquatic fauna compared with other pesticides used as Simulium larvicide in a tropical environment

Insecticidal properties of etofenprox for the control of Ephestia kuehniella, Rhyzopertha dominica, Sitophilus oryzae, and Tribolium confusum on stored barley, maize, oats, rice, and wheat

Etofenprox is a novel pyrethroid insecticide that targets the nervous system of insects by affecting the function of the sodium channel. The current study examines the insecticidal activity of etofenprox against Ephestia kuehniella (Lepidoptera: Pyralidae) larvae, Rhyzopertha dominica (Coleoptera: Bostrychidae) adults, Sitophilus oryzae (Coleoptera: Curculionidae) adults, and Tribolium confusum (Coleoptera: Tenebrionidae) adults and larvae on different grain commodities. For this purpose, etofenprox was applied on barley, maize, oats, rice, and wheat at 0.1, 1, 5, and 10 ppm. Mortality levels were recorded after 7, 14, and 21 days of exposure. For E. kuehniella larvae, 10 ppm applied on whole rice killed 96.1% of the exposed individuals after 21 days of exposure. The application of etofenprox on oats at 5 ppm caused the death of 98.3% of the exposed R. dominica adults. Complete mortality was observed for R. dominica adults 21 days post-exposure to oats and whole rice treated with 10 ppm etofenprox. The highest concentration applied on barley caused 95.0% mortality to S. oryzae adults, while the same concentration on maize killed 76.8% of T. confusum adults after 21 days of exposure. Larvae of T. confusum exhibited high mortality levels reaching 99.4% after 21 days of exposure to barley treated with 10 ppm etofenprox. Progeny production of parental R. dominica adults was almost suppressed on all commodities treated with 5 ppm etofenprox. The offspring emergence of S. oryzae ranged between 4.4 and 24.6 adults per vial at 10 ppm. No T. confusum progeny was produced at 10 ppm etofenprox. Our results document that etofenprox is highly effective as grain protectant against several insect species, their developmental stages and their progeny production, but its performance depends on the type of the commodity that it is applied on.

Etofenprox as grain protectant for the management of five key stored-product insect pests

Etofenprox is a broad spectrum pyrethroid insecticide with low toxicity to mammals, fishes, and honeybees. In the present study it was evaluated as grain protectant against Ephestia kuehniella (Lepidoptera: Pyralidae) larvae, Prostephanus truncatus (Coleoptera: Bostrychidae) adults, Rhyzopertha dominica (Coleoptera: Bostrychidae) adults, Sitophilus oryzae (Coleoptera: Curculionidae) adults, and Tribolium confusum (Coleoptera: Tenebrionidae) larvae and adults. Etofenprox was applied at 0.1, 1, 5, and 10 ppm on wheat, or maize in the case of P. truncatus, and tested at different combinations of temperatures (20, 25, and 30 °C) and relative humidity (RH) levels (55 and 75%). Progeny production of the tested coleopteran adult species was also assessed. For E. kuehniella, after 21 days of exposure 75.6% of the exposed larvae were killed at 20 and 30 °C/55% RH. Mortality of P. truncatus adults reached 99.4 and 97.8% at 10 ppm of 55 and 75% RH, respectively, at 30 °C. For S. oryzae, after 21 days of exposure, mortality was moderate at both RH levels, even at the elevate doses, reaching 66.7% at 10 ppm at 20°C/75% RH. All R. dominica adults died 21 days post-exposure at 30°C/55% RH and 25 or 30°C/75% RH at 10 ppm. For T. confusum adults, mortality was 81.1% 10 ppm 21 days post-exposure at 20°C/75% RH. Etofenprox killed 99.4% of the exposed T. confusum larvae at 10 ppm respectively 14 days post-exposure at 25°C/55% RH. Concerning progeny production, complete suppression was recorded for P. truncatus, R. dominica, and T. confusum in various combinations of temperature/RH. Our findings indicate that etofenprox is a well-promising insecticide for the protection of stored grains. However, its performance differs among insect species and abiotic conditions.

Distinct functional properties of sodium channel variants are associated with usage of alternative exons in Nilaparvata lugens

Voltage-gated sodium channels (Na_v) are essential for electrical signaling in the nervous system. They are also the primary targets of several classes of insecticides including pyrethroids. There is only one sodium channel gene in most insect species, whereas mammals possess at least nine sodium channel genes. Extensive alternative splicing and RNA editing of sodium channel transcripts have been documented in many insect species. However, the functional consequences of these post-transcriptional events have been evaluated only in DmNa_v and BgNa_v from Drosophila melanogaster and Blattella germanica, respectively. In this study, we isolated 41 full-length cDNA clones encoding 34 sodium channel (NlNa_v) variants from a major rice pest, the brown planthopper (Nilaparvata lugens Stål). The 34 NlNa_v variants represent 24 distinct splicing types based on the usage of nine alternative exons, six of which, including exon b, have been previously reported in other insect species. When expressed in Xenopus oocytes, NlNa_v variants lacking exon b generated significantly larger sodium currents than variants possessing exon b, suggesting an inhibitory effect of exon b on sodium current expression. A similar effect has been reported for exon b from BgNa_v. Mutational analysis showed that three conserved amino acid residues encoded by exon b are critical for its inhibitory effect. In addition, mutually exclusive exons k/l contribute to distinct functional properties and channel sensitivity to pyrethroids. Altogether, these results show that alternative splicing generates functional diversity of sodium channels in this insect species and that the role of exon b in regulating neuronal excitability is likely conserved among insect species.

Freshwater shrimps as sensitive test species for the risk assessment of pesticides in the tropics

The aquatic risk assessment of pesticides in tropical areas has often been disputed to rely on toxicity data generated from tests performed with temperate species. Given the differences in ecosystem structure between temperate and tropical ecosystems, test species other than those used in temperate regions have been proposed as surrogates for tropical aquatic effect assessments. Freshwater shrimps, for example are important components of tropical freshwater ecosystems, both in terms of their role in ecosystem functioning and their economic value. In the present study, available toxicity data of (tropical and sub-tropical) freshwater shrimps for insecticides and fungicides were compiled and compared with those available for Daphnia magna and other aquatic invertebrates. Freshwater shrimps appeared to be especially sensitive to GABA-gated chloride channel antagonist and sodium channel modulator insecticides. However, shrimp taxa showed a moderate and low sensitivity to acetylcholinesterase inhibiting insecticides and fungicides respectively. Implications for the use of freshwater shrimps in tropical pesticide effect assessments and research needs are discussed.

Impaired reproduction and individual growth of the water flea Daphnia magna as consequence of exposure to the non-ester pyrethroid etofenprox

The effect of the pesticide etofenprox (0.76, 0.95, 1.18, 1.48, and 1.85 μg L^-1) on survival, reproduction, and growth of Daphnia magna organisms was monitored using 21-day exposure tests. In order to test pesticide effects on D. magna, survival, length, mean total neonates per female, mean brood size, time to first reproduction, mean number broods per female, cumulative molting, and the population parameter intrinsic rate of natural increase (r) were used. Reproduction was seriously affected by etofenprox. Concentrations of etofenprox higher than 1.18 μg L^-1affected all the reproductive parameters analyzed as well as individual length. However, daphnids' survival after 21 days of pesticide exposure did not exhibited differences among experimental and control groups. The no observed effect concentration (NOEC), the lowest observed effect concentration (LOEC), and the maximum acceptable toxicant concentration (MATC) were calculated for the different parameters. A MATC estimation of 1.32 μg L^-1 was calculated for mean brood size, mean number of broods per female, mean number of neonates per female, and the intrinsic rate of growth population. Etofenprox effect on the algae Nannochloris oculata was also evaluated. The selected etofenprox concentrations did not affect algal growth rate (μ) after 24 h; however, N. oculata exposed during 48 and 72 h to the highest etofenprox concentration showed a decreased in its population rate.

Metabolic resistance in Nilaparvata lugens to etofenprox, a non-ester pyrethroid insecticide

Etofenprox, a non-ester pyrethroid insecticide, will be registered to control rice pests such as the brown planthopper (BPH, Nilaparvata lugens Stål) in mainland China. Insecticide resistance is always a problem to the effective control of N. lugens by chemical insecticides. An etofenprox resistance selection of N. lugens was performed in order to understand the related mechanisms. Through successive selection by etofenprox for 16 generations in the laboratory, an etofenprox-resistant strain (G16) with the resistance ratio (RR) of 422.3-fold was obtained. The resistance was partly synergised (2.68-fold) with the metabolic inhibitor PBO, suggesting a role for P450 monooxygenases. In this study, 11 P450 genes were significantly up-regulated in G16, among which eight genes was above 2.0-fold higher than that in US16, a population with the same origin of G16 but without contacting any insecticide in the laboratory. The expression level of four genes (CYP6AY1, CYP6FU1 and CYP408A1 from Clade 3, and CYP425A1 from Clade 4) were above 4.0-fold when compared to US16. RNA interference (RNAi) was performed to evaluate the importance of the selected P450s in etofenprox resistance. When CYP6FU1, CYP425A1 or CYP6AY1 was interfered, the susceptibility was significantly recovered in both G16 and US16, while the knockdown of CYP408A1 or CYP353D1 did not cause significant changes in etofenprox susceptibility. We supposed that CYP6FU1 was the most important P450 member for etofenprox resistance because of the highest expression level and the most noticeable effects on resistance ratios following RNAi.

Evaluation of suitable endpoints for assessing the impacts of toxicants at the community level

Assessment of ecological impacts of toxicants relies currently on extrapolation of effects observed at organismal or population levels. The uncertainty inherent to such extrapolations, together with the impossibility of predicting ecological effects of chemical mixtures, can only be resolved by adopting approaches that consider toxicological endpoints at a community or ecological level. Experimental data from micro- and mesocosms provide estimates of community effect levels, which can then be used to confirm or correct the extrapolations from theoretical methods such as species sensitivity distributions (SSDs) or others. When assessing impacts, the choice of sensitive community endpoints is important. Four community endpoints (species richness, abundance, diversity and similarity indices) were evaluated in their ability to assess impacts of two insecticides, imidacloprid and etofenprox, and their mixture on aquatic and benthic communities from artificial rice paddies. Proportional changes of each community endpoint were expressed by ratios between their values in the treatment and control paddies. Regression lines fitted to the endpoint ratios against the time series of chemical concentrations were used to predict percentile impacts in the communities. The abundance endpoint appears to be the most sensitive indicator of the communities' response, but the Czekanowski similarity index described best the structural changes that occur in all communities. Aquatic arthropods were more sensitive to the mixture of both insecticides than zooplankton and benthic communities. Estimated protective levels for 95% of aquatic species exposed to imidacloprid (<0.01-1.0 μg l(-1)) were slightly lower than predicted by SSD, whereas for etofenprox the protective concentrations in water (<0.01-0.58 μg l(-1)) were an order of magnitude lower than SSD's predictions.

Implications of differences between temperate and tropical freshwater ecosystems for the ecological risk assessment of pesticides

Despite considerable increased pesticide use over the past decades, little research has been done into their fate and effects in surface waters in tropical regions. In the present review, possible differences in response between temperate and tropical freshwaters to pesticide stress are discussed. Three underlying mechanisms for these differences are distinguished: (1) climate related parameters, (2) ecosystem sensitivity, and (3) agricultural practices. Pesticide dissipation rates and vulnerability of freshwaters appear not to be consistently higher or lower in tropical regions compared to their temperate counterparts. However, differences in fate and effects may occur for individual pesticides and taxa. Furthermore, intensive agricultural practices in tropical countries lead to a higher input of pesticides and spread of contamination over watersheds. Field studies in tropical farms on pesticide fate in the enclosed and surrounding waterways are recommended, which should ultimately lead to the development of surface water scenarios for tropical countries like developed by the Forum for the co-ordination of pesticide fate models and their use for temperate regions. Future tropical effect assessment studies should evaluate whether specific tropical taxa, not represented by the current standard test species in use, are at risk. If so, tropical model ecosystem studies evaluating pesticide concentration ranges need to be conducted to validate whether selected surrogate indigenous test species are representative for local tropical freshwater ecosystems.

Long-term, large-scale biomonitoring of the unknown: assessing the effects of insecticides to control river blindness (onchocerciasis) in West Africa

The control of river blindness (onchocerciasis), a human disease transmitted by black flies, has been an economic and public health success in West Africa. It involved insecticide applications to as many as 50,000 km of rivers, almost weekly, in 11 countries between 1974 and 2002. The long-term biomonitoring of the effects of insecticide use on the nontarget invertebrate (primarily insect) and fish communities was initially designed on the basis of limited knowledge available for West African rivers and on information from other areas. Routine monitoring surveys demonstrated little effect on fish but produced inconclusive results for invertebrates. Research conducted beyond these surveys and current views in river and general ecology indicate that permanent damage to invertebrates from insecticiding was unlikely. The scientific progress made during the 29 years of this biomonitoring program is relevant to future, large-scale, long-term programs worldwide.

Investigation of acute toxicity of permethrin on guppies Poecilia reticulata

Permethrin, a synthetic pyrethroid pesticide and potential toxic pollutant contaminating aquatic ecosystems, was investigated in the present study for acute toxicity. Guppy fish (Poecilia reticulata) were selected for the bioassay experiments. The experiments were repeated 3 times and the 48-h LC(50) was determined for the guppies. The static test method of acute toxicity test was used. Water temperature was regulated at 20+/-1 degrees C. In addition, behavioral changes at each permethrin concentration were observed for the individual fish. Data obtained from the permethrin acute toxicity tests were evaluated using the probit analysis statistical method. The 48-h LC(50) value for guppy was estimated as 245.7 microg/l. Values in the range of 0.05-97.0 microg/l have been reported for various other fish species.