Insecticide Esfenvalerate Research Articles

Synergistic interaction between a toxicant and food stress is further exacerbated by temperature

Global biodiversity is declining at an unprecedented rate in response to multiple environmental stressors. Effective biodiversity management requires deeper understanding of the relevant mechanisms behind such ecological impacts. A key challenge is understanding synergistic interactions between multiple stressors and predicting their combined effects. Here we used Daphnia magna to investigate the interaction between a pyrethroid insecticide esfenvalerate and two non-chemical environmental stressors: elevated temperature and food limitation. We hypothesized that the stressors with different modes of action can act synergistically. Our findings showed additive effects of food limitation and elevated temperature (25 °C, null model effect addition (EA)) with model deviation ratio (MDR) ranging from 0.7 to 0.9. In contrast, we observed strong synergistic interactions between esfenvalerate and food limitation at 20 °C, considerably further amplified at 25 °C. Additionally, for all stress combinations, the synergism intensified over time indicating the latent effects of the pesticide. Consequently, multiple stress substantially reduced the lethal concentration of esfenvalerate by a factor of 19 for the LC50 (0.45–0.024 μg/L) and 130 for the LC10 (0.096–0.00074 μg/L). The stress addition model (SAM) predicted increasing synergistic interactions among stressors with increasing total stress.

Ultra-low Esfenvalerate concentrations increase biomass and may reduce competitiveness of Daphnia magna populations

Aquatic communities are frequently exposed to pesticides at sublethal concentrations, known to affect fitness parameters such as feeding, reproduction and population growth. Beside adverse effects, beneficial responses to toxicants at low concentrations may also occur. Positive effects, however, are thought to involve trade-offs. To identify such trade-offs, we quantified the population level effects on Daphnia magna during population carrying capacity in laboratory nanocosms after exposure to a single pulse of the pyrethroid insecticide esfenvalerate, including ultra-low concentrations ≤1/30 EC50. Population abundance and biomass were monitored 3 times per week for 3 months using a non-invasive imaging technique. High concentrations ≥1/10 EC50 resulted in reduced fitness endpoints. In contrast, ultra-low concentrations in the range of 0.01 μg/L significantly increased the population abundance of small (+160 %), medium (+130 %) and large organisms (+340 %) and their combined biomass (+200 %) during the 2 months after exposure. During the first five days after exposure to 0.01 μg/L and 0.03 μg/L esfenvalerate, population biomass increased by 0.1 mg/day while staying constant in the controls. While high control mortality makes firm conclusions about population responses of D. magna to esfenvalerate difficult, we hypothesize that population increases at ultra-low concentrations may be due to a hormetic response, where reduced intraspecific competitiveness is the trade-off that enables this response.

Синергетическое действие пиретроидного инсектицида и энтомопатогенного гриба на Daphnia magna Straus

<p>The interaction between the entomopathogenic fungus <em>Metarhizium robertsii</em> and the pyrethroid insecticide esfenvalerate on <em>Daphnia magna</em> Straus was investigated. A synergy in the mortality of daphnids was detected after simultaneous treatment with sub-lethal doses of the fungus (1×10<sup>5</sup> conidia/ml) and esfenvalerate (0.1 mkg/l). The defense strategies of daphnids infected by fungus and treated with esfenvalerate and untreated insects were compared to investigate the mechanisms of this synergy. Activity of enzymes of the detoxification system and concentration of dopamine were measured. We have shown changes in the activities of the enzymes and dopamine concentration of daphnids under combined treatment of esfenvalerate and fungus. Fungus enhanced activity of glutathione-S-transferase and non-specific esterase but did not affect the dopamine level. Esfenvalerate inhibited the activity of enzymes in the detoxification system and cause a rise in dopamine level. We assume that the suppression of the detoxification system may be one of the reasons of synergy between <em>M. robertsii</em> and esfenvalerate.</p>

Realistic pesticide exposure through water and food amplifies long-term effects in a Limnephilid caddisfly

Pesticides are increasingly recognized as relevant stressors in stream ecosystems. Stream biota is exposed to pesticides with low water solubility, e.g. pyrethroid insecticides, via water, habitat, and food. However, long-term effects of simultaneous exposure pathways are unknown. In this context, we conducted a microcosm experiment with the caddisfly Anabolia nervosa exposing the larvae to the pyrethroid insecticide esfenvalerate (EFV) at 0.1 and 1.0μgL-1 via (i) water, (ii) food or a (iii) combination of water and food. Combined exposure through water and food significantly reduced emergence by 60% and significantly postponed emergence timing at the highest EFV level, whereas none of the single-phase exposures showed significant effects. Moreover, our study revealed that successfully emerged females from the highest biphasic treatment level were characterised by altered composition of storage lipids indicative of reduced energy reserves. Consequently, a realistic test scenario that represents simultaneous exposure of organisms and their food may reveal substantially increased long term effects of pyrethroids when compared with current ecological risk assessment applying only single phase exposure. We recommend that relevant concurrent exposure routes of pesticides should be considered in order to derive realistic regulatory acceptable concentrations of pesticides.

The insecticide esfenvalerate modulates neuronal excitability in mammalian central nervous system in vitro

Pyrethroids are neurotoxic insecticides showing significant selective toxicity on insects over mammals, but effects on mammalian nervous system are not negligible. These substances act on the voltage-gated sodium channel, prolonging the duration of the open state. The present study focused on the effect of the pyrethroid esfenvalerate on the excitability of neuronal networks in vitro. From isolated rat brain slices, neocortical and hippocampal evoked field potentials were recorded; four concentrations (5–40μM) of esfenvalerate were tested using in vitro administration of the commercial product Sumi-Alpha 5 EC®. Basic excitability and short- and long-term synaptic plasticity were studied. Application of the lowest concentration elicited epileptiform discharges in neocortex, while the highest concentration exerted a strong inhibitory effect on the excitability of both brain areas. The amplitude of population spikes in hippocampal slices was decreased by all applied concentrations. Significant decrease in basic excitability was accompanied by increase of paired-pulse facilitation in hippocampus and decreased efficacy of the development of long-term potentiation in both regions. Pyrethroids have been scarcely studied on brain slices so far, but our results are in concordance with literary data obtained on other in vitro neuronal test systems. It has been described previously that lower concentrations of pyrethroids lead to overexcitation of neurons and repetitive firing (which is in the background of hyperexcitatory symptoms occurring in case of in vivo exposure). Higher concentrations, however, may lead to depolarization block and to inhibition of neuronal firing.

Responses of earthworms to repeated exposure to three biocides applied singly and as a mixture in an agricultural field

The study aimed at investigating effects of three differently acting biocides; the insecticide esfenvalerate, the fungicide picoxystrobin and the bactericide triclosan, applied individually and as a mixture, on an earthworm community in the field. A concentration–response design was chosen and results were analyzed using univariate and multivariate approaches. Effects on juvenile proportions were less pronounced and more variable than effects on abundance, but effects in general were species- and chemical-specific, and temporal variations distinct. Esfenvalerate and picoxystrobin appeared to elicit stronger effects than triclosan at laboratory-based ECx values, which is in accordance with our previous laboratory study on Eisenia fetida. The mixture affected abundance and juvenile proportions, but the latter only at high mixture concentrations. Esfenvalerate and picoxystrobin appeared to be the main drivers for the mixture's toxicity. Species-specific toxicity patterns question the reliability of mixture toxicity predictions derived on E. fetida for field earthworms. Biocide concentrations equaling EC50s (reproduction) for E. fetida provoked effects on the field earthworms mainly exceeding 50%, indicating effect intensification from the laboratory to field as well as the influence of indirect effects produced by species interactions. The differing results of the present field study and the previous laboratory study imply that lower- and higher-tier studies may not be mutually exclusive, but to be used in complementary.

Environmental stressors can enhance the development of community tolerance to a toxicant.

Ecosystems are subject to a combination of recurring anthropogenic and natural disturbances, such as climate change and pesticide exposure. Biological communities are known to develop tolerance to recurring disturbances due to successive changes at both the community and organismal levels. However, information on how additional stressors may affect the development of such community tolerance is scarce to date. We studied the influence of hydrological disturbance on the reaction of zooplankton communities to repeated insecticide pulses in outdoor microcosms. The communities were exposed to three successive pulses of the insecticide esfenvalerate (0.03, 0.3, and 3µg/L) and to the gradual removal of water and its subsequent replacement over three cycles or to a constant water level. Except at the highest esfenvalerate concentration, the communities developed tolerance to the toxicant, as indicated by their decreasing reaction to subsequent insecticide applications, and this development was enhanced by hydrological disturbance. The pronounced decline of the key taxa Daphnia spp. through the combined action of the two stressors was identified as the main mechanism responsible for the increase in community tolerance under a fluctuating water level. Under a constant water level, the abundance of Daphnia spp. did not decrease significantly without the insecticide treatment, indicating that other mechanisms were responsible for the observed community tolerance. The present study shows that additional stressors can facilitate the development of community tolerance and that such facilitation is propagated through community-level mechanisms.

An enantioselective amidase from Burkholderia multivorans for the stereoselective synthesis of esfenvalerate.

Using racemic (R,S)-2-(4-chlorophenyl)-3-methylbutyramide, an intermediate for the chiral pyrethroid insecticide Esfenvalerate, as a sole nitrogen source in a minimal medium, several strains with high enatioselectivity (≥98%) were isolated by enrichment techniques. One of the strains, LG 31-3, was identified as Burkholderia multivorans, based on physiological and morphological tests by a standardized Biolog station for carbon source utilization. A novel amidase was purified from B. mutivorans LG 31-3 and characterized. The enzyme exhibited (S)- selective amidase activity on racemic (R,S)-2-(4-chlorophenyl)-3-methylbutyramide. Addition of the racemic amide induced the production of the enantioselective amidase. The molecular mass of the amidase on SDS-PAGE analysis was shown to be 50 kDa. The purified amidase was subjected to proteolytic digestion with a modified trypsin. The N-terminal and internal amino acid sequences of the purified amidase showed a high sequence homology with those deduced from a gene named YP_366732.1 encoding indole acetimide hydrolase from Burkholderia sp. 383.

Comparison of Straw Mulch, Insecticides, Mineral Oil, and Birch Extract for Control of Transmission of Potato virus Y in Seed Potato Crops

Potato virus Y (PVY) is a major pathogen of potato and transmitted non-persistently by aphids. Aphis fabae is the main vector of PVY in the High Grade Seed Potato Production Area (HG area) in Finland, where the number of aphids and infection pressure with PVY are rather low, but problems with PVY occur in PVY-susceptible cultivars. The aim of the study was to test straw mulch, mineral oil, birch extract, and insecticides for control of PVY in small-scale field experiments and, additionally, at farm level in growers’ fields in the HG area of Finland. The insecticide esfenvalerate reduced the incidence of PVY in the progeny tubers by 29% in one of the 3 years, whereas other chemical treatments or birch extract had no significant effect on PVY incidence. Spraying foliage with mineral oil (Sunoco 11 E/3) reduced the incidence of PVY in 2 years by 43 to 58%, respectively. Straw mulch spread to the field at the time of plant emergence reduced PVY incidence in all 3 years by 50–70%. At farm level, straw mulch reduced the incidence of PVY in the progeny tubers by 25–47%, respectively, in both years tested; however, combining application of straw mulch and mineral oil did not further reduce incidence of PVY. Successful control of PVY in the HG area of Finland using straw mulch may be explained by transmission of PVY early in the growing season at the time of plant emergence and the relatively low number of vector aphids.

A New Multi-cell Exposure System for Continuous Tracking of Daphnia Behavior for Toxicity Assessments

For several years, video tracking systems have been developed to analyze alterations in the swimming behavior of daphnia to provide early signals of chemical stress. However, these systems have limited testing abilities that do not allow for a systematic analysis of the robustness of behavioral endpoints. With recent advances in behavior tracking technology, we were able to develop a new behavioral analysis multi-cell exposure system named “Multi-DaphTrack” with a high-throughput testing capacity for assessing the behavioral response of Daphnia magna. The insecticide esfenvalerate was chosen as chemical model and tested on daphnid neonates at several concentrations for 48 h to (i) evaluate the performance of this new system and (ii) compare the sensitivity of our new multi-cell system with the standard immobilization assay and the Bbe®Daphnia Toximeter. Overall, the results demonstrated that our new “Multi- DaphTrack” system can detect significant behavioral effects of esfenvalerate at concentrations as low as 0.14 μg/L from a minimum of 1 h of exposure. Similar rapid behavioral effect trends were observed with the Bbe®Daphnia Toximeter. The behavior proved to be more sensitive than the standard immobilization endpoint. Significant behavioral changes were observed at the esfenvalerate concentrations that occur in contaminated rivers from agricultural areas in Europe and North America. Our results indicate that the “Multi-DaphTrack” system represents a powerful and convenient tool for the assessment of c and water quality

Growth Assessment of Marine-Derived Fungi in the Presence of Esfenvalerate and its Main Metabolites

The growth and biodegradation potential of marine-derived fungi were evaluated by measuring the radial growth of colonies. It was observed that Penicillium raistrickii CBMAI 931, Aspergillus sydowii CBMAI 935, Cladosporium sp. CBMAI 1237, Microsphaeropsis sp. Dr(A)6, Acremonium sp. Dr(F)1, Westerdykella sp. Dr(M2)4 and Cladosporium sp. Dr(M2)2 were able to grow and develop in the presence of the pyrethroid insecticide esfenvalerate (S,Sfenvalerate) and its main metabolites (3-phenoxybenzaldehyde, 3-phenoxybenzoic acid, 3-phenoxybenzyl alcohol and 2-(4-chlorophenyl)-3-methylbutyric acid), showing the possibility of esfenvalerate biodegradation by these strains. The presence of technical grade esfenvalerate and its metabolites caused growth inhibition, while fungal development was not affected by the presence of the commercial insecticide SUMIDAN 150 SC in the culture medium. This fact might show that the biodegradation of the esfenvalerate in the commercial insecticide is slower than that of the technical grade active ingredient, since slower biodegradation of esfenvalerate would reduce the concentration of phenolic compounds and thus the growth inhibition. Future studies will focus on the quantitative biodegradation analysis of technical grade esfenvalerate and active ingredient in the commercial insecticide.

Elevated temperature prolongs long‐term effects of a pesticide on Daphnia spp. due to altered competition in zooplankton communities

Considerable research efforts have been made to predict the influences of climate change on species composition in biological communities. However, little is known about how changing environmental conditions and anthropogenic pollution can affect aquatic communities in combination. We investigated the influence of short warming periods on the response of a zooplankton community to the insecticide esfenvalerate at a range of environmentally realistic concentrations (0.03, 0.3 and 3 μg L(-1) ) in 55 outdoor pond microcosms. Warming periods increased the cumulative water temperature, but did not exceed the maximum temperature measured under ambient conditions. Under warming conditions alone the abundance of some zooplankton taxa increased selectively compared to ambient conditions. This resulted in a shift in the community composition that had not recovered by the end of the experiment, 8 weeks after the last warming period. Regarding the pesticide exposure, short-term effects of esfenvalerate on the community structure and the sensitive taxa Daphnia spp. did not differ between the two temperature regimes. In contrast, long-term effects of esfenvalerate on Daphnia spp., a taxon that did not benefit from elevated temperatures, were observed twice as long under warming than under ambient conditions. This resulted in long-term effects on Daphnia spp. until 4 months after contamination at 3 μg L(-1) esfenvalerate. Under both temperature regimes, we identified strength of interspecific competition as the mechanism determining the time until recovery. However, enhanced interspecific competition under warming conditions was prolonged and explained the delayed recovery of Daphnia spp. from esfenvalerate. These results show that, for realistic prediction of the combined effects of changing environmental factors and toxicants on sensitive taxa, the impacts of stressors on the biotic interactions within the community need to be considered.

Two stressors and a community – Effects of hydrological disturbance and a toxicant on freshwater zooplankton

Climate change models predict an increase in the frequency and intensity of extreme fluctuations in water level in aquatic habitats. Therefore, it is necessary to understand the combined effects of hydrological fluctuations and toxicants on aquatic biological communities. We investigated the individual and combined effects of the insecticide esfenvalerate and recurring fluctuations in water level on zooplankton communities in a system of 55 outdoor pond microcosms. The communities were exposed to esfenvalerate contamination as a single pulse (at 0.03, 0.3, or 3μg/L) and gradual removal of water and its subsequent replacement over three cycles and monitored until 84 days after contamination. The results showed that the sensitivities of the community and its constituent populations to the toxicant were increased by the hydrological stress. Specifically, for both the community structure and abundance of Daphnia spp. the lowest-observed-effect concentrations (LOEC) were 0.03 and 0.3μg/L for the series with fluctuating and constant water levels, respectively. Despite these differences in sensitivity, the interactive effects of the two stressors were found to be additive for both the community structure and the abundance of the most affected species. Presumably, it was not possible to detect synergism due to the strong individual effects of the water level fluctuations. Recovery times in the series exposed to the highest pesticide concentration were 64 and 55 days under fluctuating and constant water level regimes, respectively. Competition and water quality are suggested to be the major factors that underlie the observed effects of fluctuations in the water level. For the ecological risk assessment of toxicants, the present results suggest that (i) community sensitivity may vary substantially, depending on the environmental context, and (ii) this variability can be assessed experimentally to derive safety factors (coefficients used to avoid unexpected effects and define safe concentrations of toxicants) based on empirical findings. This contrasts with the current approach where such factors are usually defined arbitrarily.

Multiyear Evaluation of an Orange Peel Oil-based Spray Additive for Managing Insect Pests and Brown Rot of Nectarine

Adjuvants are often added to pesticide formulations to enhance their effectiveness. In this multiyear field study, a proprietary formulation of orange peel oil-based spray additive containing alcohol ethoxylate (OPO-AE) was used alone or in combination with the pyrethroid insecticide esfenvalerate or the demethylation inhibitor fungicide fenbuconazole for pest and disease control of nectarine. Field performance of fenbuconazole for preharvest and postharvest brown rot control was not improved when OPO-AE was added to the spray tank. However, OPO-AE alone reduced preharvest but not postharvest fruit rot compared to the nontreated control. Esfenvalerate was consistently the best treatment to control chewing insects but the insecticidal effect of the pyrethroid was negated when the adjuvant was added. Leaf damage likely due to insect feeding was significantly higher in the esfenvalerate + OPO-AE treatment compared to esfenvalerate alone. The OPO-AE treatment by itself had significantly greater leaf damage compared to the untreated control indicating that the orange peel oil-based formulation is an insect attractant likely due to the presence of d-limonene. In conclusion, our studies do not support claims that OPO-AE formulated as Vintre increases insecticidal or fungicidal efficacy of commercial products. Accepted for publication 14 May 2012. Published 17 June 2012.

Photo-Fenton degradation of the insecticide esfenvalerate in aqueous medium using a recirculation flow-through UV photoreactor

The aim of the study was to evaluate the efficiencies of photo-Fenton (Fe 2+) and (Fe 3+) processes in the degradation of high-concentrations of esfenvalerate (in the form of aqueous emulsion of a commercial formulation) using a recirculation flow-through photoreactor irradiated with UV light from a 15 W lamp (254 nm emission peak). The results obtained using a basic photo-Fenton (Fe 2+) reaction (esfenvalerate 17 mg L −1; ferrous sulphate 1 mM; hydrogen peroxide 25 mM; pH 2.5) were compared with those acquired when ferrioxalate (1, 3 or 5 mM) served as the iron source. Degradation of the active component of the commercial formulation was significantly greater, and the rate of oxidation more rapid, using a photo-Fenton (Fe 3+) process compared with its Fe 2+ counterpart. The most efficient degradation of the insecticide (75% in 180 min) was achieved with a reaction mixture containing 5 mM ferrioxalate. However, under the same experimental conditions, degradation of pure esfenvalerate preceded much faster (99% in 60 min) and was 100% complete within 180 min reaction time.

Environmental context determines community sensitivity of freshwater zooplankton to a pesticide

The environment is currently changing worldwide, and ecosystems are being exposed to multiple anthropogenic pressures. Understanding and consideration of such environmental conditions is required in ecological risk assessment of toxicants, but it remains basically limited. In the present study, we aimed to determine how and to what extent alterations in the abiotic and biotic environmental conditions can alter the sensitivity of a community to an insecticide, as well as its recovery after contamination. We conducted an outdoor microcosm experiment in which zooplankton communities were exposed to the insecticide esfenvalerate (0.03, 0.3, and 3 μg/L) under different regimes of solar radiation and community density, which represented different levels of food availability and competition. We focused on the sensitivity of the entire community and analysed it using multivariate statistical methods, such as principal response curves and redundancy analysis. The results showed that community sensitivity varied markedly between the treatments. In the experimental series with the lowest availability of food and strongest competition significant effects of the insecticide were found at the concentration of 0.03 μg/L. In contrast, in the series with relatively higher food availability and weak competition such effects were detected at 3 μg/L only. However, we did not find significant differences in the community recovery rates between the experimental treatments. These findings indicate that environmental context is more important for ecotoxicological evaluation than assumed previously.

Flight activity of Sitophilus oryzae (L) and Sitophilus zeamais Motsch (Coleoptera: Curculionidae) and its relationship with susceptibility to insecticides

Insect-pest mobility can influence insect susceptibility to the insecticides used to control them. The objective of this work was to evaluate the flight activity of Sitophilus oryzae (L) and Sitophilus zeamais Motsch populations reared on corn and wheat grains, and its relationship with insecticide susceptibility. Unsexed adult insects with ages between 10 and 20 days were placed on a plastic tray. A 40-watt incandescent light bulb was positioned at a 50 cm height relative to the tray. Flight activity was evaluated during 30 min. In the LC50 estimation bioassays, the insects were exposed to dry residues of the organophosphorus insecticide fenitrothion and of the pyrethroid insecticide esfenvalerate on the internal surface of glass vials. Mortality was evaluated 24 h after installation of the experiments. Sitophilus zeamais showed greater flight activity when compared with S.oryzae; likewise, insects reared on corn had greater flight activity than those reared on wheat. Sitophilus oryzae was less susceptible to the insecticides studied than S. zeamais. Adults reared on wheat were more susceptible to the insecticides than those reared on corn. This study demonstrates that the lower flight activity of S. oryzae is related to its greater tolerance to insecticides.

Linking mechanistic and behavioral responses to sublethal esfenvalerate exposure in the endangered delta smelt; Hypomesus transpacificus (Fam. Osmeridae).

BackgroundThe delta smelt (Hypomesus transpacificus) is a pelagic fish species listed as endangered under both the USA Federal and Californian State Endangered Species Acts and considered an indicator of ecosystem health in its habitat range, which is limited to the Sacramento-San Joaquin estuary in California, USA. Anthropogenic contaminants are one of multiple stressors affecting this system, and among them, current-use insecticides are of major concern. Interrogative tools are required to successfully monitor effects of contaminants on the delta smelt, and to research potential causes of population decline in this species. We have created a microarray to investigate genome-wide effects of potentially causative stressors, and applied this tool to assess effects of the pyrethroid insecticide esfenvalerate on larval delta smelt. Selected genes were further investigated as molecular biomarkers using quantitative PCR analyses.ResultsExposure to esfenvalerate affected swimming behavior of larval delta smelt at concentrations as low as 0.0625 μg.L-1, and significant differences in expression were measured in genes involved in neuromuscular activity. Alterations in the expression of genes associated with immune responses, along with apoptosis, redox, osmotic stress, detoxification, and growth and development appear to have been invoked by esfenvalerate exposure. Swimming impairment correlated significantly with expression of aspartoacylase (ASPA), an enzyme involved in brain cell function and associated with numerous human diseases. Selected genes were investigated for their use as molecular biomarkers, and strong links were determined between measured downregulation in ASPA and observed behavioral responses in fish exposed to environmentally relevant pyrethroid concentrations.ConclusionsThe results of this study show that microarray technology is a useful approach in screening for, and generation of molecular biomarkers in endangered, non-model organisms, identifying specific genes that can be directly linked with sublethal toxicological endpoints; such as changes in expression levels of neuromuscular genes resulting in measurable swimming impairments. The developed microarrays were successfully applied on larval fish exposed to esfenvalerate, a known contaminant of the Sacramento-San Joaquin estuary, and has permitted the identification of specific biomarkers which could provide insight into the factors contributing to delta smelt population decline.

Acute, sublethal exposure to a pyrethroid insecticide alters behavior, growth, and predation risk in larvae of the fathead minnow (Pimephales promelas)

The present study determined the effects of environmentally relevant, short-term (4-h) exposure to the pyrethroid insecticide esfenvalerate on mortality, food consumption, growth, swimming ability, and predation risk in larvae of the fathead minnow (Pimephales promelas). Acute effect concentrations were determined, and in subsequent experiments, fish were exposed to the following measured sublethal concentrations: 0.072, 0.455, and 1.142 microg/L of esfenvalerate. To measure growth rates (% dry wt/d), 8-d-old fathead minnows were exposed to esfenvalerate for 4 h, then transferred to control water and held for 7 d. Food consumption and abnormal swimming behavior were recorded daily. Additional behavioral experiments were conducted to evaluate how esfenvalerate affects the optomotor response of the fish. To quantify predation risk, esfenvalerate-exposed fathead minnow larvae were transferred to 9.5-L aquaria, each containing one juvenile threespine stickleback (Gasterosteus aculeatus). Sticklebacks were allowed to feed for 45 min, after which the number of surviving minnows was recorded. No mortality occurred during 4-h exposures to esfenvalerate, even at nominal concentrations of greater than 20 microg/L. Delayed mortality (50%) was observed at 2 microg/L after an additional 20 h in clean water. Fish exposed to 0.455 and 1.142 microg/L of esfenvalerate exhibited impaired swimming and feeding ability as well as reduced growth compared to fish exposed to 0.072 microg/L and controls. Predation risk also was significantly increased for larvae exposed to 0.455 and 1.142 microg/L of esfenvalerate. These results demonstrate that larval fish experiencing acute exposures to sublethal concentrations of this insecticide exhibit significant behavioral impairment, leading to reduced growth and increased susceptibility to predation, with potentially severe consequences for their ecological fitness.

Lethal and Sublethal Activities of Imidacloprid Contribute to Control of Adult Japanese Beetle in Blueberries

Field-based bioassays and residue profile analysis were used to determine the relative importance of lethal and sublethal effects of imidacloprid on adult Japanese beetle, Popillia japonica Newman, in blueberries, Vaccinium corymbosum L. Field-based bioassays assessed adult mortality and knockdown, and fruit and leaf injury from Japanese beetles exposed to 4-h and 7-d field-aged residues of imidacloprid, and the conventional insecticides azinphosmethyl and esfenvalerate. Azinphosmethyl and imidacloprid caused high levels of mortality when beetles were exposed to blueberry shoots with ripe fruit 4 h postapplication, and all compounds protected blueberry fruit and foliage from beetle feeding. Azinphosmethyl and esfenvalerate caused significant Japanese beetle mortality when adults were exposed to blueberry shoots 7 d postapplication, whereas imidacloprid residues caused effects that protected leaves, although not of ripe fruit. When beetles were exposed to shoots with immature green fruit, relatively more leaf feeding and mortality were observed, suggesting that earlier treatment timings may be most effective for systemic neonicotinoids. Japanese beetle mortality was highly correlated with imidacloprid fruit and leaf surface residues, whereas sublethal feeding deterrent effects were observed after the surface residues diminished. The value of the plant-insect-chemistry model for describing the spatial and temporal dimensions of insecticide modes of activity is discussed in terms of optimizing crop protection.