Concentrations Of Insecticides Research Articles

Implications of Sublethal Insecticide Exposure and the Development of Resistance on Mosquito Physiology, Behavior, and Pathogen Transmission.

Simple SummaryMosquitoes are one of the greatest threats to human lives; they transmit a wide range of pathogens, including viruses that cause lethal diseases. Mosquitoes are found in both aquatic (as larvae or pupae) and terrestrial (as adults) environments during their complex life cycle. For decades, insecticides have been systematically used on mosquitoes with the aim to reduce their population. Little is known about how the stress resulting from the exposure of mosquitoes to insecticides impacts the tri-partite relationship between the mosquitoes, their vertebrate hosts, and the pathogens they transmit. In this work, we review existing experimental evidence to obtain a broad picture on the potential effects of the (sub)lethal exposure of hematophagous mosquitoes to different insecticides. We have focused on studies that have advanced our understanding of their physiological and behavioral responses (including the mechanisms behind insecticide resistance) and the spread of pathogens by these vectors—understudied but critically important issues for epidemiology. Studying these exposure-related effects is of paramount importance for predicting how they respond to insecticide exposure and whether this exposure makes them more or less likely to transmit pathogens.For many decades, insecticides have been used to control mosquito populations in their larval and adult stages. Although changes in the population genetics, physiology, and behavior of mosquitoes exposed to lethal and sublethal doses of insecticides are expected, the relationships between these changes and their abilities to transmit pathogens remain unclear. Thus, we conducted a comprehensive review on the sublethal effects of insecticides and their contributions to insecticide resistance in mosquitoes, with the main focus on pyrethroids. We discuss the direct and acute effects of sublethal concentrations on individuals and populations, the changes in population genetics caused by the selection for resistance after insecticide exposure, and the major mechanisms underlying such resistance. Sublethal exposures negatively impact the individual’s performance by affecting their physiology and behavior and leaving them at a disadvantage when compared to unexposed organisms. How these sublethal effects could change mosquito population sizes and diversity so that pathogen transmission risks can be affected is less clear. Furthermore, despite the beneficial and acute aspects of lethality, exposure to higher insecticide concentrations clearly impacts the population genetics by selecting resistant individuals, which may bring further and complex interactions for mosquitoes, vertebrate hosts, and pathogens. Finally, we raise several hypotheses concerning how the here revised impacts of insecticides on mosquitoes could interplay with vector-mediated pathogens’ transmission.

A pilot nationwide baseline survey on the concentrations of Neonicotinoid insecticides in tap water from China: Implication for human exposure

Neonicotinoids (NEOs) have become the most widely used insecticides in the world. However, information on the NEO concentrations in tap water based on nationwide surveys is limited in China. In this study, the levels of six NEOs were measured in tap water samples collected from 38 cities in China. Across all sampling locations, the overall frequency of detection for at least one NEO was 100%, indicating that NEOs are ubiquitous in tap water from China. Imidacloprid was the most abundant NEO (median: 7.59 ng/L), followed by (in decreasing order) clothianidin (5.46 ng/L), dinotefuran (4.55 ng/L), thiamethoxam (4.50 ng/L), acetamiprid (2.72 ng/L), and thiacloprid (0.38 ng/L). Significantly positive correlations (r = 0.655–0.902, p < 0.001) among all pairs of NEOs were observed, which showed that the sources of NEOs in tap water were common or related. Across all sampling locations, regional differences in concentrations (ΣNEOs; sum of six NEOs varied from 0.79 ng/L to 415 ng/L) were observed within China, showing an increasing trend from northern to southern China. Although the estimated daily intake of NEOs were much lower than the reference dose, the potential health risk of NEOs via tap water consumption should raise more public concern considering the high detection rates of NEOs in tap water.

Toxicogenomic differentiation of functional responses to fipronil and imidacloprid in Daphnia magna.

Active substances of pesticides, biocides or pharmaceuticals can induce adverse side effects in the aquatic ecosystem, necessitating environmental hazard and risk assessment prior to substance registration. The freshwater crustacean Daphnia magna is a model organism for acute and chronic toxicity assessment representing aquatic invertebrates. However, standardized tests involving daphnia are restricted to the endpoints immobility and reproduction and thus provide only limited insights into the underlying modes-of-action. Here, we applied transcriptome profiling to a modified D. magna Acute Immobilization test to analyze and compare gene expression profiles induced by the GABA-gated chloride channel blocker fipronil and the nicotinic acetylcholine receptor (nAChR) agonist imidacloprid. Daphnids were expose to two low effect concentrations of each substance followed by RNA sequencing and functional classification of affected gene ontologies and pathways. For both insecticides, we observed a concentration-dependent increase in the number of differentially expressed genes, whose expression changes were highly significantly positively correlated when comparing both test concentrations. These gene expression fingerprints showed virtually no overlap between the test substances and they related well to previous data of diazepam and carbaryl, two substances targeting similar molecular key events. While, based on our results, fipronil predominantly interfered with molecular functions involved in ATPase-coupled transmembrane transport and transcription regulation, imidacloprid primarily affected oxidase and oxidoreductase activity. These findings provide evidence that systems biology approaches can be utilized to identify and differentiate modes-of-action of chemical stressors in D. magna as an invertebrate aquatic non-target organism. The mechanistic knowledge extracted from such data will in future contribute to the development of Adverse Outcome Pathways (AOPs) for read-across and prediction of population effects.

Contributions of nearby agricultural insecticide applications to indoor residential exposures

BACKGROUND AND AIM: Pesticide exposure has been associated with adverse health effects; individuals may be exposed to pesticide drift from nearby agricultural fields. We evaluated relationships between agricultural insecticide applications and insecticide levels in carpet dust. METHODS: We measured concentrations (ng/g) of allethrin, azinphos-methyl, carbaryl, chlorpyrifos, cyfluthrin, cypermethrin, deltamethrin, diazinon, malathion, permethrin, phosmet, propoxur, tetramethrin in carpet-dust samples collected from 558 California homes. After using the California Pesticide Use Reporting database (reporting unit: ~2.59km2) to estimate agricultural insecticide use within buffers with radii of 0.5-, 1-, 2-, 3-, and 4km around each home, we calculated the density of use (kg/km2) during 30-, 60-, 180-, and 365-day periods prior to dust collection and evaluated relationships between insecticide density and concentrations in dust. We modeled natural-log transformed dust concentrations using Tobit regression for insecticides with 40% detection. For insecticides detected ≤40%, odds of detection were modeled with logistic regression. Models were adjusted for season, year, occupation, and home/garden uses. RESULTS:Detection frequencies ranged from 10% for allethrin, azinphos-methyl, and malathion to 80% for diazinon, chlorpyrifos, and permethrin. Chlorpyrifos applications within 1-4km of the residence during all time periods were associated with higher dust concentrations compared to homes without nearby applications. Carbaryl applications within 2-4km of homes 30- and 60-days prior to dust collection were associated with higher concentrations (30-days/2km, β any applications vs. none=8.2, 95%CI 1.8-37.6; 60-days/4km, β median density vs. none=4.2, 95%CI 1.1-15.7). Cyfluthrin and phosmet applications 180- and 365-days prior to dust collection were associated with higher odds of detection (365-days/4km, highest density vs. none: OR=2.2, 95%CI 1.2-4.0 and 6.2, 95%CI 3.3-12.0, respectively) compared to homes with no nearby use. CONCLUSIONS:Agricultural insecticide use within 4km of a home could be an important determinant of indoor contamination. Our findings provide valuable information for the development of exposure metrics for epidemiologic health studies. KEYWORDS: Pesticides, Exposures, Exposure assessment, Environmental epidemiology, Children's environmental health

Histological effects of sublethal concentrations of insecticide Lindane on intestinal tissue of grass carp (Ctenopharyngodon idella).

This study investigates acute toxicity and histological effects of Lindane insecticide on intestinal tissues of immature grass carp (Ctenopharyngodon idella). For these purposes, 105 fish were exposed to different concentrations of Lindane for 96h in 5 groups with 3 replications. Samples of intestinal tissues were prepared in both control and exposure groups during and after the toxicity test. Vaculation, necrosis, bleeding and epithelial degeneration were apparent in the intestine tissue of treated individuals. The LC50 96h of Lindane was 0.788ppm in the present study, also the results showed besides pesticide-induced lesions, symptoms of abnormal swimming, anxiety, tendency to swim near the surface, and death due to terminal toxicity with mouth widely open. The exposed fish were pale in color, showed oxygen deficit and severe respiratory problems. Overall, our results confirm the toxicity of different concentrations of Lindane insecticide affecting behavior, intestinal function and inducing tissue lesions of immature grass carp.

Bioaccumulation potential of chlorpyrifos in resistant Hyalella azteca: Implications for evolutionary toxicology

Given extensive use of pesticides in agriculture, there is concern for unintended consequences to non-target species. The non-target freshwater amphipod, Hyalella azteca has been found to show resistance to the organophosphate (OP) pesticide, chlorpyrifos, resulting from an amino acid substitution in acetylcholinesterase (AChE), suggesting a selective pressure of unintended pesticide exposure. Since resistant organisms can survive in contaminated habitats, there is potential for them to accumulate higher concentrations of insecticides, increasing the risk for trophic transfer. In the present study, we estimated the uptake and elimination of chlorpyrifos in non-resistant US Lab, and resistant Ulatis Creek (ULC Resistant), H. azteca populations by conducting 24-h uptake and 48-h elimination toxicokinetic experiments with 14C-chlorpyrifos. Our results indicated that non-resistant H. azteca had a larger uptake clearance coefficient (1467 mL g−1 h−1) than resistant animals (557 mL g−1 h−1). The half-life derived from the toxicokinetic models also estimated that steady state conditions were reached at 13.5 and 32.5 h for US Lab and ULC, respectively. Bioaccumulation was compared between non-resistant and resistant H. azteca by exposing animals to six different environmentally relevant concentrations for 28 h. Detection of chlorpyrifos in animal tissues indicated that resistant animals exposed to high concentrations of chlorpyrifos were capable of accumulating the insecticide up to 10-fold higher compared to non-resistant animals. Metabolite analysis from the 28-h concentration experiments showed that between 20 and 50 % parent compound was detected in H. azteca. These results imply that bioaccumulation potential can be more significant in chlorpyrifos resistant H. azteca and may be an essential factor in assessing the full impacts of toxicants on critical food webs, especially in the face of increasing pesticide and chemical runoff.

Cross-Ecosystem Fluxes of Pesticides from Prairie Wetlands Mediated by Aquatic Insect Emergence: Implications for Terrestrial Insectivores.

Contaminants alter the quantity and quality of insect prey available to terrestrial insectivores. In agricultural regions, the quantity of aquatic insects emerging from freshwaters can be impacted by insecticides originating from surrounding croplands. We hypothesized that, in such regions, adult aquatic insects could also act as vectors of pesticide transfer to terrestrial food webs. To estimate insect-mediated pesticide flux from wetlands embedded in an important agricultural landscape, semipermanetly and temporarily ponded wetlands were surveyed in cropland and grassland landscapes across a natural salinity gradient in the Prairie Pothole Region of North Dakota (USA) during the bird breeding season in 2015 and 2016 (n = 14 and 15 wetlands, respectively). Current-use pesticides, including the herbicide atrazine and the insecticides bifenthrin and imidacloprid, were detected in newly emerged insects. Pesticide detections were similar in insects emerging from agricultural and grassland wetlands. Biomass of emerging aquatic insects decreased 43%, and insect-mediated pesticide flux increased 50% along the observed gradient in concentrations of insecticides in emerging aquatic insects (from 3 to 577 ng total insecticide g-1 insect). Overall, adult aquatic insects were estimated to transfer between 2 and 180 µg total pesticide wetland-1 d-1 to the terrestrial ecosystem. In one of the 2 study years, biomass of emerging adult aquatic insects was also 73% lower from agricultural than grassland wetlands and was dependent on salinity. Our results suggest that accumulated insecticides reduce the availability of adult aquatic insect prey for insectivores and potentially increase insectivore exposure to insect-borne pesticides. Adult aquatic insects retain pesticides across metamorphosis and may expose insectivores living near both agricultural and grassland wetlands to dietary sources of toxic chemicals. Environ Toxicol Chem 2021;40:2282-2296. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

Occurrence, sources, and ecological risks of three classes of insecticides in sediments of the Liaohe River basin, China.

The frequent and extensive use of insecticides has caused serious aquatic pollution, thus posing a great threat to ecosystems and public health. In this study, three classes of insecticides including 20 organochlorine pesticides (OCPs), 6 organophosphorus pesticides (OPs), and 8 pyrethroids were analyzed in 24 sediments from the Liaohe River basin. The results showed that all sediment samples were contaminated with insecticides, with the total concentrations ranging from 7.3 ng/g dry weight (dw) to 242.8 ng/g dw. Among them, pyrethroids (2.2-102.5 ng/g dw) contributed 55% of the total insecticide concentration, followed by OCPs (1.3-94.8 ng/g dw) and OPs (2.6-45.5 ng/g dw), representing 24% and 21% of the total concentrations, respectively. For OCPs, hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) showed the highest concentrations of 0.37-37.5 ng/g dw and 0.05-23.2 ng/g dw, respectively. Historical inputs of lindane and technical DDT were the major sources of HCHs and DDTs, respectively, as indicated by isomer or metabolite ratios. Additionally, dichlorvos (0.26-17.1 ng/g dw) was the main OP, while cypermethrin dominated the pyrethroids with the concentrations of 1.6-32.6 ng/g dw. The spatial distribution revealed that significantly higher residues of insecticides were observed in sediments from the Daliao River system than those from the Liao River. This implied that these insecticides were most likely from the discharge of highly polluted sewage and industrial wastewater from adjacent industrial and populous cities as well as urban applications (e.g., landscape maintenance and household pest control). An ecological risk assessment based on risk quotients suggested that the three classes of insecticides analyzed here pose a low risk to aquatic organisms in the study area.

Response of Acetylcholinesterase to Insecticides in Reticulitermes chinensis Snyder (Isoptera: Rhinotermitidae)

Abstract The subterranean termite Reticulitermes chinensis Snyder is an important pest in China. We determined the inhibition of six selected insecticides to acetylcholinesterase (AChE) extracted from R. chinensis. Our results yielded half maximal inhibitory concentrations (I50) for each of the insecticides to be 3.49 × 10–3 M for methomyl, 3.87 × 10–2 M for phoxim, 2.18 × 10–3 M for triazophos, 1.89 × 10–3 M for profenosos, 1.10 × 10–3 M for malathion, and 4.39 × 10–2 M for omethoate. Furthermore, the inhibitory activity of AChE by the six insecticides was increased with the increase of insecticide concentration from 3.3 × 10–7 to 5 × 10–3 M. These results provide a theoretical basis for the management of R. chinensis.

Efficacy of Two Neonicotinoid Insecticides against Invasive Wood Borer Aromia bungii Larvae in Dietary Toxicity Test.

Simple SummaryThis study investigated the effects of two neonicotinoid insecticides (thiamethoxam and dinotefuran) on alien wood borer Aromia bungii, which invaded Japan recently. Small neonates and large larvae were fed artificial diet with different insecticide concentrations and then reared for 3 (neonates) or 12 (large larvae) weeks in the laboratory. Diet excavation immediately dropped in larvae exposed to high concentrations of both insecticides (≥1 ppm in neonates and ≥10 ppm in large larvae). Their growth was significantly suppressed, and the survival rate gradually declined over time (≥87% decline over 12 weeks in large larvae). These effects were similar between neonates and large larvae, but neonates were affected more by lower insecticide concentrations than large larvae. The two insecticides gradually debilitate A. bungii larvae. In practical use, rapid suppression of A. bungii wood boring damage can be expected by injecting these insecticides into infested trees. However, a relatively long–term retention of the insecticides may be required to kill the larvae in the trees, especially large larvae. Neonates may be controlled with less insecticides and shorter exposure than large larvae.In recent years, insecticide trunk injection was put into practical use for controlling wood boring pests. However, few studies have investigated the dose–response relationships between insecticides and wood–boring pests in detail. This study used two commercial formulations of the neonicotinoid insecticides thiamethoxam and dinotefuran and investigated their dose–response relationships with invasive wood borer Aromia bungii (Coleoptera: Cerambycidae) larvae. Neonates and late instar larvae were reared with an artificial diet containing different insecticide concentrations (0.01–100 ppm) in the laboratory, and their diet excavation activity, survival rate, and weight change were recorded. Diet excavation immediately dropped in larvae exposed to high concentrations of thiamethoxam or dinotefuran (≥1 ppm in neonates and ≥10 ppm in late instar larvae). The weight and survival rate gradually declined over 12 weeks in late instar larvae. These results suggest that the two neonicotinoids intoxicate and debilitate A. bungii larvae gradually to death. In practical use, rapid suppression of A. bungii wood boring damage can be expected by trunk injection of neonicotinoid insecticides. However, a relatively long-term retention of the insecticides may be required to kill large larvae. Neonates may be controlled with lower insecticide dosage and shorter exposure than larger larvae.

Improving houses in the Bolivian Chaco increases effectiveness of residual insecticide spraying against infestation with Triatoma infestans, vector of Chagas disease

Failure to control domestic Triatoma infestans in the Chaco is attributed to vulnerable adobe construction, which provides vector refuges and diminishes insecticide contact. We conducted a pilot to test the impact of housing improvement plus indoor residual spraying (IRS) on house infestation and vector abundance in a rural community in the Bolivian Chaco. The intervention included three arms: housing improvement + IRS [HI], assisted IRS [AS] in which the team helped to clear the house pre-IRS and routine IRS [RS]. HI used locally available materials, traditional construction techniques and community participation. Vector parameters were assessed by Timed Manual Capture for 2 person-hours per house at baseline and medians of 114, 173, 314, 389 and 445days post-IRS-1. A second IRS round was applied at a median of 314days post-IRS-1. Post-intervention infestation indices and abundance fell in all three arms. The mean odds of infestation was 0.29 (95% CL 0.124, 0.684) in the HI relative to the RS arm. No difference was observed between AS and RS. Vector abundance was reduced by a mean 44% (24.8, 58.0) in HI compared to RS, with no difference between AS and RS. Median delivered insecticide concentrations per house were lower than the target of 50mg/m2 in >90% of houses in all arms. Housing improvement using local materials and community participation is a promising strategy to improve IRS effectiveness in the Bolivian Chaco. A larger trial is needed to quantify the impact on reinfestation over time.

Insecticidal effect of thiamethoxam against seven stored-product beetle species

Bioassays were carried out in order to assess the insecticidal value of the neonicotinoid thiamethoxam in different concentrations against seven important beetle species that are major pests of stored grains. These species were Prostephanus truncatus (Horn), Rhyzopertha dominica (F.), Sitophilus oryzae (L.), Sitophilus granarius (L.), Oryzaephilus surinamensis (L.), Tribolium confusum Jacquelin du Val, and Cryptolestes ferrugineus (Stephens). Adults of these species were exposed to grains treated with thiamethoxam at dose rates of 0 (control), 0.01, 0.1, 0.5, 1, 2, 5 or 10 ppm. Our results indicate that with the increase of the insecticide concentration, there was also an increased adult mortality and a reduction in progeny production. To illustrate the relative sensitivity to thiamethoxam of the seven insects, starting with the most susceptible, we can classify them as P. truncatus > R. dominica = S. granarius = S. oryzae > T. confusum = O. surinamensis > C. ferrugineus. The findings of the present research show that thiamethoxam can be recommended for its efficacy at a rate of 10 ppm and duration of 14 days that could be used to control all insects and their progeny.

Minimizing insecticides for control of spotted wing drosophila (Drosophila suzukii) in soft fruit using bait sprays

AbstractDrosophila suzukii is a major pest of soft fruits, laying eggs in fruit before it is harvested. Control remains dependent on routine applications of insecticides. In semi‐field experiments, we tested the possibility of reducing the amount of insecticide needed to control D. suzukii by combining lower rates, volumes and area of application, in combination with phagostimulant baits in comparison with full field rates of the insecticides and an untreated control. The baits were (1) Combi‐protec—a proprietary mixture of plant extract, proteins and sugars, (2) a suspension of the yeast Hanseniaspora uvarum and (3) molasses. Low insecticide rates were 4% of the full rates and were attained by diluting the insecticide concentration in the spray and reducing the sprayed volume. The low rate was applied as a coarse quality spray in a swath across the middle of the strawberry or raspberry crop. The full rate was applied as fine droplets to the entire crop canopy. In strawberry, the Combi‐protec with a low rate of cyantraniliprole resulted in the same level of control of D. suzukii as the full rate. Combi‐protec was a more effective bait than the H. uvarum suspension. In raspberry, the average spray deposit coverage on the crop was approximately eight times higher with the full rate application compared with the low rate application. However, low rates of cyantraniliprole and spinosad with Combi‐protec or molasses baits were equally effective in D. suzukii control compared with the full rates of insecticides. In raspberry, the cost of the four full rate sprays of insecticides was £74 ha‐1 or £314 ha‐1 more than the four low rate insecticide sprays with Combi‐protec or molasses, respectively. The low rates of application resulted in fruit insecticide residues being less than 11% of those from raspberries sprayed with the full rates.

Effects of sublethal concentrations of some biorational insecticides in predation potential of Cryptolaemus montrouzieri on Dactylopius opuntiae

Effects of sublethal concentrations of some biorational insecticides in predation potential of Cryptolaemus montrouzieri on Dactylopius opuntiae

Efficacy of Chlorpyrifos and Bacillus Thuranginsis Israelinsis against Culex Pipiens (L.)

Culex pipiens (L.) (Diptera: Culicidae) is the most important medical insect in many parts of the world. Biological and natural chemicals have many advantages over the traditional ones in case of mosquito control. The efficacy of two insecticides belonging to different groups chlorpyrifos-ethyle (oranophosphate) and Bacillus thuranginsis var israelinsis) (bio-insecticides)were evaluated against the field and laboratory individuals of late 3rd instar larvae of Culex pipiens at different concentrations and three periods of exposure under laboratory conditions. Results obtained showed that the laboratory strain showed higher susceptibility to the tested insecticides than the mosquito populations collected from Abo-Rewash City, Giza Governorate and the mortality percentage was increased gradually with increasing the insecticide concentrations and the mortality percentage showed significant differences between concentrations and control. Also, The activity of acetyl cholinesterase (AChE), the glutathione S- transferase (GST), Total proteins and the activities of both Aspartate aminotransferase AST(GOT) and Alanine aminotransferase ALT(GPT) were determined were determined after 72 hrs of insecticidal exposure.

Assessment of pesticide residues in waters and soils of a vineyard region and its temporal evolution

Sustainable agriculture practices and integrated pest management for avoiding environmental pollution are necessary to maintain a high yield in vineyard areas. Pesticide residues in groundwater in a vineyard area of La Rioja (Spain) have been evaluated in previous years, and they could now have varied after farmers have adopted the different measures recommended. Accordingly, this research's objectives were (i) to evaluate the occurrence and seasonal distribution (spring, summer, and autumn samplings) of pesticides (36) plus their degradation products (DP) (11) in water and soil samples (23 + 15) in La Rioja (Northern Spain), and (ii) to compare the current water quality (2019) with that determined previously (2011). A multi-residue method based on solid phase extraction (for water samples) or solid liquid extraction (for soil samples) and high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS) was used to determine and quantify pesticides. The results reveal the presence in waters of 30 compounds from those selected (15 fungicides + 2 DP, 7 insecticides + 1 DP, and 3 herbicides +2 DP), with 14 of them at concentrations > 0.1 μg L−1 (water quality threshold for human consumption). The highest number of compounds was detected in summer (waters) and spring (soils). The pesticides most frequently detected in water samples were the fungicides metalaxyl, tebuconazole, and boscalid, with the last one being the compound found in the highest number of soil samples. The comparison of water pollution in 2011 and 2019 indicates a significant decrease in the total concentration of herbicides, fungicides and insecticides in 95–100%, 76–90%, and 42–85% of samples in the three campaigns, respectively. The results indicate that an optimized and sustainable use of pesticides in intensive and high-yield agricultural areas could reduce environmental pollution.

Sublethal concentration of insecticide amplifies interference competition in a tortrix moth

Insecticides are extensively used worldwide to kill insect pests, yet organisms are most often exposed to insecticides at sublethal concentrations. Our understanding of sublethal effects on life histories is needed to predict the impact of insecticides on population dynamics and improve insecticide use and pest control. Sublethal concentrations can impact life histories directly and indirectly through changes in the intraspecific competition. Yet, few studies have evaluated the sublethal effects on intraspecific competition and these do not disentangle the insecticide effects on interference competition versus exploitative competition. As such, sublethal effects on the relative contribution of each pathways in shaping life histories are largely unknown, despite the fact that this can impact population dynamics. In this study, we focused on the neurotoxic insecticide spinosad and investigated its sublethal effects on interference among the aggressive larvae of the tortrix moth Adoxophyes honmai and the consequences for life histories. We conducted a set of paired experiments to disentangle the insecticide effects on interference from the ones on exploitation. Spinosad was found to amplify interference with most effects on mortality which lets us suggest that the insecticide likely increases the level of aggressive interactions resulting in more conspecific killings (e.g. cannibalism). Spinosad exposure was found to impair movement ability. Less movements may increase susceptibility to conspecific attacks and or increase aggresivity for better defence, two plausible mechanisms that could explain the increase in interference with insecticide. This study shows that insecticide at sublethal concentration can impact life histories by altering the strength of interference competition. Many organisms (pest and non-target species) compete through interference and theory predicts that a change in interference can substantially change dynamics. Our finding therefore reveals the importance of assessing the effect of insecticides on the mechanisms of competition when predicting their impact on populations.

Selección de Resistencia y Efectos Subletales de Cipermetrina en la Palomilla Dorso de Diamante (Plutella xylostella L.)

Plutella xylostella es una importante plaga de cultivos de brassicas en más de 100 países. El principal método de control de P. xylostella se basa en el uso de insecticidas químicos. Sin embargo, esta especie se caracteriza por su rápido desarrollo de resistencia a casi todos los insecticidas. Se ha reportado que la aplicación de concentraciones bajas de insecticidas afecta la fisiología, bioquímica y ecología de los insectos. En este estudio, se realizó una selección de resistencia de cipermetrina durante ocho generaciones de P. xylostella y se determinó la dosis subletal (CL20) de la línea resistente y de la línea susceptible. Posteriormente, la dosis subletal se aplicó a larvas de tercer instar para investigar su efecto en el porcentaje de pupación, peso de pupas, emergencia de adultos en dos generaciones (progenitores y descendientes), así como los tiempos de desarrollo de cada fase de desarrollo de P. xylostella. Se observó una disminución el porcentaje de pupas formadas, adultos emergidos y peso de pupas. Por otro lado, el número de huevos depositados aumentó cuando los individuos fueron expuestos al insecticida. Lo anterior puede ser un factor importante para el manejo y control de esta plaga cuando se presenten problemas de resistencia a cipermetrina.

Blooming of insecticides from polyethylene mesh and film

Malaria remains a public health concern with vector control still the vital component of disease prevention, control, and elimination strategies. Recent years has seen a “stalling” in the progress made towards the reduction in the global malaria burden, highlighting the need to develop new, innovative, and safe alternative tools and delivery systems to achieve global malaria elimination. Interventions based on the use of indoor residual spraying (IRS) and long-life insecticidal bed nets (LLINs), i.e. insecticide-containing wall linings (IWLs), can contribute towards the reduction of malaria. Both LLINs and IWLs rely on the presence of insecticides on the fibre or filament surfaces. However, materials directly incorporating the insecticides into the polymer melt during extrusion, allows for effective killing of the mosquitoes when they come into contact with the surface of the material, only if there is insecticide present there. This means that the insecticide must migrate to the surface and precipitate there (bloom). Over time the internal concentration of insecticide will decay. This investigation was done using Fourier transform infrared spectroscopy (FTIR) in both the transmission and attenuated total reflection (ATR) modes to better understand the blooming of three World Health Organization-approved contact insecticides, i.e. alphacypermethrin, fipronil and chlorfenapyr, from mesh or film to better understand the likeliness of insecticides within the materials to migrate to the surface. Film-based samples were prepared in addition to wall lining mesh, because of their easier characterisation than the irregular shaped mesh filaments. FTIR, in ATR and in transmission modes, enabled the tracking of the migration of the three insecticides, over time to the surface of polyethylene mesh or film. This made it possible to estimate the apparent solubility of the insecticides in the polymer matrix. However, scanning electron microscopy (SEM) revealed that a portion of the insecticide is trapped, in a crystalline state, inside the polymer matrix. These results suggest the possibility of developing products-based insecticides for protection against infective mosquito bites in malaria-endemic regions.

Increasing plant density increases Bt toxin concentration of boll wall in cotton by decreasing boll setting speed

BackgroundIn order to uncover the mechanism of significantly reduced insect resistance at the late developmental stage in cotton (Gossypium hirsutum L.), the relationship between boll setting rate under different planting densities and Bacillus thuringiensis (Bt) insecticidal concentrations in the boll wall were investigated in the present study. Two studies were arranged at Yangzhou, China during the 2017–2018 cotton growth seasons. Five planting densities (15 000, 25 000, 45 000, 60 000 and 75 000 plants per hectare) and the flower-removal treatment were imposed separately on Bt cotton cultivar Sikang3 to arrange different boll setting rates, and the boll setting rates and Bt toxin content were compared.ResultsHigher boll setting rate together with lower Bt toxin contents in boll wall was observed under low planting density, whereas lower boll setting rate and higher Bt toxin contents were found under high planting density. Also, higher Bt protein concentration was associated with higher soluble protein content, glutamic-pyruvic transaminase (GPT), and glutamic oxaloacetate transaminase (GOT) activities, but lower amino acid content, and protease and peptidase activities. It was further confirmed that a higher boll setting rate with lower Bt protein content under flower-removal.ConclusionsThis study demonstrated that the insecticidal efficacy of boll walls was significantly impacted by boll formation. Reduced protein synthesis and enhanced protein degradation were related to the reduced Bt toxin concentration.