Sublethal Doses Of Insecticides Research Articles

Effects of Melia azedarach extract on demographic and biochemical characteristics of the cabbage aphid, Brevicoryne brassicae

The cabbage aphid, Brevicoryne brassicae L. (Aphididae: Hemiptera) a destructive aphid, is native to Europe and is now found in many other parts of the world. Currently, one of the main problems of Iranian cabbage growers is the significant damage caused by this pest. Also, due to the fresh eating of cabbage, it is necessary to use non-chemical methods to control the pests. Our bioassay tests showed that Melia azedarach L. (Meliaceae) fruit extract showed high toxicity to cabbage aphid. In this study, sublethal effects of M. azedarach extract was investigated on some demographic and biochemical properties of B. brassicae. The results showed that the sublethal concentrations (LC10 and LC20) and LC50 values were 0.68, 1.16, and 3.42 μg/ml, respectively. Compared to the control, sublethal concentrations of insecticide significantly decreased the gross reproductive rate (GRR), net reproductive rate (R0), intrinsic rate of increase (rm), finite rate of increase (λ), intrinsic rate of birth (b), intrinsic rate of death (d), weekly growth rate (rw), reproductive rate and adult longevity of the pest. Meanwhile, the mean generation time (T) and population doubling time (DT) of this aphid increased significantly. Additionally, sublethal doses of insecticide reduced the energy reserves of the pest such as carbohydrate, protein and lipid content compared to the controls. In addition to modify the pH, this extract also changed the distribution and concentration of sodium and potassium ions in haemolymph. Therefore, sublethal concentrations of M. Azedarach fruit extract can be used in the management program of B. brassicae.

Intergenerational Effects of Sublethal Lambda-Cyhalothrin Exposure on Aphis gossypii Glover (Hemiptera: Aphididae) Reproduction and Development.

Aphis gossypii Glover, a widespread insect, presents a substantial danger to global agriculture. Lambda-cyhalothrin is a pyrethroid insecticide that has been widely studied for its effects on arthropods. Studies have reported that sublethal doses of insecticides can produce various consequences on arthropod reproduction. Hence, the objective of this research was to examine the potential effects of a sublethal dose of lambda-cyhalothrin (LC30, 1.15 mg/L) on A. gossypii, for which we created life tables and conducted qPCR analysis. Adult longevity, fecundity, net reproductive rate (R0), body length, width, weight, and the expression of vitellogenin (Vg) and vitellogenin receptor (VgR) genes were not significantly altered by lambda-cyhalothrin treatment at LC30 concentration in the F0 generation of A. gossypii adults. The intrinsic rate of increase (r) and finite rates of increase (λ) decreased significantly, while the mean generation time (T) increased. In addition, Vg and VgR gene expression levels were significantly higher in the F1 and F2 generations, whereas body length, width, and weight were notably reduced. The developmental duration, longevity, r, and λ did not differ significantly from those of the control group. Thus, the sublethal and intergenerational stimulatory effects of lambda-cyhalothrin were observed in A. gossypii, and the alterations in Vg and VgR in A. gossypii were strongly associated with sublethal effects. The results of this research offer valuable knowledge regarding the indirect impacts of lambda-cyhalothrin on A. gossypii, which can be utilized as a theoretical foundation for the prudent utilization of insecticides to combat this pest and devise strategies for managing resistance.

Sublethal doses of insecticide reduce thermal tolerance of a stingless bee and are not avoided in a resource choice test.

Insecticides and climate change are among the multiple stressors that bees face, but little is known about their synergistic effects, especially for non-Apis bee species. In laboratory experiments, we tested whether the stingless bee Tetragonula hockingsi avoids insecticide in sucrose solutions and how T. hockingsi responds to insecticide and heat stress combined. We found that T. hockingsi neither preferred nor avoided sucrose solutions with either low (2.5 × 10-4 ng µl-1 imidacloprid or 1.0 × 10-4 ng µl-1 fipronil) or high (2.5 × 10-3 ng µl-1 imidacloprid or 1.0 × 10-3 ng µl-1 fipronil) insecticide concentrations when offered alongside sucrose without insecticide. In our combined stress experiment, the smallest dose of imidacloprid (7.5 × 10-4 ng) did not significantly affect thermal tolerance (CTmax). However, CTmax significantly reduced by 0.8°C (±0.16 SE) and by 0.5°C (±0.16 SE) when bees were fed as little as 7.5 × 10-3 ng of imidacloprid or 3.0 × 10-4 ng of fipronil, respectively, and as much as 1.5°C (±0.16 SE) and 1.2°C (±0.16 SE) when bees were fed 7.5 × 10-2 ng of imidacloprid or 3.0 × 10-2 ng of fipronil, respectively. Predictions of temperature increase, and increased insecticide use in the tropics suggest that T. hockingsi will be at increased risk of the effects of both stressors in the future.

Translaminar activity of different insecticides against Bemisia tabaci

One of the main mechanisms of action for many insecticides is translaminar redistribution or local systemic. The present study was carried out at Chaudhary Charan Singh Haryana Agricultural University, Hisar, Haryana during 2019 and 2020 to investigate the translaminar activity of different insecticides having different doses and sprays on treated brinjal plant having Bemisia tabaci (Gennadius) nymphs. Different treatments, i.e. diafenthiuron 50% WP (150, 210, and 300 g a.i./ha), fenpropathrin 30% EC (50, 70, and 100 g a.i./ha), thiamethoxam 25% WG (25, 35, and 50 g a.i./ha), and deltamethrin 2.8% EC (7.5, 10.5 and 15 g a.i./ha) were frequently sprayed on brinjal plants (var. Hisar Shyamal) growing in pots. Insecticides effectiveness was measured through nymphal mortality of B. tabaci (whitefly). Similar study was conducted in 2020 to ensure reliability of results. The results revealed that, almost similar trendswere obtained during 2019 and 2020, hence proving reliability. Among all tested insecticides, maximum translaminar effect was observed in thiamethoxam 25% WG treated plant at 50 g a.i./ha (50.72% nymphal mortality). Whereas, deltamethrin 2.8% EC treated plant at 15 g a.i./ha showed minimum translaminar effect (0.63% nymphal mortality) as compared to other treatments. Translaminar effect of leaves treated with diafenthiuron 50% WP and fenpropathrin 30% EC was found at par with each other. Nymphal mortality is low in sub-lethal doses of insecticides as compared to lethal doses. It can be concluded that resistance may develop due to sub-lethal doses of insecticides. Farmers and agricultural experts would benefit from this study's findings.

Hormetic effects of neonicotinoid insecticides on Rhizoglyphus robini (Acari: Acaridae)

The stimulation of biological processes by sublethal doses of insecticides or other stressors is known as hormesis. Here, we have evaluated whether exposure to field-relevant or low concentrations of neonicotinoids induce changes in the reproductive capacity of the bulb mite Rhizoglyphus robini (Acari: Acaridae). Among the tested neonicotinoids imidacloprid, thiamethoxam, and dinotefuran, the highest hormetic effect on the reproduction of R. robini occurred 24 h after the 48 h exposure period to imidacloprid at concentrations of 70 and 140 mg a.i./L. Despite the stimulating effects of imidacloprid on mite reproduction, no significant differences were observed in the offspring (F1) for biological aspects including egg hatch rate, embryonic period and sex ratio, while an increase was found in the duration of development time from egg to adult. Evaluation of the detoxification enzyme activities of treated adults showed that the highest activity of carboxyl/cholinesterases, cytochrome P450s, and glutathione S-transferases was obtained when exposed to 70, 140 and 70 mg a.i./L imidacloprid, immediately after the exposure period, respectively. Also, an increase in the activity of the antioxidant enzyme catalase was observed compared to that of the control. After imidacloprid pretreatment (140 mg a.i./L), the tolerance of adult mites to diazinon was increased about two-fold. This study shows that exposure to imidacloprid can induce hormetic effects on R. robini and could severely complicate its control due to a higher reproduction, enhanced detoxification enzyme activities, and increased tolerance against other pesticides.

Effect of insecticides on locomotory behaviour and enzyme activity of Spodoptera litura (Fabricius) populations from Punjab

Aim: The variations in locomotory behaviour and enzyme activity, i.e., acetylcholinesterase and general esterases of Spodoptera litura Fabricius larval populations collected from different regions of Punjab, i.e., Amritsar, Kapurthala and Ludhiana were investigated in the laboratory prior exposure to different insecticides. Methodology: The test larvae were exposed to sublethal doses of different insecticides via surface and food treatment. For locomotory behaviour, they were allowed to move on treated surface and their movements were recorded with an automated video tracking system, Ethovision while on other hand food treatment was opted for observing the influence on enzyme activity. Results: The pronounced variations were observed in the locomotor behaviour of S. litura upon surface exposure of different insecticides. The larva travelled more distance with higher speed and larger turn angle on insecticide-treated surfaces than the untreated ones, while on comparison of different larval populations, the Amritsar population larvae travelled less distance with low speed and maximum turnings. The decrease in acetylcholinesterase and general esterase activity was recorded in treated larvae than untreated ones. The influence of emamectin benzoate was recorded more on locomotion and enzyme activity of S. litura as compared to the remaining insecticides and the Amritsar population was least affected. Interpretation: The sublethal doses of insecticides influenced the overall behavioural physiology of S. litura and this biological parameter could be useful in designing the management strategies for S. litura. Key words: Acetylcholinesterase, Esterases, Insecticides, Locomotory behaviour, S. litura

Effects of imidacloprid-induced hormesis on the development and reproduction of the rose-grain aphid Metopolophium dirhodum (Hemiptera: Aphididae).

Field populations of insect pests are affected by sub-lethal doses of insecticides, leading to hormesis. Imidacloprid is a neonicotinoid insecticide widely used to control various sucking insect pests, including aphids. In this study, the effects of sub-lethal concentrations of imidacloprid on the life table traits of the rose-grain aphid Metopolophium dirhodum (Walker) were evaluated on parental and first filial generations. The results showed that sub-lethal concentrations of imidacloprid significantly reduced the fecundity, adult longevity, and reproductive period of M. dirhodum in parental generation (F0). However, the imidacloprid-induced hormetic effects on development and reproduction were detected in the F1 generation. These hormetic effects were indicated by significantly higher adult longevity, fecundity, survival rate, intrinsic and finite rates of increase, and net reproductive rate of first filial generation (F1) of M. dirhodum. Our finding indicated that the application of sub-lethal concentrations of imidacloprid inhibited parental generation (F0), but it significantly stimulated the population growth of filial generation (F1) in the M. dirhodum. The results support the inclusion of insecticides in integrated pest management programs for managing wheat aphids.

Sublethal and transgenerational effects of synthetic insecticides on the biological parameters and functional response of Coccinella septempunctata (Coleoptera: Coccinellidae) under laboratory conditions.

Synthetic insecticides have been an inevitable part of plant protection throughout the world. Sublethal effects of these chemicals on beneficial insect species are one of the contemporary issues these days. Using the age-stage, two-sex life table model, this study evaluated the sublethal and transgenerational effects of six synthetic insecticides (imidacloprid, thiamethoxam, lambda-cyhalothrin, cypermethrin, chlorpyrifos and profenofos) commonly applied to winter vegetables, on the fitness and predation of the seven-spotted ladybeetle, Coccinella septempunctata, which is an efficient predator of aphids worldwide. According to results, all insecticides at their sublethal doses (LC30) significantly suppressed the emergence of adults, adult weight, fertility and fecundity of the parental generation compared to control treatment. The larval stage was prolonged and oviposition, fecundity and total longevity of the adult beetles were decreased in unexposed progeny whose parents were exposed to sublethal doses of all insecticides. Moreover, the biological parameters of adults, including the intrinsic rate of increase (r), finite rate of increase (λ) and net reproductive rate (R 0) were significantly reduced when exposed to sublethal doses of insecticides. The predation rate of the F1 generation adults was also decreased after exposure to the sublethal doses of insecticides. However, chlorpyrifos, profenofos, lambda-cyhalothrin and cypermethrin exhibited more deleterious effects on the fitness and population parameters of beetles than imidacloprid and thiamethoxam.

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Scientific research was conducted from 2020 to 2022 under laboratory conditions and on cabbage plantations (plot and industrial). It has been confirmed that cabbage plantations in the Lukashin community of the Armavir region had a high population of cabbage moth caterpillars. Local bacterial cultural liquids of Bacillus thuringiensis species tested separately and in combination with sublethal doses of insecticides showed high biological effectiveness against phytophagous caterpillars of ages I III, which does not differ significantly from the reference indicator: commercial bacterial preparation Lepidocide. According to the results of laboratory examination of the bodies of the deceased larvae, it was found out that the decomposing body tissues of the pest larvae were filled with insecticidal sporocrystalline components, which confirmed that the death of the phytophagous larvae is the result of the effect of the tested insecticides. When struggling against cabbage moth caterpillars, it is proposed to use bacterial culture fluids alone with a lethal dose of 300 million spores/ml and in combinations with their sublethal quantity (titer of 150 million spores/ml) with the chemical insecticide calypso (0.033 % suspension).

Effects of a systemic insecticide on stretching and production of wax in domestic bees Apis mellifera intermissa in Northen Africa (Algeria)

Imidacloprid is a well-known systemic insecticide which has a deleterious impact on honeybees. Beekeepers in the Tizi-Ouzou wilaya (Algeria) where the imidacloprid insecticide is used, report unusual losses and deaths of bee colonies. Even at sublethal doses, insecticid can impact the most crucial tasks of a bee colony such as comb building. This study was conducted in order to investigate the effect of an imidacloprid based insecticide (Confidor®Supra) on the production of wax by the honeybee Apis mellifera intermissa. After the imidacloprid LD50 was determined in controlled conditions, three sublethal doses were tested. The mortality, the syrup consumption and the weight of the wax generated were recorded.
 The imidacloprid insecticide LD50 at 48 hours was evaluated at 3.5 ng.per bee on 4 days old spring worker bees. We found that the three sublethal doses (0.175 mg.L-1, 0.087 mg.L-1 and 0.035 mg.L-1) had an impact on the syrup consumption and the wax production by adult bees. Bees exposed to sublethal doses of insecticide consumed less syrup and produced less wax that the control bees. A dose response was observed regarding the production of wax.
 The reduction of wax production by bees caused by an exposure to an imidacloprid based insecticide ads up to the many other effects of imidacloprid described in the literature. This kind of impact could have harmful consequences for bee colonies as wax production is the basis of nest building. The physiological causes of the reduction of wax production remain to be investigated.

The Synergistic Effect of Thiamethoxam and Synapsin dsRNA Targets Neurotransmission to Induce Mortality in Aphis gossypii.

Sublethal doses of insecticides have many impacts on pest control and agroecosystems. Insects that survive a sublethal dose of insecticide could adapt their physiological and behavioral functions and resist this environmental stress, which contributes to the challenge of pest management. In this study, the sublethal effects of thiamethoxam on gene expression were measured through RNA sequencing in the melon aphid Aphis gossypii. Genes regulating energy production were downregulated, while genes related to neural function were upregulated. To further address the function of genes related to neurotransmission, RNA interference (RNAi) was implemented by transdermal delivery of dsRNA targeting synapsin (syn), a gene regulating presynaptic vesicle clustering. The gene expression of synapsin was knocked down and the mortality of aphids was increased significantly over the duration of the assay. Co-delivery of syn-dsRNA and thiamethoxam reversed the upregulation of synapsin caused by low-dose thiamethoxam and resulted in lethality to melon aphids, suggesting that the decreased presynaptic function may contribute to this synergistic lethal effect. In addition, the nanocarrier star polycation, which could bind both dsRNA and thiamethoxam, greatly improved the efficacy of lethality. These results increase our knowledge of the gene regulation induced by sublethal exposure to neonicotinoids and indicated that synapsin could be a potential RNAi target for resistance management of the melon aphid.

Sublethal effects of a pyrethroid insecticide on cuticle thickness, wing size and shape in the main vector Triatoma infestans.

Exposure to sublethal doses of insecticide may affect biological traits in triatomines. We investigated the effects of toxicological phenotype (pyrethroid resistance status) and exposure to sublethal doses of deltamethrin on two traits of Triatoma infestans Klug (Heteroptera: Reduviidae) using a phenotypic plasticity experimental design. First-instar nymphs from 14 and 10 full-sib families from pyrethroid-susceptible and pyrethroid-resistant populations, respectively, were used. For the susceptible population, we treated first instars topically with acetone (control) or deltamethrin (treatment) once. For the resistant population, instars were treated once, twice and three times as first, third or fifth-instar nymphs, respectively. We measured cuticle thickness, wing size and wing shape of 484 emerging adults, and tested for treatment effects using mixed ANOVA and MANOVA models. Toxicological phenotype, exposure to deltamethrin and full-sib family exerted significant effects on cuticle thickness, wing size and wing shape. Adult triatomines previously treated with deltamethrin developed significantly thicker cuticles than control triatomines only in the resistant population and significantly bigger wings in both populations. Mean cuticle thickness and wing size increased with increasing exposures to deltamethrin. Exposure to sublethal doses of deltamethrin generated morphological modifications that may affect insect survival and flight dispersal, and hence may have evolutionary and epidemiological consequences.

Exposure to a sublethal dose of imidacloprid induces cellular and physiological changes in Periplaneta americana: Involvement of α2 nicotinic acetylcholine subunit in imidacloprid sensitivity

Neonicotinoids are the most important class of insecticides used as pest management tools during several decades. Exposition of insect to sublethal dose of insecticide induces physiological and cellular changes that could contribute to the adaptation of the insects in order to loss their sensitivity to insecticides. The aim of our study is to demonstrate that a subchronic exposure to a sublethal dose of a neonicotinoid imidacloprid is sufficient to induce molecular changes leading to a loss of imidacloprid sensitivity. We report that in the cockroach, Periplaneta americana, subchronic exposure to a sublethal dose of imidacloprid induced weak changes in detoxification enzyme activity and a significant decrease of the nicotinic acetylcholine α2 mRNA. This molecular effect is correlated to a decrease of imidacloprid sensitivity of cockroaches. Using RNA interference, we shown the key role of nicotinic acetylcholine α2 subunit in imidacloprid sensitivity. Thus, quantitative changes in insecticide targets lead to decreased sensitivity to insecticides. This parameter needs to be considered in order to develop sustainable insect resistance management strategies.

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.

The impact of sublethal permethrin exposure on susceptible and resistant genotypes of the urban disease vector Aedes aegypti.

BACKGROUNDIn urban environments, some of the most common control tools used against the mosquito disease vector Aedes aegypti are pyrethroid insecticides applied as aerosols, fogs or residual sprays. Their efficacy is compromised by patchy deployment, aging residues, and the evolution and invasion of pyrethroid‐resistant mosquitoes. A large proportion of mosquitoes in a given environment will therefore receive sublethal doses of insecticide. The potential impact of this sublethal exposure on the behaviour and biology of Ae. aegypti carrying commonly reported resistance alleles is poorly documented.RESULTSIn susceptible insects, sublethal exposure to permethrin resulted in reductions in egg viability (13.9%), blood avidity (16.7%) and male mating success (28.3%). It caused a 70% decrease in the lifespan of exposed susceptible females and a 66% decrease in the insecticide‐resistant females from the parental strain. Exposure to the same dose of insecticide in the presence of the isolated kdr genotype resulted in a smaller impact on female longevity (a 58% decrease) but a 26% increase in eggs per female and a 37% increase in male mating success. Sublethal permethrin exposure reduced host‐location success by 20–30% in all strains.CONCLUSIONThe detrimental effects of exposure on susceptible insects were expected, but resistant insects demonstrated a less predictable range of responses, including negative effects on longevity and host‐location but increases in fecundity and mating competitiveness. Overall, sublethal insecticide exposure is expected to increase the competitiveness of resistant phenotypes, acting as a selection pressure for the evolution of permethrin resistance. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Insecticide exposure affects intergenerational patterns of DNA methylation in the Colorado potato beetle, Leptinotarsa decemlineata.

Insecticide use is pervasive as a selective force in modern agroecosystems. Insect herbivores exposed to these insecticides have been able to rapidly evolve resistance to them, but how they are able to do so is poorly understood. One possible but largely unexplored explanation is that exposure to sublethal doses of insecticides may alter epigenetic patterns that are heritable. For instance, epigenetic mechanisms, such as DNA methylation that modifies gene expression without changing the underlying genetic code, may facilitate the emergence of resistant phenotypes in complex ways. We assessed the effects of sublethal insecticide exposure, with the neonicotinoid imidacloprid, on DNA methylation in the Colorado potato beetle, Leptinotarsa decemlineata, examining both global changes in DNA methylation and specific changes found within genes and transposable elements. We found that exposure to insecticide led to decreases in global DNA methylation for parent and F2 generations and that many of the sites of changes in methylation are found within genes associated with insecticide resistance, such as cytochrome P450s, or within transposable elements. Exposure to sublethal doses of insecticide caused heritable changes in DNA methylation in an agricultural insect herbivore. Therefore, epigenetics may play a role in insecticide resistance, highlighting a fundamental mechanism of evolution while informing how we might better coexist with insect species in agroecosystems.

Development of precise micro analytical tool to identify potential insecticide hazards to bees in guttation fluid using LC–ESI–MS/MS

This paper illustrates the development of a miniaturized and precise analytical tool for biomonitoring of honey bee exposure to insecticides. This is the first work describing an analytical method for determination of very low concentrations of a wide range of insecticides in maize guttation fluid. Seed treatment with systemic insecticides or their foliar application causes the accumulation of compounds in the guttation liquid, which consists of excess water and compounds removed by plants and is a source of water for bees. A micro-QuEChERS protocol using 1 g of sample was used for analysis of over 140 insecticides belonging to 30 different chemical classes by LC–ESI–MS/MS. The determination of insecticides in guttation fluid is a difficult analytical task due to 1) the complexity of the sample matrix, 2) small amounts of test samples and 3) trace levels of analytes (often equal sublethal dose of insecticide for bees). An efficient sample treatment is proposed, involving 1 g of sample, extraction with 1% formic acid in acetonitrile, frozen, ultrasound-assisted, centrifugation and dispersive solid phase extraction with nano graphene oxide. Other tested sorbents: Fe3O4MNPs and two mixtures PSA/C18/GCB and Z-Sep did not give satisfactory parameters during sample purification. The graphene oxide proved to be the best, ensuring negligible matrix effects and analyte recoveries between 70% and 120% with relative standard deviations <20% for most of the compounds studied. The proposed method enables assessment of risk to honey bees resulting from exposure to guttation fluids containing toxic insecticides at very low concentrations.

Consequences of larval competition and exposure to permethrin for the development of the rodent malaria Plasmodium berghei in the mosquito Anopheles gambiae

BackgroundMosquitoes and other vectors are often exposed to sublethal doses of insecticides. Larvae can be exposed to the run-off of agricultural use, and adults can be irritated by insecticides used against them and move away before they have picked up a lethal dose. This sublethal exposure may affect the success of control of insect-borne diseases, for it may affect the competence of insects to transmit parasites, in particular if the insects are undernourished.MethodsWe assessed how exposure of larvae and adults to a sublethal dose of permethrin (a pyrethroid) and how larval competition for food affect several aspects of the vector competence of the mosquito Anopheles gambiae for the malaria parasite Plasmodium berghei. We infected mosquitoes with P. berghei and measured the longevity and the prevalence and intensity of infection to test for an effect of our treatments.ResultsOur general result was that the exposure to the insecticide helped mosquitoes deal with infection by malaria. Exposure of either larvae or adults decreased the likelihood that mosquitoes were infected by about 20%, but did not effect the parasite load. Exposure also increased the lifespan of infected mosquitoes, but only if they had been reared in competition. Larval competition had no effect on the prevalence of infection, but increased parasite load. These effects may be a consequence of the machinery governing oxidative stress, which underlies the responses of mosquitoes to insecticides, to food stress and to parasites.ConclusionsWe conclude that insecticide residues are likely to affect the ability of mosquitoes to carry and transmit pathogens such as malaria, irrespective of the stage at which they are exposed to the insecticide. Our results stress the need for further studies to consider sublethal doses in the context of vector ecology and vector-borne disease epidemiology.

Triazophos-induced vertical transmission of rice stripe virus is associated with host vitellogenin in the small brown planthopper Laodelphax striatellus.

Rice stripe virus (RSV) is one of the most serious rice diseases in East Asia. The small brown planthopper (SBPH), Laodelphax striatellus, is an economically important rice pest. SBPH transmits RSV horizontally and vertically, resulting in serious rice economic losses. Exposure to sublethal doses of insecticides can induce many physiological and cellular changes in insects. However, the mechanism underlying triazophos-induced RSV vertical transmission remains unclear. Here, we investigated the role of vitellogenin (Vg) in triazophos-induced RSV vertical transmission. RSV vertical transmission rates were significantly induced by sublethal exposure to triazophos. The transcript abundance of viral RNA3 segment (RNA3) and capsid protein (CP) in the ovaries of SBPH were also significantly increased. Triazophos induced the expression level of Vg in L. striatellus (LsVg) and increased the contents of ovarian protein and fat body protein. Knockdown of Vg significantly reduced the expression levels of LsVg and Vg receptor (LsVgR), and decreased RSV accumulations in the ovaries. Double-stranded Vg (dsVg)-mediated down-regulation could be rescued by exposure to triazophos. Vertical transmission rate of the dsVg-injected group was significantly decreased compared with the dsGFP-injected group, and triazophos significantly rescued the RSV vertical transmission rate of the dsVg-injected group. Our results indicate that triazophos-induced RSV vertical transmission is associated with Vg. This work will help us to further elucidate sublethal doses of insecticides-mediated effects and develop new strategies for pest control. © 2019 Society of Chemical Industry.

Transcriptional responses of soybean aphids to sublethal insecticide exposure

Insecticides are a key tool in the management of many insect pests of agriculture, including soybean aphids. The selection imposed by insecticide use has often lead to the evolution of resistance by the target pest through enhanced detoxification mechanisms. We hypothesised that exposure of insecticide-susceptible aphids to sublethal doses of insecticides would result in the up-regulation of genes involved in detoxification of insecticides, revealing the genes upon which selection might act in the field. We used the soybean aphid biotype 1 reference genome, version 6.0 as a reference to analyze RNA-Seq data. We identified multiple genes with potential detoxification roles that were up-regulated 12 h after sublethal exposure to esfenvalerate or thiamethoxam. However, these genes were part of a dramatic burst of differential gene expression in which thousands of genes were up- or down-regulated, rather than a defined response to insecticides. Interestingly, the transcriptional burst observed at 12 h s declined dramatically by 24-hrs post-exposure, suggesting a general stress response that may become fine-tuned over time.