Doses Of Insecticides Research Articles

Superadditivity between control methods in pest management

AbstractPest Management (PM) has its 1959 origin in Integrated Control, a combination of a reduced dose of insecticide with biological control. At the time, it was not recognised that the interaction between these two control methods was more than additive. This ‘superadditivity’ can also be achieved with the full dose of insecticide, for example, by localising its application in space. There is also likely to be superadditivity in the interaction between partial plant resistance and biological control. Pests on resistant hosts are usually smaller and the same mortality can often be obtained with just two‐thirds or one‐half of the dose of insecticide needed on susceptible plants, giving superadditivity between partial plant resistance and chemical control. These positive interactions between biological control, chemical control and partial host plant resistance form a ‘Pest Management Triad’, though legislation and risk‐aversion may limit the practicability of protocols based on the Triad.

Insecticide Resistance in Aedes aegypti from the National Capital Region of the Philippines.

Human arboviral diseases such as dengue, chikungunya, and Zika can be transmitted by the mosquito Aedes aegypti. The insecticide-based vector control strategy is critical in reducing transmission of these Aedes-borne diseases but is threatened mainly by the emergence of insecticide resistance. Adult Ae. aegypti from the National Capital Region (NCR), Philippines, were subjected to bioassays to determine their susceptibility to diagnostic doses of pyrethroid, organochlorine, and organophosphate insecticides following the standard World Health Organization insecticide susceptibility test. This study reports the detection of insecticide resistance to pyrethroids and organochlorine in Ae. aegypti from the Philippines for the first time. Most of the Ae. aegypti populations from NCR exhibited phenotypic resistance to permethrin, etofenprox, and DDT. Varying resistance levels to deltamethrin, cyfluthrin, and lambda-cyhalothrin were observed in the different mosquito populations, while all populations tested to malathion were susceptible to this organophosphate. This finding should alert public health authorities to consider modifying the existing vector management package for greater control efficacy. Best practices proven to prevent or delay the development of insecticide resistance, such as insecticide rotation, should also be implemented, while alternative chemicals with a different mode of action should be explored to ensure the continuing efficacy of program interventions.

Improving Sphenophorus levis Adult Mortality Through Solid Insecticide Applications and Increased Insecticide Dose.

The sugarcane weevil (Sphenophorus levis Vaurie, 1978) is currently considered the most important sugarcane pest in Brazil, causing significant yield losses. Application methods of insecticides for S. levis control have not been effective, mostly due to the insect's cryptic behavior below the soil surface which suppresses the correct placement of insecticide active ingredients on target. Two experiments were conducted using an innovative bioassay methodology that simulates sugarcane field conditions to effectively evaluate S. levis adult mortality and insecticide residues in the soil under different treatments. The first experiment aimed to assess the efficacy of two liquid- and solid-applied insecticides, while the second aimed to examine the effect of increasing the dose of lambda-cyhalothrin + thiamethoxam on S. levis adult control. The novel bioassays simulated liquid and solid insecticide applications on sugarcane by exposing S. levis adults to chemical residuals on rhizomes and in soil after insecticide application. In the first experiment, low S. levis adult control was detected (< 53% mortality) across all treatments, where both solid and liquid applications of lambda-cyhalothrin + thiamethoxam provided greater efficacy levels than imidacloprid and control treatments, respectively. Solid applications maintained higher insecticide concentrations in the soil for longer periods than liquid insecticide applications, providing maximum insect control levels 7days after application. The second experiment revealed that solid applications at higher insecticide doses significantly improved control of S. levis adult (76.7% mortality) and resulted in greater insecticide concentrations in the soil compared to the recommended label rate (58.8% mortality).

Impact of triflumezopyrim (insecticide) on blood and serum biochemistry of freshwater fish, subadult Labeo rohita (Hamilton, 1822)

The impact of insecticides on water bodies can be evaluated by studying the physiology and health of fish. These chemicals pose a significant and direct risk to aquatic ecosystems and hence aquatic animals like fish. Therefore, this study was designed to investigate the toxic effects of sub-lethal concentrations of triflumezopyrim, a novel synthetic insecticide commonly used in crop protection, on the biochemical and hematological parameters of freshwater sub-adult Labeo rohita L. Here, fish were subjected to sub-lethal doses of triflumezopyrim at various concentrations (1.41 ppm, 3.27 ppm, and 4.97 ppm) for 21 days. In addition, fish were grown in an insecticide-free control group to determine the toxic effects of the insecticides. The obtained data on various biochemical and hematological parameters of the fish were analyzed using state-of-the-art statistics. Our findings suggest that triflumezopyrim exposure has a significant effect on blood variables. However, variable response, such as mean corpuscular volume, hemoglobin concentration, neutrophils, and eosinophils were unaffected by insecticide treatment, regardless of the dose. Our interhematological parameter analysis revealed varying interrelationships at various insecticide doses. Similarly, triflumezopyrim exposure significantly affected the response of serum biomarker profiles i.e., the difference in mean treatment pairs (control and three doses of triflumezopyrim) had a significant effect on the response of most serum profile parameters.

Investigating the enzymatic response of Plutella xylostella L. (Lepidoptera: Plutellidae) to Metarhizium anisopliae (Metschnikoff) Sorokin (Ascomycota: Hypocreales) Infection: A Comprehensive study

The diamondback moth (DBM), Plutella xylostella, poses a significant threat to cruciferous crops due to its resistance to conventional insecticides. Entomopathogenic fungi (EPF), such as Metarhizium anisopliae offer a promising solution for the management of P. xylostella. When exposed to lethal or sub-lethal doses of microbial insecticides especially EPF, insects often mount various immune responses as a survival mechanism, including the activation of detoxification and protective enzymes. In this study, M. anisopliae (Ma1) isolated from soil resulted in 94.00 ± 0.245 percent mortality of DBM at a conidial load of 1 x 109 conidia/ml, with an LC50 value of 2.70 x 106 conidia/ml. The activity of various detoxifying and free radical scavenging enzymes was assessed in whole-body samples of P. xylostella at varying time intervals after inoculation with the entomopathogenic fungi. The results showed that the activity of the enzymes increased after 48 h of inoculation, reaching a maximum at 96 h after inoculation. After 96 h, the activity of these enzymes started to decline significantly. In conclusion, the M. anisopliae isolate Ma1 was found to be highly effective against P. xylostella. Therefore, it could be formulated using appropriate carrier material and used as a component in Integrated pest management programs. Elevated levels of detoxification and free radical scavenging enzyme expression helps in understanding the immune mechanisms in P. xylostella in response to M. anisopliae infection.

Baseline susceptibility of an A1 quarantine pest - the South American tomato pinworm Tuta absoluta (Lepidoptera: Gelechiidae) to insecticides: past incidents and future probabilities in line to implementing successful pest management.

Tomato is a widely cultivated crop significant for its economic and nutritional benefits. The South American tomato pinworm, Tuta absoluta, originated in Peru South America and has invaded many nations, causing up to 100% yield loss in tomatoes. The pest was classified as a quarantine pest by the European Plant Protection Organization, before invading the Spain region. Later, this quarantine pest also invaded other regions of Europe, Africa and Asian countries. Invasive insect pests cause global economic losses of 70 billion dollars annually. Among the several management measures suggested against pests, insecticides are the primary method in practice among growers due to significant results, easier operations, and other crucial advantages. Anyhow, repeated application of insecticides has caused the pest to evolve resistance against most of the insecticides in vogue, resulting in a chain of events like management failures, using increased doses of insecticides, intensified chemical residues in the food chain, and irreparable environmental contamination. Major insecticides globally used to control T. absoluta belong to organophosphates, synthetic pyrethroids, neonicotinoids, diamides, avermectins, spinosyns, and oxadizines. Understanding the baseline susceptibility of pests to insecticides helps for better pest management options and is the same for T. absoluta populations to insecticides. The current review paper discusses the T. absoluta distribution, biology, spread, host range, baseline insecticide susceptibility, global insecticide resistance status, and possible management inputs based on our understanding of insecticide susceptibility. The pest can be managed with integrated insecticide resistance management including molecular approaches.

What happens when the insecticide does not kill? A review of sublethal toxicology and insecticide resistance in triatomines.

Chagas disease is considered one of the most important human parasitosis in the United States. This disease is mainly transmitted by insects of the subfamily Triatominae. The chemical vector control is the main tool for reducing the incidence of the disease. However, the presence of triatomines after pyrethroids spraying has been reported in some regions, as in the case of Triatoma infestans in Argentina and Bolivia. The presence of insects can be explained by the colonization from neighbouring areas, the reduction of insecticide dose to sublethal levels due to environmental factors, and/or by the evolution of insecticide resistance. In the last two scenarios, a proportion of the insects is not killed by insecticide and gives rise to residual populations. This article focuses on the toxicological processes associated with these scenarios in triatomines. Sublethal doses may have different effects on insect biology, that is, sublethal effects, which may contribute to the control. In addition, for insect disease vectors, sublethal doses could have negative effects on disease transmission. The study of sublethal effects in triatomines has focused primarily on the sequence of symptoms associated with nervous intoxication. However, the effects of sublethal doses on excretion, reproduction and morphology have also been studied. Rhodnius prolixus and T. infestans and pyrethroids insecticides were the triatomine species and insecticides, respectively, mainly studied. Insecticide resistance is an evolutionary phenomenon in which the insecticide acts as a selective force, concentrating on the insect population's pre-existing traits that confer resistance. This leads to a reduction in the susceptibility to the insecticide, which was previously effective in controlling this species. The evolution of resistance in triatomines received little attention before the 2000s, but after the detection of the first focus of resistance associated with chemical control failures in T. infestans from Argentina in 2002, the study of resistance increased remarkably. A significant number of works have studied the geographical distribution, the resistance mechanisms, the biological modifications associated with resistance, the environmental influences and the genetic of T. infestans resistant to pyrethroid insecticides. Currently, studies of insecticide resistance are gradually being extended to other areas and other species. The aim of this article was to review the knowledge on both phenomena (sublethal effects and insecticide resistance) in triatomines. For a better understanding of this article, some concepts and processes related to insect-insecticide interactions, individual and population toxicology and evolutionary biology are briefly reviewed. Finally, possible future lines of research in triatomine toxicology are discussed.

Transgenerational Sub-Lethal Pyrethroid Exposure Affects Shape Variation and Fluctuating Asymmetry in Seed Beetles

One method of crop protection is the application of a widely used group of pesticides—pyrethroids. As xenobiotics, sub-lethal doses of insecticides cause stress in pests, resulting in a change in the shape and size of their organs or bodies. The stress caused by pesticides may lead to acute destabilization of development, but also to transgenerational canalization through the process of genetic assimilation. Fluctuating asymmetry (FA), small random deviations between the right and left sides of bilaterally symmetrical traits, is an outcome of developmental instability and is a measurable indicator of phenotypic response to stress. We exposed four populations of the seed beetle Acanthoscelides obtectus to sub-lethal doses of cypermethrin for ten generations in a laboratory evolution experiment. Using geometric morphometrics, we analyzed size and shape changes and the level of fluctuating asymmetry in untreated beetles and in samples from the fifth and tenth generation. Exposure over ten generations led to an increase in the body size of the beetles, shortening of their pronotum and elongation of their thorax and abdomen. After ten generations of exposure to cypermethrin, FA levels decreased, indicating a canalization of development. This study provides new insights into the phenotypic markers of environmental pollution from agricultural activities.

Temperature and time of host-seeking activity impact the efficacy of chemical control interventions targeting the West Nile virus vector, Culex tarsalis.

West Nile virus (WNV) is the leading mosquito-borne disease causing-pathogen in the United States. Concerningly, there are no prophylactics or drug treatments for WNV and public health programs rely heavily on vector control efforts to lessen disease incidence. Insecticides can be effective in reducing vector numbers if implemented strategically, but can diminish in efficacy and promote insecticide resistance otherwise. Vector control programs which employ mass-fogging applications of insecticides, often conduct these methods during the late-night hours, when diel temperatures are coldest, and without a-priori knowledge on daily mosquito activity patterns. This study's aims were to 1) quantify the effect of temperature on the toxicity of two conventional insecticides used in fogging applications (malathion and deltamethrin) to Culex tarsalis, an important WNV vector, and 2) quantify the time of host-seeking of Cx. tarsalis and other local mosquito species in Maricopa County, Arizona. The temperature-toxicity relationship of insecticides was assessed using the WHO tube bioassay, and adult Cx. tarsalis, collected as larvae, were exposed to three different insecticide doses at three temperature regimes (15, 25, and 35°C; 80% RH). Time of host-seeking was assessed using collection bottle rotators with encephalitis vector survey traps baited with dry ice, first at 3h intervals during a full day, followed by 1h intervals during the night-time. Malathion became less toxic at cooler temperatures at all doses, while deltamethrin was less toxic at cooler temperatures at the low dose. Regarding time of host-seeking, Cx. tarsalis, Aedes vexans, and Culex quinquefasciatus were the most abundant vectors captured. During the 3-hour interval surveillance over a full day, Cx. tarsalis were most-active during post-midnight biting (00:00-06:00), accounting for 69.0% of all Cx. tarsalis, while pre-midnight biting (18:00-24:00) accounted for 30.0% of Cx. tarsalis. During the 1-hour interval surveillance overnight, Cx. tarsalis were most-active during pre-midnight hours (18:00-24:00), accounting for 50.2% of Cx. tarsalis captures, while post-midnight biting (00:00-06:00) accounted for 49.8% of Cx. tarsalis. Our results suggest that programs employing large-scale applications of insecticidal fogging should consider temperature-toxicity relationships coupled with time of host-seeking data to maximize the efficacy of vector control interventions in reducing mosquito-borne disease burden.

Synergism of (E)-β-farnesene and Its Analogue to Insecticides against the Green Peach Aphid Myzus persicae.

With high aphid-repellent activity but low stability, (E)-β-farnesene (EβF), the major component of the aphid alarm pheromone, can be used as a synergist to insecticides. Some EβF analogues possess both good aphid-repellent activity and stability, but the synergistic effect and related mechanism are still unclear. Therefore, this study investigated the synergistic effect and underlying mechanism of the EβF and its analogue against the aphid Myzus persicae. The results indicated that EβF and the analogue showed significantly synergistic effects to different insecticides, with synergism ratios from 1.524 to 3.446. Mechanistic studies revealed that EβF and the analogue exhibited effective repellent activity, significantly upregulated target OBP genes by 161 to 731%, increased aphid mobility, and thereby enhanced contact with insecticides. This research suggests that the EβF analogue represents a novel synergist for insecticides, with the potential for further application in aphid control owing to its enhanced bioactivity and the possibility of reducing insecticide doses.

Toxicological Assessment of Pesticide Exposure in Wistar Rats: An Acute and Sub-Acute Inhalation Study

Background: Pesticide ubiquity and extensive applications have attendant public health implications. This study examines the immediate and prolonged inhalation toxicity of various commonly used insecticides in male Wistar rats. Methods: 192 male Wistar rats were utilized and kept in regular housing. The study was carried out in three stages: a preliminary test, an acute test, and a sub-acute. Wistar rats, housed in an improvised chamber, were exposed to varying doses of insecticides in each phase to assess their toxicities to insecticides. For comparativeness, we withdrew 57 of the rats from exposure to ascertain possible recovery. The study included monitoring behavioral changes, recording mortality rates, and conducting necropsies to evaluate organ pathology. Dose-response relationships were analyzed to determine lethal doses (LD50) and potential sublethal effects. Results: Overall, we found a dose-related increase in the severity of the response, which potentially indicates an alteration of a specific biochemical process. The range-finding test assessed the effects of DD Force, Sniper, Industrial Camphor, Edible Camphor, Kerosene, and combined pesticides. It revealed significant physiological impacts followed by mortalities at specific dosage levels. Subsequent acute toxicity testing determined LC50 values for each insecticide. Rats showed a dose-dependent health deterioration following sub-acute exposure, particularly in the combined pesticide group, indicating synergistic toxicity. Conclusion: Exposure to the combined pesticide at high doses was associated with severe toxicities in the tested rats. This evidence suggests that commonly used pesticides could potentiate adverse health outcomes when results are extrapolated in humans.

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.

Multigenerational responses of wheat aphids to multiple stresses: interactions between sublethal thermal stress types and a low insecticide dose

Multigenerational responses of wheat aphids to multiple stresses: interactions between sublethal thermal stress types and a low insecticide dose

Enhancing spinach (Spinacia oleracea L.) resilience in pesticide-contaminated soil: Role of pesticide-tolerant Ciceribacter azotifigens and Serratia marcescens in root architecture, leaf gas exchange attributes and antioxidant response restoration

This study unveils the detoxification potential of insecticide-tolerant plant beneficial bacteria (PBB), i.e., Ciceribacter azotifigens SF1 and Serratia marcescens SRB1, in spinach treated with fipronil (FIP), profenofos (PF) and chlorantraniliprole (CLP) insecticides. Increasing insecticide doses (25–400 μg kg−1 soil) significantly curtailed germination attributes and growth of spinach cultivated at both bench-scale and in greenhouse experiments. Profenofos at 400 μg kg−1 exhibited maximum inhibitory effects and reduced germination by 55%; root and shoot length by 78% and 81%, respectively; dry matter accumulation in roots and shoots by 79% and 62%, respectively; leaf number by 87% and leaf area by 56%. Insecticide application caused morphological distortion in root tips/surfaces, increased levels of oxidative stress, and cell death in spinach. Application of insecticide-tolerant SF1 and SRB1 strains relieved insecticide pressure resulting in overall improvement in growth and physiology of spinach grown under insecticide stress. Ciceribacter azotifigens improved germination rate (10%); root biomass (53%); shoot biomass (25%); leaf area (10%); Chl-a (45%), Chl-b (36%) and carotenoid (48%) contents of spinach at 25 μg CLP kg−1 soil. PBB inoculation reinvigorated the stressed spinach and modulated the synthesis of phytochemicals, proline, malondialdehyde (MDA), superoxide anions (O2•–), and hydrogen peroxide (H2O2). Scanning electron microscopy (SEM) revealed recovery in root tip morphology and stomatal openings on abaxial leaf surfaces of PBB-inoculated spinach grown with insecticides. Ciceribacter azotifigens inoculation significantly increased intrinsic water use efficiency, transpiration rate, vapor pressure deficit, intracellular CO2 concentration, photosynthetic rate, and stomatal conductance in spinach exposed to 25 μg FIP kg−1. Also, C. azotifigens and S. marcescens modulated the antioxidant defense systems of insecticide-treated spinach. Bacterial strains were strongly colonized to root surfaces of insecticide-stressed spinach seedlings as revealed under SEM. The identification of insecticide-tolerant PBBs such as C. azotifigens and S. marcescens hold the potential for alleviating abiotic stress to spinach, thereby fostering enhanced and safe production within polluted agroecosystems.

Different Sensitivity of Flower-Visiting Diptera to a Neonicotinoid Insecticide: Expanding the Base for a Multiple-Species Risk Assessment Approach.

Insects play an essential role as pollinators of wild flowers and crops. At the same time, pollinators in agricultural environments are commonly exposed to pesticides, compromising their survival and the provision of pollination services. Although pollinators include a wide range of species from several insect orders, information on pesticide sensitivity is mostly restricted to bees. In addition, the disparity of methodological procedures used for different insect groups hinders the comparison of toxicity data between bees and other pollinators. Dipterans are a highly diverse insect order that includes some important pollinators. Therefore, in this study, we assessed the sensitivity of two hoverflies (Sphaerophoria rueppellii, Eristalinus aeneus) and one tachinid fly (Exorista larvarum) to a neonicotinoid insecticide (Confidor®, imidacloprid) following a comparative approach. We adapted the standardized methodology of acute contact exposure in honey bees to build dose-response curves and calculate median lethal doses (LD50) for the three species. The methodology consisted in applying 1 µL of the test solution on the thorax of each insect. Sphaerophoria rueppelli was the most sensitive species (LD50 = 10.23 ng/insect), and E. aeneus (LD50 = 18,176 ng/insect) the least. We then compared our results with those available in the literature for other pollinator species using species sensitivity distribution (SSD). Based on the SSD curve, the 95th percentile of pollinator species would be protected by a safety factor of 100 times the Apis mellifera endpoint. Overall, dipterans were less sensitive to imidacloprid than most bee species. As opposed to most bee species, oviposition and fecundity of many dipteran species can be reliably assessed in the laboratory. We measured the number of eggs laid following exposure to different insecticide doses and assessed the potential trade-off between oviposition and survival through the sublethal sensitivity index (SSI). Exposure to imidacloprid had a significant effect on fecundity, and SSI values indicated that oviposition is a sensitive endpoint for the three dipteran species tested. Future studies should integrate this information related to population dynamics in simulation models for environmental risk assessment.

A new exposure protocol adapted for wild bees reveals species-specific impacts of the sulfoximine insecticide sulfoxaflor

Wild bees are crucial pollinators of flowering plants and concerns are rising about their decline associated with pesticide use. Interspecific variation in wild bee response to pesticide exposure is expected to be related to variation in their morphology, physiology, and ecology, though there are still important knowledge gaps in its understanding. Pesticide risk assessments have largely focussed on the Western honey bee sensitivity considering it protective enough for wild bees. Recently, guidelines for Bombus terrestris and Osmia bicornis testing have been developed but are not yet implemented at a global scale in pesticide risk assessments. Here, we developed and tested a new simplified method of pesticide exposure on wild bee species collected from the field in Belgium. Enough specimens of nine species survived in a laboratory setting and were exposed to oral and topical acute doses of a sulfoximine insecticide. Our results confirm significant variability among wild bee species. We show that Osmia cornuta is more sensitive to sulfoxaflor than B. terrestris, whereas Bombus hypnorum is less sensitive. We propose hypotheses on the mechanisms explaining interspecific variations in sensitivity to pesticides. Future pesticide risk assessments of wild bees will require further refinement of protocols for their controlled housing and exposure.

Residues of chlorpyrifos in the environment induce resistance in Aedes albopictus by affecting its olfactory system and neurotoxicity

Aedes albopictus, a virus-vector pest, is primarily controlled through the use of insecticides. In this study, we investigated the mechanisms of resistance in Ae. albopictus in terms of chlorpyrifos neurotoxicity to Ae. albopictus and its effects on the olfactory system. We assessed Ca2+-Mg2+-ATP levels, choline acetyltransferase (ChAT), Monoamine oxidase (MAO), odorant-binding proteins (OBPs), and olfactory receptor (OR7) gene expression in Ae. albopictus using various assays including Y-shaped tube experiments and DanioVision analysis to evaluate macromotor behavior. Our findings revealed that cumulative exposure to chlorpyrifos reduced the activity of neurotoxic Ca2+-Mg2+-ATPase and ChAT enzymes in Ae. albopictus to varying degrees, suppressed MAO-B enzyme expression, altered OBPs and OR7 expression patterns, as well as affected evasive response, physical mobility, and cumulative locomotor time under chlorpyrifos stress conditions for Ae. albopictus individuals. Consequently, these changes led to decreased feeding ability, reproductive capacity, and avoidance behavior towards natural enemies in Ae. albopictus populations exposed to chlorpyrifos stressors over time. To adapt to unfavorable living environments, Ae. albopictus may develop certain tolerance mechanisms against organophosphorus pesticides. This study provides valuable insights for guiding rational insecticide usage or dosage adjustments targeting the nervous system of Ae. albopictus.

Mesoporous silica nanospheres-mediated insecticide and antibiotics co-delivery system for synergizing insecticidal toxicity and reducing environmental risk of insecticide

Mesoporous silica nanoparticles (MSNs) are efficient carriers of drugs, and are promising in developing novel pesticide formulations. The cotton aphids Aphis gossypii Glover is a world devastating insect pest. It has evolved high level resistance to various insecticides thus resulted in the application of higher doses of insecticides, which raised environmental risk. In this study, the MSNs based pesticide/antibiotic delivery system was constructed for co-delivery of ampicillin (Amp) and imidacloprid (IMI). The IMI@Amp@MSNs complexes have improved toxicity against cotton aphids, and reduced acute toxicity to zebrafish. From the 16S rDNA sequencing results, Amp@MSNs, prepared by loading ampicillin to the mesoporous of MSNs, greatly disturbed the gut community of cotton aphids. Then, the relative expression of at least 25 cytochrome P450 genes of A. gossypii was significantly suppressed, including CYP6CY19 and CYP6CY22, which were found to be associated with imidacloprid resistance by RNAi. The bioassay results indicated that the synergy ratio of ampicillin to imidacloprid was 1.6, while Amp@MSNs improved the toxicity of imidacloprid by 2.4-fold. In addition, IMI@Amp@MSNs significantly improved the penetration of imidacloprid, and contributed to the amount of imidacloprid delivered to A. gossypii increased 1.4-fold. Thus, through inhibiting the relative expression of cytochrome P450 genes and improving penetration of imidacloprid, the toxicity of IMI@Amp@MSNs was 6.0-fold higher than that of imidacloprid. The greenhouse experiments further demonstrated the enhanced insecticidal activity of IMI@Amp@MSNs to A. gossypii. Meanwhile, the LC50 of IMI@Amp@MSNs to zebrafish was 3.9-fold higher than that of IMI, and the EC50 for malformation was 2.8-fold higher than IMI, respectively, which indicated that the IMI@Amp@MSNs complexes significantly reduced the environmental risk of imidacloprid. These findings encouraged the development of pesticide/antibiotic co-delivery nanoparticles, which would benefit pesticide reduction and environmental safety.

INSECTICIDE TOXICITY TO HONEY BEES: LESSONS LEARNED FROM STUDIES BY THE UNIVERSITY OF FLORIDA URBAN ENTOMOLOGY LABORATORY

Laboratory and field studies comparing the relative tolerance of mosquitoes (Aedes aegypti and Aedes albopictus) and non-target species, including the honey bee (Apis mellifera), and other non-target insects have shown that the non-target species can tolerate fairly well when exposed to insecticides used in mosquito control operations. Tolerance levels of non-target species vary due to factors such as the development of insecticide resistance in mosquitoes which require higher insecticide doses to reduce populations to adequate levels. However, well-planned mosquito control programs, can lower risks to honey bees and other non-target species. This review discusses the toxicity of mosquito control insecticides to the honey bee and other non-target insects.

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.