Insecticide Mixtures Research Articles

Potential demographic impact of the insecticide mixture between thiacloprid and deltamethrin on the cotton aphid and two of its natural enemies.

The use of pesticides impairs biological control in the agroecosystems and thus compromises the effectiveness of natural enemies against populations of pest species. The concerns over pesticides should expand beyond mortality and encompass their sublethal effects and their consequences to the target insect species and natural enemies to aid in our understanding of the potential and consequential use of these compounds. The present study aimed to determine the effects of an insecticide mixture on life-history and demographic parameters of the cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae) and two of its main parasitoids - Aphidius flaviventris Kurdjumov (Hymenoptera: Aphelinidae) and Aphidius colemani Viereck (Hymenoptera: Braconidae). Based on the obtained results, thiacloprid + deltamethrin in its lethal concentration dose 20% of the pest population (LC20) significantly affected the cotton aphid for two generations, increasing developmental time and demographic parameters. The LC20 manifested changes in many demographic parameters of the parasitoid A. flaviventris. This concentration also increased preadult and female longevity, total pre-ovipositional period, and mean generation time (T) of A. colemani, but no other demographic parameters were affected. Nonetheless, the insecticide mixture did not affect the parasitism rate of A. colemani. Thus, the thiacloprid + deltamethrin mixture significantly impaired the cotton aphid population and its parasitoid A. flaviventris. Therefore, the use of thiacloprid + deltamethrin is not encouraged for controlling the parasitoid A. flaviventris, but it is a relatively safe compound for A. colemani.

Quantifying exposure of bumblebee (Bombus spp.) queens to pesticide residues when hibernating in agricultural soils

Exposure to pesticides is a major threat to bumblebee (Bombus spp.) health. In temperate regions, queens of many bumblebee species hibernate underground for several months, putting them at potentially high risk of exposure to soil contaminants. The extent to which bumblebees are exposed to residues in agricultural soils during hibernation is currently unknown, which limits our understanding of the full pesticide exposome for bumblebees throughout their lifecycle. To generate field exposure estimates for overwintering bumblebee queens to pesticide residues, we sampled soils from areas corresponding to suitable likely hibernation sites at six apple orchards and 13 diversified farms throughout Southern Ontario (Canada) in fall 2019–2020. Detectable levels of pesticides were found in 65 of 66 soil samples analysed for multi-pesticide residues (UPLC-MS/MS). A total of 53 active ingredients (AIs) were detected in soils, including 27 fungicides, 13 insecticides, and 13 herbicides. Overall, the frequency of detection, residue levels (median = 37.82 vs. 2.20 ng/g), and number of pesticides per sample (mean = 12 vs. 4 AIs) were highest for orchard soils compared to soils from diversified farms. Ninety-one percent of samples contained multiple residues (up to 29 different AIs per sample), including mixtures of insecticides and fungicides that might lead to synergistic effects. Our results suggest that when hibernating in agricultural areas, bumblebee queens are very likely to be exposed to a wide range of pesticide residues in soil, including potentially harmful levels of insecticides (e.g., cyantraniliprole up to 148.82 ng/g). Our study indicates the importance of empirically testing the potential effects of pesticide residues in soils for hibernating bumblebee queens, using field exposure data such as those generated here. The differences in potential exposure that we detected between cropping systems can also be used to better inform regulations that govern the use of agricultural pesticides, notably in apple orchards.

Insecticide Resistance Profiles and Synergism of Field Aedes aegypti from Indonesia.

Information on the insecticide resistance profiles of Aedes aegypti in Indonesia is fragmentary because of the lack of wide-area insecticide resistance surveillance. We collected Ae. aegypti from 32 districts and regencies in 27 Indonesian provinces and used WHO bioassays to evaluate their resistance to deltamethrin, permethrin, bendiocarb, and pirimiphos-methyl. To determine the possible resistance mechanisms of Ae. aegypti, synergism tests were conducted using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioates (DEF). The Ae. aegypti from all locations exhibited various levels of resistance to pyrethroids. Their resistance ratio (RR50) to permethrin and deltamethrin ranged from 4.08× to 127× and from 4.37× to 72.20×, respectively. In contrast with the findings of other studies, most strains from the highly urbanized cities on the island of Java (i.e., Banten, Jakarta, Bandung, Semarang, Yogyakarta, and Surabaya) exhibited low to moderate resistance to pyrethroids. By contrast, the strains collected from the less populated Kalimantan region exhibited very high resistance to pyrethroids. The possible reasons are discussed herein. Low levels of resistance to bendiocarb (RR50, 1.24–6.46×) and pirimiphos-methyl (RR50, 1.01–2.70×) were observed in all tested strains, regardless of locality. PBO and DEF synergists significantly increased the susceptibility of Ae. aegypti to permethrin and deltamethrin and reduced their resistance ratio to less than 16×. The synergism tests suggested the major involvement of cytochrome P450 monooxygenases and esterases in conferring pyrethroid resistance. On the basis of our results, we proposed a 6-month rotation of insecticides (deltamethrin + synergists ➝ bendiocarb ➝ permethrin + synergists ➝ pirimiphos-methyl) and the use of an insecticide mixture containing pyrethroid and pyrimiphos-methyl to control Ae. aegypti populations and overcome the challenge of widespread Ae. aegypti resistance to pyrethroid in Indonesia.

Can insecticide mixtures be considered to surmount neonicotinoid resistance in Bemisia tabaci?

Cotton whitefly, Bemisia tabaci is an important polyphagous pest worldwide. It is exposed to various chemical insecticides throughout the year, resulting in the rapid development of insecticide resistance. Mixtures of insecticides with distinct modes of action could enhance the toxicity of chemicals more effectively than sequences or rotations in resistant pest populations. Bioassays were conducted to study the efficacy of mixtures of neonicotinoid and ketoenol insecticides at different ratios against a laboratory susceptible (Lab-WB) and a neonicotinoid resistant (TMX-SEL) strain of B. tabaci Asia I. The results showed that mixtures of imidacloprid, acetamiprid, thiamethoxam or dinotefuran with spiromesifen at 1:1, 1:10 and 1:20 ratios and of imidacloprid, thiamethoxam or dinotefuran with spirotetramat at 1:1 ratio significantly increased (p < 0.05) toxicity to neonicotinoids in TMX-SEL strain. The combination indices of each tested neonicotinoids + ketoenols at 1:1 ratio and of acetamiprid + spiromesifen, and imidacloprid or dinotefuran + spirotetramat at 1:10 ratio for TMX-SEL strain were significantly below 1, suggesting synergistic interactions. The inhibitors PBO and DEF largely overcame resistance to the tested neonicotinoids, while none of the synergists significantly restored the susceptibility of B. tabaci to ketoenols. Increased activities of P450 monooxygenase and esterase were observed in TMX-SEL strain with an elevated 2.76 and 1.32-fold, respectively. Mixtures of neonicotinoids with spiromesifen or spirotetramat at a 1:1 ratio could be used to restore the neonicotinoid susceptibility in B. tabaci.

Simplified Procedures for Managing Insecticidal Waste: A Case Report of KCMUCo-PAMVERC Vector Control Product Testing Facility in North-Eastern Tanzania

Insecticide testing facilities that evaluate a variety of vector control products may generate a large number of hazardous wastes from routine operations. These wastes originate from degraded technical grade materials, sprayed substrates with Indoor Residual Spraying (IRS), and redundant stock or working insecticidal solutions. The washing of Long-Lasting Insecticidal Nets (LLINs) during preparation for laboratory and experimental hut trials also contribute to wastewater with insecticide content. Human and environmental exposure to insecticidal waste can occur during transport, categorization, storage, and disposal, resulting in environmental pollution and potential health effects. Various national and international guidelines have been devised for safe disposal and should be strictly followed to avoid adverse effects on humans or environment. To facilitate proper insecticidal waste management, this paper outlines simple but safe practices derived from international and national guidelines that can be adopted by other similar facilities. National and international policies related to chemical management were reviewed and translated into Standard Operating Procedures (SOPs), training pathways, and manuals. National Environmental Management Council (NEMC) assessed the test facility and recommended disposal procedures. NEMC recommendations were followed to construct the soak pits for liquid waste disposal while chemical transporters and incinerators were contracted for solid waste disposal. An environmental expert was contracted for environmental audit and annual monitoring. Studies and activities at the facility were evaluated for their waste generation index. Safety manual and SOPs on risk assessment, waste management and disposal, handling hazardous materials, health and safety procedures, and chemical usage were written. At KCMUCo-PAMVERC, an annual average of 0.02 and 24.9 cubic meters of liquid waste, which mainly includes a mixture of water, insecticides, and solvents, were generated from laboratory experiments (phase I) and semi-field LLIN experiments (phase II), respectively, while the IRS semi-field experiments generated an annual average of 88 L of liquid waste and 6.3 tons of solid waste. An annual average of 0.18 cubic meters of liquid waste results from other sources, including expired laboratory reagents. Well-translated national and international policies/regulations may be adopted by insecticide test facilities for proper and effective waste disposal.

Comparative Efficacy of Superheated Dry Steam Application and Insecticide Spray Against Common Bed Bugs Under Simulated Field Conditions.

The common bed bug, Cimex lectularius L., is a difficult urban pest to control. A simulated field study was conducted to compare the efficacy of steam application and an insecticide mixture spray (0.05% acetamiprid and 0.06% bifenthrin mixture) against C. lectularius. Three types of furniture (desk chair, upholstered armchair, and wooden table) were treated in the laboratory. The efficacy of the treatments was evaluated by visual inspection and placement of interceptor traps under the legs of the furniture. One hundred mixed stages of an insecticide-resistant population of C. lectularius were released onto each furniture item. After a 10-day acclimation period, each furniture item received steam treatment, insecticide spray, or no treatment. The second application of treatment was conducted 14 d later. Bed bug counts from interceptors and visual inspections were recorded at 13 d and 28 d after the initial treatment. At 28 d, the mean (± SE) live bed bug count in the steam, spray, and control group was 1 ± 0, 2 ± 1, and 83 ± 10, respectively. Both treatment methods were highly effective in controlling bed bugs on furniture. The mean bed bug count from interceptors in the steam, spray, and control groups were 0.3 ± 0.2, 11 ± 7, and 47 ± 9, respectively. There was no significant difference in the efficacy between steam and spray treatments based on either visual inspection or bed bug counts from interceptors. However, based on interceptor counts, the steam treatment caused faster bed bug population reduction than insecticide sprays.

Thiacloprid + deltamethrin against the cotton aphid and the parasitoid wasp Aphidius colemani: From lethal to sublethal population effects

AbstractThe side effects of insecticides on non‐target species are important to secure the intended effectiveness of pest management programmes. The cotton aphid Aphis gossypii is a frequent problem in industrial greenhouse cultivation, and insecticide and parasitoids are often used for crop protection. Among insecticides, mixtures are playing increasing roles in pest management in the greenhouse production system, as well as parasitoid use. The insecticide mixture thiacloprid + deltamethrin and the parasitoid wasp Aphidius colemani are the main agents used against the cotton aphid and are the focus of this study. Here, we report the effects of the thiacloprid + deltamethrin on A. gossypii and Ap. colemani. The low concentrations 2.79 g a.i/L (LC10) and 7.28 g a.i/L (LC30) compromised the life parameters of the aphid progeny and increased the development time at all juvenile stages. In addition, fecundity, longevity and other parameters (r, R0 and T) were significantly impaired by thiacloprid + deltamethrin at both concentrations. The median lethal time estimate (LT50) for Ap. colemani was 18.73 h; the parasitoid mortality was significant up to 24 h after application but decreased afterward. Regardless, the parasitoid life table parameters were also compromised by insecticide exposure, similarly to the parasitoid population growth and parasitism efficacy. These results demonstrate the effect of the insecticide mixture against A. gossypii, and the increased risk of its adverse impacts on the parasitoid Ap. colemani, which signals against their simultaneous application to control this pest species.

Industrial treatment of soybean seeds subjected to high volumes of fungicides, insecticides, biostimulants and micronutrients during storage

The objective of this study was to examine the performance of soybean seeds at different storage periods as well as their physiological quality after the application of spray mixtures of insecticides, fungicides, polymers, micronutrients and biostimulants. The experiment was laid out in a completely randomized design with four replicates. Treatments were as follows: T1 - untreated seeds (control); T2 - insecticide and fungicide + polymer + drying powder; T3 - insecticide and fungicide + polymer + drying powder + micronutrient; and T4 - insecticide and fungicide + polymer + drying powder + micronutrient + biostimulant. For each industrial seed treatment (IST), the specific spray volumes tested were 0, 400, 600 or 1100 mL 100 kg seeds-1. Soybean seeds were stored for 0, 15, 30, 45, 60 and 90 days and subsequently evaluated for physiological potential. At each storage period, the following tests were conducted: germination, first count, accelerated aging, emergence speed index, final emergence in sand substrate, whole-seedling length, shoot length and root length. Industrial seed treatment reduces seed physiological quality. The seed treatment corresponding to the highest spray volume provided the lowest means in all tested treatments. For all analyzed variables, the ST4 treatment, to which biostimulant was added, presented the lowest averages, indicating that the greater the volume of spray, the greater the damage caused to the physiological quality of the seeds, both before and after storage

IMPACTS OF BARRIER INSECTICIDE MIXTURES ON MOSQUITO, AEDES AEGYPTI AND NON-TARGET HONEY BEE, APIS MELLIFERA

Four novel commercial insecticide mixtures, composed of pyrethroid and nicotinoid active ingredients, were evaluated in a series of experiments in the laboratory, semi-field and field to determine acute toxicity (LC50) against pyrethroid-susceptible (ORL1952) and resistant (Puerto Rico) strains of Aedes aegypti L., and non-target adult European honey bees, Apis mellifera L. The four products were Tandem, Temprid FX, Transport Mikron, and Crossfire. The acute toxicity data showed that pyrethroid-resistant Ae. aegypti PR exhibited decreased sensitivity to all 4 insecticide mixtures, compared to pyrethroid-susceptible Ae. aegypti ORL1952. Tandem, Temprid FX, and Transport Mikron were more toxic to Ae. aegypti ORL1952 than to A. mellifera, but Crossfire was the least toxic. Transport Mikron was also more toxic to Ae. aegypti PR than to A. mellifera. The Honey bee Tolerance Indexes, determined with LC50 data of pyrethroid-susceptible mosquitoes, demonstrated that while Transport Mikron, Tandem, and Temprid FX were more toxic to Ae. aegypti ORL1952 than to A. mellifera, Crossfire was less toxic. The honey bee Tolerance Indexes decreased substantially when calculated with LC50 data from pyrethroid- resistant mosquitoes, but honey bees remained tolerant of Transport Mikron. Notably, while the insecticide mixtures did not control the PR resistant Ae. aegypti strain when applied as residual sprays to perimeter vegetation at label rates, susceptible Ae. aegypti ORL1951 were controlled, but applications affected honeybees (A. mellifera) for up to 28 days after treatment. Temprid FX resulted in 74% and 99% mortality, in adult Ae. aegypti ORL1952 and A. mellifera, respectively, for 28 days post-treatment. Transport Mikron and Tandem residues killed Ae. aegypti ORL1952 for up to 21 days post-treatment, while the effect of Crossfire lasted only 14 days. All three insecticides killed A. mellifera for up to 28 days post-treatment but at decreased mortality rates. For operational mosquito control, these data indicate that Transport Mikron has a reasonable safety margin (~25%) when targeting susceptible mosquitoes, compared to Tandem, Temprid FX, and Crossfire. The tested insecticide formulations need to be applied in higher doses to control resistant strains of mosquitoes that may be detrimental to honey bees. The ULV data indicated that pyrethroid resistance can be overcome with the insecticide mixtures.

Bio-efficacy of insecticide and fungicide mixtures against leaf folder, stem borer, BPH and sheath blight of rice

Bio-efficacy assessment with four insecticides and two fungicides was carried out in Agricultural College farm, Naira during kharif, 2019 against leaf folder, stem borer, brown plant hopper (BPH) and sheath blight of rice. The treatments include four insecticides [Flonicamide 50 WG (0.4 g/l), Pymetrozine 50 WG (0.6 g/l), Chlorantraniliprole 18.5 SC (0.3 g/l), Acephate 75 SP (1.5 g/l)], two fungicides [(Difenoconazole 25 EC (0.5 ml/l), Azoxystrobin 23 EC (0.75 ml/l] and Untreated Control. Results indicated that treatment Chlorantraniliprole 18.5 SC (0.3 g/l) was effective against leaf folder (per cent leaf folder damage: 3.29) and stem borer (% DH: 1.17, % WE: 2.11) which was on par to both of its fungicide combinations viz., Azoxystrobin 23 EC (0.75 ml/l) (per cent leaf folder damage: 3.02, % DH: 1.29, % WE: 2.51) and Difenoconazole 25 EC (0.5 ml/l) (3.85, 1.76, 2.64). Against brown planthopper, treatment Pymetrozine 50 WG + Difenoconazole 25 EC (0.6 g/l + 0.5 ml/l) (reduction over control- 92.95%) was effective and pertinent to sheath blight, treatment chlorantraniliprole + azoxystrobin (PDI: 5.14) along with all the four test insecticide combinations of azoxystrobin proved their best.

Interaction of Insecticides and Fungicides in Bees.

Honeybees and wild bees are among the most important pollinators of both wild and cultivated landscapes. In recent years, however, a significant decline in these pollinators has been recorded. This decrease can have many causes including the heavy use of biocidal plant protection products in agriculture. The most frequent residues in bee products originate from fungicides, while neonicotinoids and, to a lesser extent, pyrethroids are among the most popular insecticides detected in bee products. There is abundant evidence of toxic side effects on honeybees and wild bees produced by neonicotinoids, but only few studies have investigated side effects of fungicides, because they are generally regarded as not being harmful for bees. In the field, a variety of substances are taken up by bees including mixtures of insecticides and fungicides, and their combinations can be lethal for these pollinators, depending on the specific group of insecticide or fungicide. This review discusses the different combinations of major insecticide and fungicide classes and their effects on honeybees and wild bees. Fungicides inhibiting the sterol biosynthesis pathway can strongly increase the toxicity of neonicotinoids and pyrethroids. Other fungicides, in contrast, do not appear to enhance toxicity when combined with neonicotinoid or pyrethroid insecticides. But the knowledge on possible interactions of fungicides not inhibiting the sterol biosynthesis pathway and insecticides is poor, particularly in wild bees, emphasizing the need for further studies on possible effects of insecticide-fungicide interactions in bees.

Effect of Acaricide and Insecticide Mixtures Against Citrus Leprosis Vector, Brevipalpus Yothersi, Under Laboratory and Field Conditions

Effect of Acaricide and Insecticide Mixtures Against Citrus Leprosis Vector, Brevipalpus Yothersi, Under Laboratory and Field Conditions

Various routes of formulated insecticide mixture whole-body acute contact toxicity to honey bees (Apis mellifera)

Honey bees, Apis mellifera (Linnaeus) are crucial pollinators, however large overwinter losses of managed hives and declines in feral colonies have occurred since 2006. Increased insecticide use and the introduction of new insecticide classes have been proposed as factors contributing to these declines. Previous studies have demonstrated contact toxicity of single active ingredient insecticides to honey bees. However, the field realistic contact toxicity of formulated (pre-mix) insecticide mixtures containing multiple active ingredients (each with a different mode of action) to honey bees has not been thoroughly assessed. Here, we simulate whole body contact to spray applications made at low label recommended field rates of thiamethoxam + lambda-cyhalothrin, imidacloprid + beta-cyfluthrin, chlorantraniliprole + lambda-cyhalothrin and methoxyfenozide + spinetoram to honey bees under three realistic scenarios in field crops: (1) continuous exposure, (2) spray-only exposure, and (3) residual exposure. A customized spray tower in a laboratory setting was used to apply insecticides at the lowest recommended dose in the Environmental Protection Agency regulated label of each insecticide. Acute toxicity was determined by screening resulting mortality up to 96-hours post treatment. Mortality varied significantly between treatments at all evaluation periods for all experiments except residual exposure. For continuous and spray-only exposure, thiamethoxam + lambda-cyhalothrin and imidacloprid + beta-cyfluthrin resulted in 80–90% mortality at 48-hours, while at 96-hours we observed close to complete mortality for all treatments. This difference in mortality onset between treatments highlights the importance of extended observation beyond the 48-hours recommended by the USDA-EPA. Our finding of overall high mortality demonstrates the importance of comparing both combined and individual active ingredients in determining insecticide risk to honey bees.

Use of Antiviral Virucides in the Prevention of Some Viral Diseases Causing on Tobacco Plants in Vietnam

In recent years, some viral diseases have been increasing in the tobacco-growing regions of Vietnam and cause serious damage to the tobacco yield and quality. If it has not an effective control, viral diseases will injure seriously in the tobacco field in next time. To control the effect of viral diseases, study use of some antiviral virucides is necessary on tobacco plants. In 2021, Vietnam Tobacco Institute experimented with the effective control of Ditacin 8SL, Sat 4SL, and Exin 4.5SC for TMV, CMV, PVY, and TNRV on the tobacco field in Bac Giang province. Results of the study show the antiviral agents are effective in the control of the virus disease on tobacco. When only spray Ditacin 8SL, effective prevention for viral diseases ranges from 22.4 - 30.3%; Sat 4SL: 5.5 - 30.2%, and Exin 4.5SC: 8.2 - 24.1%. Spraying a mixture of antiviral agents and insecticides gives higher efficiency than spraying a kind. For example, spray Ditacin 8SL + Confodor 100SL, effective control reaches from 34.3 to 100%; Sat 4SL + Confidor 100SL: 32.6 - 92.3, and 38.5 - 100% with Exin 4.5SC + Confidor 100SL. The spray treatments have a higher yield and quality than the control without spraying.

Association between Haematological Parameters and Exposure to a Mixture of Organophosphate and Neonicotinoid Insecticides among Male Farmworkers in Northern Thailand.

Exposure to insecticides may result in various health problems. This study investigated the association between haematological parameters and exposure to a mixture of organophosphate (OP) and neonicotinoid (NEO) insecticides among male farmworkers in Fang district, Chiang Mai province, northern Thailand. Concentrations of urinary dialkylphosphates, non-specific metabolites of OPs, and NEOs and their metabolites and haematological parameters were measured in 143 male farmworkers. The Bayesian kernel machine regression model was employed to evaluate the associations. Exposure to a mixture of insecticides was significantly associated with the mean corpuscular haemoglobin concentration (MCHC) when the concentrations of all the compounds and their metabolites were at the 60th percentile or higher compared with the 50th percentile. Furthermore, exposure to clothianidin (CLO) showed a decreasing association with MCHC when all the other insecticides were at their mean concentrations. CLO was the most likely compound to reduce MCHC, and this was confirmed by sensitivity analysis. These findings suggest that exposure to NEO insecticides, especially CLO, affects the haematological status relating to haemoglobin parameters.

Effect of Pesticide and Humic Preparation on the Soil Structure during Pea and Chickpea Cultivation

The article presents the results of a 3-year experiment to study the soil structure with the combined use of insecticides and a humic preparation. Crops were peas (Pisum sativum) and chickpeas (Cicer arietinum). The experiment was carried out in 2019–2021 at the experimental fields of the Federal Rostov Agrarian Scientific Center, located in the Rostov region in the south of the European part of Russia (47°21′ N, 39°52′ E). Soil was Calcic Chernozem Loamic. The studies were carried out both without fertilization and with the use of mineral fertilizers (N40P40K40). Sowings of leguminous crops were treated with a mixture of insecticides and a humic preparation in the phase of bean formation. The humic preparation BIO-Don10 was obtained according to the authors’ technology by alkaline extraction from vermicompost—a product of manure processing by compost worms of the Eisenia foetida species. The preparation contains salts of humic acids and fulvic acids in the amount of 1.9 g/L; the concentration in the mixture with the insecticide was 0.002%. An increase in the structure and water resistance coefficients was observed. A decrease in the block fraction and an increase in the total number of agronomically valuable aggregates were substantiated. It was found that in the cultivation of legumes, the application of mineral fertilizers had a negative effect on the structure of the soil, while, when using pesticides, the structure was preserved better by the end of the growing season. The revealed patterns can be associated with the activity of microorganisms participating in the hydrolysis of organic compounds that stabilize soil aggregates.

Mixture toxicity assessment of selected insecticides to silver perch fingerling, Bidyanus bidyanus

The organophosphorus (OP) and carbamate (CB) insecticides are responsible for inhibition of the Acetylcholinesterase (AChE) enzyme. The AChE activity, therefore, has been demonstrated to be a potent biomarker for these insecticides in terrestrial and aquatic environments. The objective of this study was to investigate the response of AChE in the brain of four-week old fingerlings of silver perch, Bidyanus bidyanus exposed to OP and CB insecticides. The fish fingeling were exposed to three OPs and one CB insecticide as individual and their binary mixtures for 48 h. The OP insecticides with oxon (PO) as well as thion (PS) group gets oxidized to oxon analogs in biological systems. The 50% AChE inhibition (48 h EC50) in fingerling exposed to chlorpyrifos (CPF) and triazophos (TRZ) was evident at 2.3 and 6.7 µg/L, respectively. The toxicological interaction of three OPs and one CB insecticide was evaluated using the toxic unit method. A strong synergism was observed for binary combination of CPF with profenofos (PRF), and CPF with TAZ. In contrast, the mixture of TAZ with PRF and carbofuran (CBF) with CPF and PRF showed antagonistic behavior. Although OP and CB insecticides can break down rapidly in the environment, this study suggests that non-target aquatic biota may be exposed to mixtures of ChE-inhibiting insecticides for a period of several months, in agricultural regions where insecticides are applied for extended periods of the year. And at environmentally relevant concentrations such mixtures may lead to deleterious effects in non-target organisms.

Assessing the anti-resistance potential of public health vaporizer formulations and insecticide mixtures with pyrethroids using transgenic Drosophila lines

BackgroundInsecticide resistance—and especially pyrethroid resistance—is a major challenge for vector control in public health. The use of insecticide mixtures utilizing alternative modes of action, as well as new formulations facilitating their uptake, is likely to break resistance and slow the development of resistance.MethodsWe used genetically defined highly resistant lines of Drosophila melanogaster with distinct target-site mutations and detoxification enzymes to test the efficacy and anti-resistance potential of novel mixture formulations (i.e. Fludora® Fusion consisting of deltamethrin and clothianidin), as well as emulsifiable concentrate transfluthrin, compared to alternative, currently used pyrethroid insecticide formulations for vector control.ResultsThe commercial mixture Fludora® Fusion, consisting of both a pyrethroid (deltamethrin) and a neonicotinoid (clothianidin), performed better than either of the single active ingredients against resistant transgenic flies. Transfluthrin, a highly volatile active ingredient with a different molecular structure and primary exposure route (respiration), was also efficient and less affected by the combination of metabolic and target-site resistance. Both formulations substantially reduced insecticide resistance across different pyrethroid-resistant Drosophila transgenic strains.ConclusionsThe use of mixtures containing two unrelated modes of action as well as a formulation based on transfluthrin showed increased efficacy and resistance-breaking potential against genetically defined highly resistant Drosophila flies. The experimental model remains to be validated with mosquito populations in the field. The possible introduction of new transfluthrin-based products and mixtures for indoor residual spraying, in line with other combination and mixture vector control products recently evaluated for use in public health, will provide solutions for better insecticide resistance management.Graphical abstract

Plant Polysaccharides Modulate Biofilm Formation and Insecticidal Activities of Bacillus thuringiensis Strains.

After the biological pesticide Bacillus thuringiensis (Bt) is applied to the field, it has to remain on the surface of plants to have the insecticidal activities against insect pests. Bt can form biofilms on the surface of vegetable leaves, which were rich in polysaccharides. However, the relationship between polysaccharides of the leaves and the biofilm formation as well as the insecticidal activities of Bt is still unknown. Herein, this study focused on the effects of plant polysaccharides pectin and xylan on biofilm formation and the insecticidal activities of Bt strains. By adding pectin, there were 88 Bt strains with strong biofilm formation, 69 strains with weak biofilm formation, and 13 strains without biofilm formation. When xylan was added, 13 Bt strains formed strong biofilms, 98 strains formed weak biofilms, and 59 strains did not form biofilms. This indicated that two plant polysaccharides, especially pectin, modulate the biofilm formation of Bt strains. The ability of pectin to induce biofilm formation was not related to Bt serotypes. Pectin promoted the biofilms formed by Bt cells in the logarithmic growth phase and lysis phase at the air–liquid interface, while it inhibited the biofilms formed by Bt cells in the sporangial phase at the air–liquid interface. The dosage of pectin was positively correlated with the yield of biofilms formed by Bt cells in the logarithmic growth phase or lysis phase at the solid–liquid interfaces. Pectin did not change the free-living growth and the cell motility of Bt strains. Pectin can improve the biocontrol activities of the spore–insecticidal crystal protein mixture of Bt and BtK commercial insecticides, as well as the biofilms formed by the logarithmic growth phase or lysis phase of Bt cells. Our findings confirmed that plant polysaccharides modulate biofilm formation and insecticidal activities of Bt strains and built a foundation for the construction of biofilm-type Bt biopesticides.

The role of detoxification enzymes in the susceptibility of Brevipalpus californicus exposed to acaricide and insecticide mixtures

The intense spraying of pesticides to control different arthropod pests has resulted in negative side effects for the management of pests. It was previously discovered that exposure to non-acaricidal insecticides alone or in a mixture, results in lower efficiency of the acaricide spirodiclofen used for Brevipalpus spp. control. We investigate here whether the induced expression of detoxification enzymes by non-lethal insecticides may antagonize spirodiclofen toxicity. Brevipalpus californicus mites exposed to the insecticide phosmet alone or in combination with spirodiclofen showed increased activity of P450 monooxygenases (P450s). No antagonistic effects in mite mortality were observed by the combination of phosmet and spirodiclofen. On the other hand, mites exposed to the insecticide imidacloprid alone or in combination with spirodiclofen showed an increase in the activity of P450s, carboxylcholinesterases (CCE), and glutathione-S-transferases (GST). An antagonistic effect on mite mortality was observed when mites were exposed to the LC25 of spirodiclofen combined with the field rate treatment of imidacloprid. The addition of PBO (a P450 monooxygenase inhibitor) to the mixture of spirodiclofen and imidacloprid resulted in a synergistic effect over mite mortality but the addition of DEM (a GST inhibitor) resulted in an antagonist effect. Taken together, this study showed that the combination of imidacloprid with spirodiclofen is antagonistic for the control of B. californicus, and this results from the induction of detoxification enzymes, such as P450s, CCE, and GST. The use of inhibitors highlights the role of these enzymes in the antagonism of the mixture.