Insecticide Mixtures Research Articles

The ecological effects of a herbicide–insecticide mixture on an experimental freshwater ecosystem

The effects of a co-occurring insecticide–herbicide mixture were evaluated using model ecosystems (microcosms) in the laboratory. Microcosms dosed with a high concentration (10 μg/L) of the insecticide terbufos, alone and as a mixture with the herbicide atrazine (25 μg/L), exhibited community level effects attributed to the elimination and decline of invertebrate populations, and also indirect effects. There were no community level effects at a lower concentration of terbufos (0.1 μg/L) alone or in a mixture with atrazine, although delayed population effects were observed. Female chironomids also emerged later and those from terbufos-only microcosms were smaller. Exposure to atrazine alone was also associated with lower abundances of cladocerans and reduced emergence of chironomids. The risk posed by atrazine is low and is unlikely to exacerbate the effects of terbufos. Nevertheless, the population-level effects highlight that terbufos poses a potential risk to aquatic ecosystems, regardless of whether atrazine is also present.

Repeated and multiple stress (exposure to pesticides) on aquatic organisms

A systematic literature search identified publications relevant to repeated (94 papers) and mixture exposure (152 papers) of aquatic organisms. Limited data are available on pulsed exposure of pesticides and reports on repeated pulse or fluctuating exposures are even rarer. Although there has been recognition of the need for more realistic testing scenarios these lack a systematic approach. Among the reports on pesticide mixtures most of the plant studies evaluated interactions between mixtures of herbicides or fungicides / algicides. A small number of reports evaluated the effects on invertebrates of mixtures of pesticides with the same mode of action and these showed additive toxicity. More studies in invertebrates assessed interactions between pesticides with different modes of action including herbicide/ insecticide combinations some of which showed toxicity greater than additive. The majority of studies in fish have investigated the toxicity of insecticide mixtures. The toxicity of most combinations was at most additive, with a small number antagonistic. A small number of papers reported mixture effects of pesticides in amphibians; more than additive effects were observed with atrazine combinations. Simple models can be used to determine the additive toxicity of pesticide mixtures based on concentration addition or independent action. More complex models to determine the scale of synergy are speciesand dose-dependent and rely on an understanding of the interactions involved. Further work is required to develop a greater understanding of the species, dose and time dependence of exposure to pesticide mixtures in which more complex interactions occur. In the interim, in the majority of cases the increase in toxicity is no greater than 3 fold when compared to additive, the deviation from additivity decreases with the increasing number of components in the mixture, and where no known interactions have been reported this may be an appropriate factor to include in risk assessments.

The potency of Chloropyrifos and Camphor extract on Spodoptera littoralis (BOISD.)

The biological and biochemical effects chloropyrifos, camphor extract and their combination were studied against the 4 th instars of Spodoptera littoralis under semi-field conditions. The results indicated that the LC50 for chloropyrifos was 0.08 ppm and 13.3 x 10 3 ppm for the camphor extract. The estimated Co-toxicity factor was 13.2 So, there is an additive effect between camphor oil and chloropyrifos against S. littoralis. Oil extract of camphor prolonged larval and pupal duration also the same effect happened when using mixture of camphor extract and chloropyrifos. This prolongation was accompanied with a reduction in pupal weight of the treated larvae. While when using chloropyrifos only the larval and pupal duration were shortened Also % of pupation and % of adult emergence were more decrease in plant extract and insecticide mixture than each compound alone. Biochemical studies showed that, total protein content of larval instars decreased by 31, 26 and 13.5 % for camphor extract, chloropyrifos and its combination, respectively. Also, the activity of acid phosphatase, α-esterase was significantly decreased. Where the alkaline phosphatase, activity increased When compared with control.

Toxicity of Thiamethoxam and Mixtures of Chlorantraniliprole Plus Acetamiprid, Esfenvalerate, or Thiamethoxam to Neonates of Oriental Fruit Moth (Lepidoptera: Tortricidae)

To assess the toxicity ofthiamethoxam and three mixtures of insecticides to oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), we added the insecticides to diet and fed it to neonates of two laboratory colonies; mortality was assessed after 96 h. Thiamethoxam was much less toxic than insecticides previously tested. Five of six analyses of the joint action of chlorantraniliprole plus acetamiprid, esfenvalerate, or thiamethoxam indicated that toxicity was not independent and not correlated. For chlorantraniliprole plus acetamiprid, mortality was slightly lower than expected at low concentrations and greater than expected at high concentrations. For chlorantraniliprole plus esfenvalerate, mortality was less than expected at nearly all concentrations, suggesting antagonism despite the two compounds' different modes of action. For chlorantraniliprole plus thiamethoxam, observed mortality exceeded expected mortality at low concentrations, but this trend did not continue at higher concentrations. Although the null hypothesis of independent and uncorrelated toxicity was rejected for chlorantraniliprole plus acetamiprid and chlorantraniliprole plus thiamethoxam in three of four analyses, differences between observed and expected mortality were minor and inconsistent over the range of concentrations tested. We do not expect these mixtures to exhibit significant synergism or antagonism in the field. Apparent antagonism between chlorantraniliprole and esfenvalerate is particularly relevant because these insecticides (or chlorantraniliprole plus a different pyrethroid) may be used together in apples or peaches for control of oriental fruit moth and hemipteran pests. The effectiveness of each insecticide against oriental fruit moth might be reduced in such applications.

Incompatibilidade física de misturas entre herbicidas e inseticidas

Objetivou-se, com este trabalho, avaliar a interação física entre misturas em tanque de diferentes classes de defensivos agrícolas. O experimento foi conduzido no laboratório de Química da Universidade do Estado de Mato Grosso, no período de junho a agosto de 2010. Os tratamentos foram constituídos pelas misturas de seis herbicidas (glyphosate SC, glyphosate WG, lactofen CE, fomesafen SC, haloxifop-R CE e fluazifop-pbutil EW) com seis inseticidas (methomyl CS, clorpirifós CE, teflubenzuron SC, triflumuron SC, cipermetrina CE e tiametoxam + lambda-cialotrina SC) na ausência e presença de dois redutores de pH (ácido pirolenhoso e ácido bórico), com quatro repetições. Utilizou-se escala de 1 a 5, visando avaliar o grau de incompatibilidade, em que 1 é a separação imediata da mistura e recomenda-se não aplicar e 5 é a homogeneidade das misturas. As maiores incompatibilidades físicas nas misturas de herbicidas e inseticidas foram observadas na presença dos herbicidas glyphosate na formulação WG e lactofen CE. O ácido pirolenhoso e o ácido bórico demonstraram ser boas alternativas, como redutores de pH, no preparo de calda de pulverização com misturas de herbicidas e inseticidas. Devem-se evitar misturas em tanque de glyphosate na formulação SC + clorpirifós CE e lactofen CE + clorpirifós CE.

Influence of pesticide-treated seeds on survival of Mesorhizobium sp. Cicer, symbiotic efficiency and yield in chickpea

Chemical seed protectants are used to reduce the adverse effects of seedling fungal pathogens or insect attack on legume pastures and crops. Chickpea seeds are also frequently treated with Mesorhizobium sp. Cicer inoculant to promote effective symbiotic nitrogen fixation (SNF), which seems to be a cost effective measure. The population of viable Mesorhizobium sp. Cicer on seeds of chickpea declined with time of storage (4°C) in pesticide treated and untreated chickpea seeds in vitro. A significant reduction in chickpea rhizobia was observed in seed treatment with Captan followed by Endosulfan and Chlorpyrifos. In a field experiment during the winter season 2006–2008, no difference in the emergence count of chickpea plants was observed. Treatments inoculated with Mesorhizobium sp. Cicer alone or along with Captan, Chlorpyrifos or Endosulfan showed improved plant growth and symbiotic parameters (plant height, nodulation, leghaemoglobin content, and nitrogen content) in comparison with the uninoculated control treatment. Significantly higher grain yield (9.6%) was observed in the treatment inoculated with Mesorhizobium sp. Cicer alone as compared to the uninoculated control. A non-significant difference in grain yield among treatments where Mesorhizobium sp. Cicer along with a mixture of fungicide and insecticides was applied was observed in contrast to the Mesorhizobium sp. Cicer treatment. In conclusion, the recommended rates of fungicide and insecticides as seed treatment were not detrimental to chickpea-Mesorhizobium sp. Cicer symbiosis, hence they can be safely used to obtain higher productivity.  

Rapid determination of pesticide mixtures using disposable biosensors based on genetically modified enzymes and artificial neural networks

We present a one-step inhibition biosensor method that can be used to determine mixtures of three organophosphorus compounds. We propose to calculate the rate of irreversible inactivation of the enzyme (kp) to demonstrate the direct relationship between enzymatic biosensors and Chlorpyriphos-oxon (CPO), Chlorfenvinphos (CFV) and Azinphos-methyl oxon (AZMO) insecticides. The array of biosensors was designed using only two acetylcholinesterases from Drosophila melanogaster (wild-type and genetically modified). We used the values the slope of inhibitions mi from an array of biosensors and an artificial neural network to solve mixtures of CPO, CFV and AZMO insecticides The errors were low between the obtained and expected values for a set of 20 external test samples.

A spatially and temporally explicit risk assessment for salmon from a prey base exposed to agricultural insecticides

This risk assessment applied a framework for determining probable co-occurrence of juvenile spring Chinook salmon (Oncorhynchus tshawytscha) with agricultural pesticides in the Willamette Basin, Oregon (Teply et al. this issue) to characterize risk to the threatened population. The assessment accounted for spatial and temporal distribution of 6 acetylcholinesterase-inhibiting insecticides in salmonid habitat within the basin and their relative contributions to mixture toxicity estimated from chemical monitoring data. The 6 insecticides were chlorpyrifos, diazinon, malathion, carbaryl, carbofuran, and methomyl. Seasonal distributions of the juvenile salmon prey base across the basin were determined and compared to co-occurrence with the insecticide mixture to determine the probability of prey reduction and reduced production of juvenile fish. Probability of effect on freshwater aquatic invertebrates was based on acute toxicity species sensitivity distributions (normalized to the most potent compound, chlorpyrifos) using a novel approach to apply the toxicological concept of concentration addition to species sensitivity distributions with differing slopes. The chlorpyrifos distribution was then used to determine relative sensitivity among various species tested within the important taxa making up the prey base. A prey base index was devised, incorporating diet composition and prey availability, to evaluate the indirect effects of the insecticide mixture on juvenile salmon production occurring as a result of a reduction in the prey base. Our analysis targeted fish use of backwater and off-channel habitat units, because they generally coincide with agricultural lands in lowlands and represent shallow habitat with limited water exchange. The percentage of agricultural land use within 300 m of critical habitat stream reaches was used to scale chemical measurement data from a site with high agricultural land use across the full extent of the basin to provide estimates of chemical exposure in each reach. Seasonal impacts were evaluated from mean monthly concentrations. Stressor impact on 5 key taxa was evaluated at each time step and for each reach, and the outcome was compared to a conservation threshold assigned to the prey base index. Only 13% of juveniles reared in backwater, off-channel habitat within 300 m of agricultural land. Percent reduction of carrying capacity as a consequence of reduced prey was estimated to be 5% over the entire brood year. This can be considered lost capacity that is probably compensated elsewhere via increased occupancy (emigration to other habitat units within the reach), which is not accounted for in the model.

Organochlorine Insecticides Lindane and Dieldrin and Their Binary Mixture Disturb Calcium Homeostasis in Dopaminergic PC12 Cells

Current hypotheses link long-term environmental exposure of humans to persistent organochlorine (OC) insecticides lindane (HCH) and dieldrin (HEOD) to the development of neurodegenerative disorders, such as Parkinson's disease. Primary adverse neurological effects of these insecticides are directed at inhibition of GABA(A) and glycine receptors, although GABA-independent effects have also been reported. In this paper we describe the effect of dieldrin and a binary mixture of dieldrin and lindane on a critical parameter of neuronal function and survival, i.e., intracellular calcium homeostasis. The intracellular calcium concentration ([Ca(2+)](i)) has been monitored using real-time single-cell fluorescence microscopy in dopaminergic PC12 cells loaded with the calcium-sensitive dye Fura-2. The results demonstrate that nanomolar concentrations of dieldrin time- and concentration-dependently inhibit depolarization-evoked influx of Ca(2+). Co-exposure of PC12 cells to a mixture of dieldrin and lindane revealed an additive inhibition of the depolarization-evoked increase in [Ca(2+)](i), whereas the lindane-induced increase in basal [Ca(2+)](i) is inhibited by dieldrin. The combined findings indicate that dieldrin and binary mixtures of organochlorines affect [Ca(2+)](i) already at concentrations below commonly accepted effect concentrations and close to human internal dose levels. Consequently, current findings illustrate the need to take mixtures of OC insecticides into account in human risk assessment.

Aktivitas dan Keefektifan Insektisida Berbahan Aktif Majemuk Thiodicarb dan Triflumuron terhadap Hama Ulat Kantong Metisa plana pada Tanaman Kelapa Sawit

Activity and effectiveness of insecticide mixtures (thiodicarb and triflumuron) against physics caterpillar pests Metisa plana on oil palm plantation. The objectives of this study were to evaluate the joint action of thiodicarb and triflumuron insecticides in the laboratory, and to determine their effectiveness in supressing population of M. plana in the field. The mortality bioassays were conducted by a spraying method. The results showed that the inseticide mixtures between thiodicarb and triflumuron possessed a sinergistict activity against M. plana larvae with insecticide combination index of 0.49%. Iinsecticide mixtures at a range dose of 250 - 1250 ml/ha spraying on oil palm planst effectively suppressed population of M. plana larvae.

Evaluation of suitable endpoints for assessing the impacts of toxicants at the community level

Assessment of ecological impacts of toxicants relies currently on extrapolation of effects observed at organismal or population levels. The uncertainty inherent to such extrapolations, together with the impossibility of predicting ecological effects of chemical mixtures, can only be resolved by adopting approaches that consider toxicological endpoints at a community or ecological level. Experimental data from micro- and mesocosms provide estimates of community effect levels, which can then be used to confirm or correct the extrapolations from theoretical methods such as species sensitivity distributions (SSDs) or others. When assessing impacts, the choice of sensitive community endpoints is important. Four community endpoints (species richness, abundance, diversity and similarity indices) were evaluated in their ability to assess impacts of two insecticides, imidacloprid and etofenprox, and their mixture on aquatic and benthic communities from artificial rice paddies. Proportional changes of each community endpoint were expressed by ratios between their values in the treatment and control paddies. Regression lines fitted to the endpoint ratios against the time series of chemical concentrations were used to predict percentile impacts in the communities. The abundance endpoint appears to be the most sensitive indicator of the communities' response, but the Czekanowski similarity index described best the structural changes that occur in all communities. Aquatic arthropods were more sensitive to the mixture of both insecticides than zooplankton and benthic communities. Estimated protective levels for 95% of aquatic species exposed to imidacloprid (<0.01-1.0 μg l(-1)) were slightly lower than predicted by SSD, whereas for etofenprox the protective concentrations in water (<0.01-0.58 μg l(-1)) were an order of magnitude lower than SSD's predictions.

Toxicity and biochemical impacts of some new insecticide mixtures on cotton leafworm Spodoptera littoralis (Boisd.)

The susceptibility to five new insecticide mixtures: chlorosan, feroban, cygron, engeo, and kingbo was studied in the 2&lt;sup&gt;nd&lt;/sup&gt; and 4&lt;sup&gt;th&lt;/sup&gt; instar larvae of the cotton leafworm Spodoptera littoralis (Boisd.). The efficiency and residual effects of these compounds against S. littoralis under field conditions were also investigated. Obtained results revealed that feroban was the most effective compared with the other toxicants, while engeo was the least toxic insecticide in both instars after 2 and 5 days from treatment. Data also indicated that feroban had the longest half-life (Lt&lt;sub&gt;50&lt;/sub&gt;) while engeo recorded the shortest one. Biochemical analysis showed that the tested compounds caused pronounced changes in acetyl cholinesterase and phenol oxidase.

Insecticide resistance, mixture potentiation and fitness in populations of the maize weevil ( Sitophilus zeamais)

High levels of pyrethroid resistance and emerging organophosphate resistance in Brazilian populations of the maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) led to the registration of esfenvalerate + fenitrothion against them. Thus, a survey of physiological and behavioural resistance was carried out in 27 insect populations for two pyrethroids, esfenvalerate and permethrin, and the esfenvalerate + fenitrothion mixture. Physiological resistance to fenitrothion was also assessed, as was the potentiation of the mixture. The potential fitness cost associated with insecticide resistance was also investigated. The resistance levels were low to fenitrothion (<14.1-fold), low to moderate to the pyrethroids (1.6–70.0-fold) and low to the pyrethroid-organophosphate mixture (<5-fold) with a high heterogeneity of response among populations. The potentiation of insecticidal activity achieved with the insecticide mixture was very high (>350-fold) reinforcing its usefulness for managing weevils. There was little variation in walking behaviour (and insecticide avoidance) among populations; there was no significant variation in fitness, body mass and respiration rate among the populations of the insect. These however, displayed variable rates of grain consumption and activity of amylase and lipase. A decrease in insecticide resistance in maize weevil populations was observed relative to previous studies, but with an initial development of resistance to the insecticide mixture. Behavioural and physiological resistance were not correlated and not associated with fitness cost. Our results support the use of esfenvalerate + fenitrothion against the maize weevil, which is likely to have reduced the levels of pyrethroid resistance in field populations. However, resistance to this mixture seems to be evolving, justifying concerns regarding its use.

Testing the Dose Addition Hypothesis: The Impact of Pyrethroid Insecticide Mixtures on Neurons

Vol. 119, No. 9 News | Science SelectionsOpen AccessTesting the Dose Addition Hypothesis: The Impact of Pyrethroid Insecticide Mixtures on Neuronsis accompanied byAdditivity of Pyrethroid Actions on Sodium Influx in Cerebrocortical Neurons in Primary Culture Kris S. Freeman Kris S. Freeman Search for more papers by this author Published:1 September 2011https://doi.org/10.1289/ehp.119-a399aAboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Pyrethroid insecticides are used extensively in agriculture and in homes to control fleas, cockroaches, bedbugs, and other insects. In a new in vitro study researchers tested the hypothesis that mixtures of pyrethroids have a dose-additive effect—that is, that pyrethroids as a chemical group produce toxicity in mammals via a common mode of action and that the combined toxicity of a pyrethroid mixture reflects the sum of its constituents’ toxicities [EHP 119(9):1239–1246; Cao et al.]. Using increased sodium ion influx as a specific functional measure of toxicity, the researchers found that effects of a mixture of commonly used pyrethroids were consistent with a dose-additive effect on mammalian neurons.Pyrethroids act on the nervous system by disrupting the normal function of voltage-gated sodium channels (VGSCs), which control the influx of sodium ions into neurons to transmit nerve signals. When VGSCs open, the influx of sodium generates the nerve signal; when they close, the electrical signal halts abruptly. Pyrethroids bind to VGSCs and delay their closing, which causes repetitive nerve stimulation that can lead to muscle tremors as well as interfere with the ability of the channels to respond to stimulation.Previous research demonstrated that a mixture of 11 pyrethroids had a dose-additive effect on the rat nervous system, decreasing the animals’ motor activity at doses below the threshold dose of each constituent compound. The authors of the current study exposed neurons cultured from the cerebral cortices of embryonic mice to the same 11 pyrethroids, then examined how VGSCs responded. To measure sodium influx without disrupting cell function, neurons were treated with a sodium-sensitive dye that fluoresced when VGSCs were open.Seven of the pyrethroids tested increased sodium influx in a dose-dependent manner (from highest to lowest potency: deltamethrin, S-bioallethrin, β-cyfluthrin, λ-cyhalothrin, esfenvalerate, telfluthrin, fenpropathrin). Cypermethrin and bifenthrin had only a marginal effect on sodium influx, whereas permethrin and resmethrin had no effect. Despite these variations in activity, the results when neurons were exposed to all 11 compounds together were consistent with a cumulative, dose-additive effect on neuronal sodium influx.People are commonly exposed to low doses of pyrethroid mixtures, which tend to persist as residues on treated surfaces and in household dust. Currently the U.S. Environmental Protection Agency is determining whether a cumulative dose-additive model is appropriate to evaluate potential human health effects of pyrethroid mixtures. This model shows that simultaneous exposure to multiple compounds will produce an effect that is consistent with additivity at the VGSC molecular target.FiguresReferencesRelatedDetailsRelated articlesAdditivity of Pyrethroid Actions on Sodium Influx in Cerebrocortical Neurons in Primary Culture10 June 2011Environmental Health Perspectives Vol. 119, No. 9 September 2011Metrics About Article Metrics Publication History Originally published1 September 2011Published in print1 September 2011 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Cytogenetic effects of commercial formulations of deltamethrin and/or thiacloprid on wistar rat bone marrow cells

Deltamethrin (DEL) and thiacloprid (THIA) are two insecticides that are widely used in agriculture either separately or in combination. Studies on genotoxicity and cytotoxicity of TIA and the mixture of DEL and THIA insecticides have not been reported so far. Therefore, we investigated the cytotoxic and genotoxic effects of commercial formulations DEL and/or THIA in rat bone marrow cells, using mitotic index (MI), micronucleus (MN) and chromosome aberrations (CA) assay. In vivo cytokinesis-block micronucleus (CBMN) assay using cytochalasin-B in bone marrow cells was performed for the first time in this study. Rats were orally gavaged with a single dose of DEL (15 mg/kg), THIA (112.5 mg/kg) or DEL + THIA (15 + 112.5 mg/kg) for 24 h (acute treatments), or DEL (3 mg/kg/day), THIA (22.5 mg/kg/day) or DEL + THIA (3 + 22.5 mg/kg/day) for 30 days (subacute treatments). A corn oil vehicle control group and cyclophosphamide (50 mg/kg) positive control group were also included. All DEL and/or THIA treatments significantly decreased MI and binucleated (BN) cell numbers, and significantly increased CA, as compared to the vehicle control group. The results of CBMN assay indicated that the combination of DEL and THIA for both treatment times and the 30-day treatment with THIA alone caused a significant increase in micronucleus formation in BN cells. The present findings indicated the combined exposure of DEL and THIA showed genotoxic and cytotoxic effects more than those of individual exposure of DEL or THIA in rat bone marrow cells.

Evaluation of the risk of mixtures of paddy insecticides and their transformation products to aquatic organisms in the Sakura River, Japan

To assess the risk of mixtures of six paddy insecticides and their transformation products (TPs) to aquatic organisms in the Sakura River, Japan, their concentrations in the river water were monitored during the rice cultivation season in 2008 and 2009, and acute toxicity tests for Cheumatopsyche brevilineata (caddisflies) and Daphnia magna (daphnids), surrogate test species for caddisflies and cladocerans, respectively, were conducted. The mixture of fipronil, applied in the rice nursery box, and its desulfinyl, sulfide, and sulfone TPs were detected in the river for several months after transplanting, and they were more toxic to C. brevilineata than the other tested compounds. The toxicities of the parent compound and its TPs, such as fipronil and its TPs, may be related to their hydrophobicities. Risk quotients for mixtures (RQ(mix)) of only parent compounds did not exceed 1, but, in mid-June 2009, the RQ(mix) of parent compounds and TPs for caddisflies exceeded 1. Diazinon, fenitrothion, and fenthion sprayed on the rice crop and their TPs posed a sporadic risk for cladocerans, depending on the application timing, whereas fipronil TPs contributed to the RQ(mix) for caddisflies for several months after transplanting. The risk of mixtures of insecticides and their TPs differed seasonally between caddisflies and cladocerans, depending on insecticide application timing and the persistence and toxicity of TPs.

Eficácia da mistura Acetamiprid + Fipronil, aplicados em tratamento de sementes de algodão, no controle de Aphis gossypii Glover (Hemiptera: Aphididae)

The cotton aphid, Aphis gossypii Glover (Hemiptera; Aphididae), is one of the main cotton crop pests and the use of insecticides is important in its control. The objective of this study was to evaluate of the efficiency of mixture of acetamiprid and fipronil insecticides, in dry cotton seed coating, in controlling A. gossypii aphids. The experimental design was of randomized plots with seven treatments and four replications. Cotton seeds, from cv. Delta Opal, were submitted to the following treatments – at g of active ingredient (AI).100kg-1 of seeds: acetamiprid+fipronil - 200+50, 240+60 e 280+70, acetamiprid – 210, fipronil - 70, tiametoxam - 210 and control (without insecticide). After plants emergency, aphids on leafs of ten plants per plot were evaluated. The pest population was least on cotton crop under seed treatment with acetamiprid+fipronil, acetamiprid and tiametoxam. The mixture of acetamiprid and fipronil was effective in controlling A. gossypii in cotton crop, even at 200+50 g AI.100kg-1 of seeds, by causing 93, 82 and 93% of mortality, at 11th, 15 th and 21th days after seedling emergence, respectively.

Susceptibility of Anopheles gambiae s.l. to DDT, malathion, permethrin and deltamethrin in Ethiopia

To assess the susceptibility/resistance level of Anopheles gambiae s.l. to DDT, malathion, permethrin and deltamethrin in different parts of Ethiopia. Field collected female An.gambiae s.l. was exposed for 1 h to discriminating dosage of 4% DDT, 5% malathion, 0.75% permethrin and 0.05% deltamethrin using WHO insecticide susceptibility test kits and procedures. Knockdown and mortality rates were recorded at 10, 15, 20, 30, 40, 50 and 60 min and 24 h post-exposure respectively. Anopheles gambiae s.l. was sensitive to DDT only in 2 of 16 localities where susceptibility studies were carried out in northern Ethiopia; it was resistant in 11 sites and potentially resistant in three. To malathion, the test population was sensitive in four of the six study sites in southern Ethiopia and potentially resistant in the other two sites. In northern Ethiopia, the population was resistant in five localities and sensitive in three. Of the six localities in northern Ethiopia where permethrin was tested, populations were sensitive in three, resistant in one and potentially resistant in two. In southern Ethiopia, the populations were resistant in five of the six sites. Against deltamethrin, the population was sensitive in five of 13 localities, three in northern and two in southern Ethiopia. It was resistant only in two localities, one in northern and one in southern Ethiopia, and potentially resistant in five localities. In eastern Ethiopia at Sabure, the population was sensitive to all insecticides but DDT to which it was potentially resistant. The existence of high level of DDT and pyrethroid resistance with the possibility of cross-resistance to each other and other classes of agricultural pesticides could seriously jeopardise the efficacy of both ITNs and IRS in the country in the future. Insecticide resistance monitoring and surveillance systems as part of a malaria control programme are mandatory for proper management of resistance. The use of a mixture of unrelated insecticides for impregnating nets and rotational use of insecticides for IRS is suggested as a way forward.

Methomyl–alphamethrin poisoning presented with cholinergic crisis, cortical blindness, and delayed peripheral neuropathy

Objective. Methomyl–alphamethrin is a mixture of carbamate and pyrethroid insecticides. Carbamate insecticides function as reversible cholinesterase inhibitors, which may produce life-threatening cholinergic syndrome. Cortical blindness and delayed neuropathy were rarely reported complications of carbamate insecticide exposures. Here we reported a case of intentional methomyl–alphamethrin ingestion. Case report. A 41-year-old woman attempted suicide by drinking 200 mL of methomyl–alphamethrin insecticide and soon presented with unconsciousness, hypothermia, and shock. She developed pulseless electrical activity and regained spontaneous circulation after resuscitation. Diagnosis of carbamate poisoning was made by her clinical features, decreased levels of cholinesterases and the presence of methomyl in her urine. She complained of blurred vision and blindness 4 days post-exposure. Visual evoked potential and brain magnetic resonance imaging study confirmed the diagnosis of cortical blindness. On day 21, she had low limbs numbness, progressive weakness, and right foot drop. Electophysiological tests performed on day 27 revealed neuropathy of bilateral peroneal nerves. Conclusion. We reported a patient who manifested severe carbamate insecticide poisoning and developed cortical blindness and delayed neuropathy. Physicians should be aware of these rare toxicities among patients with severe carbamate insecticide poisoning.

Physiological and behavioral resistance to esfenvalerate + fenitrothion in populations of the maize weevil, Sitophilus zeamais

The maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae) is considered the main pest of stored maize in Brazil and its control is achieved mainly by insecticides. The massive and intensive use of these compounds may lead to selection of resistant populations and consequently compromise the control efficacy of this insect pest in Brazilian storage facilities. Therefore, we surveyed physiological and behavioral resistance to the insecticide mixture esfenvalerate + fenitrothion in 27 populations of S. zeamais collected in several Brazilian counties and Paraguay, and also investigated possible costs associated with this phenomenon. The insects were subjected to concentration-mortality bioassays to determine the lethal concentrations LC 50 and LC 95 . The populations were also subjected to two walking trials on surfaces fully-treated and partially-treated with dried insecticide residues for detection of behavioral resistance. We also determined the instantaneous rate of population increase (ri), and body mass of individuals of each population. The concentration-mortality bioassays indicated resistance ratios (at LC 50 ) ranging from 1.00 to 5.02x for the insecticide mixture esfenvalerate + fenitrothion compared with the susceptible standard population (Sete Lagoas). Although the resistance ratios were modest at LC 50 , they reached up to 232x at LC 95 (Votuporanga county, Sao Paulo, Brazil). The behavioral trait of walking in treated arena varied among populations and sex, but there was no significant avoidance to the insecticide mixture. There was no correlation between physiological and behavioral resistance, indicating that physiological resistance is independent of behavioral resistance in the populations tested. There was no significant difference in the instantaneous rate of increase (ri), and body mass among the insects. Therefore, we conclude that there was no fitness cost associated with the levels of resistance observed in the populations studied. Keywords : Insecticide resistance, Locomotion, Behavioral avoidance, Fitness cost, Rate of population growth