A physiologically-based pharmacokinetic/pharmacodynamic (PBPK/PD) model for the insecticide dimethoate.

1. Dimethoate is an organophosphate insecticide that is converted in vivo to omethoate, the active toxic moiety. Omethoate inhibits acetylcholinesterase (AChE) in the brain and red blood cells (RBCs). This paper describes the development of rat and human physiologically-based pharmacokinetic/pharmacodynamic (PBPK/PD) models for dimethoate.2. The model simulates the absorption and distribution of dimethoate and omethoate, the conversion of dimethoate to omethoate and to other metabolites, the metabolism and excretion of omethoate, and the inhibition of RBC and brain AChE. An extensive data collection program to estimate metabolism and inhibition parameters is described.3. The suite of models includes an adult rat, post-natal rat, and human model. The rat models were evaluated by comparing model predictions of dimethoate and omethoate to measured blood time course data, and with RBC and brain AChE inhibition estimates from an extensive database of in vivo AChE measurements.4. After the demonstration of adequately fitted rat models that were robust to sensitivity analysis, the human model was applied for estimation of points-of-departure (PODs) for risk assessment using the human-specific parameters in the human PBPK/PD model. Thus, the standard interspecies uncertainty factor can be reduced from 10X to 1X.

Prolonged Use of Insecticide Dimethoate Inhibits Growth and Photosynthetic Activity of Wheat Seedlings: A Study by Laser-Induced Chlorophyll Fluorescence Spectroscopy.

This paper is an extension of the work published in Journal of Fluorescence (2011) 21: 785-791. In the previous work, we studied the effect of dimethoate (50, 100 and 200 ppm) on growth and photosynthetic activity of wheat seedlings after 10 days of dimethoate treatment. In the present study, new measurement conditions (dimethoate concentration: 25 ppm, treatment period: 20 days and 30 days) were used in addition to those used in the past work. Various plant growth parameters, photosynthetic pigment content, laser-induced chlorophyll fluorescence (LICF) spectra and fluorescence induction kinetics (FIK) curves were recorded after 10, 20 and 30 days of dimethoate treatments. LICF spectra were recorded in the region of 650-780 nm using violet diode laser (405 nm). FIK curves were recorded at 685 nm using red diode laser (635 nm). Fluorescence intensity ratio (FIR) of two fluorescence peaks around 685 and 730 nm, and variable chlorophyll fluorescence decrease ratio (Rfd) were determined from LICF spectra and FIK curves respectively. Curve-fitted parameters of LICF spectra were used for determination of FIR (F685/F730). The effect of treatment of the insecticide dimethoate on growth and photosynthetic activity of wheat seedlings was examined by using these parameters as well as the past work. In 10-days treatment, 25 and 50 ppm dimethoate showed stimulatory effect with better stimulation being observed at 25 ppm. All studied concentrations higher than 50 ppm exhibited inhibitory effect on wheat seedlings. In case of dimethoate treatment studied for longer durations (more than 10 days), all concentrations showed inhibitory effect. Lower doses which showed some positive response for short time duration become toxic with the extension of treatment periods. Thus, this study clearly confirms the toxic effect of dimethoate on wheat plants.

Synthesis and antiviral effect of phosphamide modified vidarabine for treating HSV 1 infections.

Vidarabine (ARA) was one of the earliest marine-related compounds to be used clinically for antiviral therapy, however, its fast metabolism is the main defect of this drug. To overcome this, we designed and synthesized a group of phosphamide-modified ARA compounds using ProTide technology. With a phosphamide modification, these compounds could become the substrate of specific phospholipase enzymes expressed in the liver. Among all 16 synthesized compounds, most showed stronger activity against herpes simplex virus type 1 (HSV-1) than ARA (EC50 of approximately 10 µM). The top three compounds were compound 2 (EC50 = 0.52 ± 0.04 µM), compound 6 (EC50 = 1.05 ± 0.09 µM) and compound 15 (EC50 = 1.18 ± 0.08 µM) (about 2 times higher than Sp type compound 2). This study provides evidence for use of the phosphamide modification, which could give ARA higher activity and liver cell targeting.

Dimethoate blocks pubertal differentiation of Leydig cells in rats.

Dimethoate is an organophosphate pesticide. It is widely used in agriculture. However, whether it blocks pubertal development of Leydig cells remains unknown. In the current study, we exposed male Sprague Dawley rats with 7.5 and 15 mg kg-1 dimethoate from postnatal day 35-56. We also exposed Leydig cells isolated from 35-day-old rats for 3 h. Dimethoate reduced serum testosterone levels at 7.5 and 15 mg kg-1 but increased serum luteinizing hormone and follicle stimulating hormone levels at 15 mg kg-1. Dimethoate did not influence Leydig cell number but reduced Leydig cell size and down-regulated Star, Cyp11a1, and Hsd3b1 in Leydig cells as well as their protein expression. Dimethoate inhibited basal androgen output in a dose-dependent manner with the inhibition starting at 0.05 µM. It significantly inhibited luteinizing hormone and 8Br-cAMP stimulated androgen outputs at 50 µM. It significantly inhibited 22R-hydroxycholesterol and progesterone-mediated androgen outputs at 50 µM. Further study demonstrated that dimethoate also down-regulated the expression of Star, Cyp11a1, and Hsd3b1 at 5 or 50 µM in vitro. Dimethoate did not directly inhibit rat testicular steroidogenic enzyme activities at 50 µM. In conclusion, dimethoate targets Star, Cyp11a1, and Hsd3b1 transcription, thus blocking Leydig cell differentiation during puberty.

A 3D-Fluorescence Fingerprinting Approach to Detect Physiological Modifications Induced by Pesticide Poisoning in Apis mellifera: A Preliminary Study.

The combined use of 3D-fluorescence spectroscopy and independent component analysis using a differential fingerprinting approach has been applied with success to detect physiological effects of dimethoate in honeybees. Biochemical determinations combined with the identification of fluorescence zones that may correspond to proteins, NADH or neurotransmitters/neurohormones (octopamine, dopamine and serotonin) related to the physiological stress caused by the pesticide enabled phenomenological modeling of the physiological response in the honeybee using a simple and rapid method. The signals associated with the fluorophores involved in the response to stress were extracted from the fluorescence spectra using an unsupervised algorithm such as independent component analysis. The signals of different neurotransmitters were isolated on separated factorial components, thus facilitating their biochemical interpretation.

The Role of Dimethoate and UV-B on Skin of Wistar Rats.

BACKGROUND/AIM: The pesticide dimethoate (O-dimethyl-S- Nmethylcarbamoylmethyl phosphorodithioate) is able to induce severe acute toxicity in living organisms. The aim of this study was to evaluate the effects of ultraviolet radiation, alone or combined with exposure to dimethoate, on the rat skin. MATERIALS AND METHODS: A total of 38 Wistar female rats (Rattus norvegicus albinus), were distributed into four groups: A (n=9) control group, B (n=10) exposed to ultraviolet-B radiation (UV-B), C (n=10) exposed to UV-B followed by application of dimethoate (UV-B+AGRO) and group D (n=9) exposed to dimethoate (AGRO). Histological examination of the tissues, as well as immunohistochemistry for cleaved caspase 3, Ki-67 and COX-2 expression were performed to all groups. RESULTS: Animals submitted to UV-B exhibited hyperkeratosis with moderate cell atypia. Regarding exposure to UV-B+AGRO, the animals presented hyperkeratosis and atrophy, whereas in animals exposed to AGRO, only atrophy was noticed. The immunohistochemical results on skin revealed that UVB, AGRO and UVB+AGRO decreased cleaved caspase 3 and Ki-67 expression when compared to the control group (p<0.05). COX-2 expression decreased to UVB or AGRO groups compared to controls (p<0.05). CONCLUSION: UV-B or AGRO exposure is able to induce histopathological changes and altered expression of cleaved caspase-3 and Ki-67 in rat skin, thus being categorized as a risk condition for skin carcinogenesis.

Western corn rootworm pyrethroid resistance confirmed by aerial application simulations of commercial insecticides.

The western corn rootworm (Diabrotica virgifera virgifera LeConte) (WCR) is a major insect pest of corn (Zea mays L.) in the United States (US) and is highly adaptable to multiple management tactics. A low level of WCR field-evolved resistance to pyrethroid insecticides has been confirmed in the US western Corn Belt by laboratory dose-response bioassays. Further investigation has identified detoxification enzymes as a potential part of the WCR resistance mechanism, which could affect the performance of insecticides that are structurally related to pyrethroids, such as organophosphates. Thus, the responses of pyrethroid-resistant and -susceptible WCR populations to the commonly used pyrethroid bifenthrin and organophosphate dimethoate were compared in active ingredient bioassays. Results revealed a relatively low level of WCR resistance to both active ingredients. Therefore, a simulated aerial application bioassay technique was developed to evaluate how the estimated resistance levels would affect performance of registered rates of formulated products. The simulated aerial application technique confirmed pyrethroid resistance to formulated rates of bifenthrin whereas formulated dimethoate provided optimal control. Results suggest that the relationship between levels of resistance observed in dose-response bioassays and actual efficacy of formulated product needs to be further explored to understand the practical implications of resistance.

Omethoate treatment mitigates high salt stress inhibited maize seed germination.

Omethoate (OM) is a highly toxic organophophate insecticide, which is resistant to biodegradation in the environment and is widely used for pest control in agriculture. The effect of OM on maize seed germination was evaluated under salt stress. Salt (800mM) greatly reduced germination of maize seed and this could be reversed by OM. Additionally, H2O2 treatment further improved the effect of OM on seed germination. Higher H2O2 content was measured in OM treated seed compared to those with salt stress alone. Dimethylthiourea (DTMU), a specific scavenger of reactive oxygen species (ROS), inhibited the effect of OM on seed germination, as did IMZ (imidazole), an inhibitor of NADPH oxidase. Abscisic acid (ABA) inhibited the effect of OM on seed germination, whereas fluridone, a specific inhibitor of ABA biosynthesis, enhanced the effect of OM. Taken together, these findings suggest a role of ROS and ABA in the promotion of maize seed germination by OM under salt stress.

Phosphamide-containing diphenylpyrimidine analogues (PA-DPPYs) as potent focal adhesion kinase (FAK) inhibitors with enhanced activity against pancreatic cancer cell lines.

A family of phosphamide-containing diphenylpyrimidine analogues (PA-DPPYs) were synthesized as potent focal adhesion kinase (FAK) inhibitors. The PA-DPPY derivatives could significantly inhibit the FAK enzymatic activity at concentrations lower than 10.69 nM. Among them, compounds 7a and 7e were two of the most active FAK inhibitors, possessing IC50 values of 4.25 nM and 4.65 nM, respectively. In particular, compound 7e also displayed strong activity against AsPC cell line, with an IC50 of 1.66 µM, but show low activity against the normal HPDE6-C7 cells (IC50 > 20 µM), indicating its low cell cytotoxicity. Additionally, flow cytometry analysis showed that after treatment with 7e (8 µM, 72 h), both AsPC and Panc cells growth were almost totally inhibited, with a cell viability rate of 16.8% and 18.1%, respectively. Overall, compound 7e may be served as a valuable FAK inhibitor for the treatment of pancreatic cancer.

Relative Susceptibility of Phyllocnistis citrella (Lepidoptera: Gracillariidae) to Commonly Used Insecticides in Maharashtra, India.

Foliar application of insecticides has been the most commonly followed practice to manage Phyllocnistis citrella Stainton in nurseries and flush leaves in citrus groves. Leaf dip bioassays were conducted against insecticides, viz., acephate 75SP, dimethoate 30EC, abamectin 1.9EC, fenvalerate 20EC, imidacloprid 17.8SL, and thiamethoxam 25WG, and were tested against P. citrella larvae for their susceptibility. Among six insecticides tested on second-instar P. citrella larvae collected from Nagpur mandarin/acid lime cultivars during 2013-2016, abamectin was the most toxic insecticide for the initial year (LC50 values ranged from 20.99 to 49.00 ppm), while dimethoate (LC50 of 36.57-160.95 ppm) and thiamethoxam (39.90-71.96 ppm) were consistently effective against P. citrella larvae for the rest of the period. Resistance ratio (RR) values calculated based on the baseline susceptible culture, viz., abamectin (1.24-2.33), acephate (1.03-2.31), fenvalerate (1.54-3.45), dimethoate(1.28-5.63), imidacloprid (1.29-8.64), and thiamethoxam (1.05-1.80), indicated that the current RR values were in low levels (RR < 10).

Selection, Realized Heritability, and Fitness Cost Associated With Dimethoate Resistance in a Field Population of Culex quinquefasciatus (Diptera: Culicidae).

Mosquitoes are known to be vectors of numerous diseases leading to human morbidity and mortality at large scale in the world. Insecticide resistance has become a serious concern in controlling the insect vectors of public health importance. Dimethoate is an organophosphate insecticide used to control different insect pests including mosquitoes. Biological parameters of susceptible, unselected, and dimethoate-selected strains of Culex quinquefasciatus Say were studied in the laboratory to recognize resistance development potential and associated fitness cost. The dimethoate-selected strain showed 66.48-fold resistance to dimethoate compared with the susceptible strain after three continuous selections of generations. Realized heritability estimates of dimethoate resistance in Cx. quinquefasciatus yielded a value of 0.19. In dimethoate-selected strain, the biological traits including larval weight, survival from first instar to pupae, fecundity, number of next-generation larvae, relative fitness, net reproductive rate, intrinsic rate of natural increase, and biotic potential were significantly reduced as compared with the unselected strain. However, adult longevity, mean relative growth rate, weight of egg raft, female ratio, pupal duration, and emergence rate of the dimethoate-selected strain did not differ significantly compared with that of the unselected strain. This study provides useful information to devise retrospective management strategy for dimethoate resistance in Cx. quinquefasciatus.

In vitro test systems supporting the development of improved pest control methods: a case study with chemical mixtures and bivalve biofoulers.

Using the bivalve macrofouler Corbicula fluminea, the suitability of in vitro testing as a stepping stone towards the improvement of control methods based on chemical mixtures was addressed in this study. In vitro cholinesterase (ChE) activity inhibition following single exposure of C. fluminea tissue to four model chemicals (the organophosphates dimethoate and dichlorvos, copper and sodium dodecyl phosphate [SDS]) was first assessed. Consequently, mixtures of dimethoate with copper and dichlorvos with SDS were tested and modelled; mixtures with ChE revealed synergistic interactions for both chemical pairs. These synergic combinations were subsequently validated in vivo and the increased control potential of these selected combinations was verified, with gains of up to 50% in C. fluminea mortality relative to corresponding single chemical treatments. Such consistency supports the suitability of using time- and cost-effective surrogate testing platforms to assist the development of biofouling control strategies incorporating mixtures.

Effect of Dimethoate on the Activity of Hepatic CYP450 Based on Pharmacokinetics of Probe Drugs.

BACKGROUND: Dimethoate (DM), one of the most widely used systemic organophosphate insecticide, has been reported to exert toxic effects after long-time subchronic exposure. This study aims at investigating the toxic effect of DM on liver after repeated administration of low doses of DM in rats. METHODS: Twenty Sprague-Dawley rats were randomly divided into the control group (n = 10) and the DM group (n = 10). After 2 weeks' exposure to DM at low dosage (5 mg/kg), biochemical parameters of hepatic functions were measured, histology and CYP450 expressed in liver was detected. The activities of CYP1A2, CYP2C11, CYP2D1, and CYP3A2 were evaluated by the Cocktail method. RESULTS: The level of AChE (acetylcholinesterase) was significantly decreased, hepatic functions were damaged and the mRNA level of CYP2D1 was significantly increased in the DM group (p < 0.05). The pharmacokinetics of probe drug revealed AUC(0-t), AUC(0-∞), t1/2 and Cmax of metoprolol was shorten in the DM group (p < 0.05). However, there were no statistical differences in MRT, t1/2, CL and Tmax for phenacetin, tolbutamide and midazolam. CONCLUSIONS: A low dosage of DM could induce the activity of CYP2D1 in liver and increase the metabolism of metoprolol when exposed for 2 weeks.

Study the effect of insecticide dimethoate on photosynthetic pigments and photosynthetic activity of pigeon pea: Laser-induced chlorophyll fluorescence spectroscopy.

Pigeon pea is one of the most important legume crops in India and dimethoate is a widely used insecticide in various crop plants. We studied the effect of dimethoate on growth and photosynthetic activity of pigeon pea plants over a short and long term exposure. Plant growth parameters, photosynthetic pigment content and chlorophyll fluorescence response of pigeon pea (Cajanus cajan L.) plants treated with various concentrations of the insecticide dimethoate (10, 20, 40 and 80 ppm) have been compared for 30 days at regular intervals of 10 days each. Laser induced chlorophyll fluorescence spectra and fluorescence-induction kinetics (FIK) curve of dimethoate treated pigeon pea plants were recorded after 10, 20 and 30 days of treatment. Fluorescence intensity ratio at the two fluorescence maxima (F685/F730) was calculated by evaluating curve-fitted parameters. The variable chlorophyll fluorescence decrease ratio (Rfd) was determined from the FIK curves. Our study revealed that after 10 days of treatment, 10 ppm of dimethoate showed stimulatory response whereas 20, 40 and 80 ppm of dimethoate showed inhibitory response for growth and photosynthetic activity of pigeon pea plants, but after 20 and 30 days of treatment all the tested concentrations of dimethoate became inhibitory. This study clearly shows that dimethoate is highly toxic to the pigeon pea plant, even at very low concentration (10 ppm), if used for a prolonged duration. Our study may thus be helpful in determining the optimal dose of dimethoate in agricultural practices.

Oral delivery mediated RNA interference of a carboxylesterase gene results in reduced resistance to organophosphorus insecticides in the cotton Aphid, Aphis gossypii Glover.

BACKGROUND: RNA interference (RNAi) is an effective tool to examine the function of individual genes. Carboxylesterases (CarE, EC 3.1.1.1) are known to play significant roles in the metabolism of xenobiotic compounds in many insect species. Previous studies in our laboratory found that CarE expression was up-regulated in Aphis gossypii (Glover) (Hemiptera: Aphididae) adults of both omethoate and malathion resistant strains, indicating the potential involvement of CarE in organophosphorus (OP) insecticide resistance. Functional analysis (RNAi) is therefore warranted to investigate the role of CarE in A. gossypii to OPs resistance. RESULT: CarE expression in omethoate resistant individuals of Aphis gossypii was dramatically suppressed following ingestion of dsRNA-CarE. The highest knockdown efficiency (33%) was observed at 72 h after feeding when dsRNA-CarE concentration was 100 ng/µL. The CarE activities from the CarE knockdown aphids were consistent with the correspondingly significant reduction in CarE expression. The CarE activity in the individuals of control aphids was concentrated in the range of 650-900 mOD/per/min, while in the individuals of dsRNA-CarE-fed aphids, the CarE activity was concentrated in the range of 500-800 mOD/per/min. In vitro inhibition experiments also demonstrated that total CarE activity in the CarE knockdown aphids decreased significantly as compared to control aphids. Bioassay results of aphids fed dsRNA-CarE indicated that suppression of CarE expression increased susceptibility to omethoate in individuals of the resistant aphid strains. CONCLUSION: The results of this study not only suggest that ingestion of dsRNA through artificial diet could be exploited for functional genomic studies in cotton aphids, but also indicate that CarE can be considered as a major target of organophosphorus insecticide (OPs) resistance in A. gossypii. Further, our results suggest that the CarE would be a propitious target for OPs resistant aphid control, and insect-resistant transgenic plants may be obtained through plant RNAi-mediated silencing of insect CarE expression.

Additive effects of predator cues and dimethoate on different levels of biological organisation in the non-biting midge Chironomus riparius.

The combined effects of a pesticide and predation risk on sublethal endpoints in the midge Chironomus riparius were investigated using a combination of predator-release kairomones from common carp (Cyprinus carpio) and alarm substances from conspecifics together with the pesticide dimethoate. Midge larvae were exposed for 30 days to three sublethal dimethoate concentrations (0.01, 0.1 and 0.25 mg L(-1)) in the presence or absence of predator cues. Sublethal endpoints were analysed at different levels of biological organisation. Available energy reserves, enzyme biomarkers, feeding rate and life history endpoints were investigated. Three endpoints were significantly affected by the two highest dimethoate concentrations, i.e. AChE activity, age at emergence and emergence success, with a significant decrease in response after exposure to 0.25, 0.1 and 0.01 mg L(-1) dimethoate, respectively. Four sublethal endpoints were significantly affected by predator stress: Total protein content, GST activity and biomass decreased only in the presence of the predation risk, while AChE activity further decreased significantly in the presence of predation cues and effects on AChE of combined exposure were additive. From this study we can conclude that sublethal life history characteristics should be included in ecotoxicity testing as well as natural environmental stressors such as predator stress, which might act additively with pollutants on fitness related endpoints.

Mating Disruption or Mass Trapping, Compared With Chemical Insecticides, for Suppression of Chilo suppressalis (Lepidoptera: Crambidae) in Northeastern China.

Asiatic rice borer, Chilo suppressalis (Walker), larvae cause extensive crop losses worldwide. Because chemical control is problematic, and sex pheromone applications are a valuable management tactic in China, judicious timing of a minimal density of pheromone dispensers is important in developing a cost-effective C. suppressalis IPM program. During June-October in 2011, 20, 30, 40, and 50 dispensers per hectare for mass trapping, and 200, 300, 400, and 500 dispensers per hectare for mating disruption were placed in northeastern China rice fields. Based on those results, only the two highest mass trapping densities were used in 2012-2013. The 40, 50, and 500 dispenser densities reduced egg masses to <2.0 per 100 tillers, compared with >9.5 in the insecticide-treated plots in 2011-2013. The reduced oviposition resulted in >85% reduction of larval damage, which was comparable with the currently used insecticides, dimethoate and deltamethrin (0.35 kg/ha), which gave no egg reduction, but ≍80 and 89% reduction in larval damage. The 40 and 500 densities are recommended to Chinese rice farmers for mass trapping and mating disruption programs, respectively.

Dimethoate induces kidney dysfunction, disrupts membrane-bound ATPases and confers cytotoxicity through DNA damage. Protective effects of vitamin E and selenium.

Dimethoate (DM) is an organophosphate insecticide widely used in agriculture and industry and has toxic effects on non-target organisms especially mammalian. However, we still know little about DM-induced kidney injury and its alleviation by natural antioxidants. In the present study, selenium (Se), vitamin E, DM, Se+DM, vitamin E+DM, Se+vitamin E+DM were given to adult rats for 4 weeks. Plasma creatinine and uric acid, kidney MDA, PC, H2O2 and AOPP levels were higher, while Na(+)-K(+)-ATPase and LDH values were lower in the DM group than those of controls. A smear without ladder formation on agarose gel was shown in the DM group, indicating random DNA degradation and DM-induced genotoxicity. A decrease in kidney GSH, NPSH and plasma urea levels and an increase in GPx, SOD and catalase activities were observed in the DM group when compared to those of controls. Plasma cystatin C levels increased, indicating a decrease in glomerular filtration rate. When Se or vitamin E was added through diet, the biochemical parameters cited above were partially restored in Se+DM and vitamin E+DM than DM group. The joint effect of Se and vitamin E was more powerful against DM-induced oxidative stress and kidney dysfunction. The changes in biochemical parameters were substantiated by histological data. In conclusion, our results indicated a possible mechanism of DM-induced nephrotoxicity, where renal genotoxicity was noted, membrane-bound ATPases and plasma biomarkers were disturbed. Se and vitamin E ameliorated the toxic effects of this pesticide in renal tissue suggesting their role as potential antioxidants.

Comparative toxicities and synergism of apple orchard pesticides to Apis mellifera (L.) and Osmia cornifrons (Radoszkowski).

The topical toxicities of five commercial grade pesticides commonly sprayed in apple orchards were estimated on adult worker honey bees, Apis mellifera (L.) (Hymenoptera: Apidae) and Japanese orchard bees, Osmia cornifrons (Radoszkowski) (Hymenoptera: Megachilidae). The pesticides were acetamiprid (Assail 30SG), λ-cyhalothrin (Warrior II), dimethoate (Dimethoate 4EC), phosmet (Imidan 70W), and imidacloprid (Provado 1.6F). At least 5 doses of each chemical, diluted in distilled water, were applied to freshly-eclosed adult bees. Mortality was assessed after 48 hr. Dose-mortality regressions were analyzed by probit analysis to test the hypotheses of parallelism and equality by likelihood ratio tests. For A. mellifera, the decreasing order of toxicity at LD50 was imidacloprid, λ-cyhalothrin, dimethoate, phosmet, and acetamiprid. For O. cornifrons, the decreasing order of toxicity at LD50 was dimethoate, λ-cyhalothrin, imidacloprid, acetamiprid, and phosmet. Interaction of imidacloprid or acetamiprid with the fungicide fenbuconazole (Indar 2F) was also tested in a 1∶1 proportion for each species. Estimates of response parameters for each mixture component applied to each species were compared with dose-response data for each mixture in statistical tests of the hypothesis of independent joint action. For each mixture, the interaction of fenbuconazole (a material non-toxic to both species) was significant and positive along the entire line for the pesticide. Our results clearly show that responses of A. mellifera cannot be extrapolated to responses of O.cornifrons, and that synergism of neonicotinoid insecticides and fungicides occurs using formulated product in mixtures as they are commonly applied in apple orchards.

Alteration of leaf metabolism in Bt-transgenic rice (Oryza sativa L.) and its wild type under insecticide stress.

Insecticide is always used to control the damage from pests, while the potential influence on plants is rarely known. Time-course metabolic changes of wild and Bacillus thuringiensis (Bt) transgenic rice (Oryza sativa L.) plants after insecticide treatment were investigated by using gas chromatography-mass spectrometry (GC-MS). A combined statistical strategy of 2-way ANOVA and multivariate analyses (principal component analysis and hierarchal cluster analysis) was performed to find the stress-associated effects. The results reveal that a wide range of metabolites were dynamically varied in both varieties as a response to insecticide, in multiple metabolic pathways, such as biosynthesis and metabolism of amino acids, carbohydrates, fatty acids, TCA cycle, and the shikimate/phenylpropanoid pathway, and most of the changes were correlated with the exposure time and dependent on the variety. A set of stress defenses were activated, including phytohormone signaling pathway, antioxidant defense system, shikimate-mediated secondary metabolism, and so on. In particular, insecticide led to much stronger regulations of signaling molecules (salicylate and the precursor of jasmonate) and antioxidants (α-tocopherol and dehydroascorbate/ascorbate) in Bt-transgenic variety at the early stage. Our results demonstrated that the Bt-transgenic rice had a more acute and drastic response to insecticide stress than its non-transgenic counterpart in antioxidant system and signaling regulation.