Efficacy of alpha-cypermethrin and thiamethoxam against Trogoderma granarium Everts (Coleoptera: Dermestidae) and Tenebrio molitor L. (Coleoptera: Tenebrionidae) on concrete

Laboratory bioassays were conducted to evaluate alpha-cypermethrin and thiamethoxam for the control of adults, small larvae and large larvae of the khapra beetle Trogoderma granarium, and the yellow mealworm beetle Tenebrio molitor, on concrete. Factors such as dose (0.025 and 0.1 mg alpha-cypermethrin or thiamethoxam/cm²), exposure interval (1, 3 and 7 d), and formulation (alpha-cypermethrin SC and thiamethoxam WG) were evaluated. Apart from immediate assessment at end of exposure, an assessment of delayed mortality was performed with the survivors of the 7-d exposure by removing them from the treated substrate and keeping them on untreated surfaces for 7 more days. After the 7-d exposure, more T. granarium adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. Small larvae were generally less susceptible than adults. After 7 d, small larval mortality reached 64.4% for alpha-cypermethrin, while for thiamethoxam it was <6%. Large T. granarium larvae were more tolerant than the small ones. Delayed mortality of T. granarium adults was generally high for both insecticides and doses, and ranged between 43.3 and 63.3% of those that were still alive immediately after the 7-d treatment. For both larval categories, delayed mortality was higher for larvae that had been previously exposed to alpha-cypermethrin, than with thiamethoxam. For T. molitor, after the 7-d exposure, significantly more adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. For small larvae mortality was 38.9% at the lowest thiamethoxam dose, but in the other cases ranged between 88.9 and 95.6%. In the case of large larvae, the overall mortality was low in all tested combinations. Regarding delayed mortality of this species, it remained at low levels, for both adults and small larvae. Our results indicate that T. molitor was more susceptible than T. granarium in both insecticides tested, but alpha-cypermethrin was more effective than thiamethoxam.     

A test house study of pesticides and pesticide degradation products following an indoor application

Preexisting pesticide degradates are a concern for pesticide biomonitoring studies as exposure to them may result in overestimation of pesticide exposure. The purpose of this research was to determine whether there was significant formation and movement, of pesticide degradates over a 5‐week period in a controlled indoor setting after insecticide application. Movement of the pesticides during the study was also evaluated. In a simulated crack and crevice application, commercially available formulations of fipronil, propoxur, cis/trans‐permethrin, and cypermethrin were applied to a series of wooden slats affixed to the wall in one room of an unoccupied test house. Floor surface samples were collected through 35 days post‐application. Concentrations of the pesticides and the following degradates were determined: 2‐iso‐propoxyphenol, cis/trans 3‐(2,2‐dichlorovinyl)‐3‐3‐dimethyl‐(1‐cyclopropane) carboxylic acid, 3‐phenoxybenzoic acid, fipronil sulfone, fipronil sulfide, and fipronil desulfinyl. Deltamethrin, which had never been applied, and chlorpyrifos, which had been applied several years earlier, and their degradation products, cis‐3‐(2,2‐dibromovinyl)‐2,2‐dimethylcyclopropane‐1‐carboxylic acid, and, 3,5,6‐trichloro‐2‐pyridinol, respectively, were also measured. Propoxur was the only insecticide with mass movement away from the application site. There was no measurable formation or movement of the degradates. However, all degradates were present at low levels in the formulated product. These results indicate longitudinal repetitive sampling of indoor degradate levels during short‐term studies, is unnecessary.     

Analysis of polychlorinated biphenyls, pyrethroid insecticides and fragrances in human milk using a laminar cup liner in the GC injector

 Since 1970 the State Laboratory of Basle City has been periodically analyzing human milk from the region (the latest in 1998/99) as a bioindicator for the environmental load of organochlorine pesticides [1, 2]. The analysis of human milk is very complex including several clean-up steps and is therefore time consuming. The focus is mainly on organochlorine pesticides, polychlorinated biphenyls (PCB), and nitro-musk compounds; analytes which are easily detectable with gas chromatography and electron capture detection (ECD). Our aim was to minimize the clean-up steps for the analysis of ECD sensitive substances. Furthermore, analytes insensitive to EC detection that require MS detection, such as polycyclic musk substitutes, were of interest. With the help of a specially designed GC liner in the vaporizing injector of the gas chromatograph, the laminar cup liner, we have considerably reduced the time and effort in the sample preparation. With the described clean-up procedure we analyzed 53 human milk samples from the region of Basle for PCB, pyrethrins, and pyrethroid insecticides and fragrances (nitro-musk compounds and polycyclic musk substitutes). While PCB showed a general downward trend in mean concentrations since 1980, residues of the polycyclic musk substitutes galaxolide and tonalide were detectable in almost every sample (e.g., 73 μg/kg fat of HHCB, 74 μg/kg fat of AHTN). Pyrethrins and pyrethroid insecticides were detected only at low concentrations between 0.03 and 0.46 mg/kg fat. Received: 28 September 1999 / Revised version: 2 May 2000     

Colorimetric determination of pyrethroids based on core-shell Ag@SiO2 nanoparticles

A highly sensitive colorimetric probe for pyrethroids based on surface amine-modified silver-silica core-shell nanoparticles (Ag@SiO₂-NH₂ NPs) was described here. The Ag@SiO₂-NH₂ NPs were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and ultraviolet-visible spectroscopy (UV-vis). The Ag@SiO₂-NH₂ NPs provided a simple and rapid strategy to detect pyrethroids and allowed a rapid quantitative assay of lambda-cyhalothrin (LC) down to the concentration of 1.0 × 10⁻⁶ M, which was below the European Union maximum residue limit (MRL) of 1 mg/kg. The possible mechanism that Ag@SiO₂-NH₂ NPs can bind well with LC through hydrogen bond interactions was discussed.     

Determination of Pyrethroid Insecticides in Crude and Canned Vegetable Samples by Supercritical Fluid Chromatography

A supercritical fluid chromatography method for the determination of seven pyrethroid insecticides (allethrin, resmethrin, phenothrin, permethrin, tetramethrin, cypermethrin, deltamethrin) and one of their common metabolites, phenoxybenzyl alcohol, in whole and peeled potatoes and mixed vegetables was developed. The efficiencies of the two extraction techniques, supercritical fluid extraction and microwave-assisted extraction, for the extraction of pyrethroids from vegetable samples were also compared. The retention times of various pyrethroids ranged from 8.4 to 22.9 min, while all of the peaks were well-resolved and distinctly identified. The limits of detection of pyrethroid insecticides ranged between 0.31 and 0.54 ppm, whereas the limits of detection of phenoxybenzyl alcohol was 0.62 ppm. The recoveries of pyrethroid insecticides from whole potatoes, peeled potatoes, and mixed vegetables ranged as 93.83–99.8%, 92.3–105.8%, and 93.67–102.7%, respectively, with the use of supercritical fluid extraction. The corresponding recovery ranges while using microwave-assisted extraction were 94.2–102%, 96.6–101.2%, and 96–103.2%. These findings suggested that supercritical fluid chromatography was a sensitive and rapid technique for the analysis of pyrethroids in complex matrices, such as vegetables, fruits, and other agricultural products.     

The Behaviour of Pyrethroids Indoors: A Model Study

Abstract Pest control agents containing three different formulations of the pyrethroids permethrin and deltamethrin and/or pyrethrines and the synergist piperonyl butoxide were applied in a model house simulating indoor pest control. The concentrations of the agents were monitored in the gas phase, on suspended particles, house dust and on furniture surfaces over a period of 24 months. Permethrin and deltamethrin were detected only in the gas phase immediately after application of the agents. High concentrations of deltamethrin (?2 μg/m³) and permethrin (?40 μg/m³) were found on suspended particles directly after application. This concentration decreased rapidly within two days (deltamethrin ?5 ng/m³, permethrin ?100 ng/m³) but much more slowly during the following 24 months. In house dust, deltamethrin was observed with initial concentrations of ?50 mg/kg and permethrin at initial concentrations of 150–800 mg/ kg (depending on the formulation). The concentration levels of both compounds decreased by a factor of ?10 within the first 12 months but remained almost constant thereafter. Decontamination of the rooms using a commercially available household cleanser has little effect on the pyrethroid concentration found on suspended particles, but leads to a substantial reduction of the contamination level in house dust and on furniture surfaces.     

全自动加压溶剂萃取仪在测定蔬果中拟除虫菊酯的应用

本文采用全自动加压溶剂萃取仪对蔬果中拟除虫菊酯农药残留进行前处理分析,对部分蔬果进行了添加回收率实验,并与传统的农药残留预处理方法进行了比较,5种拟除虫菊酯采用全自动加压溶剂萃取仪进行分析,添加回收率达到80-110%,明显优于传统方法。结果表明,该方法简单、快速、自动化程度高,对实验室操作人员危害小,适合于蔬果中多种拟除虫菊酯农药残留的测定。     

Monitoring of pesticide residues in Egyptian fruits and vegetables during 1997

A total of 2318 domestic samples of different types of fruits and vegetables were collected from eight Egyptian local markets in six different regions of the country. All samples were examined for residues of 54 pesticides, including organophosphorus, organonitrogen, organohalogen and certain pyrethroides. However, dithiocarbamates were analysed in only 318 samples. Overall, 81.5% of the samples had no detectable pesticide residues. Of the contaminated samples, 18.5% contained detectable residues and 1.9% exceeded their maximum residue limits (MRLs). Root and leafy vegetables showed the lowest contamination rates (1.9 and 4.7%, respectively), slightly exceeding the MRLs in leafy vegetables. However, fruit samples showed a slightly higher proportion of contamination than vegetables (29 and 14.3%, respectively). Fruit also exhibited a higher level of violation than vegetables (2.3 and 1.9%, respectively). The contamination and violation rates were lower than the percentages recorded in previous years' monitoring studies. Dicofol and dimethoate were the most frequently occurring pesticide residues at 5.1 and 5.0%, respectively. Dimethoate showed higher violation levels (0.69%). However, dicofol showed a slight violation rate (0.09%) which indicates good agricultural practices for dicofol use. Dithiocarbamates residues were found in 21 of the 318 samples analysed, which when expressed as a percentage contamination was 6.6%, and only one sample exceeded the MRL.     

Control failure and insecticides resistance in populations of Rhyzopertha dominica (Coleoptera: Bostrichidae) from Colombia

The lesser grain borer Rhyzopertha dominica is a serious pest that causes significant economic damages in stored grains. The presence of this pest is mainly controlled using a small number of insecticides increasing risks of compromising the control efficacy due to the selection of resistant populations. Here, the control failure and potential resistance to pyrethroid and organophosphate insecticides frequently used for the control of R. dominica in Colombia were assessed. Concentration–mortality bioassays with synergized and unsynergized insecticides were used to assess potential metabolic-based pyrethroids resistance mechanisms. Based on the field recommended doses, the results revealed that while the pirimiphos-methyl is still efficient against R. dominica, both type I (i.e., bifenthrin) and type II (i.e., deltamethrin) pyrethroids presented control failure and their insecticidal activity was compromised. Although no differences in susceptibilities between the populations were found for the bifenthrin insecticide, the LC₅₀s of Ibagué (1.83 μl/gr of grains) and El Espinal (1.67 μl/gr of grains) populations were higher than the recommended rate. Furthermore, significant differences in susceptibility to deltamethrin resulted in resistance ratios RR₅₀ > 32-fold and RR₉₅ > 188-fold between the least (El Espinal) and the most (Ibagué) susceptible populations. Moreover, when synergized, the toxicity of deltamethrin was enhanced but resistance ratios kept at high levels (RR₅₀ > 11-fold and RR₉₅ > 40-fold) indicating possible existence of simultaneous metabolic and altered action-site mechanisms of resistance to pyrethroids in Colombian populations. Our results highlight the urgent need for nationwide monitoring of insecticides control failure and resistance in stored pests for better management schemes.     

Insecticidal and residual effect of three pyrethroids against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on stored wheat

Laboratory tests were conducted to assess the use of the pyrethroids, deltamethrin, beta-cyfluthrin and alpha-cypermethrin at the rates of 0.125 and 0.25 ppm, as grain protectants in stored wheat against the rice weevil, Sitophilus oryzae (L.). For this purpose, clean untreated wheat was sprayed with these insecticides and stored for 6 months. During this period, four bioassays were carried out, in order to evaluate the residual efficacy of each pyrethroid. In each bioassay, treated wheat was infested with S. oryzae adults, and dead insects were counted after 1, 2 and 7 d of exposure. In addition, S. oryzae progeny production was estimated on each bioassay, until the production of the F₄ generation. The results indicated that deltamethrin and beta-cyfluthrin, both at 0.25 ppm, were significantly more efficient than the other treatments. Efficacy was notably higher after 7 d of exposure, than after 1 and 2 d. At the same exposure level, 1, 2 and 3.5 months after treatment, at 0.25 ppm, mortality for deltamethrin was approximately 89%, 92% and 86%, respectively, while the corresponding percentages for beta-cyfluthrin were 97%, 83% and 62%, and for alpha-cypermethrin 50%, 49% and 33%. However, at the rate of 0.125 ppm, mortality was ?58% in all cases. In all treatments appearance of F₁-F₄ generations was observed, with the exception of both deltamethrin and beta-cyfluthrin at 0.25 ppm, where only a few F₁ adults were noted, without the production of subsequent generations.