Aquatic organisms and pyrethroids

Under laboratory conditions, in water without particulate matter, pyrethroid insecticides have a high toxicity to fish and some aquatic invertebrates. The pyrethroids are of very low water solubility/high lipophilicity, and therefore are rapidly and strongly adsorbed to particulate material. In the adsorbed state their bioavailability to aquatic organisms is greatly reduced. Consequently, under field conditions the aquatic impact of these insecticides is likely to be much less than might be predicted by laboratory acute or chronic toxicity test data. Over the past 10 years a large number of aquatic field studies have been carried out with pyrethroids, in natural farm ponds, streams and lakes and also in mesocosms (experimental ponds and enclosures). Recent investigations, to meet the requirements of the United States Environmental Protection Agency, have been most extensive. These studies, done in replicated experimental ponds of at least 0-04 ha, each require at least 20 man-years of effort. Following agricultural applications of the pyrethroid insecticides, spray-drift or run-off may cause minor effects upon some aquatic organisms. Algae, microorganisms, annelids, gastropods and fish are all unaffected, but some impact may occur upon certain zoo-plankton and on aquatic stages of insects. However, with products for which realistic field studies have been reported, the effects are mostly transient and are unlikely to cause adverse changes in the populations or productivity of aquatic ecosystems.     

Natural products that have been used commercially as crop protection agents

Many compounds derived from living organisms have found a use in crop protection. These compounds have formed the basis of chemical synthesis programmes to derive new chemical products; they have been used to identify new biochemical modes of action that can be exploited by industry-led discovery programmes; some have been used as starting materials for semi-synthetic derivatives; and many have been used or continue to be used directly as crop protection agents. This review examines only those compounds derived from living organisms that are currently used as pesticides. Plant growth regulators and semiochemicals have been excluded from the review, as have living organisms that exert their effects by the production of biologically active secondary metabolites.     

农用微生物杀菌剂剂型研究进展

农用微生物杀菌剂的主要剂型有粉剂(DP)、可湿性粉剂(WP)、颗粒剂(GR)、水分散粒剂(WG)和悬浮剂(SC)等。我国现有的农用微生物杀菌剂剂型种类较为单一,主要为可湿性粉剂,未来应加强其他剂型如水分散粒剂和悬浮剂等的研究开发。生防菌的活菌数、制剂加工和贮存条件以及田间环境因素等对农用微生物杀菌剂的防效均有很大影响,科学合理地评价这些影响,并研究其形成原因和内在规律,对农用微生物杀菌剂的深入研究开发具有重要意义。文章从剂型种类、性质、质量控制以及生产条件、贮存条件和田间环境条件对制剂性质与防效的影响等方面,对农用微生物杀菌剂剂型的研究现状和存在问题进行了详细的综述,并分析了其未来发展趋势。     

Mites for the control of pests in protected cultivation

The production of crops under protected conditions is increasing worldwide. Owing to growing consumer demands for healthy and green produce, and intensifying pesticide resistance, non-chemical solutions--foremost among which is biological control--are being sought. The authors review recent advances related to the application of predatory mites for the control of greenhouse pests, and discuss interactions among acarine biocontrol agents (ABAs) and the effects of crop plants and new technologies on ABAs, such as artificial lighting, elevated carbon dioxide levels and genetically modified organisms. This is followed by a discussion of the problems associated with the search for and use of new ABAs, including management, the benefits of modelling and avenues of future research.     

Integrating soil conservation practices and glyphosate-resistant crops: impacts on soil

BACKGROUND: Conservation practices often associated with glyphosate-resistant crops, e.g. limited tillage and crop cover, improve soil conditions, but only limited research has evaluated their effects on soil in combination with glyphosate-resistant crops. It is assumed that conservation practices have similar benefits to soil whether or not glyphosate-resistant crops are used. This paper reviews the impact on soil of conservation practices and glyphosate-resistant crops, and presents data from a Mississippi field trial comparing glyphosate-resistant and non-glyphosate-resistant maize (Zea mays L.) and cotton (Gossypium hirsutum L.) under limited tillage management. RESULTS: Results from the reduced-tillage study indicate differences in soil biological and chemical properties owing to glyphosate-resistant crops. Under continuous glyphosate-resistant maize, soils maintained greater soil organic carbon and nitrogen as compared with continuous non-glyphosate-resistant maize, but no differences were measured in continuous cotton or in cotton rotated with maize. Soil microbial community structure based on total fatty acid methyl ester analysis indicated a significant effect of glyphosate-resistant crop following 5 years of continuous glyphosate-resistant crop as compared with the non-glyphosate-resistant crop system. Results from this study, as well as the literature review, indicate differences attributable to the interaction of conservation practices and glyphosate-resistant crop, but many are transient and benign for the soil ecosystem. CONCLUSIONS: Glyphosate use may result in minor effects on soil biological/chemical properties. However, enhanced organic carbon and plant residues in surface soils under conservation practices may buffer potential effects of glyphosate. Long-term field research established under various cropping systems and ecological regions is needed for critical assessment of glyphosate-resistant crop and conservation practice interactions.     

Safe nanotechnologies for increasing the effectiveness of environmentally friendly natural agrochemicals

Natural compounds and living organisms continue to play a limited role in crop protection, and few of them have reached the market, despite their attractiveness and the efforts made in research. Very often these products have negative characteristics compared to synthetic compounds, e.g., higher costs of production, lower effectiveness, lack of persistence, and inability to reach and penetrate the target plant. Conversely, nanotechnologies are having an enormous impact on all human activities, including agriculture, even if the production of some nanomaterials is not environmentally friendly or could have adverse effects on agriculture and the environment. Thus, certain nanomaterials could facilitate the development of formulated natural pesticides, making them more effective and more environmentally friendly. Nanoformulations can improve efficacy, reduce effective doses, and increase shelf‐life and persistence. Such controlled‐release products can improve delivery to the target pest. This review considers certain available nanomaterials and nanotechnologies for use in agriculture, discussing their properties and the feasibility of their use in sustainable crop protection, in particular, in improving the effectiveness of natural bio‐based agrochemicals. © 2019 Society of Chemical Industry     

An ecological risk assessment for spinosad use on cotton

Spinosad is a reduced-risk insecticide with a novel mode of action that provides an alternative to older classes of insecticides such as organophosphates, carbamates and pyrethroids. A comprehensive ecological risk assessment for spinosad use in US cotton crops is presented within a framework of tiered levels of refinement following the guidelines of the US EPA for ecological risk assessments. Toxicity information for a variety of species is documented and utilized, environmental concentrations estimated, and risk characterizations in the form of risk quotients are quantified. Results indicate that spinosad use in cotton does not exceed the most conservative Tier I levels of concern (LOC) values for groundwater, mammals and birds or acute risk to aquatic organisms. Use of very conservative Tier I screening methods resulted in exceeding LOC values for chronic exposure for some aquatic organisms, thus prompting further refinement. When the exposure prediction was refined using less conservative, Tier II mechanistic environmental fate transport models to predict offsite transport and environmental concentrations, chronic risk was not predicted for these species. Spinosad is acutely toxic to bees under laboratory conditions, but toxicity of residue studies and field studies indicate that under actual use conditions the impact on bees is minimal.     

拟除虫菊酯类农药的免疫毒性研究进展

拟除虫菊酯类杀虫剂因其高效、对哺乳动物低毒和易降解等特性已被广泛使用,目前对其生态毒理学的研究主要集中在神经及内分泌干扰、发育和生殖毒性方面,而关于其免疫毒性的研究也越来越受到了关注。文章对拟除虫菊酯类农药的免疫毒性及其分子机制研究进展进行了总结,主要从免疫器官、免疫细胞、免疫分子和免疫功能等方面综述了此类杀虫剂对不同生物的免疫毒性及其可能的分子机制,同时总结了拟除虫菊酯类杀虫剂暴露与免疫相关疾病发生的关联,以期为拟除虫菊酯类农药免疫毒性的进一步探究提供参考。     

Differential susceptibilities to pyrethroids in field populations of Chilo suppressalis (Lepidoptera: Pyralidae)

To assess the feasibility of pyrethroids for rice insect control, we examined susceptibilities of six field populations of rice stem borer Chilo suppressalis (Walker) to 10 pyrethroids using the topical application method in laboratory in 2004 and 2005. Our results showed that the seven pyrethroids with high fish-toxicity (i.e., β-cyfluthrin, λ-cyhalothrin, β-cypermethrin, deltamethrin, S-fenvalerate, α-cypermethrin, and fenpropathrin) were more effective against C. suppressalis than the three compounds with low fish-toxicity (i.e., cycloprothrin, etofenprox, and silafluofen). The results also showed that all 10 of the pyrethroids were much more effective than methamidophos and monosultap for C. suppressalis control. In addition, we found that susceptibilities of some field populations of C. suppressalis to some high fish-toxicity pyrethroids were significantly reduced, and our results indicated that a Ruian (RA) field population showed a year-to-year variation in susceptibility to most tested pyrethroids between 2004 and 2005. Our data indicated that the tolerance levels increased dramatically in RA population, especially to β-cyfluthrin and deltamethrin. This study provided the first assessment of resistance to pyrethroids in field populations of C. suppressalis. In addition, a close correlation between resistance ratios to the 10 compounds and differences of the structures of these compounds was established in the RA05 population, which was resistant to most of the pyrethroids tested while it was still very susceptible to fenvalerate with no cross resistance. Finally, the feasibility and precaution were discussed in selecting pyrethroids as alternatives to replace high toxicity organophosphates for C. suppressalis control and insecticide resistance management.     

A critique of studies evaluating glyphosate effects on diseases associated with Fusarium spp.

With the large-scale adoption of glyphosate-resistant crops in North America, there are concerns that non-target microbial populations might be affected by increased frequency of glyphosate use. Stimulation of fungal species associated with crop diseases, including Fusarium spp., has been observed in laboratory and glasshouse experiments. Although field surveys in Saskatchewan detected positive associations between the incidence of Fusarium head blight and application of glyphosate formulations, few field experiments have been successful at demonstrating a stimulatory effect of glyphosate on crop diseases, including diseases associated with Fusarium spp. Taken at face value, there is little evidence from experimental field trials to support a causative link between glyphosate and crop diseases associated with Fusarium spp. However, we are concerned that the experimental field trials investigating links between glyphosate and Fusarium spp. are not representative of interactions that occur under actual farming conditions. In addition, inadequate consideration may have been given to microbial ecology during the design and maintenance of these experimental field trials. At this time, there is insufficient evidence to prove or disprove a link between glyphosate and crop diseases associated with Fusarium spp. and this area should receive high research priority, given the rapid and widespread increase in glyphosate use.     

Comparative acute toxicity of neonicotinoid and pyrethroid insecticides to non‐target crayfish (Procambarus clarkii) associated with rice–crayfish crop rotations

BACKGROUND: Most insecticides used to control rice water weevil (Lissorhoptrus oryzophilus Kuscel) infestations are pyrethroids. However, pyrethroids are highly toxic to non‐target crayfish associated with rice–crayfish crop rotations. One solution to the near‐exclusive reliance on pyrethroids in a rice–crayfish pest management program is to incorporate neonicotinoid insecticides, which are insect specific and effective against weevils but not extremely toxic to crayfish. This study aimed to take the first step to assess neonicotinoids as alternatives to pyrethroids in rice–crayfish crop rotations by measuring the acute toxicities of three candidate neonicotinoid insecticides, clothianidin, dinotefuran and thiamethoxam, to juvenile Procambarus clarkii (Girard) crayfish and comparing them with the acute toxicities of two currently used pyrethroid insecticides, lambda‐cyhalothrin and etofenprox. RESULTS: Neonicotinoid insecticides are at least 2–3 orders of magnitude less acutely toxic (96 h LC₅₀) than pyrethroids to juvenile Procambarid crayfish: lambda‐cyhalothrin (0.16 µg AI L^?1) = etofenprox (0.29 µg AI L^?1) ? clothianidin (59 µg AI L^?1) > thiamethoxam (967 µg AI L^?1) > dinotefuran (2032 µg AI L^?1). CONCLUSION: Neonicotinoid insecticides appear to be much less hazardous alternatives to pyrethroids in rice–crayfish crop rotations. Further field‐level neonicotinoid acute and chronic toxicity testing with crayfish is needed. Copyright © 2009 Society of Chemical Industry     

Development of resistance to pyrethroids in insects resistant to other insecticides

Resistance to pyrethroids in insects is rare, but its recent rapid development in the field suggests that this resistance may be facilitated by previous exposure to or by resistance to insecticides of unrelated groups. To test this houseflies of strain 49_r2b, originally resistant to dimethoate in the field, were selected eight times during ten generations with either pyrethrum extract or bioresmethrin with or without piperonyl butoxide or with dimethoate. Selecting with any of the pyrethroids led to resistance to these insecticides and in particular to pyrethrum/piperonyl butoxide. Selecting with pyrethrum/piperonyl butoxide resulted in strongest resistance to the pyrethroids tested, whereas selecting with bioresmethrin/piperonyl butoxide resulted in least resistance. These results show that dimethoate-resistant flies selected with pyrethroids can readily develop resistance to these insecticides, but development of resistance can be minimised by using bioresmethrin/piperonyl butoxide. The implications of these findings on the sequential use of insecticides are discussed.     

The crayfish stretch receptor organ: A useful model system for investigating the effects of neuroactive substances: I. The effect of DDT and pyrethroids

The crayfish stretch receptor organ is a useful model system for investigating the effects of neuroactive compounds on an invertebrate sensory cell. The receptor neuron is very sensitive to pyrethroids, DDT, and veratridine, and comparisons were made between the effects of α-cyano substituted pyrethroids (cypermethrin and deltamethrin) and pyrethroids without a cyano group (permethrin and bioallethrin). A comparison of the effects of pyrethroids on this single sensory cell with those recorded from the flight muscles of a whole insect (Lucilia sericata) indicates that the effects are similar in both preparations.     

Prediction of Pests,Diseases and Losses: Principles and Computer Applications1

Efficacy of plant protection is closely related to an appreciation of the seasonal development and population changes of harmful organisms. This necessitates national surveys on pest population dynamics and on the epiphytotics of plant diseases. From these surveys, regional forecasts can be produced to give advice to the farmers. This work needs highly sophisticated systems to cover both numerical and spatial aspects of pest situations. Thus, there is an urgent need to exploit computer applications in solving forecasting problems. However, the use of computers for forecasting the incidence of harmful organisms and losses is in its initial phase. At present, single pest and disease models prevail. Numerical aspects have been approached both empirically and experimentally. Empirical models, based on multiple regression analysis, are relatively simple and easy to use for various harmful organisms. However, simulation models of harmful organisms are expected to lead to much more reliable results, although, so far, little experience is available on their predictive powers in crop protection. Spatial aspects have been approached with a routine computer mapping technique, which seems to be an effective tool for recognizing and forecasting distribution trends, while loss predictions can be based on crop models, incorporating submodels forecasting the incidence of harmful organisms. The prospect for operational use, in forecasting, of the computer techniques mentioned is discussed.     

Management of insecticide resistance in Oriental fruit moth (Grapholita molesta; Lepidoptera: Tortricidae) populations from Ontario

The development of resistance in the Oriental fruit moth, Grapholita molesta (Busck) to organophosphorus (OP) insecticides (azinphos-methyl and phosmet) is a serious threat to the tender fruit industry in Ontario (50% crop losses in 1994). Resistance to carbamate insecticides and increased survival of field-collected moths at diagnostic concentrations of pyrethroids were widespread. As a result, four different treatment regimes were tested to manage resistance in G molesta, and the changes in resistance frequencies under each treatment regime were monitored from 1996 to 1999. The data indicated that the levels of resistance were significantly influenced by the various treatment regimes. The seasonal pattern of resistance was similar for all treatment regimes, in that resistance peaked in mid-season and declined in the late season. Levels of resistance in G molesta to OPs decreased from 55% to 14% and that to pyrethroids declined from 30% to 10% from 1996 to 1999 under a treatment regime consisting of endosulfan-organophosphate-pyrethroid rotation. Similarly, under a treatment regime implemented in commercial orchards (organophosphate-pyrethroid rotation), resistance to OP insecticides declined from 50% to 12% and resistance to pyrethroids evolved to around 16%. The overall data indicated that resistance was unstable; a strategy based on rotation of insecticides by class for each generation of G molesta was successful in managing resistance to both OP and pyrethroid insecticides. The rotational strategy has been widely adopted by growers and is applied to ca 85% of the acreage.     

Promotion of norepinephrine release and inhibition of calcium uptake by pyrethroids in rat brain synaptosomes

A series of 25 pyrethroids were assessed for their effects on Na⁺-dependent norepinephrine release and on Ca²⁺ uptake in vitro using a crude rat brain synaptosomal preparation. The most effective pyrethroids required a concentration of 3–10 μM to promote norepinephrine release. Plotting release data versus lipophilicity (as log P) for each compound resulted in a parabolic curve with log P_opt being 5.4 for maximal release. The release promoted by most of the compounds assessed at 30 μM could not be or was only partially reversed by either tetrodotoxin or substituting choline for Na⁺ conditions which readily reversed the release promoting effects of veratridine. Thus, many pyrethroids, particularly those without the α-cyano group, did not display their expected effects on the Na⁺ channel in rat brain. When assessed at 5 μM, pyrethroids inhibited, had no effect, or caused increases in the amount of Ca²⁺ incorporated in the presence of ATP. The effectiveness of the various pyrethroids to inhibit Ca²⁺ uptake again displayed a parabolic relationship with log P_opt being 6.4. It was concluded that the variations in pyrethroid effects on norepinephrine release and Ca²⁺ uptake are not solely related to their particular chemical structures, but to lipophilicity. The effects of many pyrethroids on Ca²⁺ metabolism, particularly displacement of bound Ca²⁺, better explain the transmitter release promoting properties in vitro rather than a direct effect on the Na⁺ channel. No direct relationship between known toxicity to mammals and Ca²⁺ inhibition by pyrethroids was established.     

Effects of Environmental Conditions on the Development of <Emphasis Type="Italic">Fusarium</Emphasis> Ear Blight

Recent research on the epidemiology of Fusarium ear (or head) blight (FEB or FHB) of small-grain cereals is reviewed, focusing on inoculum, infection and disease forecasting. Both conidia and ascospores have been shown to be important for causing FEB. For Fusarium graminearum, propagules from crop debris are the main source of initial inoculum. Inoculum production is critically dependent on rainfall although the precise relationship is not clear. Recent work on understanding the effects of climatic variables on FEB development has been based on field observations. These field-based studies confirmed that warm and moist conditions during anthesis are the key factors for FEB development. Several empirical models were derived from the field data and proposed for use in disease forecasting. However, these models may not be applicable to a broader range of areas because of the limited nature of the field data. Several areas are proposed for future research, focusing on the development of more generally applicable forecasting models and on understanding the relationships between disease severity, fungal biomass and the production of associated mycotoxins.     

Development of resistance to pyrethroids in field populations of danish houseflies

Houseflies (Musca domestica) on Danish farms have developed high multiresistance to organophosphorus compounds, after successive use of several OPs, mainly dimethoate, in recent years. Topical application tests 1971–73 with flies from many farms showed that the high OP-resistance did not involve resistance to pyrethroids (± the synergist piperonyl butoxide (pb)) above a level of 3–7 x, unless field pressure with synergised pyrethrum (py/pb) or other pyrethroids was applied. In 1971–72 moderate to high, often heterogeneous, pyrethroid resistance was found on a few trial farms treated frequently with pyrethroid aerosols (mainly py/pb) and in 1973 on most of 23 trial farms treated intensively with aerosols (or space spray) containing py/pb, bioresmethrin ± pb, tetramethrin/pb or tetramethrin/resmethrin. The effect of field pressure with these different pyrethroids on development of pyrethroid resistance is summarised and discussed. Maximum resistance ratios, R/S at LD₅₀-LD₉₅, were: py/pb (1:5), 40->100; bioresmethrin, 191–770; bioresmethrin/pb (1:5), 55–133; tetramethrin/pb (1:5), 171->200; tetramethrin/resmethrin (1:5), 78->370. The intensity of selection pressure with pyrethroids is believed to be an important factor. Although py/pb has been widely used as a supplementary fly control on Danish non-trial farms, pyrethroid resistance has only been found on a few of them.     

Field relevance of a synergistic effect observed in the laboratory between an EBI fungicide and a chloronicotinyl insecticide in the honeybee (Apis mellifera L,Hymenoptera)

It had been found earlier that the chloronicotinyl insecticide thiacloprid (as the 480 g litre(-1) SC Calypso) poses a favourably low toxicity hazard to the honeybee, Apis mellifera L. As with pyrethroids, the metabolization of chloronicotinyl compounds involves monooxygenases, which are known to be inhibited by some ergosterol biosynthesis inhibitor (EBI) fungicides potentially co-applied with these insecticides. The potential synergistic enhancement of the toxicity of thiacloprid to honeybees when co-applied with such fungicides was therefore studied under laboratory and semi-field conditions. Fungicides of other chemical classes were also examined for synergistic potential to reveal other metabolic interactions. In the laboratory, only a slight synergistic effect was observed with the anilinopyrimidine fungicide examined, while a significant enhancement of thiacloprid toxicity to honeybees was found with EBI fungicides. In three tunnel tests conducted under different environmental conditions to simulate field exposure, no increased mortality was observed when honeybees were directly sprayed with thiacloprid (Calypso) alone or in combination with the EBI fungicide tebuconazole (250 g litre(-1) EW, Folicur). There was also no synergized reduction in the foraging intensity on the treated crop. In general, the foraging intensity decreased after thiacloprid treatment but was restored within 24-48 h. The hive vitality was not affected by either thiacloprid or its tank mix with tebuconazole. Our results suggest that, at the recommended use rates, thiacloprid poses a negligible lethal risk to honeybees when applied either alone or in tank mixes with fungicides of various chemical classes.     

Effects of residues of fenvalerate and permethrin on the feeding behaviour of Tetranychus urticae (Koch)

The effects of synthetic pyrethroids on the feeding behaviour of the two-spotted spider mite Tetranychus urticae (Koch) were studied using a modified leaf disc technique. Four different concentrations of the pyrethroids fenvalerate and permethrin and of the organophosphorous insecticide phosmet were sprayed on to Henderson lima bean plants in the laboratory. A water spray was used as a control. Leaf discs were taken from each treatment, including the control, at 2h, 1, 2, 4, 7, 11 and 14 days after treatment. One mite was placed on each disc, allowed to acclimatise and then observed for 1 h. Experiments were conducted under laboratory light at 25 (±1.5)°C and 30 (±2)% r.h. Mites on untreated and phosmet-treated discs spent an average 70–95% of the time feeding; mite behaviour appeared to be unaffected by phosmet. In contrast, mites often spent only 5–40% of the time feeding on discs treated with fenvalerate or with the higher rates of permethrin. In response to pyrethroid residues mites exhibited hyperactivity, longer search periods and reduced feeding, reduced oviposition and a preference for areas with lower residues. These changes in mite behaviour may partially explain mite outbreaks in the field on apple trees following treatment with pyrethroids.