Fipronil is a relatively new insecticide that controls a broad spectrum of insects at low field application rates. It is a “new generation” insecticide because its mode of action, interference with the normal function of γ-aminobutyric acid (GABA)-gated channels, differs from the classical insecticides, such as organophosphates and carbamates, to which some insects have developed resistance. Fipronil is extensively used throughout the world and numerous studies have evaluated its toxicity and environmental fate. However, a concise review summarizing and combining the recent scientific findings available in the scientific literature is lacking even though the pesticide has been found to be highly toxic to some aquatic organisms. Thus, this document evaluates, summarizes, and combines important toxicological and environmental fate information from recent scientific articles and other literature to produce a detailed review of fipronil.
The review deals with the applications of solution state 1H NMR to the metabolic profiling of plant tissue extracts. NMR is introduced as one of several measurement techniques that are being used in metabolomics. Samples are measured as extract mixtures without any chromatographic separation of individual compounds. Although a limited quantitative measurement of individual components is feasible, the data analysis generally relies on the application of multivariate statistical methods to the whole spectral traces. Design of experiments and sample preparation and measurement procedures are discussed. Applications are grouped under three major headings: classification and taxonomy; genetically modified plants; chemical treatments, environmental influences and pathogens. The final section introduces some of the newer technologies that will extend the scope of NMR metabolic profiling, including the hyphenation of HPLC with UV, MS and NMR detection.
A mixture of deltonin and 25-isodeltonin (approx. 1 : 1) was found to be the molluscicidal principle in seeds of Balanites aegyptiaca (L.) Del. The disposition in the schistosomiasis vector Biomphalaria glabrata and in mice was studied. Snails were exposed to 3H-labelled saponin in water. Administration to mice was oral (O) and intravenous (IV). Snails absorbed the compounds rapidly and showed a high degree of bioaccumulation. The highest concentration was found in the foot followed by the intestines. Snails could excrete the compounds from all organs investigated. Saponin given orally to mice was partly hydrolysed in the intestine, a fraction of genuine and hydrolysed compound being absorbed. Genuine saponin given IV was rapidly distributed to the liver, kidney (medulla), lung and spleen. Compounds did not pass the placenta nor enter the CNS. Excretion was mainly biliary, a minor fraction being excreted in the urine all as genuine compound. About 80% was excreted within 72 hr. While only two (more lipophilic) metabolites were formed in significant amounts by the mice, three such metabolites were seen in extracts of snails. The final toxic agent and the mode of action to target snails remains to be further investigated.
Trichoderma asperellum SKT-1 and Gibberella fujikuroi, known as causal agents of “Bakanae” disease, were both transformed with genes encoding green fluorescent protein (GFP) and hygromycin B (hygB) by restriction enzyme- mediated integration (REMI). Rice seeds inoculated with GFP-tagged G. fujikuroi showed “Bakanae” symptoms. GFP-tagged SKT-1 maintained biocontrol activity against the pathogen by soaking seeds in SKT-1 spore suspension. Then, we monitored in situ interactions between SKT-1 and G. fujikuroi on rice seeds using GFP-tagged transformations under confocal scanning laser stereomicroscopy. G. fujikuroi disappeared from the embryo of rice seeds after treatment with SKT-1, whereas SKT-1 was observed on the embryo 24 hr after initiation of germination. In addition, the hyphae of G. fujikuroi were penetrated by the hyphae of SKT-1, and degradation of the cell walls of G. fujikuroi was observed under SEM in co-culture. The cell wall of G. fujikuroi on the embryo of rice seeds was lysed, suggesting that mycoparasitism is the mode of action of T. asperellum SKT-1.
Dieldrin uptake by cucumber fruits was examined using a variety of cucumber scions and squash rootstocks. The effect of activated carbon on reducing uptake was also determined. Three varieties of cucumber (Cucumis sativus L.; Sharp 1, Natsusuzumi and Nankyoku 2) and three varieties of squash (Cucurbita spp.; Kirameki, Yuyuikki-black and Shintosa) were used. There was no significant difference in dieldrin uptake between cucumber scion varieties. The order of uptake between the varieties of rootstock was Shintosa > Yuyuikki-black > Kirameki = self-rooted plants. In the case of Shintosa, a change to Kirameki or self-rooted plants reduced the dieldrin concentration to 53–34%, treatment of soil with activated carbon to 57%, and the combination of changing the rootstock to Kirameki with activated carbon to 16%. In the case of Kirameki, treatment of soil with activated carbon reduced the dieldrin concentration in cucumber fruits to 42%. In the case of self-rooted plants, a change to grafting culture with Kirameki rootstock and treatment of soil with activated carbon was effective in reducing dieldrin concentration.
We examined the effect of Cucurbita sp. rootstock on dieldrin concentration in grafted cucumber (Cucumis sativus L.) fruits grown in two types of contaminated soils by pot experiment. The two soils consisted of an Andosol and a Brown Lowland soil and contained 319 and 89 μg dieldrin/kg on a dry weight basis, respectively. Dieldrin concentration in cucumber fruits grafted on low-uptake rootstock (ca. 14–40 μg/kg on a fresh weight basis) decreased by 50–70% compared with those grafted on high-uptake rootstock, for each case of two scion cultivars used. Dieldrin concentration in grafted cucumber fruits basically depended on the content in the aerial part, and not on the dieldrin distribution or the water content in the fruits. Selecting low-uptake rootstock is a promising practical technique to reduce dieldrin concentration in cucumber fruits grown in contaminated fields.
A novel timed-release system with a certain lag time (or release-suppression time) of pesticides has been developed using coated water-swelling granules including a slightly water-soluble herbicide. The lag time and release profile of the herbicide are controlled by the polymer composition of the membrane that contains low-density polyethylene (LDPE), talc and water-permeable materials such as surfactant, highly water-absorbent resin (HWAR) and paraffin.
Fentrazamide [4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,5-dihydro-5-oxo-1H-tetrazole-1-carboxamide] is a new tetrazolinone class herbicide. Fentrazamide at and above 1 μM showed marked phytotoxic activity on the growth of early watergrass 15 days after treatment (95% reduction in the total dry weight at 100 μM), but showed less toxicity to rice. Dry weight of early watergrass and rice was reduced by 50% with 1.8 μM and 95.1 μM of fentrazamide, respectively. The pattern of soluble amino acid composition in early watergrass treated with fentrazamide was more similar to that treated with cafenstrole (an inhibitor of fatty acid elongation) than that with mefenacet (an inhibitor of cell division). The inhibition of fatty acid elongation in microsomal fractions of early watergrass by fentrazamide was comparable to that by cafenstrole, but inhibition by fentrazamide was 28–38% even at the highest concentration (2 μM). The cell division of leek roots was not affected by 100 μM of fentrazamide. Cycloheximide (an inhibitor of protein biosynthesis) at 10 μM showed a marked inhibitory effect on the incorporation of 14C-leucine into protein, but fentrazamide showed less inhibitory effect even at 100 μM; however, fentrazamide at and above 10 μM markedly reduced the soluble protein content in early watergrass by 84%, which was much greater than that in rice. These results suggest that fentrazamide has a mode of action which leads to the degradation of protein.
The synthesis of 2,6-dinitro-4-pentafluorosulfanyl-N,N-dipropylaniline, 2, was achieved in a straightforward manner from commercially available 1-nitro-4-pentafluorosulfanylbenzene. In post-emergence screening 2 was found to be approximately twice as potent as trifluralin with the same general spectrum of activity. In contrast, in pre-emergence tests, 2 was nearly 5 fold more potent against quackgrass and crabgrass. Given the existing structure–activity-relationship for adverse properties of the dinitroaniline herbicides, 2 is proposed to have properties quite comparable to the commercial agent trifluralin.
Five new neonicotinoid compounds bearing a 5-chloro-6-fluoronicotinyl group were prepared and their insecticidal activity against brown rice planthopper, green peach aphid and common cutworm under laboratory conditions was compared with 1-(6-chloro-5-fluoronicotinyl)-2-nitroiminoimidazolidine. 5-Fluoroimidacloprid controlled the two hemipteras at 0.2 ppm at the same dose level of imidacloprid, while the positional isomers showed far lower activity. None of the tested compounds controlled the lepidoptera at 200 ppm.
Sesquiterpenes, such as zingiberene, β-elemene, α-bergamotene, β-caryophyllene and (E,E)-α-farnesene were identified as volatile organic compounds (VOCs) from the leaves of Polygonum longisetum treated with jasmonic acid (JA) exogenously. Sesquiterpenes were emitted with 1 μM JA, and their amounts and relative proportions altered according to the concentration. Experiments with silver thiosulfate (STS) suggested that ethylene might be involved in the JA-inducible emission of sesquiterpenes, but the responses of sesquiterpenes against STS were different among them. The conjugate of JA and 1-aminocyclopropane-1-carboxylic acid (JA-ACC) was also active in emitting sesquiterpenes, while conjugates of JA and amino acids, such as Leu, Ile and Val, were inactive. Mevastatin suppressed almost all the sesquiterpenes, but zingiberene and β-elemene were not fully suppressed. It was suggested that JA might stimulate both the mevalonate and methylerythritol pathways in P. longisetum.
Orysastrobin is effective against major fungal diseases of rice plants. Acute toxicity is moderate and no skin or eye irritation or skin sensitisation occurred. Secondary, adaptive and reversible, changes in the duodenal mucosa (increased proliferation of the epithelium to increase iron absorption) and thyroid (increased proliferation of follicular cells to increase thyroid hormone synthesis) resulted in increased tumor incidence in the duodenum of rats and mice, and in the thyroid of male rats. In view of a reversible mechanism of action with a clear threshold dose and the absence of mutagenic potential in vivo, and the well-established excessive sensitivity of rats to TSH elevation, orysastrobin is not considered to present a carcinogenic risk to humans. The compound was not selectively toxic to reproduction. The ADI should be derived from a chronic rat study with a NOAEL of 100 ppm.
Ligand-gated ion channels (LGICs) mediate fast synaptic neurotransmission and are important targets for insecticides. Thus, the actions of several insecticides have been explored in electrophysiological studies on recombinant and native insect neuronal LGICs. I have shown that non-competitive antagonists of γ-aminobutyric acid gated Cl− channels also act on glutamate-gated Cl− channels, albeit at higher concentrations. Neonicotinoids are more potent agonists on recombinant hybrid nicotinic acetylcholine receptors (nAChRs) consisting of Drosophila Dα2 and vertebrate β2 subunits than those consisting of only vertebrate nAChR subunits (α4β2). Using this hybrid nAChR, clothianidin and related compounds containing a acyclic guanidine moiety were found to be super-agonists. Similar super-agonist actions of neonicotinoids were also observed on cultured Drosophila cholinergic neurons. Single channel nAChR recordings show that a clothianidin analogue induces a high conductance state in channel opening more frequently than acetylcholine, thereby offering a possible explanation for its super-agonist action. Unlike the case for clothianidin, imidacloprid attenuates the acetylcholine-induced re-sponse of native neuronal nAChRs when co-applied with ACh. These new discoveries add to our understanding of both the selectivity and the diverse actions of insecticides targeting LGICs.
Systemic acquired resistance (SAR) is a plant defense system against a broad range of pathogens and is induced through the salicylic acid (SA)-mediated pathway. We investigated the mode of action of SAR-inducible chemicals, N-cyanomethyl-2-chloroisonicotinamide (NCI), 3-chloro-1-methyl-1H-pyrazole-5-carboxylic acid (CMPA), and N-(3-chloro-4-methylphenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (tiadinil, TDL), by analyzing disease resistance and the expression of SAR marker genes in tobacco and Arabidopsis. NCI, CMPA, TDL and its active metabolite 4-methyl-1,2,3-thiadiazole-5-carboxylic acid (SV-03) induced SAR by activating the site between SA accumulation and NPR1 in the SAR signaling pathway.
The matrix effect of spinach on residue analysis by commercially available ELISA kits was significant and different by every kit used. In particular, a serious influence was observed with the kit for imidacloprid and fenitrothion measurement. The substances that caused the matrix effect were removed with ultrafiltration (UF10000). It was conjectured that these substances is hydrophobic particles in the suspension.