Accelerated Degradation of Fenamiphos and Its Metabolites in Soil Previously Treated with Fenamiphos

The degradation of fenamiphos, fenamiphos sulfoxide, and fenamiphos sulfone was determined in a greenhouse experiment using autoclaved and nonautoclaved soil from field plots treated or not treated with fenamiphos. Fenamiphos degradation and formation of fenamiphos sulfoxide was faster in uonautoclaved soil than in autoclaved soil. In nonautoclaved soil, previous exposure to fenamiphos was associated with increased rate of degradation of fenamiphos snlfoxide. Fenamiphos total toxic residue degraded more rapidly in nonautoclaved soil previously exposed to fenamiphos than in nonautoclaved soil never exposed to fenamiphos. This accelerated degradation was due to more rapid degradation of fenamiphos sulfoxide and appears to be biologically mediated.     

Effect of Simulated Rainfall on Efficacy and Leaching of Two Formulations of Fenamiphos

Recoverable fenamiphos in the soil and residue in squash following different simulated rainfall treatments after nematicide application were determined in a 2-year study. Efficacy of fenamiphos also was evaluated. Fenamiphos treatments (3 SC and 15 G) were broadcast (6.7 kg a.i./ha) over plots and incorporated into the top 15 cm of soil immediately before planting ''Dixie Hybrid'' squash. Simulated rainfall treatments of 0, 2.5, and 5.0 cm water were applied 1 day after fenamiphos application. Soil samples from 0- to 8-cm, 8- to 15-cm, and 15- to 30-cm soil depths were collected 1 day after the simulated rainfall applications and analyzed for fenamiphos, fenamiphos sulfoxide (FSO), and fenamiphos sulfone (FSO₂). Squash was analyzed for total fenamiphos residue. Greater concentrations of fenamiphos were present in the 0- to 8-cm soil layer following application of 15 G than 3 SC formulation. Simulated rainfall treatments did not alter fenamiphos concentrations in any soil layer (except for the 0- to 8-cm depth in 1992) or concentration of FSO and total fenamiphos residue in the 15- to 30-cm soil layer. Root-gall indices were greater from untreated than most fenamiphos-treated plots, but were not affected by formulations of fenamiphos or simulated rainfall treatments. Concentrations of total residue in squash ranged from 1 to 4 μg FSO₂/g.     

Hydrolysis of fenamiphos and its oxidation products by a soil bacterium in pure culture,soil and water

A bacterium, identified as Brevibacterium sp. MM1, readily hydrolysed fenamiphos, a widely used organophosphorus insecticide and its toxic oxides (fenamiphos sulfoxide, fenamiphos sulfone), which all contain a common P-O-C bond, in a mineral salts medium. The bacterium also hydrolysed fenamiphos and its oxides in soil and groundwater. Interestingly, fenamiphos phenol, fenamiphos sulfoxide phenol and fenamiphos sulfone phenol, formed during bacterial hydrolysis of fenamiphos and its oxides, persisted in the mineral salts medium, but were transitory in soil and groundwater due to their further metabolism by indigenous micro-organisms. The cell-free preparation (crude enzyme) of this bacterium was very effective in hydrolysing fenamiphos. This is the first report on exceptionally rapid hydrolysis of fenamiphos by a bacterium in pure cultures, soil and groundwater.     

Inhibition of Acetylcholinesterases from Aphelenchus avenae by Carbofuran and Fenamiphos

Exposure to carbofuran and fenamiphos for 72 hours reduced the numbers of active Aphelenchus avenae in aqueous suspension by > 75%. When nematicides were removed, many A. avenae exposed to carbofuran resumed normal movement but A. avenae treated with fenamiphos did not recover. Acetylcholinesterase (AChE) activity was suppressed by > 95% in nematodes treated with carbofuran or fenamiphos. However, 48 hours after treated nematodes had been placed in water, AChE activity in carbofuran treated populations was 98% of the levels in control nematodes. Nematodes that had been treated with fenamiphos showed only slight AChE recovery. The antidotes, atropine sulfate and 2-PAM, were largely ineffective in counteracting the toxic effects of the nematicides.     

Use of Nematodes as Biomonitors of Nonfumigant Nematicide Movement through Field Soil

Three field experiments were established in a loamy sand soil in the Coastal Plain of North Carolina to determine downward movement of aldicarb and fenamiphos with a nematode bioassay. Penetration of bioassay plant roots by Meloidogyne incognita was measured at 1, 3, 7, 14, 21, and 28 days after treatment in the greenhouse as a means of determining nematicide effectiveness. Chemical movement was similar in planted and fallow soil. Nematicidal activity was greater in soil collected from the 0 to 10 cm depth than from the 10 to 20 cm depth. Fenamiphos suppressed host penetration by the nematode more than aldicarb under the high rainfall (19 cm) and low soil temperatures that occurred soon after application in the spring. During the summer, which had 13 cm precipitation and warmer soil temperatures, both chemicals performed equally well at the 0 to 10 cm depth. At the lower soil level (10 to 20 cm), aldicarb limited nematode penetration of host roots more quickly than fenamiphos. Both of these chemicals moved readily in the sandy soil in concentrations sufficient to control M. incognita. Although some variability was encountered in similar experiments, nematodes such as M. incognita have considerable potential as biomonitors of nematicide movement in soil.     

Role of soil pH in the development of enhanced biodegradation of fenamiphos

Repeated treatment with fenamiphos (ethyl 4-methylthio-m-tolyl isopropylphosphoramidate) resulted in enhanced biodegradation of this nematicide in two United Kingdom soils with a high pH (>/= 7.7). In contrast, degradation of fenamiphos was slow in three acidic United Kingdom soils (pH 4.7 to 6.7), and repeated treatments did not result in enhanced biodegradation. Rapid degradation of fenamiphos was observed in two Australian soils (pH 6.7 to 6.8) in which it was no longer biologically active against plant nematodes. Enhanced degrading capability was readily transferred from Australian soil to United Kingdom soils, but only those with a high pH were able to maintain this capability for extended periods of time. This result was confirmed by fingerprinting bacterial communities by 16S rRNA gene profiling of extracted DNA. Only United Kingdom soils with a high pH retained bacterial DNA bands originating from the fenamiphos-degrading Australian soil. A degrading consortium was enriched from the Australian soil that utilized fenamiphos as a sole source of carbon. The 16S rRNA banding pattern (determined by denaturing gradient gel electrophoresis) from the isolated consortium migrated to the same position as the bands from the Australian soil and those from the enhanced United Kingdom soils in which the Australian soil had been added. When the bands from the consortium and the soil were sequenced and compared they showed between 97 and 100% sequence identity, confirming that these groups of bacteria were involved in degrading fenamiphos in the soils. The sequences obtained showed similarity to those from the genera Pseudomonas, Flavobacterium, and CAULOBACTER: In the Australian soils, two different degradative pathways operated simultaneously: fenamiphos was converted to fenamiphos sulfoxide (FSO), which was hydrolyzed to the corresponding phenol (FSO-OH) or was hydrolyzed directly to fenamiphos phenol. In the United Kingdom soils in which enhanced degradation had been induced, fenamiphos was oxidized to FSO and then hydrolyzed to FSO-OH, but direct conversion to fenamiphos phenol did not occur.     

Biodegradation of the Pesticide Fenamiphos by Ten Different Species of Green Algae and Cyanobacteria

The degradation of an organophosphorus pesticide, fenamiphos, by different species of five green algae and five cyanobacteria was studied. All the species tested were able to transform fenamiphos to its primary oxidation product, fenamiphos sulfoxide (FSO), while the majority of these cultures were able to hydrolyze FSO to fenamiphos sulfoxide phenol (FSOP). Fenamiphos sulfone phenol, FSOP, and FSO were detected in the culture extracts of these algae and cyanobacteria. This is the first report on the biodegradation of a toxic pesticide, fenamiphos, by cyanobacteria. The ability of these algae and cyanobacteria to detoxify fenamiphos can be gainfully used in bioremediation of this pesticide and its toxic metabolites.     

Role of Soil pH in the Development of Enhanced Biodegradation of Fenamiphos

Repeated treatment with fenamiphos (ethyl 4-methylthio-m-tolyl isopropylphosphoramidate) resulted in enhanced biodegradation of this nematicide in two United Kingdom soils with a high pH (≥7.7). In contrast, degradation of fenamiphos was slow in three acidic United Kingdom soils (pH 4.7 to 6.7), and repeated treatments did not result in enhanced biodegradation. Rapid degradation of fenamiphos was observed in two Australian soils (pH 6.7 to 6.8) in which it was no longer biologically active against plant nematodes. Enhanced degrading capability was readily transferred from Australian soil to United Kingdom soils, but only those with a high pH were able to maintain this capability for extended periods of time. This result was confirmed by fingerprinting bacterial communities by 16S rRNA gene profiling of extracted DNA. Only United Kingdom soils with a high pH retained bacterial DNA bands originating from the fenamiphos-degrading Australian soil. A degrading consortium was enriched from the Australian soil that utilized fenamiphos as a sole source of carbon. The 16S rRNA banding pattern (determined by denaturing gradient gel electrophoresis) from the isolated consortium migrated to the same position as the bands from the Australian soil and those from the enhanced United Kingdom soils in which the Australian soil had been added. When the bands from the consortium and the soil were sequenced and compared they showed between 97 and 100% sequence identity, confirming that these groups of bacteria were involved in degrading fenamiphos in the soils. The sequences obtained showed similarity to those from the genera Pseudomonas, Flavobacterium, and Caulobacter. In the Australian soils, two different degradative pathways operated simultaneously: fenamiphos was converted to fenamiphos sulfoxide (FSO), which was hydrolyzed to the corresponding phenol (FSO-OH) or was hydrolyzed directly to fenamiphos phenol. In the United Kingdom soils in which enhanced degradation had been induced, fenamiphos was oxidized to FSO and then hydrolyzed to FSO-OH, but direct conversion to fenamiphos phenol did not occur.     

Efficacy of Selected Nonvolatile Nematicides on Control of Ditylenchus destructor in Iris

Greenhouse and field tests established that fenamiphos at 6.7 and 13.4 kg ai/ha applied in a 30-cm band directly on iris bulbs at planting effectively controlled Ditylenchus destructor. Aldicarb at rates of 5.6 to 11.2 kg ai/ha was less effective. Carbofuran, fensulfothion, and oxamyl at 6.7 to 13.4 kg ai/ha were ineffective. When applied on the bulbs, fenamiphos (granular or liquid) reduced nematode infection from 31 to 0.6% as determined by visual inspection of bulbs at harvest. Populations of D. destructor were reduced from 5.7 nematodes/g of fresh weight of bulb tissue to 0.04, 0.05, and 0.14 with applications of 13.4, 6.7, and 3.3 kg ai/ha fenamiphos, respectively. The most effective treatment was fenamiphos (granular or liquid) applied in a 30-cm band directly on the bulbs at time of planting.     

Effects of Aldicarb and Fenamiphos on Acetycholinesterase and Motility of Caenorhabditis elegans

The ability of Caenorhabditis elegans to recover from exposure to high doses of aldicarb and fenamiphos was examined at the organismal and biochemical levels by determination of movement and acetylcholinesterase activity. Nematodes recovered rapidly from a 24-hour exposure to both compounds at concentrations that caused complete paralysis. Acetylcholinesterase regained nearly full activity after a 24-hour exposure to aldicarb but only 10% activity after exposure to fenamiphos. The nematodes were able to move normally, however, on the limited activity that was regained after fenamiphos treatment. Mutant C. elegans strains deficient in various molecular forms of acetylcholinesterase were utilized to demonstrate that the mechanism of recovery did not involve new synthesis of enzyme. This result was confirmed by experiments on acetylcholinesterase reactivation from live versus dead nematodes.     

Effects of Oxime Carbamate Nematicides on Development of Heterodera schachtii on Sugarbeet

Treatment of sugarbeet, Beta vulgaris L., with aldicarb, aldicarb sulfoxide, or aldicarb sulfone 10 days after plants were inoculated with Heterodera schachtii prevented development of the nematode, but second-stage larvae penetrated the roots. These chemicals had no measurable effects on nematodes in plants treated 15 days after inoculation. The tests established that soil treatments of aldicarb are directly or indirectly lethal to larvae developing within roots of sugarbeet. Heterodera schachtii failed to develop on root slices of red table beet grown in soil treated with aldicarb or aldicarb sulfoxide. Similar treatment of plants with aldicarb sulfone or oxamyl did not affect subsequent development of H. schachtii on root slices of treated plants.     

Development of Heterodera glycines as Affected by Alachlor and Fenamiphos

A series of greenhouse experiments was conducted to elucidate the postinfection development of Heterodera glycines in response to applications of alachlor and fenamiphos. The rate of H. glycines maturation on a susceptible soybean cultivar was not altered by 1.0 μg alachlor/g soil but was completely inhibited by 1.0 or 1.5 μg fenamiphos/g soil. An alachlor-fenamiphos combination allowed development after an initial 300-degree-day delay. Nematode maturation on the resistant soybean cultivar Centennial with 1.0 μg alachlor/g soil was similar to that observed on an untreated resistant control. Twice as many females matured on Centennial plants growing in alachlor-treated soil as on untreated Centennial plants. Fenamiphos in combination with alachlor (1.0 μg a.i./g soil) allowed development on Centennial at half the rate of the resistant control. This antagonism between alachlor and fenamiphos on development may help to explain late season population resurgence of H. glycines observed with field application of these pesticides.     

Crop Yields and Nematode Population Densities in Triticale-Cotton and Triticale-Soybean Rotations

Triticale cv. Beagle 82, cotton cv. McNair 235, and soybean cv. Twiggs were arranged in three cropping sequences to determine the effects of fenamiphos and cropping sequence on nematode population densities and crop yields under conservation tillage for 4 years. The cropping sequences were triticale (T)-cotton (C)-T-C, T-soybean (S)-T-S, and T-C-T-S. Numbers of Meloidogyne incognita second-stage juveniles declined on trificale but increased on cotton and soybean each year. Root-gall indices of cotton and soybean ranged from 1.00 to 1.08 (1 to 5 scale: 1 = 0%, 2 = 1% to 25%, 3 = 26% to 50%, 4 = 51% to 75%, and 5 = 76% to 100% of roots galled) each year and were not affected by fenamiphos treatment or cropping sequence. Numbers of Pratylenchus brachyurus were maintained on trificale and generally increased more on soybean than on cotton. Population densities of Helicotylenchus dihystera were near or below detection levels in all plots during the first year and increased thereafter in untreated plots in the T-C-T-C and T-S-T-S sequences. Generally, yields of triticale in all cropping sequences declined over the years. Yields of cotton and soybean were not affected by fenamiphos at 6.7 kg a.i./ha. Cotton and soybean were grown successfully with little or no suppression in yields caused by nematodes in conservation tillage following triticale harvested for grain.     

Efficiency of different methods of extracting the rice root nematode Hirschmanniella oryzae from rice and wheat soil and root samples

The nematode extraction method of centrifugal-floatation proved to be more efficient and significant (p ≤ 0.01) in extracting the rice root nematode, Hirschmanniella oryzae adults and larvae from soil or roots of rice and wheat crops than those extracted by sieving and tissue paper filtration technique. The extracted nematode from rice roots using incubation method is time-dependent and the peak of nematodes occurred four days after incubation. The number of extracted nematode varied according to crop, nematode mobility in soil particles, the number of nematodes present and tissue paper permeability.     

Soil animal responses to moisture availability are largely scale,not ecosystem dependent: insight from a cross‐site study

Climate change will result in reduced soil water availability in much of the world either due to changes in precipitation or increased temperature and evapotranspiration. How communities of mites and nematodes may respond to changes in moisture availability is not well known, yet these organisms play important roles in decomposition and nutrient cycling processes. We determined how communities of these organisms respond to changes in moisture availability and whether common patterns occur along fine‐scale gradients of soil moisture within four individual ecosystem types (mesic, xeric and arid grasslands and a polar desert) located in the western United States and Antarctica, as well as across a cross‐ecosystem moisture gradient (CEMG) of all four ecosystems considered together. An elevation transect of three sampling plots was monitored within each ecosystem and soil samples were collected from these plots and from existing experimental precipitation manipulations within each ecosystem once in fall of 2009 and three times each in 2010 and 2011. Mites and nematodes were sorted to trophic groups and analyzed to determine community responses to changes in soil moisture availability. We found that while both mites and nematodes increased with available soil moisture across the CEMG, within individual ecosystems, increases in soil moisture resulted in decreases to nematode communities at all but the arid grassland ecosystem; mites showed no responses at any ecosystem. In addition, we found changes in proportional abundances of mite and nematode trophic groups as soil moisture increased within individual ecosystems, which may result in shifts within soil food webs with important consequences for ecosystem functioning. We suggest that communities of soil animals at local scales may respond predictably to changes in moisture availability regardless of ecosystem type but that additional factors, such as climate variability, vegetation composition, and soil properties may influence this relationship over larger scales.     

Temporal Efficacy of Selected Nematicides on Meloidogyne Species on Tobacco

Aldicarb, ethoprop, and fenamiphos were evaluated for their efficacy in controlling various species of root-knot nematodes on flue-cured tobacco and for their residual activity, as determined through periodic sampling and bioassays of soil taken from field plots. Field experiments were conducted at five locations over 2 years with flue-cured tobacco. Soil in plots treated with nematicides were formed into high, wide beds before transplanting with ''Coker 371-Gold'' or ''K 326'' tobacco. Residual control of Meloidogyne spp. was greatest (P ≤ 0.05) with fenamiphos (in some cases up to 10 weeks, as measured in tomato bioassays of infested soil and root fragments). Suppression of nematode reproduction by ethoprop was short-lived, and numbers of second-stage juveniles + eggs and numbers of galls in bioassays sometimes surpassed those of untreated plots within 4 weeks after treatment. Aldicarb gave intermediate control over time as compared to the other compounds. Although nematicidal efficacy of all compounds varied with site and season, fenamiphos and aldicarb generally produced the highest yields.     

Accelerated Degradation of Aldicarb and Its Metabolites in Cotton Field Soils

The degradation of aldicarb, and the metabolites aldicarb sulfoxide and aldicarb sulfone, was evaluated in cotton field soils previously exposed to aldicarb. A loss of efficacy had been observed in two (LM and MS) of the three (CL) field soils as measured by R. reniformis population development and a lack of cotton yield response. Two soils were compared for the first test—one where aldicarb had been effective (CL) and the second where aldicarb had lost its efficacy (LM). The second test included all three soils: autoclaved, non-autoclaved and treated with aldicarb at 0.59 kg a.i./ha, or not treated with aldicarb. The degradation of aldicarb to aldicarb sulfoxide and then to aldicarb sulfone was measured using high-performance liquid chromatography (HPLC) in both tests. In test one, total degradation of aldicarb and its metabolites occurred within 12 days in the LM soil. Aldicarb sulfoxide and aldicarb sulfone were both present in the CL soil at the conclusion of the test at 42 days after aldicarb application. Autoclaving the LM and MS soils extended the persistence of the aldicarb metabolites as compared to the same soils not autoclaved. The rate of degradation was not changed when the CL natural soil was autoclaved. The accelerated degradation was due to more rapid degradation of aldicarb sulfoxide and appears to be biologically mediated.     

Behavioral Responses of Heterodera rostochiensis Larvae to Aldicarb and its Sulfoxide and Sulfone

Temik® aldicarb pesticide [2-Methyl-2-(methylthio) propionaldehyde-O-(methylcarbamoyl) oxime] is an effective contact and systemic compound against a wide variety of agricultural pests. Its metabolism in soils may lead to aldicarb sulfoxide and aldicarb sulfone which are both toxicologically important. The comparative effects of these compounds on body activity and stylet movement of second-stage larvae of the potato cyst nematode, Heterodera rostochiensis, were investigated. Temik aldicarb was the most effective contact toxicant, rapidly inhibiting body activity and stimulating abnormal stylet movement. A 24-hr post-nematicide water treatment allowed effective recovery of body vigor and cessation of abnormal stylet movement of the larvae treated with Temik aldicarb at low concentrations, and with aldicarb sulfoxide and aldicarb sulfone at all the dosage levels used. Larvae treated with 10 ppm Temik aldicarb remained paralyzed, the toxic effect being apparently irreversible. Control of Heterodera rostochiensis by direct contact toxicity may not be effective in soil since Temik degrades to compounds having reversible toxic effect.     

14C-涕灭威在旱田土壤中的降解

研究了¹⁴C-涕灭威在5种土壤中(4ppm,1.22μCi·50g^-1 土壤干重)的生物降解。模拟试验为密闭系统,土壤中水分含量为22%,气温20-30℃在供试的5种土壤中,北京肖家河的土壤降解最快,为施人放射剂量的51.3%,以“¹⁴CO₂ 形式从土壤进出;26.0%与土壤结合,只有21.6%可以被抽出。取自浙江义乌的土壤降解较慢,收集到的¹⁴CO₂ 为施入量的23.3%.土壤中加入杀菌剂红霉素或敌茵丹降解作用明显减慢。土壤提取物中涕灭威亚砜、涕灭威亚砜肟被确认是主要的代谢产物,还发现了少量的涕灭威砜,涕灭威亚砜腈涕灭威砜腈和涕灭威砜肟等降解物。