Soil Insecticides Research Articles

Unraveling the interaction of co-encapsulated Saccharomyces cerevisiae and Metarhizium brunneum in calcium alginate-based attract-and-kill beads.

Attract-and-kill (AK) beads are biological, microbial insecticides developed as an alternative to synthetic soil insecticides. For wireworm control, beads are based on calcium alginate/starch co-encapsulating the carbon dioxide (CO2) producing yeast Saccharomyces cerevisiae H205 as the attract component, and the entomopathogenic fungus Metarhizium brunneum CB15-III as the kill component. However, the physicochemical processes inside beads during co-cultivation are still unclear. Here we reveal for the first time the spatiotemporal conditions of oxygen and pH inside AK beads measured with microelectrodes and describe the impact of S. cerevisiae on CO2 and conidia formation. Measurements revealed a steep oxygen gradient already 2 days after co-encapsulation, with an internal hypoxic zone. Encapsulating either S. cerevisiae or M. brunneum already decreased the average pH from 5.5 to 4.7 and 4.6, respectively. However, on day 3, co-cultivation lead to temporal strong acidification of beads down to pH 3.6 which followed the maximum CO2 productivity and coincided with the maximum conidiation rate. Decreasing the yeast load decreased the total CO2 productivity to half, and the conidial production by 93%, while specific productivities normalized to 1% yeast load increased eight-fold and three-fold, respectively, with day 3 being an exception. Our findings indicate a general beneficial interaction between M. brunneum and S. cerevisiae, but also suggest competition for resources. These findings will contribute to develop innovative co-formulations with maximum efficiency to save application rates and costs. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A comprehensive evaluation of influencing factors of neonicotinoid insecticides (NEOs) in farmland soils across China: First focus on film mulching

Neonicotinoid insecticide (NEO) residues in agricultural soils have concerning and adverse effects on agroecosystems. Previous studies on the effects of farmland type on NEOs are limited to comparing greenhouses with open fields. On the other hand, both NEOs and microplastics (MPs) are commonly found in agricultural fields, but their co-occurrence characteristics under realistic fields have not been reported. This study grouped farmlands into three types according to the covering degree of the film, collected 391 soil samples in mainland China, and found significant differences in NEO residues in the soils of the three different farmlands, with greenhouse having the highest NEO residue, followed by farmland with film mulching and farmland without film mulching (both open fields). Furthermore, this study found that MPs were significantly and positively correlated with NEOs. As far as we know this is the first report to disclose the association of film mulching and MPs with NEOs under realistic fields. Moreover, multiple linear regression and random forest models were used to comprehensively evaluate the factors influencing NEOs (including climatic, soil, and agricultural indicators). The results indicated that the random forest model was more reliable, with MPs, farmland type, and total nitrogen having higher relative contributions.

Co-Metabolism Kinetics of Bioremediation of Lambda Cyhalothrin, Chlorpyrifos and Malathion Contaminated Loam Soil Using Bio-Slurry Microbes

The indiscriminate use of insecticide in agricultural soils causes significant soil and water pollution and poses a serious threat to the global community. Degradation of these pollutants is therefore vital in pollution control. Microbial fuel cells have been employed in bio-remediation of organic pollutants due to its environmental friendliness and low cost. The occurrence of pesticides in soil has become a highly significant environmental problem, which has been increased by the vast use of pesticides worldwide and the absence of remediation technologies that have been tested at full-scale.
 In this study, bioremediation experiments were conducted at ambient temperature of 28-32 0C and pH 5.6-8.9 to investigate the effectiveness of the process in the clean-up of pesticide contaminated loam soils. The loam soil was assessed for macro and micro properties prior to the experiments in control procedures. A H-shaped double chamber microbial fuel cell was fabricated where the anodic chamber was loaded with 750 mL loam soil inoculated with 750 mL bio-slurry doped with 10 mL of 10 ppm lambda cyhalothrin, chlorpyrifos and malathion pesticide solutions. The cathodic chamber was loaded with 1500 mL distilled water. The setup was incubated for a 90 days’ retention time where voltage and current were recorded daily using a multi-meter. The degradation level was assessed using a GC-MS after sample extraction using standard QuEChERs method.
 The voltage generated from the pesticide doped loam soil showed an upward trend from day 0 to day 15 in lambda cyhalothrin and malathion and from day 0 to day 20 in chlorpyrifos and pesticide mixture after which constant readings were observed for three days with downward trends thereafter. The maximum generated voltage was 0.537 V, 0.571 V, 0.572 V and 0.509 V in chlorpyrifos, lambda cyhalothrin, malathion and pesticide mix (MCL) respectively. The bioremediation levels for chlorpyrifos and malathion were 65.80 % and 71.32 %, respectively while no detectable, lambda cyhalothrin was observed after day 60 of the study. This study concludes that bioremediation of lambda cyhalothrin, chlorpyrifos and malathion in Limuru loam soil can be achieved using microbial fuel cells.

Resistance management and integrated pest management insights from deployment of a Cry3Bb1+ Gpp34Ab1/Tpp35Ab1 pyramid in a resistant western corn rootworm landscape.

In Nebraska USA, many populations of western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, now exhibit some level of resistance to all corn rootworm-active Bacillus thuringiensis Berliner (Bt) proteins expressed in commercial hybrids. Therefore, a study was conducted in northeast Nebraska from 2020-2022 to reevaluate current corn rootworm management options in continuous maize (consecutive planting for ≥2 years). Results from on-farm experiments to evaluate a standard soil-applied insecticide (Aztec® 4.67G) in combination with non-rootworm Bt or rootworm-active Bt pyramided maize (Cry3Bb1 + Gpp34Ab1/Tpp35Ab1) are reported within the context of WCR Bt resistance levels present. Corrected survival from Bt pyramid single-plant bioassays (<0.3, 0.3-0.49, >0.5) was used to place populations into 3 resistance categories. Variables evaluated included root injury, adult emergence, proportion lodged maize, and grain yield. Key results: A composite analysis of all populations across resistance levels indicated that addition of soil insecticide to Bt pyramid significantly reduced adult emergence and lodging but did not significantly increase root protection or yield. Within and among resistance category analyses of root injury revealed that the Bt pyramid remained highly efficacious at any non-rootworm Bt root injury level when resistance was absent or low. When corrected survival was >0.3, mean Bt pyramid root injury tracked more closely in a positive linear fashion with mean non-rootworm Bt root injury (rootworm density x level of resistance interaction). Similar trends were obtained for adult emergence but not yield. Mean Bt pyramid root injury rating was <0.75 in most populations with Bt resistance, which contributed to no significant yield differences among categories. Results are discussed within the context of IPM:IRM tradeoffs and the need to reduce WCR densities in this system to decrease the impact of the density x resistance interaction to bridge use of current pyramids with new technologies introduced over the next decade.

Identification of Insecticide Residues in Inceptisols at The Central of Horticultural Production, Banuhampu Agam West Sumatra

The high persistence of insecticides in soil and their toxicity to farmers and agricultural land are serious problems with insecticide application. This study was to identify and characterize insecticide residues on Inceptisol in the center of horticultural production, Banuhampu Agam West Sumatra. The determination of soil samples was carried out by purposive random sampling with a quantitative survey method. Sample testing using randomized completely block design (RCBD) with four slope levels and three points of sampling : 0-8%; 8-15%; 15-25%, and 25-45% in fields at a depth of 0-20 cm and forests (25-45% slope) as control. Insecticide residues on Inceptisol in the central of horticultural production, Banuhampu Agam West Sumatra, identified as many as 5 types, namely: Cypermethrin [C22H19Cl2NO3]; Permethrin [C21H20Cl2O3]; Profenofos [C11H15BrClO3PS]; Phenthoate [C12H17O4PS2], and Diazinon [C12H21N2O3PS]. Cypermethrin was the most highly contaminated insecticide residue found in soil at 0.1 mg kg−1 and is a pyrethroid insecticide. The effect of slope level was not significant on the identification of the number of active ingredients and total insecticide residue concentration. However, the highest number of active ingredients on 0-8% and 25-45% slope each amounted to 3 units, while the highest total concentration of insecticide residues on 0-8% slope amounted to 0.499 mg kg−1.

Assessing the effectiveness of imidacloprid and thiamethoxam via root irrigation against Megalurothrips usitatus (Thysanoptera: Thripidae) and its residual effects on cowpea.

Systemic neonicotinoid insecticides (NEOs) applied by seed-treatment or root application have emerged as a prevalent strategy for early-season insect pest management. This research investigated the effectiveness of imidacloprid and thiamethoxam, administered through root irrigation, in managing thrips in cowpea [Vigna unguiculata (Linn.) Walp.], and the residual properties of both insecticides in cowpea and soil. The results show that thrips density depends on the application rate of insecticides. At the maximum application rate (1,500 µg/ml, active ingredient), imidacloprid and thiamethoxam controlled thrips densities below the economic injury level (EIL, the EIL of thrips on cowpea was 7/flower) for 20 days and 25 days with the density of 6.90 and 6.93/flower at the end of the periods, respectively. Imidacloprid and thiamethoxam residues decreased gradually over time and decreased sharply after 15 days after treatment (DAT), the 2 insecticides were not detected (<0.001 mg/kg) at 45 DAT. According to our findings, the application of imidacloprid and thiamethoxam via root irrigation proved residual control lasting up to 20-25 days for controlling thrips damage at experimental rates, with a strong association to their residual presence in cowpea (0.6223 < R2 < 0.9545). Considering the persistence of the imidacloprid and thiamethoxam, the maximum tested application rate (1,500 µg/ml) was recommended. As the residues of imidacloprid and thiamethoxam were undetectable in cowpea pods at all tested rates, it may be suggested that the use of each insecticide is safe for consumers and effective against thrips, and could be considered for integrated thrips management in the cowpea ecosystem.

Polyvinyl alcohol coating releasing fungal blastospores improves kill effect of attract-and-kill beads

Polyvinyl alcohol (PVA) is a biodegradable, water-soluble polymer with excellent film forming properties, commonly studied or used as tablet coating, food packaging or controlled release fertilizers. Attract-and-kill (AK) beads are sustainable, microbial alternatives to synthetic soil insecticides, whose onset of lethal effect largely depend on how fast the encapsulated entomopathogenic fungus forms virulent conidia. Therefore, the objective of this study was to develop a water-soluble coating accelerating the kill effect of AK beads by immediately releasing virulent Metarhizium brunneum CB15-III blastospores. We assessed three PVA types (PVA 4-88, 8-88, 10-98) which differed in their degree of hydrolysis or molecular weight for their ability to release viable blastospores from thin films after drying at 60–40 °C, and examined how polyethylene glycol and soy-lecithin impact the blastospore survival. Finally, we evaluated the effectiveness of coated AK beads in a bioassay against Tenebrio molitor larvae. The blastospore release rate quadrupled within the first 5 min with decreasing molecular weight and degree of hydrolysis, with PVA 4-88 releasing 79 ± 19% blastospores. Polyethylene glycol and soy-lecithin significantly increased the blastospore survival to 18–28% for all three PVA types. Coated beads exhibited a uniform, 22.4 ± 7.3 µm thin coating layer, with embedded blastospores, as confirmed by scanning electron microscopy. The blastospore coating increased the mortality rate of T. molitor larvae over uncoated AK beads, decreasing the median lethal time from 10 to 6 days. Consequently, the blastospore coating accelerated the kill effect of regular AK beads. These findings pave the way to enhanced pest control efficacy from coated systems such as beads or seeds.Graphical

Comparison of established and novel insecticides on survival and reproduction of Folsomia candida.

Neonicotinoid insecticides have been among the most widely and abundantly used insecticides for most of the current century. The effects of these substances on non-target terrestrial and aquatic organisms have resulted in a significant decrease in their use in many parts of the world. In response, the application of several novel classes of insecticides including diamides, ketoenols, pyridines, and butenolides has significantly increased. The hexapod subclass Collembola is an ecologically significant and widely distributed group of soil invertebrates often found in leaf litter and in surficial soils. In this study, the parthenogenic collembolan species Folsomia candida was exposed to six insecticides in a sandy loam soil for 28 days, including two neonicotinoids (thiamethoxam, clothianidin), a diamide (cyantraniliprole), a ketoenol (spirotetramat), a pyridine (flonicamid), and a butanolide (flupyradifurone) to assess the effect of each insecticide on survival and reproduction. Clothianidin, thiamethoxam, and cyantraniliprole (EC50s (reproduction): 0.19, 0.38, and 0.49 mg/kg soil, respectively) had a greater effect on survival and reproduction of F. candida than flupyradifurone, spirotetramat, and flonicamid (EC50s (reproduction): 0.73, >3.08, and 5.20 mg/kg soil, respectively). All significant impacts observed in this study were observed at concentrations below concentrations of the active ingredients that would be expected in agricultural soils. This article is protected by copyright. All rights reserved. Environ Toxicol Chem 2023;00:0-0. © 2023 SETAC.

Spinosad Application Prevents Damage by Agriotes spp. Larvae (Wireworms) and Protects Maize (Zea mays) Yield in Northeast Italy

Agriotes spp. larvae, commonly known as wireworms, are major pests that cause great economic damage to many European crops. To combat them, most farmers prophylactically apply soil insecticides, including high-impact ones such as neonicotinoids. However, due to their hidden life cycle below ground, wireworms are difficult to control, especially in organic farming where persistent, non-specific soil insecticides cannot be used. As legislation tightens regulation on chemical insecticides that have harmful effects on humans and the environment (such as the withdrawal of many chemicals and the general limitation of all of them), biological control agents are gaining attention as an alternative strategy. The aim of this study was to investigate the agronomic effectiveness of Spinosad, a bioinsecticide, in row application during planting to manage wireworms in maize (Zea mays) in Northern Italy. Based on the performance of Spinosad, even in harsh conditions as observed throughout this study, and its ability to mitigate yield losses compared to the non-treated control, we conclude that this product can be used as part of an Integrated Pest Management to mitigate the damages caused by this pest in organic agriculture. However, further studies are required to better understand how this bioinsecticide can be integrated into Agriotes spp management to reduce economic losses and have a positive impact on the environment and public health

Bioefficacy, phytotoxicity and safety of Virtako 1.5 Gr a premixed commercial insecticide against thrips, black cutworm and natural enemies in onion

Aim: This study aimed to evaluate the relative field-efficacy, natural enemies safety and phytotoxicity of premixed soil insecticide formulation Virtako 1.5 Gr (Chlorantraniliprole 0.5% + Thiamethoxam 1%) against onion thrips (Thrips tabaci) and black cutworm (Agrotis ipsilon) infesting onion. Methodology: Two field experiments were conducted in successive years (2017-18 &amp; 2018-19) to evaluate the bio-efficacy of Virtako 1.5® Gr against thrips, cutworms and natural enemies in onion. The desired dosage of Virtako 1.5® Gr was applied as soil broadcasting after 10 days of transplanting. Thrips population, cutworm damage, natural enemies and phytotoxicity observation were made using standard procedures. Results: The results revealed that Virtako® 1.5 Gr applied @ 105 and 90 g a.i ha-1 recorded the lowest mean thrips population, 18.03 and 19.50 thrips per plant, respectively. Similarly, Virtako 1.5 Gr at 105 a.i. ha-1 reduced cutworm damage by 88.5%, followed by Virtako 1.5 Gr at 90 g a.i. ha-1 (85.5%). Although no natural enemies’ activity (Coccinellids, Orius spp, and Spiders) was found in the early phase of onion growth, they were recorded in all treatments at later crop growth stages. All doses of Virtako 1.5 Gr had no noticeable phytotoxicity effects on onion plants. Interpretation: Application of Virtako 1.5 Gr effectively minimized thrips population and cutworm damage in onions. Further, it did not show any significant harmful impact on the activity to above-ground natural enemies. Therefore, Virtako 1.5 Gr at a lower effective dose 90 g a.i ha-1 can be recommended for onion against thrips and black cutworm. Key words: Cutworm, Onion thrips, Premixed insecticide, Phytotoxicty, Virtako 1.5 Gr

Adsorption and degradation of neonicotinoid insecticides in agricultural soils.

The adsorption and degradation of seven commercially available neonicotinoid insecticides in four types of agricultural soils from three states (Mississippi, Arkansas, and Tennessee) in the USA were studied. The adsorptions of all the neonicotinoids fit a linear isotherm. The adsorption distribution coefficients (Kd) were found to be below 2.0 L/kg for all the neonicotinoids in all the soils from Mississippi and Arkansas. Only in the Tennessee soilsamples, the Kd ranged from 0.96 to 4.21 L/kg. These low values indicate a low affinity and high mobility of these insecticides in the soils. The soil organic carbon-water partitioning coefficient Koc ranged from 349 to 2569 L/kg. These Kd values showed strong positive correlations with organic carbon content of the soils. The calculated Gibbs energy change (ΔG) of these insecticides in all the soils ranged from - 14.6 to - 19.5kJ/mol, indicating that physical process was dominant in the adsorptions. The degradations of all these neonicotinoids in the soils followed a first-order kinetics with half-lives ranging from 33 to 305days. The order of the insecticides with decreasing degradation rate is as follows: clothianidin > thiamethoxam > imidacloprid > acetamiprid > dinotefuran > thiacloprid > nitenpyram. The moisture content, clay content, and cation exchange capacity showed positive effects on the degradation rate of all the neonicotinoids. The Groundwater Ubiquity Score (GUS) calculated from the adsorption distribution coefficient, organic content, and half-life indicates that, except for thiacloprid, all the neonicotinoids in all the soils are possible leachers, having potentials to permeate into and through groundwater zones.

Toxicity analysis and biomarker response of Quinalphos Organophosphate Insecticide (QOI) on eco-friendly exotic Eudrilus eugeniae earthworm

An ever-increasing use of pesticides in agricultural fields has led to a catastrophic decline in crop quality and, ultimately soil fertility. To control various pests, quinalphos is commonly used in India's tea plantations. This study aims to investigate the effects of the Quinalphos organophosphate insecticide on the non-target beneficial organism Eudrilus eugeniae earthworms and the biomarkers that respond to its effects. Earthworm species, especially E. eugeniae, remains as the most trustworthy and well-suited model organism for conducting a wide variety of environmental studies. The median lethal concentration (LC50) was identified as 3.561µgcm-2 (contact filter paper) and 1.054mgkg-2 (artificial soil toxicity). The 5% and 10% of LC50 value 3.561µgcm-2 was exposed to earthworm to analyze the sublethal effects at pre-clitellum, clitellum, and post-clitellum segments. Specific enzymatic activities of neurotransmitter enzyme acetylcholinesterase; antioxidantenzymes such as lipid peroxidase, superoxide dismutase, and catalase; and detoxification enzymes including glutathione S transferase, reduced glutathione, carboxylesterase, and Cytochrome P450 were analyzed. Exposure of E. eugeniae earthworm to subacute exposures of pesticides caused significant alterations in these stress markers in a concentration-dependent manner. Morphological abnormalities like bulginess, coiling, and bleeding were observed after exposure of the insecticide treatments. Histological cellular disintegration, a reduced NRRT time, and an inhibited proteolytic zone were also identified in pesticide-exposed earthworms. Studies demonstrate that the organophosphate insecticide quinalphos causes acute toxicity in E. eugeniae; hence, it is suggested that non-target eco-friendly E. eugeniae earthworms may be at risk if exposed to the excessive concentrations of quinalphos organophosphate insecticide in soil.

Evaluation of soil insecticide treatments in sweetpotato, 2020

Evaluation of soil insecticide treatments in sweetpotato, 2020

Limited Influence of Abiotic and Biotic Factors on the Efficacy of Soil Insecticides and Entomopathogenic Nematodes when Managing the Maize Pest Diabrotica v. virgifera (Coleoptera: Chrysomelidae)

Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) is a serious pest that infects maize. Insecticides or entomopathogenic nematodes are used to control the root-damaging larvae. However, such treatments are reportedly inconsistent in terms of efficacy under farming conditions. To better understand the reasons behind these inconsistencies, we studied the control efficacy of seed coatings, such as clothianidin; granular soil insecticides, such as cypermethrin and tefluthrin; and fluid-applied entomopathogenic nematodes, such as Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae). We assessed the influence of 12 biotic and 20 abiotic factors on the reduction of Diabrotica v. virgifera populations and on the prevention of root damage in 20 field-scale experiments in Hungary between 2010 and 2020. Results confirmed that all treatment types are able to control pest populations and prevent root damage, but with high variability. Our analyses showed that most investigated factors, for example, air temperature, most soil parameters, and pest infestation levels, did not influence the efficacy of the treatments. The efficacy of clothianidin in preventing root damage decreased slightly with increasing soil bulk density but improved with late maize sowing, and therefore late treatment, as well as with increasing soil moisture in July. The efficacy of cypermethrin in preventing damage improved slightly with increasing clay content in the soil. Tefluthrin was slightly less effective in reducing D. v. virgifera with increasing soil moisture in June. However, all these factorial influences were minor in their absolute effects. Surprisingly, none of the investigated factors seemed to influence the efficacy of H. bacteriophora. In conclusion, the efficacy of chemical and biological treatments against this soil pest remains difficult to predict under farming conditions.

Review of entomopathogenic fungi and nematodes as biological control agents of tephritid fruit flies: current status and a future vision

AbstractSeveral fruit fly species (Diptera: Tephritidae) are invasive pests that damage the quality of fruits in horticultural crops and cause significant value losses worldwide. Management of fruit flies mainly depends on conventional insecticides. Unfortunately, the application of synthetic insecticides has caused environmental pollution, risks for humans and animals, and development of resistance. Furthermore, controlling fruit flies by applying synthetic insecticides is challenging because fruit containing third instars often fall from the tree – subsequently the larvae leave the decaying fruits and pupate in the soil. Consequently, both larvae and pupae are protected from surface‐applied insecticides in fruits and soil. So, there is a pressing need for more eco‐friendly and selective control measures with new modes of action. Among such measures are entomopathogenic fungi (EPFs) and nematodes (EPNs). I gathered knowledge on past and present research about EPFs and EPNs as biocontrol agents against fruit flies to investigate approaches that may improve their capacities. I also highlighted several recommendations that may help future field studies on the suppression of fruit fly populations by EPFs and EPNs.

Efficacy of Soil Insecticides Against Sucking Pests of Potato

Field experiments were conducted at three locations for two seasons, 2018 to 2020 to evaluate the efficacy of soil insecticides against sucking pests of potato. Lowest cumulative mean number of whiteflies was observed with fipronil 0.3G @ 25 kg/ ha, and it was on par with its dose of 20 kg/ ha, cartap hydrochloride 4G @ 20 and @ 25 kg/ ha; overall reduction in whiteflies over control ranged between 56.70 and 59.04% at Jalandhar; 53.17 to 60.89% at Modipuram, and 57.33 to 62.40% at Gwalior. Similar trends were noted for aphids, leaf hoppers and thrips. Based on tuber yield and benefit cost ratio, cartap hydrochloride 4G @ 20 kg/ ha (2.62) and fipronil 0.3G @ 20 kg/ ha (2.47) were found to be the most effective against the sucking pests of potato. Hence, both these can be recommended in potato in place of phorate 10G.

Management of Sucking Pests of early Season Cotton by Application of different Seed and Soil Insecticides in Pakistan

Cotton is cash crop of Pakistan and sucking insect pests are serious issue especially in early cotton season. To cope with the issue, a field experiment was conducted to investigate the post emergence effectiveness of two seed and two soil applied insecticides on populations’ development of sucking insect pests in cotton. The seed applied insecticides i.e. Imidacloprid (Confidor 70 WS) and Thiamethoxam (Actara 70 WS) were applied to the seed before sowing. Two granular insecticides i.e. Aldicarb (Temik 10 G) and Carbaryl (Sevin 10 D) were applied in furrows with a modified applicator that was calibrated to deliver the desired rate. The results showed that all the tested insecticides were very effective in controlling the targeted sucking insect pests i.e. thrips, whiteflies and jassids as compared to untreated cotton. Conversely, the seed applied insecticides i.e. Imidacloprid and Thiamethoxam showed more effectiveness compared to soil applied granular insecticides i.e. Aldicarb and Carbaryl in reducing sucking pests’ populations. Such systemic insecticides applied as treated seed can be present in sufficient quantity in germinating plants leading to toxicity to pests, and helpful for safety of natural enemies. The population trends of the three principal sucking insect pests namely thrip, whitefly and jassid were varied significantly over the study months thereby indicating that the population build up was favoured by certain factors. Consequently, the use of seed applied insecticides can be a major component to put into practice in the integrated pest management technology of cotton.

A review of spatiotemporal patterns of neonicotinoid insecticides in water, sediment, and soil across China.

Neonicotinoid insecticides (NNIs) have been widely used to control insect pests, while their environmental residues and associated hazardous impacts on human and ecosystem health have attracted increasing attention worldwide. In this study, we examined the current levels and associated spatial and temporal patterns of NNIs in multiple environmental media across China. Concentrations of NNIs in surface water, sediment, and soil were in the range of 9.94-755ng·L-1, 0.07-8.30ng·g-1 DW, and 0.009-356ng·g-1 DW, respectively. The high levels of NNIs in surface water, such as in Yangtze River (755ng·L-1), North River (539ng·L-1), Nandu River (519ng·L-1), and Minjiang River (514ng·L-1), were dominated by imidacloprid, thiamethoxam, and acetamiprid due to their extensive use. The levels of NNIs in sediments were relatively low, and the highest concentration (8.30ng·g-1 DW) was observed in Dongguan ditch. Sediment-water exchange calculated from fugacity fraction indicated that NNIs in sediment can be released back into the water due to their high solubility and low KOW. Soils from agricultural zones contained the largest residual NNIs, with imidacloprid concentrations in cultivated soil reaching 119ng·g-1 DW. The calculated leaching potential showed that clothianidin has the highest migration potential to deep soil or groundwater. The monitored data of NNIs presented a decreasing trend from 2016 to 2018, which might be caused by the implementation of relevant control policies for NNI applications. The high levels of NNIs mainly occurred in southern China due to frequent agricultural activities and warm and humid meteorological conditions. The results from this study improve our understanding of the pollution levels and environmental behavior of NNIs in different environmental media across China and provide new knowledge that is needed for making future control policies for NNIs production and application.

Mapping of Nematode Resistance in Hexaploid Sweetpotato Using an Next-Generation Sequencing-Based Association Study.

The southern root-knot nematode (SRKN; Meloidogyne incognita) is a typical parasitic nematode that affects sweetpotato [Ipomoea batatas (L.) Lam.], causing a significant decrease in crop yield and commercial value. In Japan, the SRKN is classified into 10 races: SP1–SP5, SP6-1, SP6-2, and SP7–SP9, with the dominant race differing according to the cultivation area. Soil insecticides have previously been used to reduce the soil density of SRKNs; however, this practice is both costly and labor intensive. Therefore, the development of SRKN-resistant sweetpotato lines and cultivars is necessary. However, due to the complexity of polyploid inheritance and the highly heterogeneous genomic composition of sweetpotato, genetic information and research for this species are significantly lacking compared to those for other major diploid crop species. In this study, we utilized the recently developed genome-wide association approach, which uses multiple-dose markers to assess autopolyploid species. We performed an association analysis to investigate resistance toward SRKN-SP2, which is the major race in areas with high sweetpotato production in Japan. The segregation ratio of resistant and susceptible lines in the F1 mapping population derived from the resistant “J-Red” and susceptible “Choshu” cultivars was fitted to 1: 3, suggesting that resistance to SP2 may be regulated by two loci present in the simplex. By aligning the double digest restriction-site associated DNA sequencing reads to the published Ipomoea trifida reference sequence, 46,982 single nucleotide polymorphisms (SNPs) were identified (sequencing depth > 200). The association study yielded its highest peak on chromosome 7 (Chr07) and second highest peak on chromosome 3 (Chr03), presenting as a single-dose in both loci. Selective DNA markers were developed to screen for resistant plants using the SNPs identified on Chr03 and Chr07. Our results showed that SRKN-SP2-resistant plants were selected with a probability of approximately 70% when combining the two selective DNA markers. This study serves as a model for the identification of genomic regions that control agricultural traits and the elucidation of their effects, and is expected to greatly advance marker-assisted breeding and association studies in polyploid crop species.

Microbial degradation of chlorpyrifos and carbosulfan in sterile soil under laboratory conditions

Bacterial degradation of chlorpyrifos and carbosulfan in sterile soil under laboratory condition has been investigated at different concentrations (100, 200 and 300 μg g–1 of soil for chlorpyrifos and 100 and 400 μg g–1 of soil for carbosulfan). HPLC data of chlorpyrifos after 60 days of sampling revealed that the insecticide has degraded to 98.48, 98.22 and 95.19 per cent from its initial concentrations of 100, 200 and 300 μg g−1 in sterile soil. Whereas, the degradation percentages were 29.58, 37.16 and 28.40 after 60 days from the control samples without microbial consortium. Similarly, 100 per cent degradation for carbosulfan in sterile soil by microbial consortium was achieved at 30 days after treatment for 100 μg g−1 and at 60 days for 400 μg g−1 compared to control. Faster degradation by bacterial consortium was recorded for both the insecticides which followed pseudo first order rate kinetics. The study confirmed that microbial consortium could effectively be utilized for faster bioremediation of these insecticides in sterile soil under laboratory conditions. This consortium can also be used for effective biodegradation of two insecticides in mango orchard soil under field conditions.