Toxicological effects induced by two carbamates on earthworms (Eisenia fetida): Acute toxicity, arrested regeneration and underlying mechanisms.

Eisenia fetida is recognised as advantageous model species in ecotoxicological and regeneration investigations. The intensive utilization of carbamate pesticides (CARs) imposes heavy residue burdens and grave hazards on edaphic environments as well as soil fauna therein. However, precise mechanisms whereby the specific CAR exerted toxic effects on earthworms remain largely elusive, notably from regenerative perspective. Herein, acute responses and regenerative toxicity of two carbamates (metolcarb, MEB and fenoxycarb, FEB) against E. fetida were dissected using biochemical, histological as well as molecular approaches following OECD guidelines at the cellular, tissue and organismal level. The acute toxicity data implied that MEB/FEB were very toxic/medium to extremely toxic, respectively in filter paper contact test and low to medium toxic/low toxic, respectively in artificial soil test. Chronic exposure to MEB and FEB at sublethal concentrations significantly mitigated the soluble protein content, protein abundance while enhanced the protein carbonylation level. Moreover, severely retarded posterior renewal of amputated earthworms was noticed in MEB and FEB treatments relative to the control group, with pronouncedly compromised morphology, dwindling segments and elevated cell apoptosis of blastema tissues, which were mediated by the rising Sox2 and decreasing TCTP levels. Taken together, these findings not only presented baseline toxicity cues for MEB and FEB exposure against earthworms, but also yielded mechanistic insights into regenerative toxicity upon CAR exposure, further contributing to the environmental risk assessment and benchmark formulation of agrochemical pollution in terrestrial ecosystem.

High frequency of ryanodine receptor and cytochrome P450 CYP9A186 mutations in insecticide-resistant field populations of Spodoptera exigua from China.

The beet armyworm, Spodoptera exigua is a global agricultural pest that is polyphagous, highly dispersive, and often difficult to control due to resistance to many insecticides. Previous studies showed that a target site mutation in the S. exigua ryanodine receptor (SeRyR) corresponding to I4743M contributes approximately 20-fold resistance to chlorantraniliprole, whereas a mutation in the cytochrome P450 enzyme CYP9A186 corresponding to F116V confers 200-fold to emamectin benzoate through enhanced metabolic detoxification. Here, high frequencies of mutations were found among six China S. exigua field populations collected from 2016 to 2019 resulting in SeRyR I4743M and CYP9A186 F116V substitutions, with some populations having high levels of resistance to chlorantraniliprole and emamectin benzoate, respectively. Whereas we found a significant correlation between emamectin benzoate resistance level and the allele frequency of CYP9A186 F116V, no significant correlation was found between chlorantraniliprole resistance level and SeRyR I4743M allele frequency in the six field populations. These results suggest that CYP9A186 F116V is a major resistance mechanism for emamectin benzoate in the tested field populations, whereas it is likely that resistance mechanisms other than SeRyR I4743M are responsible for resistance to chlorantraniliprole in the six China field populations. Because of the growing resistance to these two insecticides by S. exigua in China, the use of insecticidal compounds with different modes of action and/or other integrated pest management strategies are needed to further delay the evolution of insecticide resistance and effectively manage S. exigua in China.

Associations between acetylcholinesterase-1 mutations and chlorpyrifos resistance in beet armyworm, Spodoptera exigua.

Control of the beet armyworm, Spodoptera exigua depends heavily on chemical insecticides. Chlorpyrifos, an acetylcholinesterase (AChE) inhibitor, has been used in beet armyworm control for many years in China. Here we describe high level resistance to chlorpyrifos in a S. exigua strain, FX19-R, which was developed from a field-collected Chinese strain (FX) by selection with chlorpyrifos in the laboratory. FX19-R showed 1001-fold resistance to chlorpyrifos compared with the laboratory reference strain WH-S. The esterase inhibitor triphenyl phosphate (TPP) provided significant but small synergism (only 3.5-fold) for chlorpyrifos and neither of the glutathione s-transferase depletor diethyl maleate and the cytochrome P450s inhibitor piperonyl butoxide provided any detectable synergism, indicating that AChE insensitivity may play the major role in the resistance in FX19-R. Consistent with this, an amino acid substitution, F443Y (F331Y in standard Torpedo californica numbering) in AChE1 was identified in the FX19-R strain and shown to be tightly linked to chlorpyrifos resistance. Precisely homologous substitutions have been associated with organophosphate resistance in other pest species. A novel amino acid substitution, G311S (or G198S in standard numbering), was also identified in the reference strain WH-S. Recombinantly expressed AChE1 proteins carrying the G311S and F443Y substitutions were about 4.2-fold and 210-fold less sensitive to inhibition by chlorpyrifos oxon than wild-type AChE1, respectively. These results enhance our understanding of the mechanisms of chlorpyrifos resistance and provide a basis for resistance management based on monitoring the F443Y and G311S substitutions.

Effects of insecticides on malacostraca when managing diamondback moth (Plutella xylostella) in combination planting-rearing fields.

The combination of crop planting and animal rearing in the same area is popular. However, if the methods of planting and rearing are not appropriate, it will result in losses and the disruption of pest management. The toxicities of 17 insecticides to Plutella xylostella, Eriocheir sinensis, and Procambarus clarkii were tested. The recommended maximum field doses were used in 2 d and 4 d bioassays, and the levels of resistance of P. xylostella to insecticides were determined. Of five insecticides that had relatively low toxicity to E. sinensis and P. clarkii, spinetoram and MbNPV showed the best control efficacy of P. xylostella, followed by tetrachlorantraniliprole, chlorantraniliprole, and avermectin. P. xylostella had relatively little resistance to spinetoram, MbNPV, chlorantraniliprole, and avermectin. Therefore, we concluded that the best insecticides suitable for combination planting and rearing fields (cauliflower-crab or cauliflower-crayfish) were spinetoram and MbNPV, followed by chlorantraniliprole and avermectin. Other insecticides, such as emamectin benzoate, indoxacarb, and chlorfenapyr were effective at controlling P. xylostella, but they were not suitable for use in combination planting and rearing fields because of their high toxicity to crabs and crayfish.

Assessing the risk of insecticides to Actinopterygii in the combination of ecological planting and rearing.

In order to study the co-existing environment of pests and economic animals, the toxicity of 15 insecticides to Plutella xylostella, Monopterus albus, and Paramisgurnus dabryanus was tested. Combined with the recommended maximum doses in the field and bioassay, the results showed that for the three insecticides that were of relatively low toxicity to M. albus and P. dabryanus, spinetoram showed the best control effect on P. xylostella, followed by chlorfenapyr and chlorantraniliprole. However, P. xylostella showed a relatively high resistance to chlorfenapyr. Therefore, the best insecticide suitable for the fields with the cauliflower-finless eel or cauliflower-loach planting and rearing combination was spinetoram, followed by chlorantraniliprole and chlorfenapyr. Other insecticides such as emamectin benzoate, Bacillus thuringiensis (Bt), matrine, and so on were effective against the diamondback moth, but they were not suitable for use because of their high toxicity to the finless eel and loach.

Evaluation of the sublethal effect of tetrachlorantraniliprole on Spodoptera exigua and its potential toxicity to two non-target organisms.

Tetrachlorantraniliprole (TCAP) is a novel anthranilic diamide insecticide that specifically targets the ryanodine receptors of lepidopteran insect species with excellent insecticidal activity. Previous studies have reported the sublethal effects of multiple diamides on several lepidopteran species, whereas the sublethal and non-target effects of TCAP remain largely unknown. We assessed the sublethal effects of TCAP on Spodoptera exigua. We also investigated the effects of TCAP on non-target Harmonia axyridis and Eisenia fetida, S. exigua was more sensitive to TCAP than to chlorantraniliprole, as the LC50 (10.371 µg L-1 at 72 h) of TCAP was relatively lower. Compared with those of the control, sublethal concentrations of TCAP (LC10 and LC30) not only prolonged the duration of the larval and pupal stages as well as the mean generation time but also reduced certain population parameters. On the other hand, TCAP exposure, even at the highest concentration, did not induce toxic effects in H. axyridis ladybugs (1st instar larvae and adults) or E. fetida earthworms. Taken together, our results suggest that TCAP can be used as a novel and promising component of the integrated pest management (IPM) program against S. exigua due to its robust target effects and negligible non-target risks.

Mechanism of the different metabolome responses between Plutella xylostella and Pieris rapae treated with the diamide insecticides.

Diamide insecticides, such as chlorantraniliprole, cyantraniliprole, and tetrachlorantraniliprole, are a new class of insecticides that selectively target insects by affecting calcium homeostasis. While this class of insecticides are effective on a wide range of insect pests, the toxicities of diamide insecticides vary among species and life stages. In this study, we addressed the mechanism underlying the different responses of Plutella xylostella and Pieris rapae to diamide insecticides. The susceptibility to insecticides of P. xylostella and P. rapae larvae was assessed 2 and 4 days after exposure to chlorantraniliprole, cyantraniliprole, and tetrachlorantraniliprole. P. xylostella larvae treated with distilled water (Group A), chlorantraniliprole (Group B), cyantraniliprole (Group C), and tetrachlorantraniliprole (Group D) and P. rapae larvae treated with distilled water (Group E), chlorantraniliprole (Group F), cyantraniliprole (Group G) and tetrachlorantraniliprole (Group H) were subjected to metabolomics analysis. The differential metabolites in the B vs. F, C vs. G, and D vs. H groups were analyzed, followed by pathway enrichment analysis. Chlorantraniliprole, cyantraniliprole, and tetrachlorantraniliprole all showed high toxicities for P. xylostella and P. rapae larvae. P. rapae larvae were more sensitive to the diamide insecticides than P. xylostella larvae. There were 65 overlapped differential metabolites between P. xylostella and P. rapae larvae treated with these three diamide insecticides. Pathway analysis showed that the differential metabolites were closely related with fatty acid biosynthesis and metabolism-related pathways. The differential regulation of fatty acid biosynthesis and metabolism may contribute to the different response to diamide insecticides in P. xylostella and P. rapae.

The Toxicity and Detoxifying Mechanism of Cycloxaprid and Buprofezin in Controlling Sogatella furcifera (Homoptera: Delphacidae).

The effects of cycloxaprid (a modified neonicotinoid insecticide) and buprofezin (a thiadiazine insecticide) on mortality of the white-backed planthopper (WBPH), Sogatella furcifera, were determined in laboratory assays. Cycloxaprid killed WBPH nymphs and adults but buprofezin killed only nymphs, and cycloxaprid acted faster than buprofezin. One day after infestation, mortality of third-instar nymphs was >65% with cycloxaprid at 125 mg liter(-1) but was <38% with buprofezin at 148 mg liter(-1). By the 4th day after infestation, however, control of nymphs by the two insecticides was similar, and cycloxaprid at 125 mg liter(-1) caused ≥ 80% mortality of adults but buprofezin at 148 mg liter(-1) (the highest rate tested) caused almost no adult mortality. LC50 values for cycloxaprid were lowest with nymphs, intermediate with adult males, and highest with adult females. Although buprofezin was slower acting than cycloxaprid, its LC50 for nymphs 5 d after infestation was 3.79-fold lower than that of cycloxaprid. Mean carboxylesterase (CarE) specific activity of nymphal WBPH treated with cycloxaprid and buprofezin was higher than that of control, but there was no significant difference between cycloxaprid and control (no insecticide), and it was significantly higher for buprofezin than those of cycloxaprid and control. For glutathione S-transferase and mixed function oxygenase, the specific activity of nymphal WBPH treated with buprofezin was significantly higher than those of cycloxaprid and control, too.

Induction effects of host plants on insecticide susceptibility and detoxification enzymes of Bemisia tabaci (Hemiptera: Aleyrodidae).

BACKGROUND: The polyphagous B-biotype Bemisia tabaci (Gennadius) has developed a high resistance to commonly used insecticides in China. To illustrate the induced changes by host plant, bioassay and biochemical research on five different host populations were investigated. RESULTS: Except for bifenthrin, all tested insecticides showed lower toxicity to the B. tabaci poinsettia population compared with other host populations. Moreover, four insecticides, the exceptions being abamectin and fipronil, showed highest toxicity towards the tomato population. The LC(50) values of the poinsettia population, particularly towards acetamiprid, were 14.8-, 10.3- and 7.29-fold higher than those of tomato, cucumber and cabbage respectively. The CarE activities of B. tabaci cabbage and cucumber populations were all significantly higher than those of poinsettia, cotton and tomato populations. The ratio of the cabbage population was 1.97-, 1.79- and 1.30-fold higher than that of poinsettia, cotton and tomato respectively. The frequency profiles for this activity also have obvious differences. The GST and P450 activities of the cucumber population were the lowest in the five host populations. CONCLUSION: Long-term induction of host plants for B-biotype B. tabaci could influence their susceptibilities to several insecticides. Rational selection and usage of insecticides for particular hosts will be helpful for resistance management and control of this species.