Eutrophic status influences the impact of pesticide mixtures and predation on Daphnia pulex populations

Pesticides, nutrients, and ecological stressors such as competition or predation co‐occur in freshwater ecosystems impacted by agriculture. The extent to which combinations of these stressors affect aquatic populations and the role of nutrients availability in modulating these responses requires further understanding. In this study, we assessed how pesticides affecting different taxonomic groups and predation influence the response of Daphnia pulex populations under different trophic conditions. An outdoor experiment was designed following a factorial design, with the insecticide chlorpyrifos, the herbicide diuron, and the predation by Notonecta sp. individuals as key stressors. The single impact of each of these stressors, and their binary and tertiary combinations, was evaluated on D. pulex abundance and population structure under mesotrophic and eutrophic conditions for 21 days. Data were analyzed using generalized linear mixed models estimated by means of a novel Bayesian shrinkage technique. Our study shows a significant influence of each of the evaluated stressors on D. pulex abundance; however, the impacts of the herbicide and predation were lower under eutrophic conditions as compared to the mesotrophic ones. We found that binary stressor interactions were generally additive in the mesotrophic scenario, except for the herbicide–predation combination, which resulted in synergistic effects. The impacts of the binary stressor combinations in the eutrophic scenario were classified as antagonistic, except for the insecticide–herbicide combination, which was additive. The tertiary interaction resulted in significant effects on some sampling dates; however, these were rather antagonistic and resembled the most important binary stressor combination in each trophic scenario. Our study shows that the impact of pesticides on freshwater populations depends on the predation pressure, and demonstrates that the combined effect of pesticides and ecological stressors is influenced by the food availability and organism fitness related to the trophic status of freshwater ecosystems.     

Concentrations of organophosphorus pesticides in rice (Oryza sativa) and human health risk assessment from Songhua River,Northeast China

The aim of this study was to investigate organophosphorus pesticides (OPs) concentrations in rice grains and estimate potential health risk to inhabitants. A total of 102 rice samples were collected from the Irrigated Area of Songhua River, located in Jilin province, one of the most important rice production areas and a key agricultural area in China. The twelve OPs were determined by gas chromatography coupled with flame photometric detector. Results showed that OPs concentrations in rice grains did not exceed maximum residue limit. The mean concentrations obtained for the detected twelve OPs in µg kg^?1 were as follows: omethoate (0.60), diazinon (0.56), parathion-methyl (0.54), dimethoate (0.38), isocarbophos (0.38), phorate (0.31), fenitrothion (0.24), parathion (0.23), fenthion (0.23), malathion (0.13), dichlorvos (0.13), and methamidophos (0.08). Diazinon (39.2%), omethoate (31.4%), and parathion-methyl (25.5%) had the highest frequency in the detected twelve OPs. 69.6% of samples contained more than one OP, 24.5% of samples detected one OP, and only 5.9% samples did not find any OPs. The average target hazard quotients were all less than one and average hazard index for adults and children were 0.273 and 0.238, respectively. Overall, results indicated that the intake of rice may be safe for consumers.     

Toxicity of A Novel Neonicotinoid Insecticide Paichongding to Earthworm Eisenia fetida

Traditional neonicotinoid insecticides are used worldwide. Paichongding (IPP), as a novel neonicotinoid pesticide, has been widely used in China. However, the ecotoxicity of IPP to non-target invertebrates in soil ecosystem has not been reported yet. In this study, acute toxicity of IPP to earthworm Eisenia fetida, as well as the antioxidant response after IPP exposure, was evaluated. In the filter paper contact test, the LC₅₀ at 24 hr and 48 hr for IPP were 14.98 μg/cm² and 7.59 μg/cm², respectively. In artificial soil test, the LC₅₀ (lethal concentration) at 14 days and 28 days for IPP were 541.07 mg/kg and 238.51 mg/kg, respectively. The LC₅₀ of IPP is much higher than that of traditional neonicotinoid insecticides. However, earthworm body weight assessment demonstrated that the growth of earthworm was inhibited by extended exposure to IPP at sublethal doses. The activities of antioxidative enzymes superoxide dismutase and catalase in earthworms were significantly induced after IPP exposure. Malondialdehyde, a biomarker of lipid peroxidation, was also increased after IPP exposure. Although the results indicated that IPP had potentially adverse effect on earthworms, its toxicity was much lower than traditional neonicotinoids.     

Selective Inhibition of Acetylcholinesterase in the Cerebellum and Hippocampus of Mice Following an Acute Treatment with Malathion

Adult male ICR mice were treated by intraperitoneal injection with 250?mg/kg of bodyweight of commercial malathion (a dose corresponding to 1/12 the LD50). After 6?h, acetylcholinesterase (AChE) activity in blood, liver, and six brain regions was determined. A statistically significant inhibition was observed in whole blood (23%), liver (21%), and, in particular, the central nervous system; the greatest degree of AChE inhibition was observed in the cerebellum (45%), followed by the hippocampus (29%). There was no significant change in AChE activity in the caudate putamen, frontal cortex, midbrain, or pons medulla. These results demonstrate that the magnitude of AChE inhibition in peripheral tissues does not accurately reflect the central-inhibitory effects of malathion on AChE activity in specific brain regions.     

The relationships between brain,serum, and whole blood ChE activity in the wood mouse (Apodemus sylvaticus) and the common shrew (Sorex araneus) after acute sublethal exposure to dimethoate

Abstract

Inhibition of cholinesterase (ChE) activity produced by a single acute intraperitoneal administration of dimethoate was studied in the wood mouse, Apodemus sylvaticus, and the common shrew, Sorex araneus, under laboratory conditions. ChE values from serum and whole blood were compared with those obtained from brain in order to obtain a non-destructive tool for predicting the severity of brain acetylcholinesterase (AChE) inhibition. In addition, serum and brain inhibition following oral exposure to dimethoate was also measured in the wood mouse. Normal ChE activity was higher in the brain and whole blood of the shrews than in wood mice. There was no difference between species in serum ChE activity. Exposure to dimethoate caused a dose-dependent reduction in ChE activity and there was a significant recovery in activity with increasing time after administration. In both species, serum and whole blood were more sensitive than brain for revealing organophosphate-induced ChE inhibition and serum was more sensitive than whole blood. Statistically significant relationships were defined between whole blood and brain ChE activity and between serum and brain ChE activity. Compared with serum, whole blood ChE activity was the more accurate predictor of brain AChE levels. The relationships between brain and serum ChE activity did not appear to be affected by the route of administration of the pesticide.     

Susceptibility of Various Stages of Trichogrammatoidea armigera Nagaraja to Some Pesticides and Effect of Residues on Survival and Parasitizing Ability

The toxicity, persistence and effect on parasitism of 10 insecticides, eight fungicides and one acaricide on Trichogrammatoidea armigera Nagaraja, an egg parasitoid of a Helicoverpa armigera (Hb), were investigated in the laboratory and under field conditions. At field recommended dosages, the fungicides oxycarboxin, copperoxychloride, streptomycin sulphate + tetracycline hydrochloride and 2‐bromo‐2‐nitropropane‐1,3‐diol and the acaricide dicofol were safe, while the insecticide phosalone and fungicide tridemorph were moderately toxic to adults. All other insecticides tested, namely dimethoate, fenitrothion, monocrotophos, phosphamidon, endosulfan, cypermethrin, decamethrin, fenvalerate and fluvalinate, and the fungicides carbendazim, methyl thiophenate and carboxin were toxic to adults. A high level of parasitism was recorded for all fungicide treatments and for dicofol and fluvalinate. The larval stage of the parasitoid was more tolerant than other stages. The residual toxicity of all fungicides, and dicofol, did not affect the ability of the parasitoid to parasitize its host, while the insecticides phosalone and fluvalinate were slightly persistent, favouring 44.7% and 49.3% parasitism after 15 days. Residues of dimethoate, decamethrin, cypermethrin, fenvalerate, monocrotophos and phosphanidon were moderately persistent, while fenitrothion and endosulfan were persistent.     

From Metchnikoff to Monsanto and beyond: the path of microbial control

In 125 years since Metchnikoff proposed the use of Metarhizium anisopliae to control the wheat cockchafer and brought about the first field trials, microbial control has progressed from the application of naturalists' observations to biotechnology and precision delivery. This review highlights major milestones in its evolution and presents a perspective on its current direction. Fungal pathogens, the most eye-catching agents, dominated the early period, but major mycological control efforts for chinch bugs and citrus pests in the US had questionable success, and interest waned. The discoveries of Bacillus popilliae and Bacillus thuringiensis began the era of practical and commercially viable microbial control. A program to control the Japanese beetle in the US led to the discovery of both B. popilliae and Steinernema glaseri, the first nematode used as a microbial control agent. Viral insect control became practical in the latter half of the 20th century, and the first registration was obtained with the Heliothis nuclear polyhedrosis virus in 1975. Now strategies are shifting for microbial control. While Bt transgenic crops are now planted on millions of hectares, the successes of more narrowly defined microbial control are mainly in small niches. Commercial enthusiasm for traditional microbial control agents has been unsteady in recent years. The prospects of microbial insecticide use on vast areas of major crops are now viewed more realistically. Regulatory constraints, activist resistance, benign and efficacious chemicals, and limited research funding all drive changes in focus. Emphasis is shifting to monitoring, conservation, integration with chemical pesticides, and selection of favorable venues such as organic agriculture and countries that have low costs, mild regulatory climates, modest chemical inputs, and small scale farming.     

Laboratory pesticide screening method for the aphid predatory midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae)

A laboratory pesticide screening method is described for the aphid predatory midge Aphidoletes aphidimyza. Four acaricides, 10 fungicides, 11 insecticides and one herbicide, all of which are in common usage, were evaluated against both the adult and larval stages of the predator. The acaricide dienochlor, the fungicides benomyl, bupirimate, chlorothalonil, iprodione and hexaconazole, the herbicide tralkoxydim and the insecticides Bacillus thuringiensis and diflubenzuron were all safe to both adult and larval A. aphidimyza. Adults were more susceptible to the pesticides than larvae. Pesticide was exposed to adults as a residue on glass plates and to larvae on a leaf section mounted on agar. The leaf material remained healthy and supported host aphids for several days without deteriorating. The method and apparatus have potential for use with many other pests and beneficial organisms required to be caged for several days on detached leaf material.     

Effects of 67 herbicides and plant growth regulators on the rove beetleAleochara bilineata (Col.: Staphylinidae) in the laboratory

Effects of 67 herbicides — several of which were mixtures — and plant growth regulators on adult females of the rove beetle,Aleochara bilineata, were investigated in the laboratory. The pesticides were tested in concentrations equivalent to the highest recommended dosages for practical use. Mortality, egg production and hatch of the eggs were measured. Most herbicides had no serious effect on any of the parameters recorded. Among the urea herbicides, however, several showed adverse effects on egg production and/or hatch of the eggs laid. The strongest effect was exerted by methabenzthiazuron that impeded hatch of the eggs completely. Bromoxynil, pyridate and haloxyfod reduced survival, egg production and/or egg hatch to some degree, while carbaryl, which is also used as a plant growth regulator, killed all the beetles immediately. The usefulness of dose-response-studies and the importance of measuring sublethal effects are stressed, and the choice of herbicides showing no toxic effects is recommended.

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Résumé Des expériences ont été faites au laboratoire pour tester les effets de 67 herbicides — dont plusieurs étaient des mélanges — et régulateurs de croissance des plantes sur les femelles adultes d'Aleochara bilineata. Les pesticides ont été testés à des concentrations équivalant aux dosages les plus élevés recommandés pour l'usage agricole. La mortalité, la production et l'éclosion des oeufs ont été mesurés. La plupart des herbicides n'ont pas d'effet important sur aucun des paramètres retenus. Parmi les herbicides à base d'urée cependant, plusieurs montrent des effets négatifs sur la production d'oeufs et/ou l'éclosion des oeufs. L'effet le plus fort a été provoqué par le métabenzthiazuron qui empêchait complètement l'éclosion des oeufs. Le bromoxynil, le pyridate et l'haloxyfop réduisaient la survie, la production d'œufs et/ou, jusqu'à un certain point, l'éclosion des œufs. Le carbaryl par contre, qui est aussi employé comme régulateur de croissance des plantes, tuait immédiatement tous les staphylins. L'utilité des études dose-réponse et l'importance de mesurer les effets sublétaux sont soulignés; le choix des herbicides ne montrant pas d'effet toxiques est recommandé.

     

The side-effects of pesticides used in integrated production of peaches in Brazil on the egg parasitoid Trichogramma cacoeciae Marchal (Hym., Trichogrammatidae)

Abstract: The side‐effects of six pesticides used on peaches in Brazil were tested on the hymenopteran egg parasitoid Trichogramma cacoeciae using four laboratory tests: (a) adult parasitoid exposure to fresh pesticide residue on glass plates (worse case); (b) direct spray of host eggs enclosing the parasitoid egg, larvae or pupae (less‐exposed life stages); (c) exposure of adults to pesticide residues on plant leaves at different intervals after application (persistence); (d) Dose–response pesticide exposures of adults on glass plates. Two dose rates were used: (1) The highest recommended field dosage (FD) and (2) the predicted initial environmental concentrations (PIEC). The results showed that the preparations greatly differed in their initial toxicity and persistence. The insecticide Valient^® (methoxyphenozide) and the fungicide Venturol^® (dodine) were considered harmless to T. cacoeciae adults as they fell into the class 1 category according to the guidelines of the International Organization for Biological Control (IOBC) when parasitoids were directly exposed to chemical residues. The insecticide/acaricide Assist^® (mineral oil) was slightly harmful at the rate of PIEC 0.4 (40% of FD) and moderately harmful at FD. Pesticides in the categories harmless and moderately harmful can be considered for use in integrated pest management (IPM). The fungicide/acaricide Kumulus DF^® (sulphur) and the insecticides Dipterex^® 500 (triclorfon) and Lebaycid^® 500 (fenthion) were harmful at both concentrations. In the persistence test, Assist^® was short lived and therefore may in special cases (i.e. reduced direct contact) be considered for use in IPM, but Kumulus^® DF, Dipterex^® 500 and Lebaycid^® 500 constantly reduced parasitism between 77 and 100% and were rated as persistent (more than 30 days). The direct spray of parasitized host eggs at intervals after parasitism showed that Assist^® and Kumulus^® DF were harmless to the parasitoid egg, larvae and pupae within the host eggs. Dipterex^® 500 was slightly harmful when sprayed one day after parasitism (parasitoid egg) and moderately harmful to the other two stages (larvae and pupae). Lebaycid^® 500 was harmful to the parasitoid egg and larvae and moderately harmful to the pupae. The dose–response test showed that Kumulus^® DF and Dipterex^® 500 were toxic to T. cacoeciae. Kumulus^® DF was harmful from 1 PIEC 0.4 to 0.125 PIEC 0.4 dosages and was slightly harmful with 0.0625 PIEC 0.4 dosage. Dipterex^® 500 was harmful to T. cacoeciae in all the dosages tested.