Acute effects of binary mixtures of Type II pyrethroids and organophosphate insecticides on <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

Pyrethroid and organophosphate insecticides have been used for more than 20 years worldwide to control a variety of insect pest in different settings. These pesticides have been detected in a variety of environmental samples, including surface waters and sediments and therefore there is significant concern about their potential toxic effects on non-target organisms. Mixtures of compounds from these groups of pesticides have been found to frequently show enhanced toxicity but it has been a challenge to predict whether or not enhanced toxicity will occur for a given combination of compounds. This study therefore studied the effects of binary pyrethroid-organophosphate mixtures using cypermethrin, deltamethrin and dimethoate in an acute toxicity test system with Oreochromis niloticus. The 96?h LC50s for individual insecticides were 9.13?µg/l, 9.42?µg/l and 45.52?mg/l for cypermethrin, deltamethrin and dimethoate respectively. These showed that the pyrethroid insecticides were highly toxic to Oreochromis niloticus and were far more toxic than dimethoate. All mixtures were also more toxic than single insecticides throughout the concentration-response curve with mixtures resulting in mortality at concentrations which the individual pesticides in the mixture were below their respective NOECs. In addition, observed mixture toxicities deviated from the predicted mixture effects based either on the Concentration Addition (CA) or Independent Action (IA) models independent of mixture ratio. However, the extent of observed mixture mortality deviation was dependent on the effect level. Significant deviations (MDR?>?2.0) were observed at lower concentrations indicating synergistic effects at lower and possibly environmentally relevant concentrations. This is not unexpected since organophosphate insecticides are known to inhibit acetylcholinesterase as well as inactivate esterase, resulting in reduced detoxification of pyrethroid insecticides and consequently greater toxicity than would be expected. This has important implications for risk assessment of mixtures since the risk of pyrethroid-organophosphate mixtures may be underestimated if either the CA or IA model is employed.     

Assessing the combined toxicity of conventional and newer insecticides on the cotton mealybug <Emphasis Type="Italic">Phenacoccus solenopsis</Emphasis>

Reduced susceptibility to insecticides often results in failure of insect pest control and repetitive use of broad-spectrum insecticides, which could have detrimental effects on beneficial arthropods and surrounding agro-ecosystems. The cotton mealybug, Phenacoccus solenopsis Tinsley is a pest of worldwide importance that can be effectively controlled using a number of insecticides. This insect has developed resistance due to injudicious use and repeated exposure to insecticides throughout the year. The aim of the present study was to investigate the toxicity of the insecticides chlorpyrifos, deltamethrin, spinosad, emamectin benzoate and indoxacarb tested either singly or in combination on laboratory susceptible (Lab-PK) and field population (Field Pop) of P. solenopsis. In the Field Pop, combination of chlorpyrifos with either spinosad or emamectin benzoate or indoxacarb showed a synergistic effect at 1:1, 1:10 and 1:20. The combination of deltamethrin with either emamectin benzoate or indoxacarb at all ratios showed synergistic effect, while the combination of deltamethrin with spinosad at 1:1 and 1:20 ratios showed antagonistic effects and that at 1:10 ratio showed synergistic effect against Field Pop. The results of synergism experiments using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) enzyme inhibitors, when combined with insecticides against the Field Pop, toxicities of all tested insecticides were significantly increased. The present study suggests that insecticide combinations and synergism could help achieve effective control of less susceptible populations of P. solenopsis. This would contribute to suitably managing resistance of this pest to insecticides with reduced negative impacts on the surrounding environment.     

Mortality from the pesticides aldrin and dieldrin in British Sparrowhawks and Kestrels

Among 1029 dead Sparrowhawks and 1055 dead Kestrels from various parts of Britain that were examined over the period 1963–90, the main causes of death were (a) collisions of various kinds (b) starvation or disease and (c) organochlorine poisoning. The main chemical which caused poisoning was HEOD, derived from the insecticides aldrin and dieldrin. Other deaths were attributed to poisoning by DDE (the main metabolite of the insecticide DDT) and by HE (heptachlor epoxide, derived from the insecticide heptachlor). Sparrowhawks whose deaths were attributed to HEOD poisoning contained 5–85 µg g^–1 HEOD in their livers (wet weight), while Kestrels contained 6–99 µg g^–1 HEOD. Such birds were typically lighter in weight than collision victims, but heavier than starved or diseased birds. In the period 1963–75, HEOD probably accounted for about 50% of all recorded Sparrowhawk deaths and 39% of all recorded Kestrel deaths in eastern arable districts, but a smaller proportion elsewhere. Geographical variation in the proportion of deaths attributed to HEOD paralleled variation in the proportion of land devoted to arable crops on which aldrin and dieldrin were mainly used. It also paralleled variation in the extent of population decline in these species. Moreover, the proportion of deaths attributed to HEOD declined between 1963–75 and 1976–86, following a marked reduction in aldrin-dieldrin use, and fell to nil in 1987–90, when aldrin and dieldrin were withdrawn altogether. Over this period, the populations of both species recovered from a decline which occurred in the late 1950s, when aldrin-dieldrin were first introduced.     

Can nutrients mask community responses to insecticide mixtures?

The ecological effect of simultaneous exposure to two nutrient gradients, three insecticides and different predator intensities was investigated over a 3-week period in 80 outdoor, artificial streams using field-collected benthic invertebrates. The experimental design consisted of a 2 × 5 factorial structure with two nutrient levels (oligotrophic or mesotrophic) and five concentrations of the ternary insecticide mixture consisting of the insecticides (chlorpyrifos, dimethoate and imidacloprid). Equivalent toxic unit doses were summed to create a ternary insecticide dose (e.g., 0.1 + 0.1 + 0.1 = 0.3 TU) resulting in a range of ternary insecticide mixture toxicity (i.e., control groundwater, 0.3, 0.6, 0.9 and 1.2 TU). Two genera of insect predators, Gomphus spp. (Odonata) and Agnetina spp. (Plecoptera) were also added into each replicate stream, at densities and sizes comparable to those found at our collection site, to evaluate how the contribution of predators may change in nutrient limited (oligotrophic) versus amended (mesotrophic) systems. We describe a causal mechanism whereby the combined action of nutrients and insecticides reshaped aquatic community structure by interacting through multiple pathways. Specifically, mesotrophic conditions reduced the toxic effects of ternary insecticide mixtures for aquatic insects which, in some cases, appeared to increase abundance of aquatic insects. However, higher levels of insecticides in mesotrophic streams negated this effect and were even more toxic; for example, to aquatic insect grazers than the same insecticide doses in oligotrophic treatment levels. Effects of predators were only significant in oligotrophic streams. Evidence is provided as to how nutrient and contaminant interactions can greatly complicate the assessment of community level responses to insecticide mixtures due to direct and indirect effects of the resulting changes in the density of different genera and functional feeding groups within a community.     

Mountain Plover responses to deltamethrin treatments on prairie dog colonies in Montana

Pyrethroid insecticides containing deltamethrin provide broad spectrum insect control that can adversely affect food supplies of insectivorous birds. I hypothesized that this could result in lowered nest survival for a ground-nesting insectivorous bird, the Mountain Plover (Charadrius montanus), which preferentially nests on prairie dog colonies. I studied Mountain Plover nest survival in 2003–2010 at a small cluster of black-tailed prairie dog (Cynomys ludovicianus) colonies in north-central Montana. Three colonies were treated with deltamethrin to control fleas and limit the spread of plague; four untreated colonies served as controls. I monitored 412 plover nests during the 8 year study (264 on treatment colonies and 148 on control colonies) and found a strong negative effect of deltamethrin treatments on nest survival (β_Dust = ?1.24, 95 % CI was ?2.00 to ?0.48) in the years following the actual treatment (2004–2006). I conclude that the observed treatment effect most likely occurred because of changes in insect (food) availability for the plover, and this in turn lowered nest survival because adults spent more time off nests or switched to less desirable insect prey. These results lend support to the need to consider the indirect effects of insecticide treatments on non-target species and suggest a potential conflict in current plague management strategies for prairie dogs.     

Resistance to conventional insecticides in Pakistani populations of Musca domestica L. (Diptera: Muscidae): a potential ectoparasite of dairy animals

The house fly, Musca domestica L., is an important hygienic pest of humans and dairy animals with the potential to develop resistance to most chemical classes of insecticides. Six adult house fly strains from dairy farms in Punjab, Pakistan were evaluated for resistance to selected insecticides from organochlorine, organophosphate, carbamate and pyrethroid classes. For a chlorocyclodiene and two organophosphates tested, the resistance ratios (RR) at LC₅₀ were in the range of 5.60–22.02 fold for endosulfan, 7.66–23.24 fold for profenofos and 2.47–7.44 fold for chlorpyrifos. For two pyrethroids and one carbamate, the RR values at LC₅₀ were 30.22–70.02 for cypermethrin, 5.73–18.31 for deltamethrin, and 4.39–15.50 for methomyl. This is the first report of resistance to different classes of insecticides in Pakistani dairy populations of house flies. Regular insecticide resistance monitoring programs on dairy farms are needed to prevent field control failures. Moreover, integrated approaches including the judicious use of insecticides are needed to delay the development of insecticide resistance in house flies.     

Insecticides reduce survival and the expression of traits associated with carnivory of carnivorous plants

While agrochemical pollution is thought to be an important conservation threat to carnivorous plants, the effects of insecticides on these taxa have not been quantified previously. Using a combination of lab- and field-based experiments, we tested the effects of commercial and technical grades of three widely used insecticides (carbaryl, lambda-cyhalothrin, and malathion) on survival and the expression of traits associated with carnivory of pink sundews (Drosera capillaris) and Venus flytraps (Dionaea muscipula). Commercial grades were generally more harmful than technical grades under lab and field conditions, but all three insecticides were capable of reducing both survival and the expression of traits associated with carnivory within recommended application rates. However, pink sundews appeared to be more susceptible to insecticides than Venus flytraps, perhaps because of larger numbers of digestive glands on the leaf surfaces. We make several recommendations for future research directions, such as examining the long-term effects of insecticides on carnivorous plant populations, for example in terms of growth rates and fitness. Additionally, future research should include representative species from a wider-range of carnivorous plant growth forms, and explore the mechanism by which insecticides are harming the plants. Given the effects we observed in the present study, we suggest that the use of insecticides should be carefully managed in areas containing vulnerable carnivorous plant species.     

Relationship between blood alcohol concentration on admission and outcome in dimethoate organophosphorus self-poisoning

AIMS

Many patients acutely poisoned with organophosphorus insecticides have co-ingested alcohol. Although clinical experience suggests that this makes management more difficult, the relationship between plasma concentration of alcohol and insecticide is unknown. We aimed to determine whether acute intoxication results in ingestion of larger quantities of insecticide in dimethoate self-poisoning and a worse clinical outcome.

METHODS

We set up a prospective study of acute dimethoate self-poisoning in Sri Lankan district hospitals. An admission plasma sample was analysed to identify the ingested insecticide; in patients with detectable dimethoate, plasma alcohol was measured.

RESULTS

Plasma from 37 of 72 (51.4%) dimethoate-poisoned patients had detectable alcohol {median concentration 1.10 g l⁻¹[110 mg dl⁻¹][interquartile range (IQR) 0.78–1.65]} a median of 3 h post ingestion. The median plasma dimethoate concentration was higher in patients who had ingested alcohol [479 µmol l⁻¹ (IQR 268–701) vs. 145 µmol l⁻¹ (IQR 25–337); P < 0.001]. Plasma dimethoate concentration was positively correlated with plasma alcohol (Spearman''s ρ= 0.34; P= 0.0032). The median alcohol concentration was higher in the 21 patients who died compared with survivors (0.94 vs. 0.0 g l⁻¹, P= 0.018). Risk of death was greater amongst individuals who consumed alcohol [odds ratio (OR) 4.3, 95% confidence interval (CI) 1.2, 16.4]; this risk was abolished by controlling for dimethoate concentration (OR 0.3, 95% CI 0.0, 8.8), indicating that deaths were not due to the direct toxic effects of alcohol.

CONCLUSIONS

Alcohol co-ingestion is associated with higher plasma concentrations of dimethoate and increased risk of death. Larger studies are required to assess this finding''s generalizability, since efforts to reduce deaths from self-poisoning may benefit from concurrent efforts to reduce alcohol consumption.     

A comparison of trimedoxime,obidoxime, pralidoxime and HI-6 in the treatment of oral organophosphorus insecticide poisoning in the rat

This study summarizes the results of examination of acute oral toxicity of 26 organophosphorus insecticides in rats. The effectiveness of trimedoxime, obidoxime, pralidoxime and HI-6, given with atropine and diazepam, was tested in the treatment of poisoning with 2 LD₅₀ of the insecticides. It was shown that the oximes were potent antidotes in poisoning with phosphate insecticides. Obidoxime, pradidoxime and HI-6 had low effectiveness in the treatment of poisoning with phosphonates and phosphorothiolates. However, none of the oximes was an effective antidote in poisoning with dimethoate and pyridafenthion. Trimedoxime was the most effective oxime in the treatment of insecticide poisoning, being successful especially at the lowest tested doses.     

The allelopathic effects of invasive plant <Emphasis Type="Italic">Solidago canadensis</Emphasis> on seed germination and growth of <Emphasis Type="Italic">Lactuca sativa</Emphasis> enhanced by different types of acid deposition

Invasive species can exhibit allelopathic effects on native species. Meanwhile, the types of acid deposition are gradually changing. Thus, the allelopathic effects of invasive species on seed germination and growth of native species may be altered or even enhanced under conditions with diversified acid deposition. This study aims to assess the allelopathic effects (using leaves extracts) of invasive plant Solidago canadensis on seed germination and growth of native species Lactuca sativa treated with five types of acid deposition with different SO₄ ^2? to NO₃ ^? ratios (1:0, sulfuric acid; 5:1, sulfuric-rich acid; 1:1, mixed acid; 1:5, nitric-rich acid; 0:1, nitric acid). Solidago canadensis leaf extracts exhibited significantly allelopathic effects on germination index, vigor index, and germination rate index of L. sativa. High concentration of S. canadensis leaf extracts also similarly exhibited significantly allelopathic effects on root length of L. sativa. This may be due to that S. canadensis could release allelochemicals and then trigger allelopathic effects on seed germination and growth of L. sativa. Acid deposition exhibited significantly negative effects on seedling biomass, root length, seedling height, germination index, vigor index, and germination rate index of L. sativa. This may be ascribed to the decreased soil pH values mediated by acid deposition which could produce toxic effects on seedling growth. Sulfuric acid deposition triggered more toxic effects on seedling biomass and vigor index of L. sativa than nitric acid deposition. This may be attributing to the difference in exchange capacity with hydroxyl groups (OH^?) between SO₄ ^2? and NO₃ ^? as well as the fertilizing effects mediated by nitric deposition. All types of acid deposition significantly enhanced the allelopathic effects of S. canadensis on root length, germination index, vigor index, and germination rate index of L. sativa. This may be due to the negatively synergistic effects of acid deposition and S. canadensis on seed germination and growth of L. sativa. The ratio of SO₄ ^2? to NO₃ ^? in acid deposition was an important factor that profoundly affected the allelopathic effects of S. canadensis on the seed germination and growth of L. sativa possibly because the difference in exchange capacity with hydroxyl groups (OH^?) between SO₄ ^2? and NO₃ ^? as well as the fertilizing effects triggered by nitric deposition. Thus, the allelopathic effects of invasive species on seed germination and growth of native plants might be enhanced under increased and diversified acid deposition.     

Effects of granular formulations of terbufos and fonofos applied to cornfields on mortality and reproductive success of songbirds

This field study used a precise method of assessing effects of insecticides on bird populations by establishing a marked population before application and determining survival rates of known individuals after application of the insecticides. We investigated the effects of two organophosphate granular insecticides applied to cornfields in southwestern Ontario to combat the corn rootworm (Diabrotica spp.). Nine control fields and 11 treated fields, six of which were treated with Fonofos (Dyfonate 20G) and five treated with Terbufos (Counter 15G), were chosen. A colour-banded population of 228 Song Sparrows (Melospiza melodia) was established and numbers monitored before and after application of the insecticides. Activity watches showed that territorial individuals spent at least some of their time foraging on the cornfields. There was no evidence that the insecticides affected the survivorship of either male or female Song Sparrows in the test population. Results from analyses of counts suggest no dramatic impact in three other species of passerines (Horned Lark Eremophila alpestris, Savannah Sparrow Passerculus sandwichensis and Vesper Sparrow Pooecetes gramineus). Sublethal effects of the insecticides on reproductive success of the Song Sparrow population were investigated. Ninety-one nests were found and their outcome (successful or failed) determined. Nest watches showed that parents collected some food for their young from cornfields in at least half of the nests. None of the reproductive parameters measured - reproductive success, clutch size, number of unhatched eggs, number of young fledged per nest - differed among the two types of treated fields and the control fields. In conclusion, the Song Sparrows studied were not ingesting the insecticide granules in lethal doses or in amounts sufficient to affect reproductive success and, hence, no differences in survivorship of adults nor in those reproductive parameters measured among the three field types were detected.     

Insecticidal compounds against mosquito larvae from Oscillatoria agardhii strain 27

It was found that Oscillatoria agardhii strain 27 produced compounds toxic against mosquito larvae (Aedes albopictus), therefore, these compounds were extracted and separated for insecticide development. Structural characterization of the toxic fraction by ¹H‐NMR and GC‐MS showed that these compounds are not the neurotoxins or hepatotoxins conventionally produced by Oscillatoria, but it contained a mixture of unsaturated fatty acids, oleic, linoleic, and γ‐linolenic acids, as well as saturated fatty acids, myristic, palmitic, and stearic acids. In a bioassay developed for these hydrophobic compounds using mosquito larvae, authentic unsaturated fatty acids were shown to be toxic, whereas saturated ones were not active. The results suggested that it might be possible to use unsaturated fatty acids as environmentally safe and effective insecticides without the side effects of the chemically synthesized insecticides. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 114–119, 2000     

Risk assessment of various insecticides used for management of Asian citrus psyllid, <Emphasis Type="Italic">Diaphorina citri</Emphasis> in Florida citrus,against honey bee, <Emphasis Type="Italic">Apis mellifera</Emphasis>

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a major pest of citrus trees worldwide. A wide variety of insecticides are used to manage D. citri populations within citrus groves in Florida. However, in areas shared by citrus growers and beekeepers the use of insecticides may increase the risks of Apis mellifera  L. (Hymenoptera: Apidae) loss and contaminated honey. The objective of this research was to determine the environmental toxicity of insecticides, spanning five different modes of action used to control D. citri, to A. mellifera. The insecticides investigated were imidacloprid, fenpropathrin, dimethoate, spinetoram and diflubenzuron. In laboratory experiments, LD₅₀ values were determined and ranged from 0.10 to 0.53?ng/μl for imidacloprid, fenpropathrin, dimethoate and spinetoram. LD₅₀ values for diflubenzuron were >1000?ng/μl. Also, a hazard quotient was determined and ranged from 1130.43 to 10893.27 for imidacloprid, fenpropathrin, dimethoate, and spinetoram. This quotient was <0.447 for diflubenzuron. In field experiments, residual activity of fenpropathrin and dimethoate applied to citrus caused significant mortality of A. mellifera 3 and 7 days after application. Spinetoram and imidacloprid were moderately toxic to A. mellifera at the recommended rates for D. citri. Diflubenzuron was not toxic to A. mellifera in the field as compared with untreated control plots. Phenoloxidase (PO) activity of A. mellifera was higher than in untreated controls when A. mellifera were exposed to 14 days old residues. The results indicate that diflubenzuron may be safe to apply in citrus when A. mellifera are foraging, while most insecticides used for management of D. citri in citrus are likely hazardous under various exposure scenarios.     

Impacts of a neonicotinoid,neonicotinoid–pyrethroid premix,and anthranilic diamide insecticide on four species of turf-inhabiting beneficial insects

Many turf managers prefer to control foliage- and root-feeding pests with the same application, so-called multiple-targeting, using a single broad-spectrum insecticide or a premix product containing two or more active ingredients. We compared the impact of a neonicotinoid (clothianidin), a premix (clothianidin + bifenthrin), and an anthranilic diamide (chlorantraniliprole), the main insecticide classes used for multiple targeting, on four species of beneficial insects: Harpalus pennsylvanicus, an omnivorous ground beetle, Tiphia vernalis, an ectoparasitoid of scarab grubs, Copidosoma bakeri, a polyembryonic endoparasitoid of black cutworms, and Bombus impatiens, a native bumble bee. Ground beetles that ingested food treated with clothianidin or the premix suffered high mortality, as did C. bakeri wasps exposed to dry residues of those insecticides. Exposure to those insecticides on potted turf cores reduced parasitism by T. vernalis. Bumble bee colonies confined to forage on white clover (Trifolium repens L.) in weedy turf that had been treated with clothianidin or the premix had reduced numbers of workers, honey pots, and immature bees. Premix residues incapacitated H. pennsylvanicus and C. bakeri slightly faster than clothianidin alone, but otherwise we detected no synergistic or additive effects. Chlorantraniliprole had no apparent adverse effects on any of the beneficial species. Implications for controlling turf pests with least disruption of non-target invertebrates are discussed.     

Sublethal effects of pyrethroid and neonicotinoid insecticides on <Emphasis Type="Italic">Iphiseiodes zuluagai</Emphasis> Denmark and Muma (Mesostigmata: Phytoseiidae)

The predator mite Iphiseiodes zuluagai Denmark & Muma is an important biological-control agent of mite pests, and it is one of the most common species found in citrus orchards. This study assessed, under laboratory conditions, the toxicity and duration of the harmful effects of five insecticides, the three pyrethroids deltamethrin, esfenvalerate and lambda-cyhalothrin, and the two neonicotinoids imidacloprid and thiamethoxam on I. zuluagai. Furthermore, we estimated the life-table parameters of the predator. Our results showed that deltamethrin and lambda-cyhalothrin caused higher mortality of larvae and adults than imidacloprid and thiamethoxam. In contrast, esfenvalerate provided larval mortality similar to imidacloprid and thiamethoxam, but it did not cause significant adult mortality of the predator. Mites that developed on pyrethroid residues showed lower survival of the immature stages, fecundity, and longevity compared to neonicotinoid residues and the control treatment. The estimated life-table parameters indicated that deltamethrin, lambda-cyhalothrin and esfenvalerate caused greater reduction in R _o and r of I. zuluagai compared with imidacloprid and thiamethoxam, which were similar to the control treatment. Besides the impacts on biological and population parameters, the duration of the harmful activity of pyrethroid insecticides was longer than the neonicotinoids. Therefore, the use of pyrethroid insecticides to control pest insects may involve serious implications for integrated pest-management programs that aim to exploit the biological control by I. zuluagai in citrus orchards.     

Screening of PAHs and DDTs in sand and acrisols soil by a rapid solid-phase microalgal bioassay

Previously we have demonstrated the rapid screening potential of a newly developed solid-phase microalgal bioassay with spiked sands. In this paper, we report further comparative results using both PAHs and DDTs spiked sands and field-collected acrisols soils. Toxicity responses obtained from standard higher plant tests with three species of plants (Lolium perenne, Cynodon dactylon and Brassica chinensis) were compared with those obtained from a cocktail of microalgae (Selenastrum capricornutum, Chlorococcum hypnosporum and the indigenous Chlorococcum meneghini). The 5-day seed germination/root elongation tests were not sensitive at all in contrast to the 4-day solid-phase microalgal tests and the 28-day early seedling growth tests in both spiked sands and contaminated soils. Sensitivities of microalgal tests were generally higher than the seedling growth tests in spiked sands. Concerning the assays with contaminated soil, the responses of microalgae and higher plants varied. However, the results demonstrated that microalgae could generally act as effective surrogates to screen xenobiotic compounds at toxic level to higher plants, with the local species C. meneghini especially sensitive to reveal phytotoxic effects. This promising rapid screening solution is possible to be used in accompany with standard seedling growth tests when assessing phytotoxicities of contaminated areas, especially for acrisols soil.     

Acetylcholinesterase inhibition and gill lesions in Rasbora caverii, an indigenous fish inhabiting rice field associated waterbodies in Sri Lanka

The present study was aimed at applying condition factor (CF), brain acetylcholinesterase (AChE) and gill histology as biomarkers for detecting possible exposure/effect induced by pesticides in fish residing rice field associated waterbodies in Sri Lanka. Biomarkers of an indigenous fish, Rasbora caverii collected from five sampling sites including canals near rice fields, a river and a reservoir (the reference site) were evaluated at four sampling stages covering pesticide application periods during rice cultivation season in 2004. Results indicated that CF of the fish did not show significant alterations regardless of the sampling sites or sampling stages. Site specific differences in AChE activities of the fish were not evident either prior to application of pesticides or at 7 days after Paraquat application to the rice fields. Two days after the application of a mixture of Fenthion and Phenthoate to the rice fields, AChE activity of the fish collected from canals near rice fields was significantly depressed (65–75%) compared to the fish in the reference site. The activities remain depressed to 50–56% even at 65 days after the insecticides application. Laboratory studies showed that prior exposure of R. caverii to Paraquat (2 μg l⁻¹, 7 days) enhanced the extent of inhibition of brain AChE activity induced by Fenthion (3 μg l⁻¹) or a mixture of Fenthion (3 μg l⁻¹) and Phenthoate (5 μg l⁻¹). Gills of fish collected from canals near rice fields exhibited abnormal multiple divisions at the tips of some secondary lamellae in addition to hyperplasia, hypertrophy and club shaped deformities. Results indicate that application of pesticides in rice culture could manifest a threat to native fish populations residing rice field associated waterbodies. The response of brain AChE and histological changes in the gills of R. caverii allowed differentiating sampling sites after insecticide applications to the rice fields. Hence, R. caverii may be considered as a surrogate species in ecotoxicological risk evaluation of agrochemicals in the region.     

Subtle effects of herbicide use in the context of genetically modified crops: a case study with glyphosate (Roundup)

Research on the effects of glyphosate and seed germination spans 30 years. Despite several studies reporting detrimental effects of the herbicide on seedling germination and growth, glyphosate is still being registered for use as a weed killer and preharvest desiccant. Its nonselective nature and low chance of species developing resistance has lead to the development of genetically modified crops tolerant to the herbicide which also raises concerns about increased reliance on herbicide use, and subtle ecological impact.This paper presents the result of a literature review on past studies mostly, on crop species, and the results of a new experiment performed with emphasis on noncrop species. The new experimental part attempted to determine whether glyphosate (Roundup®) would have an effect on the germination and growth of the F1 generation of seeds produced by plants sprayed with the herbicide. It was designed to mirror spray drift which might affect noncrop plants in nontarget drift zones. Of the 11 species tested using treatments of 0% (control), 1%, 10% or 100% of a 890 g a.i./ha label rate solution sprayed near seed maturity, seven showed a significant effect of the glyphosate treatment on germination and/or growth characteristics.Results of this experiment together with several previous studies reviewed in this paper suggest that there are significant effects to keep in mind when using herbicides such as glyphosate as severe ecological changes could occur.     

Prolonged effects of the insecticide dimethoate on locomotor behaviour in the woodlouse,Porcellio scaber Latr. (isopoda)

Beneficial invertebrates living in hedgerows and woodland adjacent to arable land, are almost inevitably exposed to small doses of pesticides. This can present a threat to these invertebrates even at sublethal levels. Locomotor behaviour is intrinsic to many more complex behavioural responses such as predator avoidance, migration, mate seeking, etc., but is also closely related to the physiological status of the animal. Further, locomotor activity is quantifiable with the aid of modern video and computer technology. In the present study, the effect of a 48 h exposure of the woodlouse Porcellio scaber to soil contaminated with one-tenth of the LD₂₀ (96 h) dimethoate dose was quantified using computer-automated video tracking. Dimethoate-exposed woodlice were recorded for one night prior to dimethoate exposure and for two nights on contaminated soil. After a recovery period of 21 days, the woodlice were recorded for a further night. Control animals were recorded in parallel on soil treated with water. Over the 48 h of exposure, dimethoate induced a gradually increasing hyperactivity in terms of time spent in activity, mean velocity and path length and a suppression of turning rate when compared with controls. No recovery was seen after the 21 days on uncontaminated soil. These effects were statistically significant only in male woodlice.     

Side effects of two reduced-risk insecticides, indoxacarb and spinosad, on two species of Trichogramma (Hymenoptera: Trichogrammatidae) on cabbage

Trichogramma pretiosum Riley and T. brassicae Bezdenko are common egg parasitoids of many lepidopteran pest species damaging vegetable, but their effectiveness can be severely curtailed by insecticide applications. To identify insecticides that are potentially compatible with these parasitoid species, the effects of indoxacarb and spinosad were bioassayed in the laboratory. The bioassays included exposure of adults to various aged residues on glass and cabbage leaf surfaces at different intervals after application, and direct spray on host eggs for effects on parasitism and development and mortality of parasitoid eggs, young and old larvae and pupae. The results showed that the glass- and leaf-surface residues of indoxacarb were harmless to both parasitoid species, whereas those of spinosad were moderately harmful to harmful to both parasitoid species depending on the rates used. The use of indoxacarb on host eggs did not affect significantly parasitism by both parasitoid species, whereas the higher rates of spinosad reduced parasitism. However, both insecticides did not affect immature development and adult emergence. Results from direct spray of host eggs with various immature stages inside showed that indoxacarb did not have significant effects on the egg, young and old larval stages and the pupal stage; whereas the high rates of spinosad when applied at the older larval and pupal stages significantly reduced adult emergence for both parasitoid species. Therefore, application of spinosad in an agro-ecosystem where Trichogramma are dominant should be carefully evaluated or avoided.