Larvicidal,ovicidal, and oviposition-deterrent activities of four plant extracts against three mosquito species

In mosquito control programs, insecticides of botanical origin have the potential to eliminate eggs, larvae, and adults. So, the larvicidal, ovicidal, and oviposition-deterrent activities of petroleum ether and ethyl acetate extracts of the leaves of Eugenia jambolana, Solidago canadensis, Euodia ridleyi, and Spilanthes mauritiana were assayed against the three vector mosquito species, namely Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus. The larval bioassay was conducted following the World Health Organization method. The maximum larval mortality was found with ethyl acetate extract of S. mauritiana against the larvae of A. stephensi, A. aegypti, and C. quinquefasciatus with LC₅₀ values of 11.51, 28.1, 14.10 ppm, respectively. The mean percent hatchability of the ovicidal activity was observed at 48-h post-treatment. The percent hatchability was found to be inversely proportional to the concentration of the extract and directly proportional to the number of eggs. The flower head extract of S. mauritiana gave 100 % mortality followed by E. ridleyi, S. canadensis, and E. jambolana against the eggs of the three mosquito vectors. For oviposition-deterrent effect, out of the five concentrations tested (20, 40, 60, 80, and 100 ppm), the concentration of 100 ppm showed a significant egg laying-deterrent capacity. The oviposition activity index value of E. jambolana, E. ridleyi, S. canadensis, and S. mauritiana against A. aegypti, A. stephensi, C. quinquefasciatus at 100 ppm were ?0.71, ?0.71, ?0.90, ?0.93, ?0.85, ?0.91, ?1, ?1, ?0.71, ?0.85, ?1, and ?1, respectively. These results suggest that the leaf/flower extracts of certain local plants have the potential to be developed as possible eco-friendly means for the control of mosquitoes.     

Susceptibility of epigeic earthworm Eisenia fetida to agricultural application of six insecticides

Ecotoxicological risks of agricultural application of six insecticides to soil organisms were evaluated by acute toxicity tests under laboratory condition following OECD guidelines using the epigeic earthworm Eisenia fetida as the test organism. The organochlorine insecticide endosulfan (LC₅₀ - 0.002 mg kg⁻¹) and the carbamate insecticides aldicarb (LC₅₀ - 9.42 mg kg⁻¹) and carbaryl (LC₅₀ - 14.81 mg kg⁻¹) were found ecologically most dangerous because LC₅₀ values of these insecticides were lower than the respective recommended agricultural dose (RAD). Although E. fetida was found highly susceptible to the pyrethroid insecticide cypermethrin (LC₅₀ - 0.054 mg kg⁻¹), the value was higher than its RAD. The organophosphate insecticides chlorpyrifos (LC₅₀ - 28.58 mg kg⁻¹), and monocrotophos (LC₅₀ - 39.75 mg kg⁻¹) were found less toxic and ecologically safe because the LC₅₀ values were much higher than their respective RAD.     

A laboratory assessment of the toxic attributes of six 'reduced risk insecticides' on Galendromus occidentalis (Acari: Phytoseiidae)

The modified excised leaf disc method was used to measure the effects of six insecticides on eggs, larvae, adults, and female fecundity of Galendromus occidentalis (Nesbitt) in a ‘worst case laboratory exposure’. This study identified insecticides that would be recommended for tier II field evaluations for an integrated pest management program. Commercially formulated insecticides were applied with a thin-layer chromatography sprayer adjusted to 10.34 kPa (1.5 psi), at the recommended label concentrations in Canada. LC₅₀ values were estimated from aliquots above and below that concentration. Spinetoram and spirotetramat were toxic at label concentrations. The label concentration for spinetoram was 34.3-fold the LC₅₀ estimate (0.006 g L⁻¹) and for spirotetramat the label concentration was 7.7-fold the LC₅₀ estimate (0.03 g L⁻¹). Clothianidin was considerably less toxic and the label concentration was 0.15-fold the LC₅₀ estimate (2.29 g L⁻¹). Estimates of LC₅₀ for novaluron and chlorantraniliprole could not be established. Both materials showed slight toxicity to at least one growth stage of the predator. Novaluron, clothianidin and chlorantraniliprole should be evaluated in the field for compatibility in IPM programs. Flubendiamide was harmless to all growth stages and it is recommended for inclusion in IPM programs without additional tier II field evaluations. Field evaluations with spinetoram and spirotetramat should be pursued only if alternatives are unavailable.     

Structure-activity relationships of larvicidal monoterpenes and derivatives against Aedes aegypti Linn

In the search for larvicidal compounds against Aedes aegypti L. (Diptera: Culicidae), a collection of monoterpenes were selected and evaluated. R- and S-limonene exhibited the highest larvicidal potency (LC₅₀ = 27 and 30 ppm, respectively), followed by γ-terpinene (LC₅₀ = 56 ppm) and RS-carvone (LC₅₀ = 118 ppm). Structural characteristics which may contribute to the understanding of the larvicidal activity of monoterpenes were empirically identified. The presence of heteroatoms in the basic hydrocarbon structure decreases larvicidal potency. Conjugated and exo double bonds appear to increase larvicidal potency. Replacement of double bonds by more reactive epoxides decreases the larvicidal potency. The presence of hydroxyls in the cyclic structure resulted in decreased potency, probably due to increased polarity indicanting that lipophilicity seems to play an important role in increasing the larvicidal potency in this set of compounds.     

Toxic effects of deltamethrin and λ-cyhalothrin on Xenopus laevis tadpoles

This study evaluates the toxic effects of deltamethrin and λ-cyhalothrin on Xenopus laevis tadpoles after 168 h of exposure. The LC₅₀ of deltamethrin and λ-cyhalothrin at 168 h was calculated as the μg of active ingredient per liter (μg AI/L). According to these values, the LC₅₀ was 6.26 and 3.94 μg AI/L for deltamethrin and λ-cyhalothrin, respectively. Several enzymes were studied for early signs of intoxication following exposure to the pesticides for 24 h. Glutathione-S-transferase,carboxylesterase, and lactate dehydrogenase were inhibited by λ-cyhalothrin, and both pesticides inhibited acid phosphatase and aspartate aminotransferase. In contrast, acetylcholinesterase was activated by deltamethrin. The results suggest that X. laevis is sensitive to the pyrethroids that were tested, and the enzyme responses suggest that they are potential biomarkers for evaluating the toxic effect of pyrethroids on amphibians in environmental conditions.     

Comparative examination on synergistic toxicities of chlorpyrifos,acephate, or tetraconazole mixed with pyrethroid insecticides to honey bees (Apis mellifera L.)

Potential synergistic toxicity of pesticide mixtures has increasingly become a concern to the health of crop pollinators. The toxicities of individual and mixture of chlorpyrifos (CHL), acephate (ACE), or tetraconazole (TET) with nine pyrethroid insecticides to honey bees (Apis mellifera L.) were evaluated to reveal any aggregated interaction between pesticides. Results from feeding toxicity tests of individual pesticides indicated that organophosphate insecticides CHL and ACE had higher toxicities to honey bees compared to nine pyrethroids. Moreover, different pyrethroids exhibited considerable variation in toxicity with LC₅₀ values ranging from 10.05 (8.60–11.69) to 1125 (922.4–1442) mg a.i. L^?1 after exposure for 7 days. Among the 12 examined pesticides, a relatively low toxicity to A. mellifera was detected from the fungicide TET. All the binary mixtures of ACE or TET in combination with pyrethroids exhibited synergistic effects. However, TET in combination with pyrethroids showed greater synergistic toxicity to A. mellifera than ACE in combination with pyrethroids. Approximately 50% binary mixtures of CHL in combination with pyrethroids also showed synergistic responses in honey bees. In particular, CHL, ACE, or TET in combination with either lambda-cyhalothrin (LCY) or bifenthrin (BIF) showed the strongest synergy in A. mellifera, followed by CHL, ACE, or TET in combination with either zeta-cypermethrin (ZCY) or cypermethrin (CYP). The findings indicated that the co-exposure of various pesticides in natural settings might lead to severe injury to crop pollinators. Therefore, pesticide mixtures should be applied carefully in order to minimize negative effects on honey bees while maintaining effective management against crop pests.

     

Survival and behavior of the insecticide-exposed predators Podisus nigrispinus and Supputius cincticeps (Heteroptera: Pentatomidae)

Pentatomid stinkbugs are important predators of defoliating caterpillars in agricultural and forestry systems, and knowledge of the impact of insecticides on natural enemies is important information for integrated pest management (IPM) programs. Thus, we assessed the toxicity and behavioral sublethal response of the predators Podisus nigrispinus and Supputius cincticeps exposed to deltamethrin, methamidophos, spinosad and chlorantraniliprole, insecticides commonly used to control the velvetbean caterpillar (Anticarsia gemmatalis) in soybean crops. With the exception of deltamethrin for S. cincticeps, all insecticides showed higher acute toxicity to the prey than to these natural enemies providing effective control of A. gemmatalis. The recommended field concentration of deltamethrin, methamidophos and spinosad for controlling A. gemmatalis caused 100% mortality of P. nigrispinus and S. cincticeps nymphs. Chlorantraniliprole was the less toxic and the most selective insecticide to these predators resulting in mortalities of less than 10% when exposed to 10× the recommended field concentration for a period of 72 h. Behavioral pattern changes in predators were found for all insecticides, especially methamidophos and spinosad, which exhibited irritability (i.e., avoidance after contact) to both predator species. However, insecticide repellence (i.e., avoidance without contact) was not observed in any of the insects tested. The lethal and sublethal effects of pesticides on natural enemies is of great importance for IPM, and our results indicate that substitution of pyrethroid and organophosphate insecticides at their field rates by chlorantraniliprole may be a key factor for the success of IPM programs of A. gemmatalis in soybeans.     

Acute and chronic toxicity of Roundup Weathermax and Ignite 280 SL to larval Spea multiplicata and S. bombifrons from the Southern High Plains, USA

Pesticides have been implicated in widespread amphibian declines. We assessed acute and chronic toxicity of two widely used herbicides to larval New Mexico (Spea multiplicata) and Plains (S. bombifrons) spadefoots from cropland and native grassland playas. Roundup WeatherMAX^® (WM) toxicity estimates (48- and 216-h LC₅₀; 48-h LC₁) for both species were similar to environmental concentrations expected from accidental overspray. Chronic (30-day) exposure to WM at predicted environmental concentrations (2.0 and 2.8 mg glyphosate acid equivalents/L) reduced survival of both species. Ignite^® 280 SL (IG) toxicity estimates (48-h LC₅₀ and LC₁) for both species were above predicted environmental concentrations of 1.0 mg glufosinate/L. Chronic exposure to predicted environmental concentrations of IG did not reduce survival of either species. Toxicity test results suggest that at predicted environmental concentrations IG would not cause extensive mortalities among larval New Mexico and Plains spadefoots. However, WM may cause extensive mortality among larvae of these species.     

Toxicity of synthetic pyrethroid insecticides to the grass shrimp,Palaemonetes pugio,parasitized with the bopyrid isopod,Probopyrus pandalicola

The grass shrimp, Palaemonetes pugio, plays a large role in the marine ecosystem, serving as a vital link in the food web between many other species. Marine parasites such as the bopyrid isopod, Probopyrus pandalicola, reduce shrimp growth and reproductive output and may also cause P. pugio to be more vulnerable to the lethal effects of contaminants. The purpose of this study was to determine the toxicity of resmethrin and bifenthrin on the grass shrimp, P. pugio, infected with the bopyrid isopod, Probopyrus pandalicola. A 96-h static renewal test was conducted to determine the toxicity of the pyrethroid insecticides resmethrin and bifenthrin to grass shrimp, Palaemonetes pugio, parasitized with the bopyrid isopod, Probopyrus pandalicola. The results were then compared to similar tests utilizing unparasitized P. pugio. Parasitized P. pugio had lower 24-h LC₅₀ (1.08 μg/L) and 96-h LC₅₀ (0.43 μg/L) values for resmethrin than unparasitized P. pugio. However, LC₅₀ ratio tests found that there was no significant difference between parasitized and unparasitized shrimp when affected by resmethrin (p = 0.1751 and 0.1108, respectively). In contrast, an LC₁₀ ratio test indicated that there was a significant difference between parasitized and unparasitized P. pugio after 96 h (p < 0.0001). When subjected to bifenthrin, parasitized P. pugio had a higher 24-h LC₅₀ (0.049 μg/L6) than unparasitized P. pugio. The LC₅₀ ratio test established that the effects of bifenthrin on parasitized P. pugio when compared to unparasitized P. pugio were significantly different at 24 h (p = 0.0065). However, there were no significant differences between parasitized and unparasitized after 96 h (p = 0.4229). In conclusion, both resmethrin and bifenthrin are toxic to the grass shrimp, P. pugio, regardless of parasite presence, and parasitized shrimp may be more susceptible to lower doses of resmethrin (when exposed in the field).     

Toxicity of lead on Ceriodaphnia dubia in the presence of nano-CeO(2) and nano-TiO(2)

Although engineered nanoparticles (NPs) could negatively impact environmental organisms, the synergistic effect of NPs and other toxic substances, which could be more significant than that of NP alone, have seldom been examined. The effect of two common NPs, nano-CeO₂ and nano-TiO₂, on the toxicity of Pb was evaluated using Ceriodaphnia dubia (C. dubia) as the model organism. Standard EPA procedures were followed in the toxicity evaluation. The toxicity of bare NPs (without Pb) was first evaluated and safe doses (levels without causing lethal effect) of NPs were used in the synergistic studies. It was found that the overall toxicity of Pb in the system containing NPs was greater than that of Pb alone, as indicted by the reduced median lethal concentration (LC₅₀) of soluble Pb. The sorption of Pb onto the NP, and the uptake of NPs in the gastrointestinal tract of C. dubia were validated. Therefore, the uptake of Pb-loaded NPs increased the exposure of C. dubia to Pb, resulting in the enhanced toxicity. Reducing the solution pH could shift Pb speciation and enhance the overall toxicity of Pb, with or without the presence of NPs.     

Investigation of insecticide leaching from potted nursery stock and aquatic health benefits of bioretention cells receiving nursery runoff

Tree nurseries and greenhouses within the USDA red imported fire ant (RIFA) quarantine zone are required to incorporate insecticides into their potting media to prevent artificial spread of RIFA. Bifenthrin and fipronil are two common insecticides that are incorporated into potting media. During irrigation and stormwater events, there is potential for insecticides to leach from nursery pots, resulting in the contamination of nearby surface waters. In this study, occurrences of insecticides in simulated nursery runoff were compared with two irrigation strategies and two types of containers in single pot leaching and field runoff simulations. In addition, toxicity of pot leachate to the aquatic invertebrate, Hyallela azteca, was measured, and removal efficiencies of insecticides from bioretention cell media were evaluated. Overhead irrigation resulted in significantly higher concentrations than drip irrigation, and RootMaker® pots allowed more leaching as compared to standard slick-wall pots. However, in all tests, the average concentration of bifenthrin during 15 days of leaching in both pot and field simulations was greater than 200 ng/L; more than 100-fold greater than the LC₅₀ for H. azteca. Toxicity studies confirmed this level of toxicity. Higher amounts of compost, 20 and 40 %, in bioretention cell media resulted in greater percent reduction of both bifenthrin and fipronil. This study determined that management techniques may be able to limit the amount of insecticide that leaches from pots and runs off to receiving water bodies. Specifically, the selection of appropriate pot types, irrigation strategies, or filtering runoff through bioretention cells may reduce contamination loads. Thus, further best management strategies such as the use of bioretention cells are needed in nursery and greenhouse facilities to prevent surface water runoff from transporting toxic insecticides.     

Effects of five insecticides used in apple orchards on Hyaliodes vitripennis (say) (Hemiptera: Miridae)

Abstract

Azinphos‐methyl, carbaryl, dimethoate, phosmet and phosalone were used in apple orchards to manage apple aphid, apple maggot, woolly apple aphid and leaf eating caterpillars. Among the five insecticides evaluated, dimethoate, carbaryl and azinphosmethyl were the most toxic to the nymphs and adults of Hyaliodes vitripennis (Say) from two regions. Phosalone was the least toxic. Nymphs were more resistant than the adults. While the LC₅₀ for dimethoate was 130 ppm for nymphs, it was 3 ppm for adults from St. Jean‐Baptiste‐de‐Rouville. There were also significant differences in the level of resistance between the two regions where the H. vitripennis were collected. At St. Alexandre the LC₅₀ for phosalone on nymphs was 19, 250 ppm whereas, at St. Jean‐Baptiste‐de‐Rouville it was 160, 000 ppm.     

Sandhopper solar orientation as a behavioural biomarker of trace metals contamination

Although many studies have focused on trace metals accumulation, investigations of talitrid amphipods as biomarkers are rare. This study explores the possibility of using the solar orientation capacity of Talitrus saltator as a behavioural marker of exposure to two essential (Cu and Zn) and two non-essential (Cd and Hg) metals. LC₅₀ analyses performed before the solar orientation tests showed that the 72 h LC₅₀ for Hg was 0.02 ppm while the 96 h LC₅₀ values for Cu, Cd and Zn were 13.28 ppm, 27.66 ppm, and 62.74 ppm, respectively. The presence of metals in seawater affects the solar orientation capacity of T. saltator in a concentration-dependent manner and according to the toxicity ranking of the metals (Hg > Cu > Cd > Zn). Therefore, the solar orientation capacity of T. saltator seems to be a promising behavioural marker for exposure to trace metals.     

The influence of environmental factors on the molluscicidal activity of Euphorbia milii latex

Abstract

The present study was undertaken to investigate the influence of biotic (snail size and presence of food during the test) and abiotic factors (temperature, water hardness and concentration of organic materials) on the molluscicidal activity of Euphorbia milii latex. Bioassays were conducted with B. glabrata (10 snails per concentration) and snail lethality was evaluated after 24 hr and 48 hr of exposure to lyophilized latex solutions. Neither the degree of water hardness, nor the presence of food during the test affected latex‐induced snail mortality. The snail size had a minor influence on E.milii‐induced snail lethality. Newly‐hatched (shell diameter ≤ 1mm) as well as young (3–8 mm) snails were slightly less susceptible than older (10–25 mm) mollusks. On the other hand, the molluscicidal effect of E.milii latex was modified by environmental factors such as temperature (i.e. LC₅₀ and LC₉₀ values were halved for every 10°C rise in temperature) and concentration of organic materials in the water (i.e. the higher the concentration of organic matter, the higher the LC₅₀ value). The efficacy of E.milii latex as a molluscicide can be modified by factors such as water temperature and concentration of organic materials, and to a lesser extent by snail size.     

Effects of carbaryl,chlorpyrifos and endosulfan on growth,reproduction and respiration of tropical epigeic earthworm,Perionyx excavatus (Perrier)

Effects of sub-lethal doses of carbaryl (1-Naphthyl-methylcarbamate), chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridinyl-phosphorothioate) and endosulfan (6,7,8,9,10,10-Hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide), respectively a carbamate, an organophosphate and an organochlorine insecticide on growth, reproduction and respiration of the tropical earthworm, Perionyx excavatus (Perrier) were investigated under laboratory conditions. The results showed significant reduction in biomass, production and hatching of cocoon and production of juveniles of the worms exposed to 0.75 to 3.03 mg/kg soil of carbaryl, 0.91 to 3.65 mg/kg soil of chlorpyrifos and 3.75 to 15.0 μg/kg soil of endosulfan corresponding to 12.5 to 50 % of LC₅₀ value of the respective insecticide for P. excavatus. Endosulfan was found most dangerous among the three insecticides followed by carbaryl and chlorpyrifos. There was no hatching of the worms at endosulfan treatment 5.0 μg/kg soil (25 % LC₅₀) or above while the highest dose of carbaryl and chlorpyrifos (50 % of LC₅₀) rendered respectively 87.13 and 24.84 % reductions in hatching as compared to control. Chlorpyrifos produced no change in respiration of the worms except at the highest dose, while the worms showed an increase in evolution of CO₂ at all doses of carbaryl and endosulfan. Based on the recommended agricultural dose of each insecticide, it was concluded that application of endosulfan and carbaryl was potentially dangerous to earthworms.     

Wild tomato leaf extracts for spider mite and cowpea aphid control

Glandular trichomes on the leaves of wild tomato, L. hirsutum f. hirsutum Mull, also known as Solanum habrochaites (Solanaceae), synthesize and accumulate high levels of methyl ketones (MKs). L. hirsutum accession LA 407, having high concentration of MKs, was grown from seeds under greenhouse conditions. Four MKs (2-undecanone, 2-dodecanone, 2-tridecanone, and 2-pentadecanone) were screened for their toxicity to spider mites, Tetranychus urticae Koch and cowpea aphids, Aphis craccivora Koch. The objectives of this investigation were to: (1) develop a bioassay for testing MKs on spider mite and cowpea aphid mortality and (2) compare the efficacies of wild tomato leaf crude extracts and pure standard materials of MKs against spider mite and cowpea aphid mortality. Our results revealed that spider mites are most sensitive to 2-tridecanone (LC₅₀ = 0.08 μmole cm^?2 of treated leaf surface) and least sensitive to 2-undecanone (LC₅₀ = 1.5 μmole cm^?2 of treated leaf surface) 4 h after treatment. Similarly, 2-tridecanone caused greatest mortality (LC₅₀ = 0.2 μmole cm^?2 of treated leaf surface), whereas 2-undecanone caused the lowest morality (LC₅₀ = 0.48 μmole cm^?2 of treated surface) of cowpea aphid. We concluded that all MKs tested in this investigation are toxic to spider mites and aphids. 2-Tridecanone is more effective in killing mites and aphids compared to other MKs. Toxicity of crude extracts, prepared from the leaves of L. hirsutum accession LA 407, to spider mites and cowpea aphids revealed greater mortality compared to a combined mixture of MKs standard material (used at the same concentration as found on LA 407 leaves). This indicates that in addition to MKs, other unidentified compounds in LA 407 leaf extract also have pesticidal properties. Accordingly, leaf extracts of LA 407 could be explored in crop protection, and they might open a new area of MK formulations and discovery of biorational alternatives for pest control in agricultural fields.     

Unexpected toxic interactions in the freshwater amphipod Gammarus pulex (L.) exposed to binary copper and nickel mixtures

To document the toxicity of copper and nickel in binary mixtures, freshwater amphipods Gammarus pulex were exposed to the metals given independently or as mixtures. Toxicity to Cu alone was relatively high: 96-h LC₁₀ and LC₅₀ were found at 91 and 196 μg L^?1, respectively. Toxicity to Ni alone was very low, with 96-h LC₁₀ and LC₅₀ of 44,900 and 79,200 μg L^?1, respectively. Mixture toxicities were calculated from single toxicity data using conventional models. Modeled toxicity was then compared with the measured toxicity of the binary mixture. Two kinds of mixtures were tested. Type I mixtures were designed as combinations of Cu and Ni given at the same effect concentrations, when taken independently, to identify possible interactions between copper and nickel. In type II mixtures, Cu concentrations varied from 0 to 600 μg L^?1 while the nickel concentration was kept constant at 500 μg L^?1 to mimic conditions of industrial wastewater discharges. Ni and Cu showed synergic effects in type I mixtures while type II mixtures revealed antagonistic effects. Low doses of Ni reduced Cu toxicity towards G. pulex. These results show that even for simple binary mixtures of contaminants with known chemistry and toxicity, unexpected interactions between the contaminants may occur. This reduces the reliability of conventional additivity models.     

Phytotoxicity of atrazine, isoproturon, and diuron to submersed macrophytes in outdoor mesocosms

The submersed macrophytes Elodea canadensis, Myriophyllum spicatum and Potamogeton lucens were constantly exposed over a five-week period to environmentally relevant concentrations of atrazine, isoproturon, diuron, and their mixture in outdoor mesocosms. Effects were evaluated investigating photosynthetic efficiency (PE) of the three macrophytes and growth of M. spicatum and E. canadensis. Adverse effects on PE were observed on days 2 and 5 after application. M. spicatum was found to be the more sensitive macrophyte. E. canadensis and P. lucens were less sensitive to atrazine, diuron and the mixture and insensitive to isoproturon. PE of M. spicatum was similarly affected by the single herbicides and the mixture demonstrating concentration addition. Growth of E. canadensis and M. spicatum was not reduced indicating that herbicide exposure did not impair plant development. Although PE measurements turned out to be a sensitive method to monitor PSII herbicides, plant growth remains the more relevant ecological endpoint in risk assessment.     

Toxicity evaluation of cypermethrin,glyphosate, and malathion,on two indigenous zooplanktonic species

In Aguascalientes, Mexico, there is a special concern about pesticides because of their intensive use on guava production areas, which are located in the vicinity of water reservoirs; thus, non-target organisms could be exposed. Thereafter, the aim of this work was to assess the effect of cypermethrin, Faena® (glyphosate), and malathion, which are the most used pesticides in Aguascalientes’ guava production, on the indigenous freshwater species Alona guttata (cladoceran) and Lecane papuana (rotifer). Acute 48-h toxicity tests were carried out, and LC₅₀ values were calculated. Then, five sublethal concentrations (1/80, 1/40, 1/20, 1/10, and 1/5 of the respective LC₅₀) were selected for the chronic assays: (a) intrinsic growth rate analysis in the rotifer and (b) partial life table analysis in the cladoceran. The results of the acute toxicity tests showed that A. guttata was more sensitive to malathion (LC₅₀ = 5.26 × 10^?3 mg/L) at concentrations found in natural environments with continuous application on guava fields, whereas L. papuana was more sensitive to Faena® (LC₅₀ = 19.89 mg/L). The somatic growth of A. guttata was inhibited for the chronic exposure to cypermethrin. In addition, cypermethrin and Faena® seemed to exert endocrine disruptive effects on A. guttata. Moreover, malathion chronic exposure significantly decreased the survival of A. guttata. Moreover, L. papuana was affected chronically for the three pesticides.     

Effects of endosulfan exposure and Taura Syndrome Virus infection on the survival and molting of the marine penaeid shrimp, Litopenaeus vannamei

Molting in crustaceans is an important endocrine-controlled biological process that plays a critical role in growth and reproduction. Many factors can affect this physiological cycle in crustaceans including environmental stressors and disease agents. For example the pathology of Taura Syndrome Virus (TSV) of shrimp is closely related to molting cycle. Similarly, endosulfan, a commonly used pesticide is a potential endocrine disruptor. This study explores interrelationships between pesticide exposure, virus infection and their interactions with physiology and susceptibility of the shrimp. Litopenaeus vannamei (Pacific white shrimp) were challenged with increasing doses of endosulfan and TSV (TSV-C, a Belize reference strain) to determine the respective median lethal concentrations (LC₅₀s). The 96-h endosulfan LC₅₀ was 5.32 μg L⁻¹, while the 7-d TSV LC₅₀ was 54.74 mg L⁻¹. Subsequently, based on their respective LC₅₀ values, a 20-d interaction experiment with sublethal concentrations of endosulfan (2 μg L⁻¹) and TSV (30 mg L⁻¹) confirmed a significant interaction (p < 0.05, χ² = 5.29), and thereby the susceptibility of the shrimp. Concurrently, molt-stage of animals, both at the time of exposure and death, was compared with mortality. For animals challenged with TSV, no strong correlation between molt-stage and mortality was observed (p > 0.05). For animals exposed to endosulfan, animals in the postmolt stage were shown to be more susceptible to acute toxicity (p < 0.05). For animals exposed to both TSV and endosulfan, interference of endosulfan-associated stress lead to increasingly higher susceptibility at postmolt (p < 0.05) during the acute phase of the TSV disease cycle.