Effect of methamidophos on the morphology and male reproductive parameters of the earthworm eisenia foetida / Efecto del metamidofos sobre la morfología y parámetros reproductivos espermáticos de la lombriz de tierra eisenia foetida

The earthworm Eisenia foetida (Annelida, Oligochaeta) is an excellent biosentinel model organism for assessing potential toxicological risks by xenobiotics in terrestrial ecosystems. Methamidophos is an organophosphorous insecticide widely used to control agricultural pests. Its main action is due to inhibition of the enzyme acetylcholinesterase. The aim of this study was to evaluate the toxicity of methamidophos on the morphology and male parameters in Eisenia foetida. After determining the LD50 for methamidophos (85.34 mg/kg soil), five groups were formed, including control subjects, and sprayed with tap water. Methamidophos treated groups were subjected to doses of 1/10, 1/6, 1/3 and 2/3 of the LD50. Each group was analyzed at day 1, 6, 14 and 30 post-treatment. The results show a significant decrease in the weight of all individuals treated with methamidophos, besides showing a coiled body in 100 percent of them. Sperm count showed a significant increase in the treated groups after 1, 6 and 14 days post exposure and a significant decrease by day 30. Using the technique of acridine orange, a significant increase in abnormal metachromatic sperm (red fluorescence) in treated animals was shown. Methamidophos alters the overall behavior in earthworms and the male reproductive parameters of Eisenia foetida possibly altering the structure and conformation of DNA.

La Lombriz de tierra, Eisenia foetida (Annelida, Oligochaeta), constituye un excelente modelo de organismo biocentinela para evaluar los riesgos tóxicos de xenobióticos, en ecosistemas terrestres. Metamidofos es un insecticida organofosforado de amplio uso para controlar plagas agrícolas. Su acción principal se debe a la inhibición de la enzima acetilcolinesterasa. El objetivo de este estudio fue evaluar la toxicidad de metamidofos sobre la morfología y parámetros espermáticos de Eisenia foetida. Una vez determinada la LD50 para metamidofos (85,34 mg/kg de tierra), se tomaron 5 grupos, entre ellos los individuos del grupo control, los cuales fueron asperjados con agua potable. Los grupos tratados con metamidofos fueron sometidos a dosis de 1/10, 1/6, 1/3 y 2/3 de la LD50. Cada grupo fue analizado al día 1, 6, 14, y 30 post tratamiento. Los resultados muestran una baja significativa en el peso de todos los individuos tratados con metamidofos, además de presentar enrrollamiento corporal, en el 100 por ciento de ellos. El recuento espermático presenta un aumento significativo en los grupos tratados a 1,6 y 14 días, para luego decaer significativamente el día 30. El uso de la técnica del naranja de acridina, mostró un aumento significativo de espermatozoides metacromáticos anormales en los animales tratados (fluorescencia de color rojo). Se concluye que Metamidofos altera el comportamiento general de la lombriz de tierra y los parámetros reproductivos espermáticos de Eisenia foetida posiblemente alterando la conformación y estructura del ADN.

Efficacy of pirimiphos-methyl (50% EC), as a larvicide for the control of Culex quinquefasciatus.

Background & objectives: Pirimiphos-methyl, an organophosphorus insecticide is known to overcome resistance mechanisms of mosquitoes to other organophosphates. Information on the duration of efficacy of pirimiphos-methyl (50% emulsifiable concentrate) for the control of immatures of Culex quinquefasciatus, the vector of bancroftian filariasis, is scanty and hence site specific field trials are necessary to determine the field dosage. Pirimiphos-methyl (50% EC) was tested for its efficacy in cesspits and drains against the immatures of Cx. quinquefasciatus at Puducherry, an endemic area for filariasis, south India. Methods: In cesspits, Pirimiphos-methyl (50% EC) was tested at the dosage of 25, 50, 100 and 200 g(ai)/ ha and in drains at 50, 100 and 200 g(ai)/ha. Immature density during pre-treatment and post-treatment periods was recorded and the efficacy was determined by calculating percentage reduction in larval and pupal densities for a period of about one month. Results: In cesspits, application of the insecticide at 25 and 50 g(ai)/ha reduced the density of larvae by >80 per cent for 2-4 days only, whereas at 100 and 200 g(ai)/ha, the efficacy lasted for 7-8 days. More than 80 per cent reduction was observed in pupal density for 4 days at 50 g(ai)/ha and for 10-12 days at 100 and 200 g(ai)/ha respectively. In drains treated with 50 g (ai)/ha, >80 per cent reduction in larval density was recorded up to 3rd day post-treatment. The efficacy showing >80 per cent reduction in larval density lasted for 12-13 days and the same in pupal density lasted for 10-12 days at 100 and 200 g(ai)/ha. Interpretation & conclusions: At the dosages of 100 and 200 g(ai)/ha, pirimiphos-methyl (50% EC) showed no difference in the control of larvae of Cx. quinquefasciatus in cesspits and drains. Pirimiphosmethyl may be applied at the field dosage of 100 g (ai)/ha at 10 day-intervals in the larval habitats of Cx. quinquefasciatus to achieve >80 per cent reduction in immature density.

Effect of anticholinesterase compound phosalone on blood-brain barrier (BBB) permeability.

To elucidate the role of acetylcholinesterase (AChE) enzyme in BBB function, phosalone, an organophosphorous compound, was studied using rat brain micro vessels in vitro. Phosalone at 100 mg/kg b. wt. induced convulsions and caused a significant inhibition of AChE resulting in increased permeability as assessed by volume distribution. The anaesthetized phosalone treated group also increased permeability as compared to the control but the values were significantly (P<0.05) lower than phosalone alone treated group. The inhibition of AChE enzyme has altered the barrier function at the dose level at which it caused convulsion and had an added effect on permeability of BBB.

Cytogenetic and genotoxic effects of the insecticides, imidacloprid and methamidophos

We examined the cytogenetic and genotoxic effects of the neonicotinoid insecticide imidacloprid and the organophosphate insecticide methamidophos, when administered alone or in combination. These insecticides were tested with the bone marrow chromosome aberration assay and micronucleus test in rats and by the bacterial mutation assay (Salmonella/microsome mutagenicity assay). Wistar albino rats were orally fed daily with laboratory chow treated with various concentrations of insecticides, 50 and 100 mg/kg imidacloprid, 2.5 and 5 mg/kg methamidophos, and 2.5 and 5 mg/kg imidacloprid plus methamidophos, respectively, for 90 days. Numerical and structural chromosomal aberrations were evaluated. Significant differences were detected between all the insecticide-administered groups versus the control group and between the two concentrations of the pesticide-treated groups. Both concentrations of the insecticides induced a dose-related increase in the micronucleus frequency (P < 0.05). Dose-related increases in the number of revertants were observed with the two Salmonella strains (TA98 and TA100). All tested doses of the insecticides demonstrated mutagenic activity in the presence of S9 mix. These results lead us to the conclusion that the synergistic effect of methamidophos and imidacloprid causes an increase in potential damage to non-target organisms.

Effect of edifenphos on follicular dynamics in albino rats.

Exposure of rats to 0.1, 0.15 and 0.20 mg/100 g body weight edifenphos (i.p.) had no significant effect on the number of healthy follicles and atretic follicles in all the stages. However, treatment with 0.25 mg dose resulted in a significant decrease in stage I and total number of healthy follicles and increase in stage V atretic follicles. A significant decrease in stage I, II, III and total number of healthy follicles, and a significant increase in stage I, III, IV and total number of atretic follicles were observed in 0.3 mg edifenphos treated rats. The results indicate that the effect of edifenphos is dose dependent.

Interaction of technical hexachlorocyclohexane and oxydemeton methyl 25 EC to female rats after dermal application.

Technical hexachlorocyclohexane (HCH, 100 mg/kg/day) and oxydemeton methyl 25 EC (125 mg/kg/day) to female rats for 7, 15 and 30 days individually and in combination through skin application caused pathomorphological changes in vital organs and significant enzymatic changes in liver and serum. However changes produced by the two compounds in combination were not suggestive of potentiation effect at the tested dose level in female rats.