Determination of insecticides' lethal concentrations and metabolic enzyme levels in Triatoma dimidiata / Determinación de concentraciones letales y niveles de enzimas metabólicas de insecticidas en Triatoma dimidiata

Abstract: Objective: The feasibility of the use of WHO impregnated paper and biochemical assays to determine lethal concentrations (LC50 and LC99) and insecticide metabolic enzyme levels of Triatoma dimidiata. Materials and methods: LC50 and LC99 were calculated with WHO papers impregnated at different concentrations of malathion, propoxur and deltamethrin; the percentage of insensitive acetylcholinesterase (iAChE); and the levels of esterases, glutathione S-transferases, and monooxygenases in laboratory nymphs of the first stage (5 to 7 days), were undertaken using the WHO biochemical assays. Results: Respectively the LC50 and LC99 µg/cm2 obtained for malathion were 43.83 and 114.38, propoxur 4.71 and 19.29, and deltamethrin 5.80 and 40.46. A 30% of the population had an iAChE, and only a few individuals had high P450 and β-eterase levels. Conclusion: Impregnated papers and biochemical tests developed by WHO for other insects, proved to be feasible methods in monitoring insecticide resistance and metabolic enzymes involved in T. dimidiata.

Resumen: Objetivo: La factibilidad de usar los papeles impregnados y ensayos bioquímicos según la OMS para determinar concentraciones letales (CL50 y CL99) y niveles enzimáticos en la resistencia a insecticidas en Triatoma dimidiata. Material y métodos: Se calcularon la CL50 y CL99 con papeles impregnados según la OMS a diferentes concentraciones de malatión, propoxur y deltametrina; el porcentaje de acetilcolinesterasa insensible (iAChE); y los niveles de esterasas, glutatión S-transferasas, y monooxigenasas en ninfas de laboratorio del estadio I (5-7 días) se determinaron usando los ensayos bioquímicos según la OMS. Resultados: Se obtuvieron las CL50 y CL99 µg / cm2 respectivamente para malatión 43.83 y 114.38, propoxur 4.71 y 19.29, y deltametrina 5.80 y 40.46. Un 30% de las chinches tuvo iAChE, y sólo pocos individuos tuvieron niveles superiores de P450 y β-eterasas. Conclusión: Los papeles impregnados y ensayos bioquímicos que describe la OMS para otros insectos demostraron ser métodos factibles para monitorear la resistencia a insecticidas y las enzimas metabólicas involucradas en T. dimidiata.

Synergic actions of polyphenols and cyanogens of peanut seed coat (Arachis hypogaea) on cytological, biochemical and functional changes in thyroid.

In animals, long-term feeding with peanut (Arachis hypogaea) seed coats causes hypertrophy and hyperplasia of the thyroid gland. However, to date there have been no detailed studies. Here, we explored the thyroidal effects of dietary peanut seed coats (PSC) in rats. The PSC has high levels of pro-goitrogenic substances including phenolic and other cyanogenic constituents. The PSC was mixed with a standard diet and fed to rats for 30 and 60 days, respectively. Animals fed with the PSC-supplemented diet showed a significant increase in urinary excretion of thiocyanate and iodine, thyroid enlargement, and hypertrophy and/or hyperplasia of thyroid follicles. In addition, there was inhibition of thyroid peroxidase (TPO) activity, 5’-deiodinase-I (DIO1) activity, and (Na+-K+)-ATPase activity in the experimental groups of rats as compared to controls. Furthermore, the PSC fed animals exhibited decreased serum circulating total T4 and T3 levels, severe in the group treated for longer duration. These data indicate that PSC could be a novel disruptor of thyroid function, due to synergistic actions of phenolic as well as cyanogenic constituents.

Persistence of DDT, malathion & deltamethrin resistance in Anopheles culicifacies after their sequential withdrawal from indoor residual spraying in Surat district, India.

Background & objectives: Under the national antimalaria programme DDT was introduced in early 1950s for vector control and later hexachloro cyclohexane (HCH) followed by malathion and recently synthetic pyrethroids in 1990s to manage the insecticide resistance in Anopheles culicifacies. Subsequent replacement led to development of multiple resistances in An. culicifacies in Surat district in Gujarat State. Indoor residual spray (IRS) was completely withdrawn in southern villages in Surat in 2002. This study was undertaken in these areas to study the persistence of resistance to DDT, malathion and deltamethrin after sequential withdrawal of IRS with these insecticides at different times. Methods: Susceptibility tests on An. culicifacies were conducted using standard WHO methods and kits. Mortality, knockdown time and lethal times were calculated for An. culicifacies exposed to WHO prescribed diagnostic concentrations of different insecticide impregnated papers. Results: Persistence of DDT-resistance was observed even after 30 yr of its withdrawal from IRS. Similarly, persistence of malathion resistance was also observed after 9 yr of its withdrawal from IRS, while reversal of deltamethrin-resistance was observed very fast within 2-3 yr after its withdrawal from IRS in 2002. Interpretation & conclusion: Present data indicate that the quantum of reversion of insecticide resistance in a population is relative and depends on the genetic stability of the respective resistance genes in the mosquitoes. In the present study withdrawal of pyrethroid-IRS resulted in increased susceptibility against pyrethroids alone and was independent of existence of resistance to insecticides of other groups. This study emphasizes that appropriate rotation of different insecticides; including carbamates may prevent or delay the onset of resistance.

Effect of methacrylonitrile on membrane bound enzymes of rat brain.

Methacrylonitrile (MeAN) is a plastic monomer. Its effect on membrane bound enzymes like Na+K+ -ATPase, Ca2+ -ATPase, Mg2+ -ATPase, NADH dehydrogenase, alkaline phosphatase (ALP) and various elements like sodium (Na+), potassium (K+), and calcium (Ca2+) in rat brain were studied. Administration of 50 mg/kg body weight/day (0.25 LD50) and 100 mg/kg body weight/day (0.5 LD50) by gavage to rats for 7 days resulted in a significant decrease in activities of Na+K+ -ATPase, Ca2+ -ATPase, Mg2+ -ATPase, and NADH dehydrogenase. A significant reduction in calcium content, potassium content and a significant increase in sodium content and alkaline phosphatase activity in MeAN treated animals were observed. Inhibition of membrane bound enzymes occurred due to either direct effect of MeAN or indirect effect of changes in ionic homeostasis in MeAN treated animals.

Effects of beta-cyfluthrin on white and sepia mutants of Drosophila melanogaster.

The effects of sublethal concentrations of a synthetic pyrethroid, beta-cyfluthrin (Bulldock 025 SC) were investigated in the F1 generations of white and sepia mutants of Drosophila melanogaster after various cross combinations of the parents which were exposed separately to the insecticide mixed diet for 24 hours. The experiment was carried out under the laboratory conditions at a temperature of 25+/-5 degrees C and 60+/-5% relative humidity. The insecticide had deleterious effect on the growth and development of both the mutant flies. Larval, pupal and total developmental periods were found to be increased as compared to controls, whereas the number of adult emerged decreased in all the treatment sets. Larval period index (LPI), pupal period index (PPI) and growth index (GI) were observed to be decreased in the entire cross combinations. Maximum effects were observed in those sets where both the sexes were treated, crossed and F1 generation was studied on the treated food having sublethal concentration of the insecticide, followed by similar treatment sets but on the fresh untreated food. Females were found to be resistant as compared to the males, whereas white mutant files were more susceptible to the test insecticide beta-cyfluthrin as compared to sepia mutant flies.

Rotational application of bioinsecticide with deltamethrin-An antilarval measure for the control of filarial vector, Culex quinquefasciatus (Culicidae: Diptera).

A laboratory investigation was undertaken to study the cyclic usage of field recommended doses of Bacillus thuringiensis israelensis (Bti), Bacillus sphaericus (Bsp) and combination of Bti and Bsp (half the recommended dose of each) with deltamethrin 2.8 EC to attain better control of mosquito larvae. To understand the susceptibility status of the Culex quinquefasciatus larvae in the field, early fourth instar field collected larvae were exposed to the above treatments of biopesticides and were monitored for their persistency till 50% mortality was obtained. The larvae those survived in each treatment were transferred to the concentration of deltamethrin that gave 50% mortality. Observations on larval mortality after the treatment with deltamethrin were recorded after 24 h. The results revealed that Bti excels Bsp, as it recorded 54% mortality only on 17th day after application. The other salient finding of this study is LC50 of deltamethrin is sufficient to follow the biopesticides application for an effective control of Culex larvae.

Methacrylonitrile induced oxidative stress in rat liver.

MeAN administration (40mg/kg body wt/day (i.e. 1/5 of LD50) resulted in increased levels of lipid peroxidation products, conjugated dienes and lipofuscin-like substances in rat liver. Significant decrease in GSH and a decreased activity of hepatic SOD, CAT and GPx were observed. There was also an increase in glutathione S-transferase and G6PD activities, decreased plasma ceruloplasmin and vitamin C implying oxidative stress caused by MeAN.

Blood and hepatic glutathione in linamarin fed rats.

Female Sprague Dawley rats were fed 5 mg linamarin daily for 10 days. Reduced glutathione (GSH) levels in blood and liver of experimental rats were analysed. The results showed an increase of 45% and 33% glutathione levels in blood and liver respectively in experimental rats. This alteration in glutathione levels could be most likely either due to increased hepatic biosynthesis or as a consequence of decreased peripheral utilization which might be appreciated due to hypothyroidal status induced by linamarin feeding.

Clinical and biochemical features of malnutrition related diabetes mellitus

The aims of this study were to characterize clinically and biochemically malnutrition related diabetes mellitus (MRDM) as it presents in Jamaica (J-type or phasic insulin dependent diabetes mellitus) and to examine the food toxin (linamarin)/malnutrition hypothesis as a possible aetiological factor in the onset of MRDM. The study was broadly divided into two major areas: (i) Clinical or patient study and (ii) Animal model study. The patient population consisted of thirty-four, (23 females, 17 males) who attend the Diabetic Outpatient Clinic of the University Hospital of the West Indies. This group consisted of 14 phasic insulin dependent diabetes mellitus (PIDDM) (8 females, 6 males) 10 non-insulin dependent diabetes mellitus (IDDM), (6 females, 4 males). Ten (10) normal (4 females, 6 males) subjects also participated. The diabetic and normal subjects were matched for age, body mass index and duration of diabetes (among diabetics). Comparitive studies were performed on insulin receptor binding, hormonal profile, glucose tolerance, blood status, renal, hepatic and pancreatic function. The results show a significantly decreased white and red blood cell binding to insulin (P<0.05), extensive kidney damage (P<0.05) and increased pancreatic echogenicity in PIDDM. These findings support a separate identity of the latter syndrome from Types 1 and 11 diabetes mellitus. In the animal model study, the dogs (male and female) were maintained on a diet of cornmeal cooked with chicken, fortified with Purina laboratory chow and water ad libitum. Malnutrition was induced by restricting the diet to a very small quantity of cornmeal only for a period of 7-10 days. The recovered dogs were re-fed the normal diet with added milk and multi-vitamin supplement. Linamarin dosage of 20 mg per kg body weight induced abnormally high glucose levels, and in two cases the hyperglycaemia was sustained for several days. There was an associated decrease in binding of insulin to erythrocytes and mononuclear leucocytes, as well as prevailng hypoinsulinaemia in the limarin-induced hyperglycaemic conditions. This animal study presents a possible aetiological model for malnutrition related diabetes mellitus (Summary)