One-pot synthesis of silver nanocomposites from Achyranthes aspera: An eco-friendly larvicide against Aedes aegypti L

Objective: To formulate silver nanocomposites from Achyranthes aspera leaf extracts and evaluate its larvicidal activity against Aedes aegypti.Methods: The silver nanocomposites were synthesized from Achyranthes aspera leaf extracts. The process was optimized and traced through UV-visible and photon correlation spectroscopy. The larvicidal potential of silver nanocomposites of Achyranthes aspera leaf extracts was assessed against the early fourth instars of Aedes aegypti and three non-target organisms. Furthermore, the most effective and eco-safe nanocomposite was characterized by different biophysical techniques including scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform-infrared spectroscopy (FT-IR). Results: The formulated silver nanocomposites exhibited efficient larvicidal efficacy against Aedes aegypti. Bioassay with silver nanocomposites formulated using different AgNO3 concentrations (3, 4, and 5 mM) revealed respective LC50 values of 37.570, 6.262 and 1.041 μg/mL; 5.819, 1.412 and 0.489 μg/mL; and 5.519, 1.302 and 0.267 μg/mL after 24, 48 and 72 h. The silver nanocomposites with 4 mM AgNO3 were selected for characterization. SEM and TEM analysis revealed spherical, poly-dispersed structure with varied diameters of 1-25 nm. The XRD analysis established the crystalline and face-centred-cubic structure of silver nanocomposites with the maximum peak at a 2θ value of 37.42°. The EDX pattern showed the presence of Ag, O and C in the nanocomposites in their order of weight％. The FT-IR displayed visibly distinct peaks in different ranges demonstrating the intricacy of silver nanocomposites. In addition, the lethal concentrations of silver nanocomposites of Achyranthes aspera leaf extracts against Aedes aegypti larvae were non-toxic to non-target organisms including Gambusia affinis, Daphnia magna and Moina macrocopa. Conclusions: Silver nanocomposites synthesized with leaf extract of Achyranthes aspera provide a cost-effective and eco-safe alternative to conventional insecticides, and can be utilized as a potent mosquito nano-larvicide.

Larvicidal and irritant activities of hexane leaf extracts of Citrus sinensis against dengue vector Aedes aegypti L

Objective:To assess the larvicidal and irritant activities of the hexane extracts of leaves of Citrus sinensis (C. sinensis) against the early fourth instars and female adults of Aedes aegypti (Ae. aegypti). Methods: The larvicidal potential of the prepared leaf extract was evaluated against early fourth instar larvae of Ae. aegypti using WHO protocol. The mortality counts were made after 24 h and LC50 and LC90 values were calculated. The efficacy of extract as mosquito irritant was assessed by contact irritancy assays. Extract-impregnated paper was placed on a glass plate over which a perspex funnel with a hole on the top was kept inverted. Single female adult, 3-day old unfed/blood-fed, was released inside the funnel. After 3 min of acclimatization time, the time taken for the first take-off and total number of flights undertaken during 15 min were scored. Results: The citrus leaf extracts from hexane possessed moderate larvicidal efficiency against dengue vector. The bioassays resulted in an LC50 and LC90 value of 446.84 and 1 370.96 ppm, respectively after 24 h of exposure. However, the extracts were proved to be remarkable irritant against adults Ae. aegypti, more pronounced effects being observed on blood-fed females than unfed females. The extract-impregnated paper was thus proved to be 7-11 times more irritable as compared with the control paper. Conclusions:The hexane extracts from C. sinensis leaves are proved to be reasonably larvicidal but remarkably irritant against dengue vector. Further studies are needed to identify the possible role of extract as adulticide, oviposition deterrent and ovicidal agent. The isolation of active ingredient from the extract could help in formulating strategies for mosquito control.

Effect of Cold Hexane Extract of Karanja (Pongamia Glabra Vent) Seed Kernel on the Development of Mosquito Larvae.

Cold Hexane extract of karanja, Pongamia glabra Vent (Fabaceae) seed kernel (HKSK) ranging at the concentrations of 4 ppm to 28 ppm was evaluated against the freshly emerged larvae of Aedes aegypti and Culex quinquefasciatus. Treatment of HKSK imparted the mortality that was correlated with the level of dosage. Before pupation,100% fatality occurred in Ae. aegypti at a concentration of 20 ppm whereas in Cx. quinquefasciatus the same degree of mortality occurred at the extract concentration of 12 ppm in the first instar larvae only. At low doses, the emerging adults of Cx. quinquefasciatus had deformed legs, wings and truncated abdomen but the adults of Ae. aegypti showed no deformities. The developmental period was prolonged significantly in a dose-dependent manner for both the species treated. In Cx. quinquefasciatus this effect was more pronounced because of increased intermoult period showing an IGR effect of the extract. The calculated growth index also decreased in dose-dependent manner significantly more in Cx. quinquefasciatus. Indeed, Ae. aegypti appeared more susceptible to HKSK than Cx. quinquefasciatus.

Rabson-Mendenhall syndrome.

Rabson-Mendenhall syndrome is characterized by growth retardation, dysmorphisms, lack of subcutaneous fat, acanthosis nigricans, enlarged genitalia, hirsutism, premature and dysplastic dentition, coarse facial features, paradoxical fasting hypoglycemia and post-prandial hyperglycemia, extreme hyperinsulinemia and pineal hyperplasia. We describe a six-month-old female child with physical features suggestive of the Rabson-Mendenhall syndrome. The child also had medullary nephrocalcinosis.

Incomplete monosymptomatic leptomeningeal angiomatosis.

Phakomatoses or neurocutaneous syndromes are an important cause of seizures in the pediatric age group. The Sturge-Weber syndrome may affect the eye, skin and brain at different times. The skin lesions need not always manifest. We report a case of isolated affection of the central nervous system in a case of Sturge-Weber syndrome in the absence of ocular or cutaneous manifestations. Our case qualifies to be called incomplete monosymptomatic leptomeningeal angiomatosis.

Microplate assay of elevated esterase activity in individual pyrethroid-resistant mosquitoes.

Involvement of esterase-mediated hydrolysis as a mechanism of pyrethroidresistance in three species of mosquitoes, viz., Aedes aegypti, Culex quinquefasciatus and Anopheles Stephensi was investigated by microplate assay of β-esterases in individual larva and adult female and male mosquitoes. Assuming an absorbance value of 0·4 and above at 555 nm as the threshold level of elevated esterase activity which confers resistance, frequency distributions of such individual test mosquitoes were constructed in resistant and susceptible populations. The results indicate the involvement of ester hydrolysis of Pyrethroids as a predominant mechanism of pyrethroid-resistance in the larvae of Culex quinquefasciatus but not in Aedes aegypti. However, a marginal role of esterases is indicated in the larvae of Anopheles stephensi.