G. Eng, Charnita P. Whitmyer, B. Sina
1999
Citations
1
Influential Citations
13
Citations
Journal
Main Group Metal Chemistry
Abstract
Fourteen triorganotin compounds were tested against the second to the fourth instar larval stages of Anopheles stephensi (An. stephensi), a vector for human malaria. In general, the tricyclohexyltin compounds were the most effective. The LC50 values of the tricyclohexyltin compounds ranged from 0.010 μΜ for the chloride to 0.258 μΜ for the fluoride substituent against the second instar larval stage. Triphenyltin hydroxide and triphenyltin fluoride were the least effective larvicides. This was attributed to their polymeric nature. The efficacy of the triorganotins declined from the second instar to the fourth instar larval stages due to the formation of a thicker chitin covering. In general, the toxicity of the triorganotin compounds was found to be more dependent on the nature of organic ligand attached to the tin atom and not the anionic substituent. INTRODUCTION Malaria is one of the most widespread infectious diseases in the world. More than 40% of the world's population lives in tropical areas where they are at risk of malaria transmission. Between 300 to 500 million people are infected each year with an estimated 1.5 2.7 million deaths per year, often among children under five years of age. Great strides were made in reducing malaria in many countries in the 195060s, but there was a worldwide resurgence due to dichlorodiphenyltrichloroethane (DDT) resistant mosquitoes· and chloroquine resistant malaria. Furthermore, many countries mistakenly believed malaria was no longer a serious threat, and reduced funding for its control. As a result of these and other factors, malaria is once again a prevalent and dangerous disease in the tropics and subtropics. Thus, the development of a more effective larvicide/insecticide to combat malaria would be of worldwide interest. Organotin compounds have a wide range of industrial applications," including usage as fungicides," aquatic biocides,and in stone preservation. For example, triphenyltin compounds are used to combat a host of fungal diseases," while tributyltins are used as the active agent in marine paints.· In addition, organotins have been demonstrated to have strong insecticidal activities against a host of pests such as the common clothes moth,· house fly, · flea and Aedes aegypti mosquito 8 which is responsible for the transmission of yellow and dengue hemorrhagic fever. In the present work, we report the results of the larvicidal activity of fourteen organotin compounds against the second to fourth instar stages of the Anopheles stephensi (An. stephensi) larvae, a vector for human malaria. EXPERIMENTAL Preparation of stock triorganotin solutions All the triorganotin compounds were obtained commercially and used without further purification since the m.p./b.p. of the compounds were those reported in the literature. Stock solutions of the triorganotin compounds (26 mg dm" to 1000 mg dm") were prepared in either 95% ethanol or dimethyl sulfoxide depending on the solubility of the triorganotin. Tricyclohexyltin chloride and bromide, triphenyltin chloride, hydroxide, fluoride and bis(triphenyltin) oxide, tributyltin acetate and trimethyltin chloride and hydroxide were dissolved in dimethyl sulfoxide. The remaining compounds, tricyclohexyltin hydroxide and fluoride, triphenyltin acetate, tributyltin chloride and trimethyltin bromide, were dissolved in 95% ethanol. Anopheles stephensi larvae The Anopheles stephensi larvae were obtained from the laboratory of Dr. Barbara Sina, Entomology Department, University of Maryland, College Park, MD, 20742. The larvae were maintained in deionized water in an environmental chamber at a temperature of 27 30 °C with a relative humidity of 80 90% and a constant 12 h light/12 h dark regimen. The developing larvae were fed a diet of finely ground dog food. Three developmental stages of the larvae were used, the 2nd instar (over 3d old), the 3rd instar (over 7 d old) and the 4th instar (over 10 d old).