Butterflies as an indicator species for the toxicity assessment of a commercial pesticide formulation containing d-tetramethrin and cyphenothrin

The use of pesticides has increased rapidly over the past few decades. Especially, in tropical regions pesticides are used extensively to control mosquitos which spread harmful diseases such as dengue and malaria. In Sri Lanka, mosquito borne diseases is a major concern. Infact, during the time period of January to July 2017, the Epidemiology Unit of the Ministry of Health has recorded 80,732 dengue victims and 215 deaths. A technique known as fogging/space spraying is used to control mosquito populations in urban areas. A chemical containing the active ingredients D-tetramethr in and cyphenothrin is mixed with diesel and fogged extensively to control mosquitos in Sri Lanka. This chemical can exert toxic effects on non-target species including butterflies which are a vital component in a balanced ecosystem. Therefore, this research was conducted to determine the toxic effects of the chemical using butterflies as indicator species. Butterflies were chosen because they are very sensitive to environment changes. The 5th instar larvae of Tirumala limniace exoticus (Blue Tiger) were used as the test species. The larvae used for the experiment were obtained by breeding the adult species in a butterfly cage. The larvae were exposed to 6 different formulations which included ‘Aged Aerated Water’ as Control, Diesel as Solvent Control and 4 increasing concentrations of the commercial pesticide (10, 100, 500 and 1000 ppm). A volume of 1μl was applied to the thorax region of the larvae (4 per each concentration). The chemical was allowed to air dry for a few seconds and observations were recorded. The larvae that were exposed to all the concentrations of the commercial pesticide including the solvent control did not manage to survive. This study concludes that the chemical has an effect on butterflies, thus on ecosystem. However, further studies including Acute and Chronic toxicity assessments must be conducted. The outcomes will be important in establishing conservation plans to protect butterflies as well as other insects that play a vital role in a balanced ecosystem.