Cocktail effect of Profenophos and Abamectin on tadpoles of Asian Common Toad (<i>Duttaphrynus</i> <i>melanostictus</i>)

Farmers mix two or more pesticides as mixing saves the spraying time and the labour cost and also with the idea that it increases the efficiency. The cocktail effect of two agrochemicals, profenophos and abamectin, was tested on the tadpoles of the Asian common toad, Duttaphrynus melanostictus under laboratory conditions. First, the 48 hr lethal concentrations (LC50) was determined. Then, a chronic exposure to a series of ecologically relevant concentrations (profenophos: 0.125, 0.25, 0.5, 1.0, 2.0 ppm and abamectin: 0.01, 0.02, 0.03, 0.04, 0.05 ppm) and a mixture of these were carried out. A control was set up using de-chlorinated tap water. Survival, growth, behaviour and development of malformations were observed until metamorphosis. The LC50 value of profenophos and abamectin were 3.78 ppm and 0.12 ppm, respectively. Both pesticides caused lethal and sub lethal effects at low concentrations while abamectin was more toxic. In the chronic exposure to field level had greatly reduced the survival of tadpoles in profenophos (Chi square test, χ2= 133.8, p = 0.001), abamectin (χ2 = 105.5, p = 0.001) and the cocktail (χ2 = 137.5, p&gt; 0.001) when compared with the control. All the exposures caused a reduction in the growth parameters with a significant reduction in snout-vent length and body mass in 15 days post-hatch tadpoles (one way ANOVA, p = 0.001). Moreover, exposed tadpoles took a longer time to metamorphose (40-42 days), developed malformations and showed behavioural abnormalities like altered feeding and swimming behaviours. Profenophos induced scoliosis and kyphosis, abamectin caused oedema while the cocktail exposed tadpoles developed both scoliosis and oedema. The effects of the cocktail exposure on survival, growth and development of malformations were higher than the lone effects. Although pesticide cocktail may have potential benefits in pest resistance management, what chemicals to be mixed have to be studied before recommending the mixing of chemicals to farmers to minimize the harmful effects on the environment