Diet Related Effects of the Pesticides Terbuthylazine and Tebuconazole on Scraper and Shredder Freshwater Invertebrates

Abstract

Leaf litter or algae are the most important basal resources for invertebrate primary consumers in freshwater ecosystems.This first level in the food chain is essential for nutrient and energy transfer to the entire food web. In streams algae grow mainly on the streambed and jointly with other microorganisms constitute the biofilm, a rich food for invertebrate scrapers. Leaf litter is colonized by microbial decomposers (aquatic hyphomicetes and bacteria) that increase nutritional quality and palatability of leaf litter.These basal source-consumer links can be influenced by chemical pollutants such as pesticides widely used in agriculture activities. Herbicides can affect algae growth in stream biofilms and fungicides in turn, may alter leaf-associated fungal community; both finally affecting food quantity and quality for invertebrate consumers.In this study we focus on the effects of terbuthylazine which is an herbicide that inhibits photosynthesis (photosystem II), and the fungicide tebuconazole an inhibitor of ergosterol biosynthesis. Both pesticides are routinely used in agriculture and frequently detected in streams and rivers [1,2]. Our aim is to evaluate the diet-related effects of these two pesticides on the consumption and growth rates of the snail Physella acuta (scraper feeding strategy) and the crustacean Echinogammarus sp (shredder). We conducted a 14-day experiment using artificial channels where biofilm, leaf-litter and invertebrates were exposed to control conditions and to both pesticides, separately and in mixture in environmentally realistic concentrations. We expect that the quantity of biofilm will decrease due to herbicide effect as well as the quality of the leaf-litter because the effect of fungicide on leaf-associated fungi, which in turn will negatively affect the growth rate of both invertebrates.