Freshwater invertebrate testing is a critical component of comprehensive ecological risk assessments for various classes of pesticides. Daphnia sp. are commonly used test species for meeting freshwater invertebrate testing requirements employing a water column exposure. Some classes of pesticides, including insect-control proteins and biologicals, pose significant challenges in water column test designs due to their limited solubility. Hyalella azteca is a freshwater epibenthic amphipod that serves as a representative species for freshwater shredders, and is a standard test organism in sediment toxicity tests due to its amenability for culture and sensitivity to a variety of chemical substances. Insect control proteins from genetically modified crops exhibit dietary modes of action and pose additional challenges in standard sediment toxicity test designs due to their high affinity binding to sediment components, thereby significantly hindering analytical confirmation of test concentrations.
Herein, we describe the development of an agar-based diet formulation that supports the growth and development of H. azteca in a toxicity test design. Dietary consumption by amphipods was demonstrated by comparing body weight measurements of organisms exposed to diet tablets to those in no-food avoidance control and standard guideline feeding regime treatment groups. An insect control protein from genetically-modified maize was incorporated into the diet to test for effects on H. azteca in a 10-day static daily renewal test design. Protein stability in the diet was confirmed under test conditions, and additionally, a potential positive control toxicant was identified and characterized. This method serves as the basis for a novel test design to evaluate the potential effects of test substances with limited solubility or dietary modes of action on a freshwater invertebrate species.
Bayer CropScience presented this research, co-authored by Mark Fitzmaurice and Michael Bradley, at the SETAC North America 44th Annual Meeting in Louisville, Kentucky.