Assessing risks to non-target arthropods via molecular analysis of trophic webs

Properly assessing the non-target risks of insecticidal products requires a clear understanding of the ecological dynamics underpinning the structure and function of arthropod communities in crop fields.  Mapping potential routes of exposure to insecticidal products in the field is essential for identifying organisms that may be at risk, and for designing assays to evaluate the potential hazards of insecticidal products for those organisms.  One major route of exposure for beneficial natural enemies is through trophic webs.  Here, we use molecular gut-content analysis to construct an arthropod trophic web from organic corn agroecosystems as a baseline for evaluating the potential non-target risks of RNAi-based transgenic corn.  RNAi poses unique challenges for risk assessment, due to the inherent difficulties in directly detecting and identifying RNAi triggers in a field setting.  Using corn-specific DNA primers to analyze the gut-contents of a variety of corn arthropods, we identify, for the first time, the composition of arthropod trophic webs in corn.  This data can be used to identify beneficial organisms that are likely to be exposed to RNAi triggers via consumption of corn tissue or herbivores that have recently fed on corn.  We suggest that similar evaluations of the potential routes of exposure should be used to guide the selection of arthropods used in all laboratory hazard assays.  This represents a fundamental shift from the current, hazard-based risk-assessment paradigm, to an ecologically-driven, exposure-based paradigm.