Effects of Feeding Fluorescent Brightener 28 and Blue Dextran to European Corn Borer Larvae

Abstract

The European corn borer (ECB), Ostrinia nubilalis, is a common pest for corn crops in the United States and most of Europe (Hudan and LeRoux, 1986). Use of traditional pesticides to control ECB has resulted in the development of resistance in pest populations and significant loss of important biological control species. As such, novel methods, such as use of RNA interference (RNAi), are necessary to overcome resistance to traditional pesticides and protect non-target insects. RNAi takes advantage of intrinsic pathways that use long double-stranded RNAs (dsRNAs) to suppress the expression of specific genes (Zhang et al., 2010), however, many insects do not produce an efficient RNAi response, at least partially as a result of the presence of double-stranded ribonucleases (dsRNases) that degrade the dsRNAs prior to incorporation into the RNAi pathway (Kim et al., 2015). These dsRNases are present in the guts of many species, including ECB and are a powerful factor limiting the efficacy of RNAi. We hypothesize that applying dsRNA when expression of dsRNases is low (such as in young ECB larvae) and degrading the gut lining will minimize contact between dsRNAs and dsRNases and increase RNAi efficiency. Fluorescent Brightener 28 (FB28) is a chemical that has been used previously to damage insect gut linings and so is a good candidate for performing these experiments (Zhang et al., 2010). In addition, blue dextran (BD) is also necessary as a marker to demonstrate successful weakening and increased permeability of the gut, however, it is still unclear what concentrations of these chemicals ECB larvae will tolerate without significant adverse effects. Accordingly, these experiments were designed to identify the optimum levels of FB28 and BD needed in the diet of larval ECB for clear visualization of gut disruption.