There are three commonly used assays to identify plant material in insect guts: the cold anthrone test for fructose, the cellulose staining test for visualizing plant tissue and gas chromatography for seeking unique sugar content profiles. Though sugar and cellulose tests can distinguish between the general sources of sugar meal (nectar versus tissue), they cannot identify the species of plant sources. Even gas chromatography profiles can be problematic; there are reported instances of intra-specific variation as well as inter-specific and intergeneric variation that can mar results. Here, we explore the potential for DNA analysis to help resolve this issue. First, Anopheles sergentii were exposed to branches of two species of highly attractive flowering bushes in the laboratory and the great majority ( approximately 90-98%) were positive for sugar from nectar while very few were positive for cellulose ( approximately 0.5-8%) and DNA (6-19%). Moreover, laboratory An. sergentii showed opposing preferences, tending to obtain sugar from nectar of one plant (Tamarix nilotica) but to feed more on tissue from the other (Ochradenus baccatus). An. sergentii are exposed to a wide variety of plants in their natural desert habitats and in the absence of flowers in the dry season, they resort to feeding specifically on tissues of a few plants. According to DNA analysis the favorite plants were Suaeda asphaltica, Malva nicaeensis and Conyza dioscoridis, which are succulents that account for less than 1% of vegetation in the area.
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