Plant DNA detection from grasshoppers’ gut contents: Method and applications

The knowledge of food diet of insect herbivores is critical for better understanding and predicting plant-insect associations in natural communities. Direct observations and laboratory feeding trials may provide limited information about actual food consumption, and are often challenging for large-scale studies on insects’ diet. A PCR method of plant DNA detection from insect gut contents allows us to confirm food digestion and accurately determine an insect diet. Although there have been such studies on a number of insect species, only a few have included grasshoppers.

We extracted DNA from the gut contents of nymph Melanoplus grasshoppers, as well as adult M. femurrubrum and M. differentialis grasshoppers after feeding them several grasses, including Bouteloua and Bothriochloa species. Fragments (~500 bp) of the non-coding region of the chloroplast trnL (UAA) gene using universal trnL c-d primers were amplified and were found to match DNA fragments obtained independently from plants. Plant DNA was detectable for up to twelve hours post ingestion in the guts of nymph Melanoplus grasshoppers and adult M. femurrubrum grasshoppers, and up to 22 hours post ingestion in the guts of M. differentialis. PCR results for foregut and [midgut+hindgut] parts of M. differentialis grasshoppers suggested that insects consumed plant food sequentially, and did not switch often between offered grasses.

This PCR method has important applications; for example, in choosing the right time interval of grasshoppers starvation before feeding trials, and/or in determining feeding preferences of insects, which we are currently working on. More specifically, we are currently extracting plant DNA from both grasshoppers and reference plants collected from the same study plot, to detect the prevalence of native and invasive plants in the insects’ diet.