Puke or poop? Comparison of regurgitate and faecal samples to infer alpine grasshopper (Paprides nitidus Hutton) diet in experimental plant communities

Characterising plant-herbivore interactions is important to understanding
the processes that influence community structure and ecosystem
functioning. Traditional methods used to identify plant-herbivore
interactions are being superseded by non-destructive molecular approaches
that can infer interactions with greater resolution and accuracy from
environmental DNA (e.g., faeces and regurgitate). However, few studies
have compared the use of different types of samples and whether they
provide similar or contrasting information about species’ diet. Here we
compared the success of DNA amplification and host plant species
identification using restriction fragment length polymorphism (RFLP) of
faecal and regurgitate samples collected from alpine grasshoppers Paprides
nitidus Hutton during a grassland community mesocosm experiment. We found
that DNA amplification success was 23% and 86% higher for faecal than
regurgitate samples from female and male grasshoppers, respectively,
whereas successful host plant identification using RFLP was 9% higher for
regurgitate than faecal samples. The mean number of host plant species
identified per sample (1.40) did not differ between sample types or
grasshopper sexes. Of the 136 paired faecal-regurgitate samples, just 41%
and 74% produced exactly or partially matching host plant identifications,
respectively, indicating that different sample types provided
complementary information about herbivore diet. Some plant species were
more likely to be identified from faecal samples than expected by chance,
and this identification bias skewed towards greater representation in
faecal samples for plant species with higher investment in leaf tissue. We
conclude that multiple sample types may be required to fully characterise
an invertebrate herbivore species’ diet.