Molecular assays to reliably detect and quantify predation on a forest pest in bats faeces

[EN] Targeted molecular methods such as conventional PCR (cPCR) and quantitative PCR (qPCR), combined with species-specific primers and probes, are widely applied for pest species detection. Besides, the potential of qPCR to quantify DNA in samples makes it an invaluable molecular tool to infer the predation levels on specific prey by analysing predators' stools. Nevertheless, studies on the diet of bats failed to find any empirical relationship, and it remains to be evaluated. Thus, we developed and evaluated two species-specific PCR assays to detect and quantify DNA of a major forest pest, the pine processionary, Thaumetopoea pityocampa, in bats' faeces. Further, we empirically compared a range of different known DNA concentrations (input) of the target species mixed with mocks and bat faecal samples against DNA abundances yielded by qPCR (output) for a quantitative assessment. Overall, cPCR showed a lower detection rate than qPCR, but augmenting the replicate effort from one to three replicates led to a greater increase in the detection rate of the cPCR (from 57 to 80%) than the qPCR (from 90 to 99%). The quantitative experiment results showed a highly significant correlation between the input and output DNA concentrations (t = 10.84, p < 0.001) with a mean slope value of 1.05, indicating the accuracy of our qPCR assay to estimate DNA abundance of T. pityocampa in bat faeces. The framework of this study can be taken as a model to design similar assays applicable to other species of interest, such as agricultural pests or insects of public health concern.We thank all who collaborate in the acquisition of samples and specially to Joxerra Aihartza for its invaluable help and support during the investigation. We are also grateful to the Sequencing and Genotyping Unit-Genomic Facilities-SGIker (UPV/EHU/ERDF, EU) for the technical support provided. This project was funded by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (CGL-2015-69069P), as well as the Government of the Basque Country (IT754-13 and IT1163-19). The Basque Government Granted UB (PRE_2019_2_0186)