[Aim]  To quickly identify the host plant composition and dietary diversity of two phytophagous scarab beetles, Holotrichia parallela and Anomala corpulenta. Using DNA metabarcoding and light trapping, the feeding preferences of these beetles were analyzed to provide a scientific basis for the environmentally-friendly control of these pests. [Methods]  Samples were collected using two methods, manual trapping of live beetles and automated collection via lethal infrared monitoring lamps. Guts of both live trapped and lamp-killed beetles were dissected, and total DNA was extracted from the gut contents. The trnL gene was amplified by PCR and sequenced on a high-throughput platform. The resulting sequences were compared against the NCBI database for taxonomic assignment. Both Alpha and Beta diversity were calculated and used to compare the diversity and composition of the plants consumed by each species. [Results]  Analysis of H. parallela gut contents revealed a diet dominated by a few plant species, primarily Prunus pseudocerasus, Bothrocaryum controversum and Salix babylonica. Of these, P. pseudocerasus was the most prevalent, with a relative abundance of 68.56%. In contrast, A. corpulenta had a more generalist diet, which included P. pseudocerasus (24.62%), Malus honanensis (19.02%), S. babylonica (14.61%) and Robinia pseudoacacia (10.70%). The Alpha and Beta diversity indices obtained using both two sampling methods (fresh samples from live-caught specimens and dry samples from light-trap killed specimens) were compared, and no significant differences (P> 0.05) were found. Both types of sample accurately reflected the abundance, and evenness, of ingested plant species, as well as the feeding preferences and dietary diversity of each species. [Conclusion]  The integration of plant DNA barcoding and high-throughput sequencing effectively enables rapid and efficient identification of the plants consumed by phytophagous insects. Gut samples obtained from pest monitoring lamps can reliably reveal the natural dietary composition of the target species. These results support the development of food-web based ecological regulation, and the development of environmentally-friendly pest control strategies.