Predation of syrphid larvae (Diptera: Syrphidae) on thrips in onion fields intercropped with barley

Syrphid larvae are well-known predators of aphids; however, we sometimes observed them on onion plants with thrips and without any aphids, which intercropped with barley in our previous study. Therefore, we hypothesized that syrphid larvae fed on thrips in the onion field in the absence of aphids, their main prey. This hypothesis was tested by analyzing the prey DNA from syrphid larvae collected from onion plants intercropped with barley. We found that they preyed on three thrips species: Thrips tabaci (Lindeman), Frankliniella occidentalis (Pergande), and Anaphothrips obscurus (Müller). Moreover, we observed that syrphid larvae collected from onion plants fed on larval T. tabaci in a laboratory setting. According to COI sequencing of their genomes, the syrphid species occurred from the onion plants were Sphaerophoria macrogaster (Thomson), Melanostoma scalare (Fabricius), Melanostoma mellinum (L.), and Platycheirus pennipes (Ohara); all of them were found to prey on thrips in the prey DNA analyses. These results and observations supported the hypothesis and suggested that intercropping barley as a living mulch may become an option for enhancing the potential of native syrphid species as generalist predators in the onion fields.