Molecular gut content analysis reveals predator feeding preferences and potential for biological control of aphids in sugar beet fields

Aphis fabae Scopoli and Myzus persicae Sulzer (Hemiptera: Aphididae) are economically important pests of sugar beet. Natural enemies have potential for pest regulation. However their contribution to the control of the two sugar beet aphids is poorly understood. To elucidate the trophic relationships, we selected three aphid predators for molecular gut content analysis: two generalists Cantharis lateralis L. (Coleoptera: Cantharidae) and Coccinella septempunctata L. (Coleoptera: Coccinellidae), and the specialist Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) larvae. The first two species were chosen for their abundance, the latter for its role as a specialist aphid predator. Predators were collected in sugar beet fields, and qPCR was used to detect A. fabae and M. persicae remains in their gut. The DNA half-life detectability was assessed in a feeding assay and was found to be between 8 h and 33 h for the three predators. In the field, the most abundant aphid was A. fabae, with densities of over 14 aphids per plant, while M. persicae densities were over 100 times lower. In total 75% of the predators tested positive for A. fabae DNA. Despite the low densities of M. persicae in the field, 28% of the predators tested positive for this aphid species, indicating a preference for M. persicae. Based on the findings of the gut content analysis and predator densities, we assessed the total predation potential of three of the predators for the two years studied. We found that generalist predators contributed to 93% of the total predation for A. fabae, while the specialist predator C. carnea played more of a role in the predation of M. persicae, where it accounted for 23% of the total predation. While A. fabae densities exceeded predator capacity, M. persicae densities remained below total predation potential. These findings suggest that the three predators contribute to aphid control in sugar beet and help prevent outbreaks of M. persicae, a particularly serious pest.