Metabarcoding versus mapping unassembled shotgun reads for identification of prey consumed by arthropod epigeal predators.

BACKGROUND: A central challenge of DNA gut content analysis is to identify prey in a highly degraded DNA community. In this study, we evaluated prey detection using metabarcoding and a method of mapping unassembled shotgun reads (Lazaro). RESULTS: In a mock prey community, metabarcoding did not detect any prey, probably owing to primer choice and/or preferential predator DNA amplification, while Lazaro detected prey with accuracy 43-71%. Gut content analysis of field-collected arthropod epigeal predators (3 ants, 1 dermapteran, and 1 carabid) from agricultural habitats in Brazil (27 samples, 46-273 individuals per sample) revealed that 64% of the prey species detections by either method were not confirmed by melting curve analysis and 87% of the true prey were detected in common. We hypothesized that Lazaro would detect fewer true- and false-positive and more false-negative prey with greater taxonomic resolution than metabarcoding but found that the methods were similar in sensitivity, specificity, false discovery rate, false omission rate, and accuracy. There was a positive correlation between the relative prey DNA concentration in the samples and the number of prey reads detected by Lazaro, while this was inconsistent for metabarcoding. CONCLUSIONS: Metabarcoding and Lazaro had similar, but partially complementary, detection of prey in arthropod predator guts. However, while Lazaro was almost 2× more expensive, the number of reads was related to the amount of prey DNA, suggesting that Lazaro may provide quantitative prey information while metabarcoding did not.

Field Efficacy of Metarhizium rileyi Applications Against Spodoptera frugiperda (Lepidoptera: Noctuidae) in Maize.

The efficacy of the fungus Metarhizium rileyi (Farlow) Kepler, S. A. Rehner & Humber (Hypocreales: Clavicipitaceae) against the fall armyworm Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) and the impact on the community of epigeans predators as well as the natural occurrence of native fungal strains were evaluated after sequential sprays in maize. In the first season, the infestation was lower than 0.2 larvae per plant throughout the three fungal sprays and no significant difference was observed in the number of infected larvae among treatments. In the second season, insect population reached an average of 0.8 larvae per plant between the second and third sprays and the number of larvae succumbed by M. rileyi was higher in fungal-treated plots in the following weeks. Molecular characterization of the collected isolates on mummified larvae revealed the introduction of a new isolate did not eliminate the native strain on the fungal-treated plots. In both seasons, the diversity and abundance of predator species in the plots were not affected by any of the treatments. We showed that applications of selected strains of M. rileyi early in the season have no significant impact on the occurrence of natural enemies in maize.