|GOMEZ-POLO, PRISCILLA - Institute De Recerca I Tecnologia Agroalimentaries (IRTA)|
|ALOMAR, OSCAR - Institute De Recerca I Tecnologia Agroalimentaries (IRTA)|
|CASTANE, CRISTINA - Institute De Recerca I Tecnologia Agroalimentaries (IRTA)|
|PINOL, JOSEP - Autonomous University Of Barcelona|
|AGUSTI, NURIA - Institute De Recerca I Tecnologia Agroalimentaries (IRTA)|
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2014
Publication Date: 7/27/2015
Citation: Gomez-Polo, P., Alomar, O., Castane, C., Lundgren, J.G., Pinol, J., Agusti, N. 2015. Analyzing predation of hoverflies (Diptera: Syrphidae) in Mediterranean lettuce crops using molecular techniques. Pest Management Science. 71:1219-1227.
Interpretive Summary: The field of gut content analysis (i.e., searching inside animal stomachs for food-associated markers to determine their diet) is rapidly expanding to include new genetic tools. Many of these tools are based on the polymerase chain reaction (PCR), which amplifies specific strands/sequences of a food’s DNA. We studied the ability of different tools (conventional PCR, quantitative PCR, and Nextgen Sequencing) to examine predation on aphids, thrips, and springtails by predatory hoverfly maggots in Mediterranean lettuce crops. Maggots are difficult to identify, so we used their DNA (DNA barcoding) to distinguish different maggot species from one another. We found that the predator frequently consumed the aphids on lettuce, regardless of whether other prey species were more or less available (thrips and springtails were also consumed, but less frequently). It was determined that qPCR was much more sensitive than conventional PCR in detecting predation. Nextgen sequencing revealed a broad swath of the predator’s diet comprised of much more than the prey species focused on in the conventional and quantitative PCR reactions, including other predators. Each of these tools has strengths and weaknesses that should be considered when designing future studies involving gut analyses.
Technical Abstract: Hoverflies are generalist predators of a great variety of primary pests. Nasonovia ribisnigri (Mosley) (Hemiptera: Aphididae) and Frankliniella occidentalis (Thysanoptera: Thripidae) are two common pests in Mediterranean lettuce crops, where they occur alongside alternative prey (e.g., Collembola). Relative trophic linkages of syrphid predators to their diverse prey diets is poorly understood. In the present study, specific primers were designed for N. ribisnigri and F. occidentalis. These primers, together with a previously designed pair of group-specific primers for Collembola, have been used for prey molecular detection using conventional PCR. A field experiment was conducted in an experimental lettuce plot involving caged infestations of N. ribisnigri, F. occidentalis and the hoverfly Episyrphus balteatus (De Geer) were introduced; the endemic arthropod community on the plants was left intact. Of the prey species tested, the trophic linkage between E. balteatus and N. ribisnigri was the strongest during both spring and summer. This was in spite of higher densities of the other prey species in summertime. Although in lower percentages, F. occidentalis and Collembolans were also detected in both seasons. qPCR was more sensitive than conventional PCR in detecting predation of N. ribisnigri by E. balteatus. To reveal other trophic interactions of E. balteatus, analyses were conducted by Next Generation Sequencing (NGS), detecting intraguild predation (IGP) on spiders, anthocorids and other hoverflies. Conventional and qPCR provided important insights into Mediterranean hoverfly species predation on focused pest and non-pest prey, whereas NGS gave a complementary approach showing the broad diet of this predator within the studied ecosystem.