Development of a multiprimer metabarcoding approach to understanding trophic interactions in agroecosystems

To understand trophic interactions and the precise ecological role of each predatory species,it is important to know which arthropod and plant resources are used by generalist predators in agroecosystems.Molecular approaches,such as the use of high-throughput sequencing(HTS),play a key role in identifying these resources.This study develops a multiprimer metabarcoding approach for screening the most common trophic interactions of two predatory arthropods with contrasting morphologies,Rhagonycha fulva(Coleoptera:Cantharidae)and Anthocoris nemoralis(Hemiptera:Anthocoridae)collected from a peach crop.To reduce the time and cost of this metabarcoding approach,we first evaluated the effect of using two different predator-pools of different size(10 and 23 individuals of the same species).We also used our system to analyze the performance of one and two primer pairs in the same library.Our results show that the analysis of 23 individuals together with the use of two primer pairs in the same library optimize the HTS analysis.Using these best-performing conditions,we then analyzed the entire bodies of field-collected predators as well as the washing solutions used to clean the insect bodies.We were able to identify both gut content(i.e.,diet)and external pollen load(i.e.,on the insects’bodies).This study also demonstrates the importance of washing predatory insects’bodies prior to HTS analysis when the target species have a considerable size(>10 mm)and hairy structures.This metabarcoding approach has significant potential for the study of trophic links in agriculture,revealing expected and unexpected trophic relationships.

Development of a PCR-based method to monitor arthropod dispersal in agroecosystems:Macrolophus pygmaeus(Hemiptera:Miridae)from banker plants to tomato crops

Development of conservation biological control programs requires the identifi-cation of sources that contribute to predator colonization of crops.Macrolophus pygmaeus(Rambur)(Hemiptera:Miridae)is an efficient polyphagous predator used in biological con-trol programs in vegetable crops in Europe.We have developed a marking method based on spraying with a solution of the brine shrimp Artemia spp.(Anostraca:Artemidac)cysts,followed by a PCR detection of Artemia DNA to monitor M.pygmaeus dispersal from banker plants to tomato crops.Experiments conducted in climatic chambers show that the topical application of this marking solution on M.pygmaeus does not significantly reduce adult longevity and that it is detected up to 6 d after the application.When this Artemia solution was applied on Calendula officinalis L.banker plants harboring M.pygmaeus and maintained outdoors,Artemia DNA was still detected on 62%of the insects after6 d.The conducted field applications in commercial greenhouses have confirmed the usefulness of this method to monitor M.pygmaeus dispersal from banker plants to a newly planted tomato crop.This method can be used to assess arthropod movement,being an interesting molecular approach for further improving future pest management strategies.

Oviposition behavior of the mirid Macrolophus pygmaeus under risk of intraguild predation and cannibalism

Zoophytophagous mirid species,that feed and develop either on prey or plant resources,are often found simultaneously on the same host.Hence,these species can engage in both intraguild predation and cannibalism,which can pose a threat to mirid eggs.Ovipositing females may respond to such risks of predation on their eggs by reducing the number of eggs laid or selecting safer oviposition sites.We tested the oviposition behavior of Macrolophus pygmaeus(Rambur)(Hemiptera:Miridae)females under the risk of cannibalism by M.pygmaeus males and intraguild predation by Nesidiocoris tenuis(Reuter)males(Hemiptera:Miridae)under laboratory conditions.Intraguild predators and cannibals were introduced during or after the oviposition period.The number of eggs laid(using counts of newly hatched nymphs)and their proportion on each part of a tomato plant were both measured.The results reveal that only cannibalism by M.pygmaeus males after the period of oviposition significantly decreased the number of hatched eggs.Cannibalism thus represents a greater risk to mirid eggs than intraguild predation.The M.pygmaeus female responded to the presence of potential intraguild predators(or competitors)by decreasing the nu mber of eggs laid in the upper leaves.The results suggest that M.pygmaeus females avoid competition by N.tenuis,by laying fewer eggs on upper leaves.Cannibalism could regulate zoophytophagous predator populations under prey scarcity conditions and minimize the risk of crop damage associated with those biological control agents.