Food webs form the basis of biological communities, though empirical research has been hindered by difficulties in quantifying interactions. Metabarcoding from predator gut content extractions with universal primers promises to provide simple and rapid insights into food web interactions. However, the highly overabundant predator DNA often completely out‐competes that of the digested prey DNA during PCR, impeding the ability to assess the abundance and diversity of prey items. Focusing on the issue of overabundance of predator DNA amplified by a commonly used COI primer pair, we use predator lineage‐specific SNPs at the 3’‐end of PCR primers to selectively block out predators from amplification. While this approach largely prevents predator amplification, it retains high taxonomic versatility for prey lineages. We introduce a novel multilocus assay, targeting four nuclear and mitochondrial rDNA markers, and test our approach in a diverse set of spiders from 12 families. We estimate the recovered prey DNA proportions and compare the taxonomic composition of prey communities between markers. Using a feeding experiment, we also explore recovery of prey DNA over time. While commonly used COI primers yield low and very unpredictable amounts of prey DNA, our assay allows for a considerable and consistent prey enrichment across all tested species. The recovered prey's taxonomic composition is comparable between markers and supports results acquired by COI. The new marker set can be amplified in a simple multiplex PCR, considerably reducing the necessary workload. Our multilocus approach allows the generation of an unprecedented amount of prey data at low cost and effort. Lineage‐specific PCR is taxonomically versatile and could readily be adapted to any prey–predator interaction, opening up the opportunity for community‐wide studies on food web interactions.

Rapid ʻŌhiʻa Death (ROD) is a deadly disease that is threatening the native Hawaiian keystone tree species, ʻōhiʻa lehua (Metrosideros polymorpha Gaudich). Ambrosia beetles (Curculionidae: Scolytinae) and their frass are hypothesized to play a major role in the spread of ROD, although their ecological niches and frass production within trees and across the landscape are not well understood. We characterized the beetle communities and associated frass production from bolts (tree stem sections) representative of entire individual ʻōhiʻa trees from multiple locations across Hawaiʻi Island by rearing beetles and testing their frass for viable ROD-causing fungi. Additionally, we estimated frass production for three beetle species by weighing their frass over time. We found that Xyleborinus saxesenii (Ratzburg), Xyleborus affinis Eichhoff, Xyleborus ferrugineus (Fabricius), Xyleborus perforans (Wollaston), and Xyleborus simillimus Perkins were commonly found on ROD-infected ʻōhiʻa and each produced frass containing viable Ceratocystis propagules. The Hawaiʻi Island endemic beetle and the only native ambrosia beetle associated with ʻōhiʻa, X. simillimus, was limited to high elevations and appeared to utilize similar tree heights or niche dimensions as the invasive X. ferrugineus. Viable Ceratocystis propagules expelled in frass were found throughout entire tree bole sections as high as 13 m. Additionally, we found that X. ferrugineus produced over 4× more frass than X. simillimus. Our results indicate the ambrosia beetle community and their frass play an important role in the ROD pathosystem. This information may help with the development and implementation of management strategies to control the spread of the disease.

Rapid ʻŌhiʻa Death (ROD) is a fungal disease of ʻōhiʻa lehua (Myrtaceae: Metrosideros polymorpha) caused by Ceratocystis lukuohia and C. huliohia. ROD is the aetiological agent of widespread mortality of this important tree on Hawaiʻi Island, but its epidemiology remains unclear. We investigated the prevalence and viability of C. lukuohia in ambrosia beetle frass in ROD‐affected ʻōhiʻa trees. A total of 200 frass traps were placed onto C. lukuohia‐infected ʻōhiʻa at four locations on the east side of Hawaiʻi Island. Frass was collected and screened for the presence of C. lukuohia DNA using a diagnostic qPCR assay. In addition, frass samples were screened for viability by carrot baiting. All trapped beetles were of the genus Xyleborus, with the majority being the non‐native X. ferrugineus. Of the frass samples tested, 62% contained C. lukuohia DNA and 17% of carrot baits were positive for the fungus. These results indicate that ambrosia beetle frass releases C. lukuohia into the environment. We discuss the potential role infested frass could play in the ROD pathosystem.

No abstract

Rapid ʻ Ohiʻa Death (ROD), caused by the fungal pathogen Ceratocystis, is killing large numbers of ʻ ohiʻa trees (Metrosideros polymorpha) in Hawaiʻi. ʻ Ohiʻa are a dominant tree in Hawaiian forests, have a range that goes from arid to wet forest climates, and are important for endangered species habitat and ecosystem function. To test whether actively planting ʻ ohiʻa seedlings is a viable restoration strategy in areas with high ROD mortality, we planted ʻ ohiʻa in a ROD-affected forest and crossed this with weeding and fencing treatments to compare ROD mortality to other stressors. We also tested for viable Ceratocystis spores in soils around planting areas. We found that seedlings were more likely to die in unweeded and unfenced treatments than controls. Although viable Ceratocystis spores were found in soil, none of the 41 dead seedlings tested positive for Ceratocystis. This indicates that competition from exotic plants and exotic feral ungulate damage are more likely to kill seedlings than ROD within the first year after planting.