Review of: "Fungal Spores in Insect Trapping Fluids: Simultaneous Sampling for Insects and Pathogens"

The manuscript aims to compare and contrast the recovery of fungal metagenomic communities from slide based spore traps and bycatch of fungi in liquid based insect traps, using metabarcoding for fungal ITS. The authors report amplifying segments of the fungal ITS1 and 5.8S rRNA encoding regions from DNA isolates using the standard primers ITS1F and ITS7G, with Illumina Miseq next-generation sequencing. The authors report isolating 1277 distinct fungal OTUs across 90 samples, taken from 6 sites, with 2 slide spore traps and 2 insect traps installed at each site. Samples were collected weekly or biweekly at the six sites between August 1 and September 13 2018, with a total of 46 slide samples and 44 insect trap fluid samples collected. The authors reported 476 OTUs were detected only in the insect trap fluids, compared with 132 OTUs detected only from the slide samples. The same relative diversity relationship also existed in the restricted set of OTUs assigned to “pathogen and forest pathogen” categories. From these observations the authors draw the inference that insect trap fluid is an underutilized source for information on fungal population structure in the environment. 669 fungal OTUs were detected in both insect trap fluid and slide trap spore samples. While the comparisons drawn are valid and insightful within the confines of the experimental design, there remain factors involved in evaluating fungal community composition and structure which the authors do not address. The improvised slide traps described are innately limited by the mechanics involved and do not represent standard spore sampling methods in current use [1]. The theory of their described ‘slide’ aerial spore samplers involves exposing an air permeable filter(grade 50 double layer cheese cloth) treated with a particulate binding coating(Sigma silicone oil #378399) to ambient air for a set period of time, then evaluating the particulates bound in the coating. This only collects, and thereby enables detection of, those particles which passively pass through the apparatus, and only until the coating becomes saturated and ceases to bind particulates. This makes for relatively low sensitivity, reproducibility, and true duration of sampling, compared to the true population of airborne particulates. It is unclear what the retention capacity of these apparatuses would be from the information provided (60 g/m2 x 28.27 sq. mm of slide surface[6mm diameter filter punch] = 1.7 mg of silicone oil/sample, viscosity 1,000 cSt at 25 °C[2]), or how much air-borne particulates would have been expected to pass through the samplers in comparison to that retention capacity. Given the materials and methodology described, it seems plausible for these ‘slides’ to reach saturation in a much shorter interval than they were collected, such that rather than reflecting an unbiased aggregation of particulates these Qeios, CC-BY 4.0 · Review, December 22, 2021