Pollen sleuthing for terrestrial plant surveys: Locating plant populations by exploiting pollen movement

Abstract

Premise of the StudyWe present an innovative technique for sampling, identifying, and locating plant populations that release pollen, without extensive ground surveys. This method (1) samples pollen at random locations within the target species’ habitat, (2) detects species’ presence using morphological pollen analysis, and (3) uses kriging to predict likely locations of populations to focus future search efforts.MethodsTo demonstrate, we applied the pollen sleuthing system to search for artificially constructed populations of Brassica rapa in an old field. Population size varied from 0–100 flowers labeled with artificial pollen (paint pellets). After characterizing the landscape, we pan‐trapped 2762 potential insect vectors from random locations across the field and washed particulate matter from their bodies to assess artificial pollen abundance with a microscope.ResultsPopulation size greatly influenced artificial pollen detection success; following random pollen trap sampling and interpolation, ground surveys would be best focused on identified areas with high pollen density and low variation in pollen density. Sampling sites most successfully detected artificial pollen when they were located at higher elevations, near showy flowering plants that were not grasses.DiscussionDetection of nascent populations using the proposed system is possible but accuracy will depend on local environmental factors (e.g., wind, elevation). Conservation and invasive species control programs may be improved by using this approach.

Can honey bees be used to detect rare plants? Taking an eDNA approach to find the last plants in a weed eradication program

“…Solitary insects and pollinators without floral constancy could also be investigated for their potential in detecting boneseed. A study using artificial pollen has shown that trapping of solitary insects could be used as a method to detect populations of invasive plants, and that these can be detected at low density although with decreased ability to track the detection to a source population (Campbell et al, 2018). Other studies have identified pollen on insects collected in traps, although not from low‐density plant populations (Gill & O'Neal, 2015).…”

Environmental DNA metabarcoding of pan trap water to monitor arthropod‐plant interactions

“…Although these identifications often require specialist expertise and may achieve low taxonomic resolution due to the lack of morphological characters for species-level identification (Bell et al, 2016;Khansari et al, 2012;Rahl, 2008). Moreover, even when plant taxa are detected from pan traps, they are rarely used to infer species-specific flower visits or pollen transport (Popic et al, 2013); the primary reasons being that (1) pollen collected from pan traps represents foraging from the entire community of arthropods captured, and; (2) pan trap plant detections may include nontarget wind-pollinated species, which could result from contamination, either airborne pollen/plant material (Johnson et al, 2019b) or herbivorous regurgitant (Sword, 2001), rather than flower visits (Campbell et al, 2018;Popic et al, 2013). Such contributions may be significant considering that wind-pollinated species produce copious quantities of pollen (see Harrington & Metzger, 1963).…”

“…Such contributions may be significant considering that wind-pollinated species produce copious quantities of pollen (see Harrington & Metzger, 1963). Despite this potential for contamination, ambient pollen (pollen dispersed by air, not invertebrates) is rarely quantified, with studies instead relying upon alternative approaches, such as artificial pollen (see Campbell et al, 2018), to circumvent this issue. Plant surveys using passive traps may, therefore, benefit from alternative approaches, like those afforded by environmental DNA (eDNA) metabarcoding, to detect both pan trap-specific and ambient pollen, in order to generate high-throughput and high-resolution pollen datasets, which can help form robust conclusions about the plant resources used by pollinator communities.…”

“…Each array was placed at a height of 1.2 m above the ground to match the height of the P. americana trees in the study orchards. All of the pan traps were filled with ~200 mL of sterile MilliQ water, and one drop of detergent to disrupt the surface tension (Campbell et al, 2018;Gervais et al, 2018). Pan trap evaporation was minimal during the sample period due to the mild temperatures (average of 19.7°C), while, the water temperature of the pan traps did not exceed 25°C.…”

“…To date, these pollen‐centric studies have favored active sampling methods (e.g., sweep netting), followed by washing or swabbing arthropods to obtain animal‐collected pollen (Evans & Kitson, 2020; Pornon et al., 2017; Prendergast et al., 2020). Increasingly, however, microscopy‐based techniques are being combined with pan traps to identify foraging resources in both natural (Ladd et al., 2019) and agricultural systems (Bowie et al., 1999; Campbell et al., 2018; Gill & O'Neal, 2015). Although these identifications often require specialist expertise and may achieve low taxonomic resolution due to the lack of morphological characters for species‐level identification (Bell et al., 2016; Khansari et al., 2012; Rahl, 2008).…”