Precision glycerine jelly swab for removing pollen from small and fragile insect specimens

Historical datasets can establish a critical baseline of plant-animal interactions for understanding contemporary interactions in the context of global change. Pollen is often incidentally preserved on animals in natural history collections. Techniques for removing pollen from insects have largely been developed for fresh insect specimens or historical specimens with large amounts of pollen on specialised structures. However, many key pollinating insects do not have these specialised structures and thus, there is a need for a method to extract pollen from these small, and fragile insects.

Here, we propose a precision glycerine jelly swab tool to allow for the precise removal of pollen from old, small, and fragile insect specimens. We use this tool to remove pollen from five families of insects collected in the late 1970s. Additionally, we compare our method with four previously published techniques for removing pollen from pinned contemporary specimens.

We show the functionality of the precision glycerine jelly swab for removing small quantities of pollen across insect families. We found that across the five methods, all removed pollen; yet, it was clear that some are better suited for fragile specimens. In particular, the traditional glycerine jelly swab and the precision glycerine jelly swabs both performed well for removing pollen from bee faces. The shaking wash resulted in specimen fracture and residue left behind, the ethanol rinses left setae matted, and the glycerol swabbing left residue on the specimen. Additionally, we present photographs documenting the effects of these methods on pinned honey bee specimens.

The precision glycerine jelly swab opens up opportunities to sample pollen from a variety of insects in natural history collections. These pollen samples can be incorporated into downstream analyses for pollen identification either via microscopy or DNA sequencing, and the resulting plant-insect interaction data can establish historical baselines for contemporary comparison. Beyond our application of this method to pollen on insects, this precision glycerine jelly swab tool could be used to explore pollen placement specialisation or to sample bryophyte, fungal, and tree fern spores dispersing on animals.

Methods
Images were captured using a Nikon AZ100M microscope with a Digital Sight DS-Ri1 (Nikon Instruments Inc., USA) mounted camera head. Stacked images were captured and measurements were taken using the NIS-Elements D imaging software (Version 5.02).