Syntaxus baccata: biology

Monday, March 24, 2025

New paper: Identification of Cholevinae larvae

In 2022, I started my Master’s in Biology, at Radboud University in the Netherlands where I had just finished my Bachelor’s degree. The Master’s programme includes two research internships of 36 EC (approx. 6 months), both of which include writing a thesis. As I had been working on a database of identification keys, I was interested in a project focused on taxonomy for my first research internship.

Thanks to Henk Siepel I ended up contacting Menno Schilthuizen at Naturalis, who suggested I work on Cholevinae larvae. Schilthuizen had been collecting Cholevinae larvae since the 1980s, and had also received material from Peter Zwick who started collecting larvae in different areas of Germany in the 1960s. The challenge was to use this material to make an identification key based on these specimens.

Although the first description of a larva of Cholevinae was published back in 1961 by J. C. Schiødte, descriptions have since been relatively few and far between. This also meant that there are almost no existing identification keys for the larval Cholevinae. Making these descriptions and keys is difficult, as you need larvae from a known species. This is only possible if the larvae are cultured from adults, which takes time and effort, if molts are collected and the emerged adults is identified, or if DNA barcoding can be used. The specimens collected by Zwick and Schilthuizen mainly used the first method.

However, there happened to be a recent, detailed description of Sciodrepoides watsoni, a species for which I also had specimens. I started by comparing the larvae of S. watosni (as well as a few of the related S. fumatus) to the drawings and descriptions made by Kilian and Mądra. From there, I could start looking at different species and identify potential areas and types of characteristics that are consistent enough within a species, but that differ between separate species. To illustrate these differences I also made schematic drawings (Fig. 1) of different sets of characteristic features. Finally, I measured certain parts of the larvae, where possible for specimens preserved in microscope slides.

Figure 1: Illustrations of Cholevinae larvae

At the end of the 6 months, I had a complete key to all species for which specimens were available, but only for the 1^st instar. When the larvae molt for the first time, they gain secondary bristles, grow in size, and more, meaning the identifying characteristics cannot always be used for both the 1^st instar, and the 2^nd and 3^rd instars. I ended up spending another year or so to finalize the key for all instars. This includes 28 of the 39 species of Cholevinae occurring in the Netherlands, and a lot of descriptions for which no (detailed) description was available previously. In a true full circle moment, I could add my own work to the aforementioned database of identification keys (as B1860).

Ultimately, collaborating with Schilthuizen, Siepel, and Zwick, this culminated in an article, Comparative morphology of the larval stages of Cholevinae (Coleoptera: Leiodidae), with special reference to those in the Netherlands. We were able to publish this in the final issue of Tijdschrift voor Entomologie, which is unfortunately being discontinued after 167 volumes. Again, many thanks to Menno Schilthuizen, Peter Zwick, and Henk Siepel for this great opportunity. Check it out!

References

Willighagen, L. (2022, augustus 6). Library of Identification Resources. Syntaxus Baccata. https://doi.org/10.59350/h8qka-z4a05
Schiødte, J. C. (1861). De metamorphosi eleutheratorum observationes: Bidrag til insekternes udviklingshistorie (pp. 1–558). Thieles Bogtrykkeri. https://doi.org/10.5962/bhl.title.8797
Kilian, A., & Mądra, A. (2015). Comments on the biology of Sciodrepoides watsoni watsoni (Spence, 1813) with descriptions of larvae and pupa (Coleoptera: Leiodidae: Cholevinae). Zootaxa, 3955(1), 45–64. https://doi.org/10.11646/zootaxa.3955.1.2
Willighagen, L. G., Schilthuizen, M., Siepel, H., & Zwick, P. (2025). Comparative morphology of the larval stages of Cholevinae (Coleoptera: Leiodidae), with special reference to those in the Netherlands. Tijdschrift Voor Entomologie, 167, 59–101. https://doi.org/10.1163/22119434-bja10033

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Saturday, August 12, 2023

Finding shield bug nymphs on iNaturalist

Working on translating a key to the European shield bug nymphs (Puchkov, 1961) I thought I would look for pictures of the earlier life stages (nymphs, Fig. 1) of shield bugs (Pentatomoidea) on iNaturalist and found few observations actually had the life stage annotation. I do not have the exact numbers of Europe as a whole at that point in time, but Denmark currently has around 19.8% and the United Kingdom has around 29.4% of the observations annotated (GBIF.org, 2023).

Figure 1: Fourth instar nymph of Nezara viridula (Linnaeus, 1758). 2023.vi.22, Bad Bellingen, Germany.

So I set out to add those annotations myself instead, starting with the Netherlands, followed by the rest of the Benelux, Germany, and Ireland. Last Monday, I finished the annotating the observations of France. These regions total to about 80 000 observations, of which I annotated a bit more than 40 000 (again, I do not have the exact numbers from before I started).

Methods

I made these annotations on the iNaturalist Identify tool which has plenty of keyboard shortcuts that I found after using the mouse for 2000 observations. This allowed me to develop some muscle memory, and I ended up annotating a single page of 30 observations in around 60 seconds, so 2 seconds per observation. Most of that time was usually spent waiting for the images to load, and there were plenty of small glitches in the interface to further slow me down (including a memory leak requiring me to reload every 10-ish pages).

I was not able to annotate 715 of the verifiable observations (i.e. those with pictures, a location, and a time). In some cases, the pictures were simply not clear enough (or taken too closely) for me to determine with certainty the life stage. Another issue I had to work around were observations of multiple individuals at different life stages. Common were observations of egg clusters and just-hatched nymphs of Halyomorpha halys (Stål, 1855); the “parent bug” Elasmucha grisea (Linnaeus, 1758) doing parenting; kale plants infested with adults and nymphs of Eurydema; and adults of various species in the process of laying eggs. However, there were also many observations containing multiple pictures where one was of an adult and a second of a nymph, with no indication that it was the same individual at different times. There is currently no way to annotate multiple life stages on a single observation on iNaturalist except through non-standard observation fields, which are a lot more laborious to use and can be disabled by users.

Results

Coloring the observations by life stage on a map clearly shows the effect of the work, with the aforementioned countries covered in red; and the most of the rest of Europe in blue (Fig. 2). (There are two other notable red patches, in Abruzzo, Italy and in Granada, Spain. These are not my doing, and seem to be caused by two prolific observers annotating their own observations, respectively esant and aggranada.)

Figure 2: Map of research-grade iNaturalist observations of Pentatomoidea in Europe, colored by whether or not they have a life stage annotation.

These annotations mean additional data is available on the seasonality of these species. For example, looking at the four most observed species already reveals that Pentatoma rufipes (Linnaeus, 1758) overwinters as nymphs, whereas the other three species overwinter as adults (Fig. 3). The larger volume of data also means that more detailed analyses with more explanatory variables can be carried out. For example, the effect of climate change on the life cycle of invasive species like H. halys.

Figure 3: Seasonality of nymphs and adults of the four most of observed shield bug species.

In addition, for less common species the classification of life stages makes it possible to find more about the morphology of the earlier life stages of these species. This is useful for individuals who are working on keys (such as me), but perhaps also for computer vision models. Classifying the not-yet identified observations of nymphs as such also allows for more targeted searches by identifiers, potentially leading to even more research-grade observations of rarer species.

It should be said though, that even Chlorochroa pinicola (Mulsant & Rey, 1852), which is not particularly common in West Europe, still has many more validated pictures on Waarneming.nl than on iNaturalist. In fact, nearly half (43.2%) of all observations with images of Pentatomoidea in Europe are in the Netherlands. These are not all annotated with a life stage though, and the Observation.org platform (which Waarneming.nl is part of) seemingly only allows curators and observers add life stage annotations to an observation.

Luckily, iNaturalist does allow for this and enables me to contribute hopefully valuable data to GBIF for further analysis, by myself or by others. I will continue adding annotations — I have now started on the observations from Switzerland, luckily a lot fewer than those from France. At the same time, I am maintaining the high rate of annotation in the countries I have already annotated. In August, this means annotating about 200 observations per day (10–15 minutes) which is entirely doable. It does quickly start to add up if you are on holiday for a week, as you do in August, but that is still fewer observations than the entirety of France. Still, for this reason I hope other identifiers (or even better, observers) start annotating more as well.

References

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