Before I ever set foot in Borneo, one of the bee groups I was most excited to encounter in the field were the tiny little 'masked bees' in the genus Hylaeus. Called 'masked bees' due to their yellow or ivory colored facial markings, Hylaeus bees are amongst the most widespread and diverse bee genera in the world, with over 500 species found worldwide. As you can see in the photos below, they are tiny, often mostly black, and relatively un-hairy, and therefore look nothing at all like their larger, fuzzy sisters in the genus Colletes that one often encounters in North America and Europe. They don't even really look like bees. What they do have in common with most Colletidae is an internal crop for carrying pollen, rather than external hairs or corbiculae as is commonly found in other bee families.
A typical North American Hylaeus bee photographed in New Jersey
So why was I so excited to see these tiny little wasp-like bees? Well, Hylaeus originated in Australia before very successfully spreading all across the globe, and reaches it's maximum diversity there (see this paper for more details). I knew from talking to Aussie bee researcher James Dorey that in Australia and surrounding regions (including South Pacific islands like Fiji), Hylaeus are highly associated with trees in the also-very-Australasian tree family Myrtacaea, which includes Eucalyptus and, of course, Syzygium. If you haven't been following the blog up 'til now, my thesis project is centered around the reproductive ecology of the genus Syzygium. So, I knew I was likely to see Hylaeus bees and probably a lot of them. What I didn't know was what species to expect.
An Australian Hylaeus nubilosus collecting pollen from a Eucalyptus flower. Photo credit Bernhard Jacobi, lifted from this interesting publication.
Reviewing Dr. John Ascher's private bee record database, I learned that only 3 Hylaeus species have previously been recorded from all of Borneo. This struck me as fishy. How could the 3rd largest island in the world, so close to Australia and so dominated by Myrtaceae, have so few Hylaeus species? Even the tiny island of Singapore has 9 species on it's list, and 12 species are already known from the greater Sunda region. In a meeting in Singapore last July, Dr. Ascher confirmed my suspicions: "Basically, nobody has looked" he said (or something like that, I'm paraphrasing). That made me very excited to see what might be at Tuanan, seeding day-dreams of new records for Borneo and maybe even previously undescribed species.
Hylaeus cf. penangensis collecting pollen from a Syzygium flower at Tuanan. On most Syzygium the Hylaeus are too small to regularly contact the stigma, and so are more likely pollen thieves than pollinators.
Sure enough, I ended up observing and capturing a lot of Hylaeus (155 specimens all in all, over 10% of the bee specimens). However, diversity amongst my samples is not high... while more than half of the Syzygium species were visited by Hylaeus bees, they appear to all be visited by the same three species. This is where it gets exciting though: none of the 3 species I collected appear to be the same as any of the 3 existing records from Borneo, and at least 1, and maybe 2, represent species previously unknown to science.
The 3 morpho-types of Hylaeus that I've collected off Syzygium flowers at Tuanan.
One of these is green, which is unusual... as far as I know, green Hylaeus haven't been recorded this far from Australia and Papua, and those that I can find images of clearly aren't related to our Tuanan species. The males have an extensive white/ivory mask, and the females have no facial markings (pics below). A very similar male was once collected in a mangrove forest in Singapore, but nobody has described/named the species yet, and the female was previously unknown. Dr. Ascher from National University Singapore thinks it's a new species from what should be a new sub-genus, and that it is likely related to a bee previously described from Java called Hylaeus jacobsoni. However, with the only specimens of H. jacobsoni being in Berlin, no photos available, and no version of the original 1914 description of the species on hand, I haven't been able to do a comparison.
Digital microscope photos of the as-of-yet undescribed green Hylaeus from Tuanan, male above and female below.
So, yeah, 3 new Hylaeus species for Borneo, including 1 or 2 new to science, doubling the known species from Borneo! These were all collected within a kilometer or so from each-other, in a single habitat type, and from flowers of a single plant genus. Imagine what might be found by sampling across more host plants, habitat types, and locations on the island...
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