How we started working on “rare” bee-killing flies

The most beautiful phorid flies are in the genus Melaloncha, also known as bee killing flies. I have no small bias in this statement, however, since I worked on them for several years and grew to be very fond of them.

Melaloncha punctifrons, female

One of the allures of these flies was their rarity when I first started. In all of the collections I surveyed, I could find only a few specimens, about 100 in total. There were many new species among these specimens, however, so I knew that the 32 described species was only the tip of the iceberg. But how was I to uncover the rest of that iceberg?

Many parasitic phorid flies seem to be attracted to masses of their hosts. Logically, aggregations of hosts should create aggregations of parasitoids, so Giar-Ann Kung and I decided to try to make aggregations of stingless bees, the known hosts of these flies. Monty Wood, a fellow dipterist who works on tachinid flies, told me that when he sprayed a mixture of honey, Coca-Cola, and water onto undergrowth vegetation in an attempt to attract his flies often attracted huge aggregations of stingless bees instead. Therefore we tried spraying honey and water, and were almost immediately successful in attracting bees, and eventually flies. There was one other required condition, however: it had to be in the sunlight, or the flies would not be attracted. This is contrary to most phorids, which tend to be more active in shade.

Melaloncha acoma attacking stingless bee

Once we adopted the honey spray and sunlight combination, we started collecting large numbers of these flies, eventually collecting thousands of them. Sometimes, we were almost too successful in attracting the bees, producing gigantic aggregations that made it impossible to breathe or see anything, necessitating the use of jury rigged bee veils. These consisted of an insect net placed over the head and sealed around the neck with rubber bands. Eventually, though, the tiny stingless bees would get in, and we’d have to beat a retreat to get the annoying things out of our eyes, ears, and noses.

Me wearing a jury-rigged "bee veil" in Argentina, 2003

It was all worth it though, as we ended up catching 50-100 Melalonchaper day at good sites, and found almost 150 new species. I think there are still many more out there to find, so we keep spraying honey wherever we go in the tropics, and keep finding the beautiful, but deadly (to bees) bee-killing flies.

Melaloncha xanthocauda, femal

Melaloncha berezovskiyi, female

Melaloncha acoma, female

Take your watch to the field

I am sure it makes perfect sense to bring your watch into the field to keep track of the time. That is not why I am advocating this practice, however. A watch once helped us make an important new observation on bee parasitizing flies in the tropics.

One unavoidable fact of tropical fieldwork is that you will stink. You sweat your clothes out within the first 10 minutes after breakfast, and remain damp and moldy all day until you hit the showers. It is impossible to wear clothes for more than one day without them getting rank and disgusting. You can either bring enough clothes to change all of them every day, do lots of laundry during the trip, or resign yourself to having some of your clothes remain not suitable for indoors and fine dining.

Things that you wear or sweat on day after day buildup in particular fragrance. For instance, my collecting bag is always covered with butterflies in the field, probably because they mistake it for a piece of carrion. Other items can be the same way.

My collecting bag swarming with bees, flies, and butterflies. It stank.

In 2001, Giar-Ann Kung and I were in Colombia with some colleagues, and it was incredibly hot and humid. We were after bee killing flies of the genus Melaloncha, which we were trying to attract with honey. Placing honey on the undergrowth attracts large numbers of bees, and once we had large numbers of bees, we hoped that the parasites would arrive as well. Problem was, it wasn’t working. The bees were much more attracted to Giar-Ann’s watch, which really stank. She took it off and put it on sheet that we had placed in the field and the bees visited it avidly. Suddenly, against the black background of the watch, Giar-Ann noticed a tiny yellow shape curling its abdomen and running towards tiny bees. She collected the fly and showed it to me – it was a female Styletta crocea, a rarely collected species whose lifestyle was completely unknown. I doubt if we would ever have seen the fly without the black watch in the background. Later, we collected Melaloncha specimens, but that Styletta was our first big break of the bee parasite project.

female Styletta crocea

It never ceases to amaze me how events unfold during a research program or field trip. No matter how much you prepare, invariably which you thought would work doesn’t, but something completely different appears or is found. It’s part of the reason why fieldwork and research remain compelling and exciting for those of us who aspire to make new discoveries.

A new parasitic phorid in honey bees

Female Apocephalus borealis specimen

Lots of press coverage is swirling around our recent paper in PloS ONE: “A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis”, available here . Note, I use the term “our” advisedly, as I am 7th of 10 authors, and thus cannot take much of the credit for this work! Unfortunately, some of the press coverage this publication is garnering is incorrect, but I’ll let my colleagues at UCSF handle that on their website. What I’d like to concentrate on is the phoridological context of this story, particularly on the genus Apocephalus.

Genus Apocephalus consists of about 300 described species, virtually all of which are found in the New World. I am pretty sure that species described from other regions do not belong in a group with the rest of Apocephalus. In the 1990s, I revised about half of the genus, describing over 200 new species, but there are still many more out there. Right now I have a grant from the National Science Foundation to revise the rest of them.

Current classification of this group places the species in 2 subgenera: Apocephalus and Mesophora. Species of subgenus Apocephalus are the original “ant decapitating flies” like the ones I videoed in Brazil a few posts ago. Subgenus Mesophora have very different hosts, however. Most of the known species are parasitoids of fireflies and soldier beetles, an extremely different group of hosts from the ants the others attack. In addition, I have described a few species that attack stingless bees in the tropics.

One species always stood out, however, and that was Apocephalus borealis. This crazy thing had been reared from bumble bees, yellowjacket wasps, and a black widow spider! It seems as though A. borealis has an extremely wide range of host acceptability. Perhaps this is what allows it to switch into new hosts, such as honey bees. We know that honey bees were not the original hosts, because they are an introduced species in North America. Probably bumble bees are their main hosts, but who knows? This species is only recorded from North America.

My colleague, Dr. Paul Smith, and I are currently studying the relationships among species of Apocephalus using molecular characters (DNA sequences), as well as morphology (body structure). Once we have a good phylogeny of Mesophora, we should know more about how the flies have shifted hosts through the group.

Apocephalus borealis on bumble bee, photo by K. O'Harrow

Of course, besides many new species to be discovered, many described species do not have any studies about their way of life. Particularly intriguing are some species from Costa Rica that seem to be closely related to A. borealis. Perhaps they are parasitoids of tropical bumble bees, but nobody has studied this yet.

One other thing to note: Apocephalus borealis is far from the only phorid that parasitizes honeybees. In South and Central America, many species of Melaloncha bee killing flies will attack honeybees, and we have even seen the tiny, 1 mm long Styletta crocea trying to attack these relatively giant hosts. Finally, Pseudohypocera kerteszi is an occasional past in honey bee nests, although they are much more prevalent in the nests of stingless bees. I will write more about these other bee parasitoids in future blog posts, but you can see photos of the flies on my website

In summary, it’s great that some phorids are getting press, and I’m sure we are going to learn a lot about this species because of its agricultural importance. Kudos to the (other) authors for their fascinating work. Don’t forget, however, that Apocephalus borealis is only one of about 4000 described species, and many more have amazing life histories still to be discovered.

A living fossil from South America

Vladimir and I sorting in the field

Hard-core dipterists know all about Sciadocera, the Australian and New Zealand fly that seems to bridge the gap between platypezids and phorids. It was immortalized by the drawing Harold Oldroyd included in his 1964 book “The Natural History of Flies” which was entitled “the most wonderful fly in the world”.

Less known is the New World species, found in South Chile and Argentina. Called Archiphora patagonica, this species is similar, but smaller than Sciadocera, and more brown in color. Hennig described a second species of Archiphora from Baltic amber, and declared that genus to have been once widespread, and now relictual in the southern hemisphere. A few years ago, I re-examined the Baltic amber fossil and showed it was probably not congeneric with A. patagonica. There are, however, three species of Baltic amber Sciadocerinae (the group is now considered part of the Phoridae), and others possibly from older amber, so it is reasonable to refer to the two living species as “living fossils”.

Elvia and Vladimir getting discouraged

I needed to collect fresh specimens of Archiphora patagonicafor a molecular project in which Dr. Paul Smith and I are trying to understand the phylogeny of phorid flies using DNA sequences. A couple of years ago, I went to southern Chile with two assistants: my old friends Vladimir Berezovskiy from here in Los Angeles and Elvia Zumbado from Costa Rica. Together, we spent three weeks scouring the forests looking for this fly. We ran Malaise traps in sites where Canadian hymenopterist Masner collected some in the 1980s, with no luck (we knew we weren’t catching them because we sorted the samples in the field, looking for the flies). Since Masner also did a lot of sweeping, we swept for hours in forest undergrowth, dumping our net contents in a bowl of soapy water and searching for the elusive flies. In a fit of inspired desperation, Vladimir even grew a beard like Masner’s to try to appease the phorid gods. We collected at a number of sites on the mainland, as well as on Chiloe Island, where we found most of the forests that Masner collected in to be gone. We even looked up the former farm of Chilean entomologist Luis Peña, where the remains of his field station still exist, and swept there extensively. We got a lot of interesting phorids, but no Archiphora patagonica.

Peña's farm

At least, that’s what we thought until we got home. When I went to the samples with a microscope, I was elated to find a single male specimen from Peña’s old farm that eluded our field sorting. Although we eventually ground the specimen up for sequencing, we took some nice photos of this fly, which show that it too is one of the “most wonderful flies in the world.”

our single Archiphora specimen