Bee Fly Parasitism of Tetracha virginica

I expected to gain a better understanding of insect photography principles and techniques at last weekend’s BugShot insect photography workshop at Shaw Nature Reserve in Gray Summit, Missouri.  I even expected that I would walk away from the event with some new friends.  The one thing I did not expect was the discovery of an apparently unreported host/parasitoid relationship amongst my beloved tiger beetles.  Nevertheless, that’s exactly what happened in a patch of barren soil just outside of the Dana Brown Education Center where the event was being held.

Tetracha virginica 3rd instar larva | Shaw Nature Reserve, Franklin Co., Missouri

I had spied the small cluster of tiger beetle burrows the previous day as we left on our first group hike.  The burrows were unmistakably those of Tetracha virginica (Virginia metallic tiger beetle) due to their size (no other tiger beetle in east-central Missouri approaches the size of this species), and in fact some of the larvae were seen sitting at the tops of their burrows.  Tetracha larvae are easily distinguished from other genera of North American tiger beetles (in addition to their size) by their distinctive white-margined pronotum.  I had to catch back up with the group but came back later in the day and took a few photographs of one of the larvae sitting in its burrow.  Some of the other BugShot attendees were there and wanted to take photographs, but the larvae dropped on their less-practiced approach.  No problem, I just “fished” a larva out of its burrow and let them take their photographs.  When they finished, I began taking my own photographs, but I only got off one shot before the larva suddenly made a bee-line for its burrow and dropped in before I could block its escape.  Oh well, I do already have photographs of the larva of this species from other locations.

Tetracha virginica 3rd instar larva | Shaw Nature Reserve, Franklin Co., Missouri

The next day I passed by the burrows again with Crystal and Lee.  I really wanted them to see the larvae, but they were not active.  No problem, I grabbed a long grass stem, chewed on one end, and inserted it to a depth of about 35 cm before it hit bottom.  A little jiggling to get the larva to bite, then a quick jerk back and out came the larva.  I never tire of seeing someone witness this for the first time—the way they jump back half-startled when they see the otherworldly larva flying through the air and landing on the grass.  I grabbed the larva and placed it on the barren clay to let them take photographs.  Crystal went first, and as she looked at the larva through her viewfinder she exclaimed, “there are wormy-things [the technical term, of course] on him.”  Lee and I looked, and sure enough there were two small “wormy-things” attached to the back of the tiger beetle.  I immediately recognized them as bee fly larvae (family Bombyliidae)—specifically Anthrax analis, the only bee fly known to parasitize tiger beetle larvae in the United States.  I was quite excited by this discovery, as I have never seen these before despite fishing untold numbers of tiger beetle larvae from their burrows over the past decade or so.  We all went camera crazy and took our turns photographing larvae and host, after which I popped it into a vial to keep for an attempt at rearing out the bee flies.

Anthrax analis larvae attached to abdomen of Tetracha virginica larva

It now seems that our find represents more than just a personal discovery, as bee flies—to my knowledge—have not yet been reported parasitizing any species of the genus Tetracha.  Of the 70 Anthrax spp. for which hosts have been recorded (Yeates and Greathead 1997), only three are known to parasitize tiger beetles.  Shelford (1913) gave the first account of A. analis (as Spogostylum anale) parasitzing Cicindela scutellaris lecontei, noting that the adult females lay their eggs by flying backward and downward while thrusting the abdomen forward until it touches the sand near the host burrow entrance.  Hamilton (1925) found Cicindelidia obsoleta parasitized by this species, and Bram and Knisley (1982) expanded its known host spectrum to include C. hirticollis, C. tranquebarica, Cicindelidia punctulata, and Ellipsoptera marginata.  Photographs of larvae (presumably of this species) parasitizing undetermined tiger beetle larvae can be seen in Pearson and Vogler (2001) and in this photo by Chris Wirth.  Anthrax gideon has been recorded parasitizing Pseudoxycheila tarsalis in Costa Rica (Palmer 1982) and Oxycheila trisis in Brazil (Arndt and Costa 2001), while a third undetermined Anthrax sp. has been reared from larvae of Pentacomia ventralis, also in Brazil (Arndt and Costa 2001).  Oxycheila and Pseudoxycheila are related to Tetracha at the tribal/subtribal level (depending on which classification you follow), so the finding of A. analis utilizing Tetracha is not unexpected.

Closer view of anteriormost Anthrax analis larva

The beetle larva and its unwelcome tagalongs is now in a container of native soil and has accepted the starter burrow that I made for it. Hopefully at least one of the bee fly larvae will complete its development and emerge as an adult to allow confirmation of its identity.  If this host association does turn out to be unreported, we will follow up with at least a short journal communication.  To that end, any literature citations you are aware of regarding bee fly parasitism of tiger beetles that is not listed below would be most welcome.

Congratulations to Ben Coulter, who wins yet another BitB Challenge with 14 points (this guy is a machine!), and Mr. Phidippus came close with 13 points.  Ben and Phiddy were the only participants that figured out the parasites were bee flies of the genus Anthrax, and Phiddy was the only participant to guess the correct genus for the host.  Ben’s win gives him a now commanding lead with 49 points in the current BitB Challenge Session #4 as we enter the home stretch.  Mr. Phidippus and Roy are still in striking distance with 39 and 28 points, respectively.  Is anybody capable of keeping him from his third title?  We shall see.

REFERENCES:

Arndt, E. and C. Costa.  2001.  Parasitism of Neotropical tiger beetles (Coleoptera: Carabidae: Cicindelinae) by Anthrax (Diptera: Bombyliidae).  Studies on Neotropical Fauna and Environment 36(1):63–66.

Bram, A. L. and C. B. Knisley.  1982.  Studies on the bee fly Anthrax analis (Bombyliidae), parasitic on tiger beetle larvae (Cicindelidae).  Virginia Journal of Science 33:90.

Hamilton, C. C. 1925. Studies on the morphology, taxonomy, and ecology of the larvae of Holarctic tiger beetles (family Cicindelidae).  Proceedings of the U.S. National Museum 65 (Art. 17):1–87.

Palmer, M. K.  1982.  Biology and behavior of two species of Anthrax (Diptera: Bombyliidae), parasitoids of the larvae of tiger beetles (Coleoptera: Cicindelidae).  Annals of the Entomological Society of America 75(1):61–70.

Pearson, D. L. and A. P. Vogler.  2001. Tiger Beetles: The Evolution, Ecology, and Diversity of the Cicindelids.  Cornell University Press, Ithaca, New York, 333 pp.

Shelford, V. E.  1913.  The life history of a bee-fly (Spogostylum anale Say) parasite of the larva of a tiger beetle (Cicindela scutellaris Say var. lecontei Hald.).  Annals of the Entomological Society of America 6(2):213–225.

Yeates, D. K. and D. J. Greathead.  1997. The evolutionary pattern of host use in the Bombyliidae (Diptera): a diverse family of parasitoid flies.  Biological Journal of the  Linnaean Society 60:149—185.

Copyright © Ted C. MacRae 2011

Magnificently Monstrous Muscomorphs

I suppose tiger beetles have gotten more than their fair share of attention here lately, so for this post I thought I’d highlight insects of a completely different group – flies! Admittedly, as a coleopterist, I tend to view flies with much the same disdain as your average insect non-enthusiast – as pesky, pestiferous vermin worthy of little more attention than a decisive swat. I don’t begrudge them their amazing diversity – at ~100,000 described species worldwide, they are strong contenders with the Lepidoptera and Hymenoptera as the second largest order of insects (of course, you need all three of these orders combined to match the diversity of the Coleoptera). I am also prepared to accept that they may well represent, at least morphologically, the pinnacle of insect evolution (a position that a few hymenopterists I know might argue with) due to their amazing flight capabilities and the morphological adaptations they have developed for such. These include the development of aristate antennae for detecting wind speed, the conversion of the second pair of wings into stabilizing organs (halteres), and the ability to beat the remaining pair of wings at incomprehensible rates – up to 1,000 times per second in some very small midges (even more baffling when one considers that the wing “beat” is actually just a passive result of rhythmic distortions of the thoracic box). I even acknowledge that the vast majority of fly species are not even pests, living their lives innocuously as herbivores, scavenging organic matter that nothing else wants, and preying upon or parasitizing other insects, including important agricultural pests. Still, flies bug me – mosquitoes prevent me from sleeping under the stars without a tent, deer flies drone around my head incessantly while I’m trying to stalk an elusive tiger beetle, stable flies trick me into assuming they are just another house fly (until they bite me!), house flies (the real ones) rudely land on my sandwich with their filthy feet, and eye gnats insist on committing hary kary in my eyes as I walk the trails (I won’t mention their other common name, derived from their habit of clustering around exposed canid genitalia).

There is, however, one group of flies that possess “cool factor” rivaling that of even the most popular insect groups – robber flies and their kin. I’ve always picked them up as an aside, even sending them off for authoritative ID and constructing an inventory of the species in my collection. The brute of a fly pictured here is not a true robber fly, but in the related family Mydidae. Mydus clavatus can be recognized easily in the field by its large size and distinctive black coloration with red/orange on top of the 2nd abdominal segment. Presumably this is an example of Batesian mimicry modeled upon spider wasps (family Pompilidae) in the genus Anoplius. This mimicry allows them to fly rather boldly in the open and is so persuasive that it can not only fool the casual observer, but even the most knowledgable of entomologists might be loathe to handle it despite knowing better. Although common across the eastern U.S., aspects of its life history are poorly understood. Adults have been reported to be predators of other insects, but apparently there are some doubts about the veracity of such reports. Patrick Coin of BugGuide has observed adults (males?) taking nectar from flowers and has suggested that reports of predation by adults might have been an erroneous assumption due to their relation and resemblance to robber flies. Larvae are reported to be predaceous on woodboring beetle larvae, and I have reared adults of this species from a dead sycamore (Platanus occidentalis) stump in southern Missouri that was infested with mature larvae of the large buprestid species, Texania campestris. This habit is similar to robber flies of the genus Laphria, which mimic bumble bees and carpenter bees.

In Greek mythology, Promachos (Προμαχοε) was “the champion” or one “who leads in battle” – an appropriate generic name for the so-called “giant robber flies” of the genus Promachus. These large flies are dominant and fearless predators that will capture just about any flying insect – even adult dragonflies. There are three species of Promachus in the eastern U.S. that exhibit the yellow and black tiger striping of the abdomen seen in this individual, identified as a female Promachus hinei by Herschel Raney at BugGuide due to its reddish femora and occurrence in the central U.S. Promachus rufipes is similar but has black femora with distinctly orangish tibiae and is more common in the southeastern U.S., whereas P. vertebratus has more muted two-toned legs with smaller dark areas dorsally on the abdominal segments and is more common in the northern states. Additional species occur in the region but lack the tiger striping of the abdomen, and even more species occur in the western U.S. Members of this genus generally lay their eggs on the ground near grass roots, and the larvae burrow into soil after hatching and feed on soil insects, roots, and decaying matter before pupating within the soil in an unlined cell.

During my recent trip to Nebraska I encountered this related robber fly genus Proctacanthus, also determined by Herschel provisionally as P. milbertii. These large robber flies with a prominent beard are similar in habit to Promachus species, laying their eggs in crevices in soil and the larvae feeding on soil insects, roots, and decaying plant matter. Proctacanthus milbertii is a late season species that occurs across much of the U.S. and reportedly loves butterflies. However, Joern & Rudd (1982), in studying predation by this species in western Nebraska (where the individual pictured here was photographed) found that grasshoppers made up 94% of the prey captured by this species. Interestingly, nearly all of the remaining prey captures were other P. milbertii, which was carefully verified as such since mating postures can be easily mistaken for prey handling positions. Grasshopper prey species taken by this species were most strongly influenced by availability rather than size, suggesting that even the largest grasshopper species could be captured as easily as smaller species – a testament to the ferocity of this robber fly.

Another family of flies modestly related to robber flies and also ranking high in “cool factor” are the bee flies (family Bombyliidae). The scaly bee fly, Lepidophora lepidocera (ID confirmed by Joel Kits at BugGuide), is a particularly attractive member of the family. The distinctive, hunch-backed shape of this southern U.S. species is shared with the more northern L. lutea, from which it is distinguished by having pale scales only on the 5th abdominal segment and not on the 4th also. Most bee flies are presumbably mimics of – yes – bees; however, the species in this genus might actually be mimics of robber flies instead. Adults are most often seen taking nectar from flowers – this individual was taken on flowers of tall boneset (Eupatorium altissimum). Larvae are characterized by Sivinski et al. (1999) as kleptoparasites on the provisions of solitary wasps in the families Vespidae and Sphecidae – meaning that the larva does not parasitize wasp larvae directly, but instead usurpes the nest provisions on which the wasp larvae were supposed to feed. The little thieves!