January 13, 2014
Our scientists found another species of ant-decapitating fly in Glendale, Pseudacteon amuletum!
Pseudacteon amuletum. Photo credit: Phyllis Sun Here's an account of this tiny, yet impressive fly, by Lisa Gonzalez, one of our BioSCAN entomologists: "For those of you who missed Lila’s exciting account of the moment Dr. Brian Brown first spotted an ant-decapitating fly in one of our BioSCAN samples as it was being sorted in front of our visitors in the Nature Lab, please enjoy this post. As Lila so eloquently described, ant decapitating flies are tiny but mighty little phorid flies that lay their eggs inside of the bodies of, you guessed it, ants. Many of these specialized flies have been the focus of our Entomology Department’s research as conducted in other, more tropical locales, so it may come as a surprise to hear that we have these incredible phorids right here in L.A. These parasitoids (a term we use to describe organisms that eventually consume and kill their host) will not just lay an egg in any ant they come across, but instead target a particular species.
Pseudacteon californiensis. Photo credit: Kelsey Bailey For instance, Pseudacteon californiensis, the first ant decapitator to turn up in a BioSCAN sample, preferentially seeks out the native velvety tree ant, small ants with an orange thorax that nest beneath bark and in tree cavities. Some ant decapitating flies, like zombie hunters, “aim for the head,” but P. californiensis has been observed hovering over the abdomens of velvety tree ant workers where they appear to “lift” the abdominal segments to insert an egg into the host. The larvae must then travel towards the head, making their way through the occipital foramen (the very narrow opening containing the connective tissue between the thorax and head), to complete their development in the head capsule, which eventually is separated from the body by enzymes released by the developing maggot. Our second Pseudacteon discovery from the same site in Glendale is P. amuletum, named from the Latin word for amulet due to its distinct horseshoe shaped oviscape that is reminiscent of a charm or pendant. One may also infer a deeper meaning of the name beyond shape but also of function: amulets can protect, and this species of Pseudacteon is important as a form of biological control against fire ants. A close relative of P. amuletum has been used to help control the spread of the imported fire ant Solenopsis invicta due in part for its rate of parasitism, but mainly because of how it affects the ant’s behavior. Solenopsis ants assume a very strange position when they detect Pseudacteon flies by lifting up their bodies and tucking their abdomens under and forward into a “C” shape with the same incredible skill of a Cirque de Soleil contortionist. It is believed that this helps protect the abdomen from egg invasion, but the trade-off is reduced foraging by the ant, which puts it at a disadvantage in relation to other more industrious, less preoccupied ant species. In this way, Pseudacteon contributes to a reduced fire ant population, which is greatly appreciated by those who know the alarming pain of a fire ant sting." I don't know about any of you, but I can't wait to hear if we find a third species of ant decapitating fly. For breaking news on what they're finding in the other BioSCAN traps, check out their blog.
November 18, 2013
I just found out we have ant-decapitating flies here in Los Angeles! Dr. Brian Brown, the Museum's Curator of Entomology and one of the world's foremost experts on flies, made a chance discovery by looking right under the nose of an unsuspecting USC student. It all started last Friday, while we were enjoying a nice stroll through the Nature Gardens. First, we checked out the Malaise trap that Brian and his staff set up as part of the BioSCAN project, which aims to survey the insect biodiversity here in Los Angeles. Then, we headed into the Nature Lab to see insects from this trap, and the 25 others that have been placed all over Los Angeles, being sorted.
As we got close to the demo table, Brian was suddenly transfixed. He'd seen something interesting on the screen that shows visitors the insects our scientists are sorting under the microscope. By some amazing coincidence, the USC student who was sorting a sample collected in Glendale, just happened to be looking at a phorid fly. Phorids, aka humpbacked flies, are the group of flies that Brian studies, and according to him, they are a mega-diverse family. How mega, you might ask? Apparently, there are estimated to be 40,000-50,000 species of phorid flies, and only 4,000 have been described by scientists so far. Wow!
But, it wasn't just any phorid fly. After taking a look through the microscope himself, Brian nonchalantly walks back over to me and said, "Yep, it's an ant decapitating fly." Whoa, what? I had no idea we had ant-decapitating flies (ADFs) here in L.A.! How could he have neglected to mention this exciting fact during all of our insect musings? Sure he's regaled me with stories of ADFs from Costa Rica and Brazil, always with devilish decapitating detail. But, he never mentioned we have phorids in the genus Pseudacteon, also known as fire ant decapitating flies, here in L.A. Fire ant decapitating flies do just as their name implies. When a female is ready to lay an egg, she locates an unsuspecting worker ant and injects her egg into the thorax. As the larva develops it migrates into the head capsule and molts a number of times. Through this entire process the ant behaves normally. However, just before pupation, the maggot begins to consume the tissue inside the ant's head, which causes the ant to act oddly, and soon after, to expire. The head falls off and the mouth parts are pushed out, so the oral cavity is clear. As the larva pupates, the adult fly emerges from the now-clear oral cavity of the ant. How's that for an alien ant birth? Later that day, Brian wrote an e-mail to the homeowner where the trap was located in Glendale: "Your backyard trap got something unusual- a phorid fly (the group of insects I study) of the genus Pseudacteon. The flies in this genus are all ant parasites, developing in the ant's head, and are referred to as 'ant-decapitating flies.' Usually, in suburban areas, the ant hosts of Pseudacteon are eliminated by the introduced Argentine ant, but you must have (or be close to) a healthy native ant fauna!" This, as Dr. Luis Chiappe, Vice President of the Museum's Research and Collections Department, put it, "is the power of science!" The presence of this parasite, allowed Brian to infer the presence of the host. If we went out to Glendale today, we'd likely be able to find native fire ants somewhere close by! And I know you all dying to join me on that adventure.