Let Us Spray (Invasive, part 2)
This psychedelic-eyed little fly is a Mediterranean Fruit Fly, one of the most infamous invasive pest species in fruit-growing regions of the U.S. People living in Southern California during the late eighties and nineties may remember the controversial helicopter spraying of Malathion across broad swaths of the region in an attempt to prevent disastrous losses in the agricultural industry. Oddly, people were a little cranky about chemicals being sprayed on them from helicopters. Especially chemicals with the prefix “mal” in them, the Latin root for which means “bad” or “evil,” such as: malfunction, malicious, malevolent, shopping mall. But we were assured the pesticide was safe, although it was recommended that everyone stay indoors and keep their pets locked up and cover their cars because the pesticide was delivered in a sticky, sweet, fly-attracting liquid. At one point, someone in charge actually swigged a big glass of (heavily-diluted) Malathion to prove how safe it was. (No word on his current health situation.)
Anyway, we no longer see formations of helicopters spraying chemicals (the helicopters now just follow high-speed chases for use on slow news days). Other, organic pesticides are usually spot-sprayed now (and as we all know, organic things are always safe, like rattlesnake venom and ricin). The other tactic used in their control was — and remains — the release of irradiated-until-they’re-sterile male individuals who then mate with wild females, but then of course produce no offspring. (The irradiating isn’t why they have day-glo eyes, by the way — that’s just the way they look.)
The fly in the photo is one of the released sterile ones; you can tell by the pink-red streaks on its forehead, between the eyes. The pink isn’t part of the fly’s natural color — it’s a dye. The idea is that scientists trapping the flies post-release can judge how well-dispersed the sterile flies are by checking for the dyed individuals; the dye shows up brightly under black lights, like the Jimi Hendrix poster in your basement. Now, when I first learned about this, I wondered who had this very strange job of decorating tiny flies. Just how small a brush would you need? When you got really good at it, could you paint little designs on the fly faces, like kids getting face-painted at a school carnival? And whose hands are that steady? Certainly one cup of coffee and you’d have to take the day off. Come to think of it, I remembered seeing a display of paintings on single grains of rice at the wonderful Museum of Jurassic Technology in Los Angeles. Maybe they hired the rice-grain artist. Then I learned the truth — the technique involves dyeing the cocoons. When the pupa hatches, the fly pushes its way out of the stained cocoon head first, thus smearing pink dye on its own face. No microscopic makeup kit needed. I guess that makes more sense… but my initial idea sounds more fun. Sure, it’s more labor intensive, but imagine some graduate student’s surprise when checking fly-faces under a microscope, and seeing a tiny fruit fly with a face painted to give him kitty whiskers or a bunny nose.