Aphid Panic
BY ALPER ÖZKAN (MSN/PhDII)
For the last two weeks, Bilkent has been suffering from a plague of tiny, green-black insects that flutter around every which way, getting snagged in clothing and ice cream cones or flying their way down unfortunate folks' nasal passages -- my coat in particular acts like flypaper for them, and even as I write this piece, I am covered in dozens of the little vermin, looking a bit like The Pain and a lot like a disgruntled sundew. Since I have a bit of notoriety as an insect aficionado, I am frequently questioned as to what exactly these swarming pests are (and especially whether they're harmful), and I figure that I might as well alleviate (or, preferably, exacerbate) the concerns about these small critters: they're plant lice, they abound on plane trees (or at least our particular breed does), they're harmless, and they will be the subject of this week's column. The word "lice" tends to make people a tad queasy, of course (and due to this very fact, my answer has been met with everything from fear to outright denial), so I will refer to them as aphids, a more proper name that readily distinguishes them from a large number of other insects that derive nourishment from plant sap.
Aphids, as anyone who has had the displeasure of being outside for the past week has no doubt noticed, are prolific breeders, a trait that allows them to suck entire trees dry and does little to endear them to gardeners. Indeed, so rapid is their reproductive cycle that certain aphids can be born "pregnant" -- aphid eggs develop inside their mother and emerge as full-fledged nymphs, which themselves contain eggs that will in turn be delivered once the newborn insects reach adulthood (aphid reproduction is parthenogenic in this stage and does not require males). Their explosive growth is consolidated by the contract many aphids have established with ants, though due not so much to bilateral agreement as to a byproduct of aphid feeding: aphids are obliged by the laws of physics to excrete a very nutritious, sweet fluid called honeydew, since the plant juices they drain are so highly pressurized that they exit straight through the insect's other opening. Ants, for their part, will stop at nothing to get at this sugary fluid, and will even chase off the myriad predators of aphids (such as ladybugs, which are in fact ravenous engines of aphid slaughter and are sometimes employed to combat aphid infestations) or "herd" aphids in their nests to increase their access to honeydew. Ants aren't the only animals that find honeydew delicious, however: geckos have been observed to coax aphids into secreting honeydew right into their mouths, and bees may collect the fluid to make honey (which in turn is quite prized by humans, but I have my reservations about eating what is essentially aphid droppings made into bee vomit).
Aphids have also demonstrated remarkable powers of genetic engineering, having hijacked the ability to synthesize carotenoids from fungi. These pigments are integral to a number of mechanisms across the animal kingdom (and every animal save the little pea aphid has to obtain them from plants or fungi), though aphids again break the mold by using them in...well, remember when I called it not-quite-photosynthesis a few columns ago? Aphid carotenoids are capable of absorbing light (as carotenoids are wont to do), and aphids with a greater carotenoid content apparently synthesize more ATP than those lacking the pigment -- suggesting that some of the energy absorbed by the carotenoids may somehow be available to the aphid. The study indicating this is quite recent, though, and more research is required to fully elucidate what aphids are really doing with their carotenoids. It is, however, known for sure that a virus is responsible for giving a certain aphid its wings: normally wingless morphs of the rosy apple aphid can be converted into winged, dispersive forms by means of infection with a densovirus, allowing the aphids, which are normally bound to a single locale, to establish themselves on new trees. (Though, no animal [yes, including humans] can beat bdelloid rotifers in the genetic modification game -- with the ability to freely incorporate foreign DNA into their own genome, these tiny rotifers would give Tyranids and the Zerg a run for their money, and are in fact so dependent on pilfering other genes in the environment that they no longer reproduce sexually [and haven't for at least the last 40 million years].)
In any case, the next time those little bugs (and I can finally use this word without fearing reprisal -- aphids are bugs proper, that is to say, they are in the order Hemiptera, as opposed to bugs improper, which may be anything from spiders to rodents) land around you, keep in mind that they're sap-sucking machines that drink so fast they have to eject most of the fluid from their other end (and self-destruct if they can't), can be born pregnant, may be photosynthetic, grow wings after being infected by a virus and, in the case of some species, can be eusocial much in the same way ants and bees are -- older individuals will even explode on predators to protect the young, scattering a sticky residue that deters would-be attackers.
That aside, avoid walking under plane trees if you can help it. If you've ever had a watery fluid drip on you from a plane tree, well, that's honeydew -- though at least it's better than bird droppings.