Wily Cockroaches Find Another Survival Trick: Laying Off the Sweets
Everyone knows that cockroaches are the ultimate survivors, with enough evolutionary tricks up their carapaces to have thrived for 350 million years and to have completely adapted to the human species.
But the nature of the adaptation that researchers in North Carolina described on Thursday in the journal Science is impressive even for such an ancient, ineradicable lineage, experts say. Some populations of cockroaches evolved a simple, highly effective defense against sweet-tasting poison baits: They switched their internal chemistry around so that glucose, a form of sugar that is a sweet come-hither to countless forms of life, tastes bitter.
The way the roach’s senses changed, experts say, is an elegant example of quick evolutionary change in behavior, and offers the multibillion-dollar pest control industry valuable insights into enemy secrets, perhaps even revealing some clues for the fight against malaria-carrying mosquitoes, which are far more dangerous to human health than roaches.
“This is a fantastic discovery,” said Walter S. Leal, the head of the entomology department in the College of Agricultural and Environmental Sciences at the University of California, Davis. (Dr. Leal was not part of the research.)
加州大学戴维斯分校(University of California, Davis)农业与环境科学学院(College of Agricultural and Environmental Sciences)昆虫系主任沃尔特·S·利尔(Walter S. Leal)没有参与该项研究，但他表示，“这是个了不起的发现。”
“Sometimes,” he said, “the science is beautiful but you don’t know whether there is going to be an application five years from now, 10 years from now or 100 years.” But in this case, he said, the impact is both fundamental and practical.
Ayako Wada-Katsumata, Jules Silverman and Coby Schal, all at North Carolina State University, who wrote the report in Science, set out to explain a well-known phenomenon: Some populations of German cockroaches (the ones that apartment dwellers see scurrying around in the kitchen at night) avoid poison bait that is laced with glucose, which is supposed to attract them.
在《科学》杂志上撰文的研究员文子·瓦达-胜间田（Ayako Wada-Katsumata，音译）、朱尔斯·西尔弗曼 (Jules Silverman)、科比·沙尔(Coby Schal)都来自北卡罗来纳州立大学(North Carolina State University)，他们着手解释了一个著名的现象：一些德国小蠊群体（就是那些公寓住户在夜间看到在厨房里快速跑来跑去的蟑螂）能避开裹有葡萄糖的毒饵。
This behavior, discovered by Dr. Silverman, “first appeared in the early ’90s,” said Jim Fredericks, chief entomologist at the National Pest Management Association, shortly after exterminators — who now prefer to be called pest management professionals — started using poison baits instead of spraying as the main method of battling roaches. To get around the problem, the industry developed new baits, but the change in roach behavior was a puzzle.
国家害虫管理协会(National Pest Management Association)昆虫科负责人吉姆·弗雷德里克斯(Jim Fredericks)称，西尔弗曼博士发现，这种行为“最早出现在20世纪90年代早期”，也就是灭虫师，即今天倾向于被称为害虫管理专家的人，开始使用毒饵代替喷药来作为除蟑的主要办法之后不久。为了解决这一问题，该行业研发了新诱饵，但蟑螂行为的变化在当时是个迷。
Grzegorz Buczkowski, an entomologist at Purdue University who was not involved in the research, said the industry was always developing new poisons, because roaches and other pests become resistant to their effects, just as bacteria become resistant to antibiotics.
普渡大学(Purdue University)昆虫学者格热戈日·布奇科夫斯基(Grzegorz Buczkowski)也没有参与这一研究，他称灭虫行业一直在研发新的毒饵，因为蟑螂和其他害虫会变得对毒药有很强的抗药性，就像细菌适应抗生素那样。
“We lose baits all the time,” he said.
But in this case, the problem was not a poison that had become ineffective. The cockroaches just seemed to avoid any bait that had glucose.
Dr. Silverman showed that this behavior was inherited, not something an individual roach learned during its brief life. And a few years ago the North Carolina researchers decided to investigate what caused the change.
Instead of taste buds, roaches have taste hairs on many parts of their bodies. The three North Carolina researchers concentrated on those around the mouth area and on two types of nerve cells that sense tastes and respond by firing electrical signals to the brain. One responds only to sugars and other sweet substances; the other responds only to bitter substances. Whenever a molecule of something sweet attaches to a sweet detector, it fires electrical impulses and the roach brain senses sweetness, which makes it want to eat whatever it is tasting. Whenever a molecule of something bitter attaches to the bitter detector, that cell fires and the brain senses bitterness, which makes the roach want to avoid that substance.
But somehow the roaches had changed so that the glucose made the bitter detector fire.
“Basically,” said Dr. Buczkowski, “when cockroaches taste glucose, they’re repelled by it because it tastes bitter to them.”
Dr. Schal said the next step was to figure out the details of the genetic mutation that had occurred. Perhaps a mutation changed the molecules that detect bitter substances so that they would be sensitive to glucose, too. Or a different sort of mutation could have caused the dedicated bitter neurons to have lots of standard glucose detectors, which did not exist on those neurons before — a shift that also would have made the insects register sweet glucose as bitter.
The research may be relevant far beyond roach control, perhaps helping to explain the behavior of mosquitoes that spread malaria, Dr. Schal said.
“The mosquito changed its behavior,” he said, “and no longer rests on walls that are treated with insecticide. Instead it tends to rest on the ceiling, or it tends to rest on the outside walls that are not treated with insecticide.
“We still don’t understand the cellular, the neural mechanism responsible for this change in behavior of the mosquito,” he said, so the approach that yielded results with the cockroach could offer useful insights.