After 350 million years of survival, it’s fair to say that cockroaches are doing something right. Over this time period, the cockroaches evolved many adaptations that made them so hardy. However, one adaptation in particular stands out. Cockroaches have changed their internal chemistry in a way in which glucose no longer tastes sweet, but bitter. This was done in order to not be attracted to a variety of sweet-tasting poisonous baits. In other words, cockroaches evolved.
This change in senses is an elegant display of rapid evolutionary change when a species is threatened by some outside factor. Of course this change is easier in insects and animals with short lifespans and quick reproduction cycles. However, it is still interesting that the adaptation resulted in such a dramatic shift, where the taste of a substance becomes its polar opposite in order to deter the consumption of certain poisons.
The discovery shed some light on the inner workings of the roach, and it has given insight to professionals in the pest control industry. Furthermore, this research can also help in the fight against mosquitoes further down the line.
The experiment was started in order to understand why German cockroaches avoid poisonous bait if it is laced with glucose, a substance which they are supposed to enjoy. This is a new behavior that was first observed in the 1990s, when pest control specialists switched to poisonous baits from insecticide sprays as the main way to battle roach infestations. Some time after the switch, roaches started avoiding the poisonous bait, puzzling researchers and pest control experts alike. This change in behavior led to a cycle of constantly developing new poisons, and the roaches becoming resistant to their effects.
In some cases, the roaches became immune to the poisons, but in others, the roaches simply avoided the poison bait. Through this experiment, researchers also proved that the behavior was inherited, not learned.
Roaches do not have taste buds. Instead they have hairs that can detect taste on various parts of their body. The hairs around the mouth area can be divided into two types – hairs that can taste sweetness and hairs that can taste bitterness. Whenever a roach senses sweetness it wants to eat the substance, and when it tastes bitterness, it wants to avoid it. However, in the case of glucose, which is a sweet substance, the roach will sense bitterness rather than sweetness. This makes any substance that contains glucose repellent to the roach.
Using the research to develop better insecticides
This type of adaptation can be seen in other species as well, including in mosquitoes. Mosquitoes have adapted to no longer rest on walls that have been treated with insecticides, choosing to rest on the ceiling or outside walls instead. The research exploring these behaviors and their development can help pest control companies better understand the lifecycle of insecticides and how to develop more effective substances.