Cockroaches are more than just a nuisance
pest they are dangerous to live with since they act as vectors for disease. We often joke about the fact that a cockroach
can survive a nuclear blast. But they are no match for a small spray of
insecticide. Have you ever wondered how insecticides affect
cockroaches? Let’s find out! Meet Joey the cockroach. He is luckier than many other insects, as
he is being granted his very own suit of armour, an exoskeleton. He is very proud of it. But just like any other armour,it can’t
offer perfect protection. Although this armour can help him withstand
more force and survive longer, it doesn’t protect him from the instant death that comes
from exposure to insecticide. Small pores and spiracles allow some of the
harmful material to enter his system. For the insecticide, entering Joey’s system
is just the beginning. It has the potential to kill him in an instant,
thanks to lethal compounds like Pyrethrins and Pyrethroids. To understand why these compounds are toxic
to Joey, you need to understand how the neurons normally function. Suppose Joey’s brain asks his legs to start
scurrying around, in order to freak out some humans. This message would travel as an impulse from
his brain to the legs, via axons in the many neurons along the path. As the ions move through the axons, their
charge gradually weakens, and this is no good, because this means the message from the brain
won’t reach Joey’s legs. If the message never arrives, he can’t scurry
around. To overcome this problem, there are ‘Voltage-gated
Sodium channels’ along the membrane that can allow positive ions or sodium ions to enter
and maintain the strength of the impulse. Since they are voltage-gated, they open like
doors, in the presence of ions around them. In this case, when a weakened impulse reaches
such a channel, they are triggered to open, allowing positive ions to enter and subsequently
increase the impulse strength back to its original condition. This allows the impulse to maintain strength
until it reaches its intended destination. That’s how it normally should function. But when exposed to an insecticide, after
it breaches the imperfect armour, the harmful compounds will disrupt this critical system. What exactly do these compounds mess with? The doors. These compounds prevent the Sodium channels
from closing. They keep the doors open. Which means the sodium ions keep entering
through the membrane, and it becomes depolarized. Since the axon is depolarized, the nerve impulses
cannot propagate, and hence, the brain cannot tell the rest of the body to do anything. Joey is instantly paralyzed, and await death
likely by starvation. Congratulations you now know how insecticides
work! And as for poor Joey, well he will be missed.