The pyrethroid keeps the sodium channels open, so the nerves fire repeatedly.

拟除虫菊酯使钠离子通道保持开放，导致神经不断反射。

But if a resistant roach is exposed to pyrethroids, it'll be just fine.

但是如果抗药性的蟑螂接触到除虫菊酯，并不会怎样。

Genetic mutations have given them sodium channels that the pyrethroids can't bind to.

基因突变使它们拥有拟除虫菊酯无法结合的钠通道。

But if a resistant roach is exposed to pyrethroids, it’ll be just fine.

但如果一只抗性蟑螂暴露于拟除虫菊酯， 它就会没事。

Pyrethroids, which are the active ingredients in many commercially available insecticide sprays, are safer, but become less effective every year.

拟除虫菊酯是许多市售杀虫剂喷雾剂中的活性成分，它更安全， 但效果逐年下降。

When a non-resistant roach walks on a surface that's been sprayed with a pyrethroid insecticide, for example, the results will likely be fatal.

例如，当无抗药性的蟑螂走在喷过拟除虫菊酯杀虫剂的表面上时，其结果很可能是致命的。