Pesticide Resistance
Pesticide Resistance is when bugs survive a spray that used to kill them.
Think of it this way
A bowl holds a mix of red and white balls. You pour a liquid over the bowl that melts all the red balls, leaving only the white ones. The white balls are moved to fill a new bowl. When you pour the same liquid again, nothing melts because every ball in the bowl is white.
Explaining pesticide resistance by grade level
Bug spray kills most roaches, but a few stay alive. Those tough ones have babies that are also hard to kill. After a while, the spray stops working on the whole group. That is why people need to switch to new kinds of bug killer.