"We would see resistance increase four- or six-fold in just one generation." Michael Scharf, Department of Entomology, Purdue University
It appears that we have a significant problem on our hands. Cockroaches have become resistant and virtually immune to insecticides, bug spray, and even entire chemical classes we use to control their populations.
Shortly, we will have to control them the old-fashioned way with traps, keeping a clean house and businesses while vacuuming; all the time. Gross. Ugh!
These insects can gain immunity in just one generation. In times of famine, they will kill and eat each other. As mentioned above, they live with humans exclusively and eat what we eat. They have a three-month-long reproductive period and use that time to lay approximately fifty eggs.
Tom Hale writes in IFL Science (2019):
The rise of the superbug cockroach is upon us. A new study has found that German cockroaches (Blattella germanica) are rapidly evolving to become resistant to many widely used bug sprays and insecticides, as well as chemicals they've never been directly exposed to, making them near-impossible to eliminate and one step closer to taking over the world.
The researchers tested out different treatments of three insecticides – abamectin, boric acid, and thiamethoxam – in numerous cockroach-infested apartments across Indiana and Illinois over six months. In one treatment, three different insecticides were rotated each month for three months and then repeated. In a second, they used two insecticides from different classes for six months. In the third, they chose one insecticide to which cockroaches had low-level starting resistance.
Regardless of the different chemical cocktails, the researchers were unable to reduce the size of the cockroach population. In the single insecticide treatment, populations grew with around 10 percent as individuals starting to evolve resistance. Even with the two insecticide treatments, the cockroach populations actually skyrocketed. The three-pronged attack managed to maintain the number of cockroaches but it was ultimately unable to reduce it.
They later backed up these findings through lab tests. As anticipated, the results showed that a considerable share of the cockroaches and their offspring had become “essentially immune” to a particular class of pesticide.
The study can be found here. The study occurred in low-rise apartment buildings in Indianapolis, IN, and Danville, IL. Chemicals have been essential in killing pests. However, resistance began to emerge in the 1950s. Resistance to chemicals can now occur once a generation.