This archive report was first published on 15 July 2019.
Kenya: Study Reveals Why Cockroaches Are Growing Immune to Insecticides ¶
Published on July 15, 2019
By Pauline Kairu
Have you ever struggled to get rid of cockroaches in your home or building, despite using various insecticides? A recent study in Kenya has found that German cockroaches have developed a cross-resistance to a range of powerful insecticides, making them nearly impossible to kill with chemicals alone.
The study, conducted by researchers at the International Centre of Insect Physiology and Ecology (icipe) in Kenya, found that the German cockroach (Blattella germanica) has become immune to most available insecticides. In fact, using spray mixture treatments not only fails to reduce cockroach numbers but may even have a repellent effect, causing the cockroaches to spread to previously uninfested areas.
According to Dr. Chrysantus Mbi Tanga, an insects' research scientist at icipe, this is a major problem that has been affecting Kenyans for years. "It is a very big problem that has concerned us scientists in Kenya. A lot of Kenyans have been complaining and looking for effective control measures because commercial products seem not to provide adequate results as intended," he said.
Cockroaches are a serious threat to human health, as they can carry a range of diseases, including diarrhoea, dysentery, typhoid fever, and cholera. They can also trigger allergies and asthma, and are a major contributor to unhealthy indoor environments.
According to the study, the German cockroach is capable of hosting tens of bacteria in its digestive tract, including antibiotic-resistant strains. This means that even if the cockroach is killed, the bacteria can survive and continue to pose a threat to human health.
The researchers tested three different courses of insecticides, including single Active Ingredient (AI) treatments, mixture and rotation of professional-grade insecticides. However, they found that even after dosing the cockroach populations with the different classes of insecticides, the resistance levels increased, and the cockroach numbers remained stable or even increased.
"Resistance levels increased to almost all AIs tested in this study," the researchers said. "In one of the experiments, the researchers tested a group of roaches that had slightly more resistance, whose number of roaches actually increased, with generations born to resistant survivors."
According to Dr. Tanga, in Kenya, Total Release Foggers (TRFs) or "bombs"-spray cans that usually contain pyrethroid, pyrethrin or both as the active ingredients- are the commonest AIs used to manufacture insecticides for cockroaches. However, the researchers found that even these insecticides were ineffective against the resistant cockroach populations.
"Some of these methods are more expensive than using only insecticides, but if those insecticides aren't going to control or eliminate a population, you're just throwing money away," said Michael Scharf, a professor and chair with the Department of Entomology at Purdue University in Indiana.
He suggested a combination of approaches, including improved sanitation, traps, and even vacuums to suck up the cockroaches, instead of relying on pesticides to do the job.
