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Here to stay: Cockroaches developing resistance to insecticides, study shows.

Eliminating cockroaches through insecticides alone are becoming 'almost impossible' as the household pests are developing cross-resistance from the chemicals, a recent study found.

'This is a previously unrealized challenge in cockroaches,' Michael Scharf, who led the study, was quoted as saying in an article posted in Purdue University's website.

'Cockroaches developing resistance to multiple classes of insecticides at once will make controlling these pests almost impossible with chemicals alone,' he added.

The study, published last month, serves as a 'seminal effort' to test insecticide resistance intervention strategies for the German cockroach, 'a medically-significant pest to urban and impoverished populations on a global scale.'

Cockroach scourge

According to the study, the German cockroach 'is a worldwide urban pest species that lives entirely in human settings' and 'impact human health through production of asthma and rhinitis-triggering allergens, vectoring of enteric pathogens and by causing psychological stress.'

'Sensitization to cockroach allergens is one of the strongest risk factors for the development of asthma in low-income urban populations worldwide,' the study further noted.

Insecticide resistance tests

Researchers from Purdue University conducted three field studies in a span of six months 'to compare three insecticide resistance intervention strategies for [German] cockroaches (Blattella germanica L.) and evaluated resistance evolution across multiple generations.'

The three resistance interventions, which included rotation, mixture or single active ingredients (AI) treatments, were done in 'low-rise' housing facilities in Illinois and Indiana.

For the first treatment, three insecticides from different classes were rotated into use each month for three months and then repeated.

Meanwhile, the second treatment used a mixture of two insecticides from different classes for six months and in the third, researchers chose to use an insecticide to which cockroaches had low-level starting resistance for six months.

'If you have the ability to test the roaches first and pick an insecticide that has low resistance, that ups the odds,' Scharf said.

'But even then, we had trouble controlling populations,' he added.

Based on the study, the cockroach populations were kept flat over the six-month period.

The researchers, however, failed to reduce them and the two-insecticide mixture did not work, increasing cockroach populations.

'We also unexpectedly found that the rotation technique, which adds increased mode-of-action diversity and reduced selection pressure on any single AI (active ingredient), was mostly ineffective at reducing cockroach populations due to cross-resistance among AIs,' the study read.

In a laboratory test conducted on the remaining cockroaches, the researchers also found that 'cross-resistance likely played a significant role.'

The test showed that a percentage of cockroaches would be resistant to a particular class of pesticide.

'Those that survived a treatment and their offspring would be essentially immune to that insecticide going forward,' Purdue University's article read.

'But they also gained resistance to other classes of insecticide, even if they hadn't been exposed to them and had not had previous resistance,' it further explained.

The researchers then concluded that it is important to gain knowledge of cross-resistance patterns between and within insecticide classes in designing rotation strategies and 'improve predictability of long-term cockroach management programs.'
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Publication:Philippines Daily Inquirer (Makati City, Philippines)
Date:Jul 8, 2019
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