In response to what researchers have identified as growing resistance among mosquitoes to the fogging insecticide malathion, the Ministry of Health maintains that the compound is still effective, since 90 per cent of the mosquitoes do die after exposure, albeit over a longer period of time.

The 90 per cent kill rate notwithstanding, the ministry says it has introduced two new chemicals – Deltamethrin and Anvil — to its vector control interventions to slow resistance to malathion.

In an interview with the Jamaica Observer last Thursday, medical entomologist and manager of the National Vector Control Programme in the Ministry of Health Dr Sherine Huntley Jones argued that although mosquitoes are taking longer to die, a “significant” portion of them them still do.

“The WHO protocol says that 90 per cent of death should occur within 30 minutes [of exposure to the insecticide]. We have 90 per cent occuring within 45 minutes. That’s still a significant number,” she maintained.

She explained, however, that the situation is not unusual as data shows that resistance will develop for any insecticide used over a prolonged period of time. For that reason, she said the ministry has an insecticide monitoring programme and has, since 2016, been collaborating with the UWI in that regard.

“Against that background we introduced two other insecticides on a rotational basis to slow the development of resistance to malathion and extend the life of the chemicals,” Dr Huntley Jones said. “Jamaica should not end up in a situation in which the chemicals are not working because we test on an annual basis to monitor all the chemicals we are using, what the vectors are becoming resistant to, and how they are becoming resistant to it,” she continued.

She was speaking in the context of the disclosure last week by research fellow at the Natural Products Institute at The University of the West Indies (UWI) and entomology manager for Zika AIRS Project (ZAP) Dr Sheena Francis.

In a 2017 paper, titled “Insecticide resistance to permethrin and malathion and associated mechanisms in Aedes aegypti mosquitoes from St Andrew, Jamaica”, Francis examined the type and level of insecticide resistance among the species of mosquitoes that transmits viral diseases such as dengue, Zika and chikungunya.

She explained her methodology and findings to the Observer.

“I tested several areas in St Andrew and I found that the mosquitoes are resistant to permethrin, found in household insecticides, and they are developing resistance to malathion, a chemical used in vector control programmes throughout the Caribbean and the world.

“I looked at what mechanisms of resistance were being used by the mosquitoes in St Andrew. I looked for enzymes and genes normally associated with resistance and, sure enough, I had both genetic and enzyme-based evidence for resistance to pyrethoid, and the mosquitoes in St Andrew are developing resistance to malathion,” she said.

Dr Francis said insecticide resistance is a global phenomenon and is not unique to Jamaica.

From the Health Ministry’s perspective, “operationally, malathion is not failing because it is still recording significant kill”.

“It’s important to note, too,” Dr Huntley Jones said, “that resistance is localised, which means that it won’t necessarily be the same in other parts of St Andrew [where the research was conducted] or the island.”

Data on resistance may shortly be available for the entire island as, under the USAID-funded ZAP project, the joint Ministry of Health/UWI Mosquito Control and Research Unit (MRCU) is currently engaged in islandwide testing. tasked with reducing and controlling the presence of mosquitoes responsible for transmitting Zika and other diseases, such as dengue and chikungunya. The project also targets capacity-building priorities, and sharing global best practices related to eliminating breeding sites, larviciding, and entomological monitoring.

“This resistsance has significance and we are working alongside the MoH to understand insecticide resistance in mosquitoes and to make them aware of what works. Also, through the use of alternatives as synergists, we plan to suggest other methods of vector control,” Dr Francis said.

To that end, the UWI entomologist said that in addition to identifying the types and level of insecticide resistance, the MCRU is researching the efficacy of Jamaica’s endemic plants in suppressing the activity of enzymes associated with insecticide resistance.

She named citronella, but declined identifying others lest she risk compromising the ongoing proprietary research.

“We are seeing mosquitoes now in Jamaica with an inceassed amount of enzymes that speed up how a toxin is broken down and driven out of he body so that it is no longer effective in killing them. If I have a blocker that blocks that specific enzyme, it means that the pesticide can now work. That is called a synergist. Citronella is a known synergist,” she explained.

“Other natural products have been found to be very effective as repellensts and insecticides, but for the study that is being conducted here at UWI on the development of synergists and alternative pesticides, we are going outside of the ususal. We are going outside of those to look at endemic flora from Jamaica to look for answers,” Dr Francis added.

Dr Francis’ work is being exhibited at this year’s UWI Mona Research Days, scheduled for February 6-8 on the UWI’s Mona campus.