Mosquito management was far more intense in the 2019/20 season than in previous years, a City of Mandurah report has revealed.
Frequent tidal surges and the continual hatching of mosquito larvae throughout the season proved havoc for the management effort with 21 aerial larviciding treatments completed.
The task to keep down the pesky insects is held by a City of Mandurah team in conjunction with the Peel Mosquito Management Group (PMMG) and Department of Health.
At a City council meeting on October 27, councillors were presented with the findings of the 2019/20 Mosquito Management Annual Report.
The report delivered by PMMG representative Scott Severn outlined the management plan and prospects for the upcoming season.
It stated early 2020 brought an unexpected change in environmental conditions and the escalation in tidal inundation required a significant increase in field surveillance and helicopter operations.
This required the program to respond with six consecutive aerial treatments on a weekly basis during February and March.
Mr Severn said this level of treatment had not been required even in the most challenging seasons.
"We did have a series of West Coast troughs and South West cold fronts in February and March of early 2020," he said.
"In that period we had to complete six back-to-back aerial treatments, which is a record for the program.
"It is quite difficult to manage mosquitoes when it's occurring because we are treating week to week and they are potentially chasing our tail if some of those treatments don't go as well as we like."
Overall, the mosquito populations were effectively restricted through this period and the report presented to the council indicated positive results given the tricky environmental conditions.
Season 2019/20 recorded slightly higher numbers of reported cases of Ross River virus and Barmah Forest virus in Mandurah with 71 people contracting the viruses compared to 52 last season.
The council report also predicted a return to La Nina conditions this season.
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La Nina occurs when equatorial trade winds become stronger, changing ocean surface currents and drawing cooler deep water up from below. This results in a cooling of the central and eastern tropical Pacific Ocean.
Those significant rises in tidal inundation events and intensity lead to greater hatching events, which means more intervention by the management program is necessary.
