Plotting the path of mosquito species in the Pacific

29 June 2023

Vector control programs designed to limit the spread of mosquito-borne diseases, including malaria and dengue, have one of the highest returns on investment in public health. But control programs require up-to-date intelligence to develop the most effective responses – a particular challenge in the Pacific region.

AITHM researchers have compiled a landmark guide to mosquitoes in the Pacific – to help nations in the region, including Australia, try to stay one step ahead of disease-carrying species that are on the move and triggering unprecedented outbreaks.

“We need to know the enemy, their distributions and behaviours. Strong surveillance systems are crucial to the development of effective vector control programs to reduce the transmission of mosquito-borne diseases which are escalating in the region,” said the guide’s lead author, AITHM Senior Research Fellow and medical entomologist, Dr Tanya Russell.

Papua New Guinea harbours the most intense malaria transmission outside Africa, and also experiences regular outbreaks of dengue, chikungunya and Zika virus. Ross River virus has gained a foothold in many Pacific countries. Japanese encephalitis is endemic in Papua New Guinea (PNG), and was recently detected in Australia.

Dr Russell spent one year compiling the guide, which provides an overview of the diversity, distribution and biology of 42 disease-carrying mosquitoes species found in the Pacific, including checklists for the species present in each of the 22 Pacific Island countries and territories.

The mammoth task involved combing through more than 250 published scientific articles on mosquitoes, as well as personal communication with Ministry of Health staff in each country, who routinely conduct mosquito surveillance – “cross-checking information to make sure it all lines up”. Frontline communication channels even yielded information on mosquito species that had invaded into new territories.

Dr Russell’s guide builds upon the foundation research of American entomologist, Professor John Belkin, who published the first comprehensive guide to mosquitoes in the South Pacific in 1962. One of the reasons that has limited ongoing research in the Pacific region is geographic isolation. The Pacific islands are very small and very remote, making access both difficult and expensive.

Ironically, this geographic isolation, which hinders research, has given rise to the largest diversity of dengue mosquito vectors in the world. There are 119 Aedes mosquito species in the Pacific, a dozen of which are implicated as dengue vectors, some of which are found on only one island. “This is Darwin’s island population theory in action. It’s fascinating,” observed Dr Russell.

However, globalization, including massive increases in commercial transport via air and sea over the past 50 years, has enabled stowaway mosquitoes to infiltrate new territory.

“There's been huge expansion in the range of the primary mosquito dengue vectors in the Pacific, Aedes aegypti and Aedes albopictus. They have spread throughout almost all the Pacific Island countries, even though historically they are not from that region,” said Dr Russell.

There is also emerging evidence of species adapting their behaviours to avoid contact with insecticides, the mainstay of protection for beleaguered Pacific communities which can completely undermine vector control operations, until alternatives are deployed.

Since the widespread introduction of insecticide-treated bed nets and other insecticide use indoors, some mosquitoes, that previously lurked inside homes, are learning to wait outside for a blood meal. Such behavioural resistance has been detected in Anopheles farauti mosquitoes in both the Solomon Islands and PNG.

In addition, there are worrying signs that some mosquito populations are developing physiological resistance to certain insecticides, which no longer kill on contact.

A guide to mosquitoes in the Pacific is designed to be a foundational reference for all those working towards reducing the transmission of mosquito-borne diseases in the Pacific region, from frontline Ministry of Health workers to entomologist researchers and vector control product developers.

“We have synthesized all this information to assist vector control programs to know what is happening in their area, which will enable them to develop more effective, locally adapted response measures,” said Dr Russell.

A guide to mosquitoes in the Pacific is an open access publication: https://purl.org/spc/digilib/doc/79hzc