In just six months, without the use of chemical pesticides or genetic modification, researchers have freed one of the atoll’s (that was owned by Marlon Brando) isletfrom Aedes polynesiensis, an invasive mosquito species that is the vector of diseases such as dengue, chikungunya, and Zika.
The society carries out Brando’s vision of researching and conserving the atoll’s natural environment. It’s supported in part by The Brando, a high-end eco-friendly resort that was another part of the actor’s vision.
It’s a simple process: Introduce certain male mosquitoes that will mate with and sterilize the wild females in a particular locale, rendering their eggs nonviable. After a few rounds of such treatment, the population is unable to reproduce itself and collapses.
Up to 60 percent of insect species carry a harmless type of bacteria called Wolbachia in their cytoplasm, the thick mixture of water, salts, and protein that fills every cell. The key is that different insect populations have different Wolbachia strains.
When a male mosquito infected with Wolbachia A mates with a female infected with Wolbachia B, the fertilized eggs fail to develop as a result of what’s called cytoplasmic incompatibility. The adults may be perfectly healthy—and could even mate successfully with other individuals if their bacterial strains matched—but mismatched insects won’t produce any offspring.
At the very beginning of the project, the team on Tetiaroa set baited traps and caught large amounts of wild mosquitoes. The bugs were given an antibiotic to wipe out the naturally occurring Wolbachia in their systems, and then they were infected with another strain of Wolbachia from a different population. The team let the treated mosquitoes breed, then worked solely from that population.
As new broods reached the pupa state, a mechanical sorter separated them by size to pull out the males, which are smaller. Samples were verified under a microscope to ensure no females had snuck into the bunch—at less than one per 10,000, the system’s record is strong.
The scientists then set the females aside with some males so they could get started making the next generation of pupae carrying the foreign strain of Wolbachia.
Fully emerged and ready to track down females and mate, these Wolbachia-incompatible males await release on the islet of Onetahi in Tetiaroa.
PHOTOGRAPH BY J. MARIE, ILM
SOURCES- National Geographic