Biological control involves the use of living organisms to shrink a target population using predators, parasites, and pathogens. The aims are always to reduce the target population to an acceptable level and at the same time avoid side-effects to the ecosystem and the conservation of biodiversity, whilst avoiding toxicological and eco-toxicological effects. In mosquito control, the regulatory power of the bionetwork is preserved by shielding the existing community of mosquito predators.
The bacterium “wolbachia pipientis” is found naturally in about fifty per cent of all insect species, but not in aedes aegypti mosquitoes which transmit dengue, zika, and chikungunya. Once artificially introduced to the aedes aegypti mosquito, the wolbachia bacterium can block the transmission of viruses to humans. Over the next ten years, the World Mosquito Program (WMP) intends to release modified mosquitoes in urban settlements across Brazil. WMP investigators uncovered that aedes aegypti infected with wolbachia are much less likely to transmit disease. This is so because the bacterium outcompetes the viruses carried by the insect.
In Australia, Vietnam, Colombia, Brazil, and Indonesia the release of wolbachia-infected mosquitoes has shown optimistic results. In Yogyakarta, Indonesia, the method produced an outstanding seventy-seven per cent reduction in dengue incidence. But trials in Brazil have had more modest results, with a sixty-nine per cent decrease in dengue cases in Niterói, and a thirty-eight percent reduction in Rio de Janeiro.
The aim of the project is to protect up to seventy million people from diseases such as dengue. Scientists have tested the release of mosquitos that carry the wolbachia bacterium that can stop the insect from transmitting viruses in Australia, Brazil, Colombia, Indonesia and Vietnam. However, this will be the first time that the technological innovation will be dispersed nationwide.
This will require the building of the first Mosquito Factory. The intervention does not involve the genetic modification of the bacteria or the mosquito. By engaging in the tedious task of injecting tiny mosquito eggs with the bacteria, scientists can propagate populations of these mosquitoes that carry the wolbachia bacterium. Once the mosquitoes are release into communities, wolbachia bacterium spreads into the wild mosquito population.
Fiocruz is Brazil’s research foundation that has a collaboration agreement with the World Mosquito Program (WMP) to expand the use of wolbachia bacterium against dengue, zika, and chikungunya—diseases transmitted by the bite of the aedes aegypti mosquito. A female mosquito carrying the wolbachia bacterium can transmit the bacteria to its offspring, even if it mates with males without the bacteria.
The goal is not to eliminate the aedes aegypti from the ecosystem, but rather to replace a population capable of transmitting disease with an inept one. The technique is currently employed in Brazil as well as in eleven other countries. In Brazil, trials were conducted by Fiocruz in collaboration with Brazil’s Ministry of Health in 2015 with the release of mosquitoes in two districts in Rio de Janeiro.
The initiative proved successful and will now be expanded to other cities and states. An agreement establishing the construction of a large biofactory in Brazil by 2024 has been reached, but its location remains undetermined. The facility would be the largest of its kind to produce mosquitoes infected with the wolbachia bacterium. The new biofactory will have the capacity to breed up to one hundred million mosquitoes per week or about five billion modified mosquitoes per year.
The project is funded by the WMP and the Paraná Institute of Molecular Biology (IBMP), which was conceived through a partnership between Fiocruz and the Paraná state government. Scaling up this technology to cover Brazil’s rambling urban areas is a challenge. It will require the building of trust within communities. The WMP is currently considering automated mosquito-dispersal methods including drones.
It is important to note that the World Health Organization (WHO) has not yet officially endorsed the technology. The WHO’s Vector Control Advisory Group plans to discuss the technology further. Given the variable successes across countries, regulators and scientists caution that the wolbachia method should be considered complementary to other public health practices, including vaccination. The struggle against mosquito-borne diseases requires an integrated approach. At this time there is no single solution on the horizon.
Other scientists have explored the use of toxorhynchites rutilus. The adult Tx. rutilus are large mosquitoes with a wingspan of almost 1.27 cm or half of an inch. The adult mosquitoes feed peaceably on nectar. They need nectars from flowers to reproduce. However, the larvae of this species are fierce cannibals. Larval Tx. rutilus ravenously pursue and devour the larvae of disease-vector mosquitoes sharing the same water. A single larval Tx. rutilus can consume up to 5,000 prey larvae before it becomes an adult mosquito. Larval Tx. rutilus prey on mosquito larvae, particularly Aedes larvae.
The use of toxorhynchites rutilus as a form of biological control has been infrequent because it is inefficient. Furthermore, predatory mosquitoes are not available commercially. And it is also difficult to produce enough of them in a laboratory to make a dent in disease vector numbers after release into an ecosystem. A future fuelled by artificial life, and biofactories that disperse modified mosquitoes using drones promises to be quite unusual.
