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Risks of Wolbachia mosquito control

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Science  18 Mar 2016:
Vol. 351, Issue 6279, pp. 1273
DOI: 10.1126/science.351.6279.1273-b

Controlling insect crop pests and disease vector populations is a huge challenge. A new control strategy involves releasing insects that have been deliberately infected by Wolbachia, a bacterium that induces modifications in host reproductive biology, such as male feminization (when a male develops as a female), cytoplasmic incompatibility (the inability to produce offspring), and reduced insect lifetimes (1). Caged and open-field experiments with infected mosquitoes are in progress (24). The Eliminate Dengue project (5) has released infected mosquitoes in Australia, Vietnam, and Brazil, and obtained promising results showing that the wMel Wolbachia strain is able to invade the Ae. aegypti population and block dengue transmission (2). Such results are very exciting, considering the number of people affected by malaria and arboviruses (dengue, chikungunya, zika, and related viruses) worldwide every year.

However, few have focused on the probability of Wolbachia strains being transferred to other insects and the potential environmental and economic impacts of this host shift. Wolbachia strains (including wMel-like strains) are capable of transferring horizontally among distantly related arthropods in a short evolutionary time (6, 7). Moreover, some parasites are able to carry Wolbachia strains to other species (6).

The benefits of Wolbachia and risks of host shift must be weighed against the benefits and risks of other mosquito control strategies, such as chemical and bacterial pesticides. Pesticides also have environmental costs: They affect nontarget organisms and can lead to the development of resistant populations of insects (8). Unlike the effects of Wolbachia, the consequences of pesticide use are well known, and are regulated in several countries (9).

Although mosquitoes deliberately infected with Wolbachia could reduce the need for insecticide use, the consequences of Wolbachia host shift to native species are, for now, unpredictable. Arthropods present complex and poorly understood ecological relationships, and alterations in reproductive parameters of nontarget species can generate ecological disturbances. The Cartagena Protocol (10)—a United Nations safety regulation for transfer, handling, and use of genetically modified organisms, signed by 170 countries—is not applicable to Wolbachia-infected mosquitoes because the bacteria are considered nontransgenic (11). Therefore, the release of insects hosting Wolbachia was not subject to these regulations. In countries where Wolbachia release was allowed, veterinary, agricultural, and health legislation were used to evaluate its environmental risks (11). As far as we are aware, no country has regulations specifically pertaining to Wolbachia-infected insect release or mitigation strategies to deal with unexpected results. Even if a country enacts such legislation, it would not extend to other countries, whereas Wolbachia-infected insects, at least in theory, can easily cross political borders.

The release of insects hosting Wolbachia strains should be more carefully considered, and further studies of the potential impact of these bacteria on biodiversity should be undertaken, before this strategy can be widely used.

References

  1. Eliminate Dengue Program (www.eliminatedengue.com/program).
  2. The Cartagena Protocol on Biosafety (https://bch.cbd.int/protocol/).

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