Researchers utilize mosquito mating to spread malaria-fighting fungi

Scientists have unveiled a novel mosquito control strategy: genetically engineered fungi that spread through mating. This strategy offers hope for reducing malaria in high-risk regions.

Research: Transmission of transgenic mosquito-killing fungi during copulation. Image Credit: Kateryna Kon / Shutterstock

In a recent study published in the journal Scientific Reports, a team of researchers in Burkina Faso and the United States investigated a novel method for controlling malaria-transmitting mosquitoes using genetically modified fungi that can kill mosquitoes through sexual transmission.

The study explored the transmission efficiency, virulence, and mortality effects of these fungi under semi-field conditions while addressing the challenges in enhancing existing vector control tools. The researchers obtained ethical approvals from the Burkina Faso National Biosecurity Agency and other regulatory bodies, ensuring compliance with biosafety guidelines.

Background

Malaria remains a significant global health challenge, especially in tropical and subtropical countries. Moreover, traditional methods such as insecticidal nets and indoor spraying often successfully target indoor mosquitoes but fail to address outdoor-resting populations. These exophilic mosquitoes exhibit diverse behaviors that make them difficult to manage with current strategies.

Innovative biological approaches, such as using entomopathogenic fungi, which naturally infect and kill mosquitoes, are being explored extensively in recent research. However, these fungi often show limited efficiency due to low transmission rates. While genetic engineering of the fungi to produce lethal toxins has improved their impact even at minimal doses, transmission remains challenging. Research indicates that a single transgenic fungal spore can be lethal to mosquitoes, significantly reducing the need for high inoculum loads observed with wild-type fungi. Sexual transmission of these fungi during mosquito mating offers a promising way to reach both indoor and outdoor populations.

About the study

The present study evaluated the ability of genetically engineered mosquito-killing fungi to spread through sexual transmission and cause significant mortality in outdoor and indoor mosquito populations. The researchers used two fungal strains—a wild-type strain and a transgenic strain expressing insect-specific toxins—to infect male mosquitoes. The study was conducted in laboratory and semi-field environments to mimic natural conditions.

Adult Anopheles coluzzii mosquitoes, reared from larvae in an area with insecticide-resistant mosquitoes, were exposed to the fungal spores. The researchers treated the male mosquitoes with fungal spores and then allowed them to mate with uninfected females. They then analyzed fungal transmission by measuring the proportion of females with fungal spores, the number of spores transferred, and the resulting mortality rates.

The study examined survival rates of female mosquitoes following exposure to males treated with either transgenic or wild-type fungi at different post-treatment intervals. The researchers also assessed whether contact with surfaces where treated males rested could lead to spore transmission. Findings indicated that females did not acquire fungal infections from contact with resting surfaces, reinforcing that direct mating is the primary mode of transmission. Additionally, the team investigated how mating rates and female mortality varied depending on the fungi type, treatment timing, and environmental factors such as the positioning of mosquito swarms relative to sunset, which influenced the number of mating pairs.

Major findings

The researchers found that transgenic mosquito-killing fungi are significantly more effective at causing mortality in female mosquitoes through sexual transmission than wild-type fungi. When males treated with transgenic fungi mated with uninfected females, up to 89.33% of the females died within two weeks, which was significantly greater than the 68% ± 4% mortality observed among the female mosquitoes exposed to males treated with wild-type fungi.

Furthermore, infection experiments demonstrated that males remained capable of transmitting spores for up to 24 hours post-treatment. The transgenic strain proved particularly lethal, even with minimal spore transfer, due to the expression of an insect-specific toxin. Females exposed to transgenic fungi showed higher mortality rates despite receiving similar spore loads as those exposed to wild-type fungi. However, fewer females died when exposed to males infected for 48 hours, suggesting a decline in fungal transmission effectiveness over time as infected males exhibited symptoms.

The study also revealed that females did not acquire infections by coming in contact with surfaces where infected males had rested. This indicated that direct mating is the primary mode of fungal transfer. Furthermore, mating rates were unaffected by the fungal treatment within the first 24 hours, suggesting that the presence of fungal spores on males did not deter female mosquitoes from mating. This finding supports the potential combination of transgenic fungi with other mosquito control strategies, such as the Sterile Insect Technique (SIT) and Wolbachia-based approaches.

Interestingly, fewer females died after mating with males infected for 48 hours compared to 24 hours, likely due to reduced spore transfer as fungal symptoms also began manifesting in the males. In semi-field experiments, mating rates were influenced by environmental factors such as the proximity of swarms to sunset locations, but the mortality patterns observed in the laboratory were consistent in these more natural settings as well.

These results highlighted the potential of transgenic fungi to serve as an effective tool for mosquito control, especially when integrated with other strategies. Furthermore, the study underscores the need for preliminary field evaluations of mating site characteristics to maximize transmission efficiency in real-world conditions.

Conclusions

To conclude, the study demonstrated that genetically modified mosquito-killing fungi could effectively transmit lethal infections during mating and significantly reduce mosquito numbers. Furthermore, the transgenic fungal strains outperformed the wild-type fungi and provided a promising approach for malaria vector control. By targeting both indoor and outdoor populations, this method also addressed the limitations of existing interventions. However, the persistence of fungal effectiveness over time and environmental influences on mating rates should be carefully considered for large-scale deployment.