Assessment of Developmental and Reproductive Fitness of Dengue-Resistant Transgenic Aedes aegypti and Improvement of Fitness Using Antibiotics

Abstract

Background. Genetic modification offers opportunities to introduce artificially created molecular defence mechanisms to vector mosquitoes to counter diseases causing pathogens such as the dengue virus, malaria parasite, and Zika virus. RNA interference is such a molecular defence mechanism that could be used for this purpose to block the transmission of pathogens among human and animal populations. In our previous study, we engineered a dengue-resistant transgenic Ae. aegypti using RNAi to turn off the expression of dengue virus serotype genomes to reduce virus transmission, requiring assessment of the fitness of this mosquito with respect to its wild counterpart in the laboratory and semifield conditions. Method. Developmental and reproductive fitness parameters of TM and WM have assessed under the Arthropod Containment Level 2 conditions, and the antibiotic treatment assays were conducted using co-trimoxazole, amoxicillin, and doxycycline to assess the developmental and reproductive fitness parameters. Results. A significant reduction of developmental and reproductive fitness parameters was observed in transgenic mosquito compared to wild mosquitoes. However, it was seen in laboratory-scale studies that the fitness of this mosquito has improved significantly in the presence of antibiotics such as co-trimoxazole, amoxicillin, and doxycycline in their feed. Conclusion. Our data indicate that the transgenic mosquito produced had a reduction of the fitness parameters and it may lead to a subsequent reduction of transgenic vector density over the generations in field applications. However, antibiotics of co-trimoxazole, amoxicillin, and doxycycline have shown the improvement of fitness parameters indicating the usefulness in field release of transgenic mosquitoes.

A novel pyrazole–pyridine derivative (PPD) targets specific biological pathways in the larval stages of the northern house mosquito Culex pipiens Linnaeus (Diptera: Culicidae)

“…Insect repellents showed serious health issues in both humans and other animals (Potera, 2008). Transgenic mosquitoes suffer from lower developmental and reproductive fitness compared to wild mosquitoes (Ramyasoma et al, 2021). In the near future, it appears that synthetic chemical insecticides will continue in the forefront of selection for pest management.…”

The impact of transgenesis on mosquito fitness: A review

“…There are two categories of fitness: (i) developmental fitness and (ii) reproductive fitness. Developmental fitness is a measure of ability to adapt and survive in the natural environment, whereas reproductive fitness measures the ability to pass genes on to the next generations ( 20 , 21 ). Since transgenic individuals are evolutionary novelties, they are frequently less fit than wild-type counterparts due to the following reasons (i) the impact of transgene products: (i) transgene products; (ii) the position effect and insertional mutagenesis; (iii) inbreeding depression resulting from laboratory adaptation and the fixation of deleterious recessive alleles during the process of creating transgenic lineage; and (iv) the hitchhiking effect resulting from transgene insertion to a point near a deleterious recessive gene in homozygous individuals ( 18 ).…”

“…The authors found a comparative reduction in oviposition, fecundity, and adult lifespan, despite the longer lifespan for larvae, in the transgenic individuals than in their wild-type counterparts. In spite of the fitness cost, further study has shown that the fitness of these transgenic mosquitoes can be improved by treatment with the antibiotics co-trimoxazole, amoxicillin, and doxycycline ( 21 ). The important aspect of these studies is that they maintained the transgenic lines as hemizygotes/heterozygotes and that the fitness cost was directly due to transgenesis (i.e., expression of transgenes and insertional mutagenesis) rather than to the genetic background of the transgenic mosquitoes.…”