Cytoplasmic Incompatibility

Cytoplasmic incompatibility (CI) is a reproductive effect caused by the bacterium Wolbachia in many insects. When an infected male mates with a female that lacks the same strain, the eggs fail to develop, but infected females can reproduce normally, which gives infected insects an advantage and helps the bacterium to spread.

Wolbachia modifies the sperm during their development through two proteins, CifA and CifB, which are encoded by genes inherited with a virus-like element in the bacterial genome. After fertilization, the modified paternal chromosomes are damaged in the first divisions of the embryo, which then dies. The same bacterium in the egg of an infected mother supplies a "rescue" that restores normal development. The effect was first observed in the mosquito Culex pipiens, and later work extended it to many insects.

Because infected females have more surviving offspring than uninfected ones, the infection can sweep through a population, even if it slightly harms the host, as in a gene drive. Wolbachia are transmitted in the egg through the mother, and they belong to the alphaproteobacteria.

In the incompatible insect technique, mass-reared male mosquitoes carrying a strain that is incompatible with the wild females are released, causing their eggs to fail, much like the sterile insect technique but without radiation. In another approach, Wolbachia strains that block viruses are established in wild populations of Aedes aegypti. In a trial in Yogyakarta, Indonesia, these releases cut cases of symptomatic dengue by about 77 percent, and they form a part of modern vector control.

• Wolbachia — the bacterium that causes it
• Sterile Insect Technique — a related control method
• Aedes aegypti — a mosquito targeted with Wolbachia