# The Perpetual Vector Mosquito Threat and Its Eco-Friendly Nemeses
## 4 Effective \"Green\" Technologies
### Wolbachia and Incompatible Insect Technique (IIT)  
_Wolbachia pipiens_ is an endosymbiotic bacterium that occurs in the cytoplasm of approximately 60% of insects and is materially (vertically) transmitted to offspring [137].  
Bacteriophages found in _Wolbachia_ are primarily responsible for the phenomenon of cytoplasmic incompatibility (CI), the most common type of reproductive interference in insects. _Wolbachia_ phages harbor incompatibility determinants, including _cifA_ and _cifB_, that regulate CI such that when male insects that have both _cifA_ and _cifB_, and, in some systems, just _cifB_, mate with females lacking _cifA_, no viable offsprings are produced [138; 139]. The IIT approach takes advantage of the fact that male mosquitoes infected with the natural endosymbiont are unable to produce offspring with female mosquitoes devoid of the bacterium or that have cytoplasmic incompatible strains of the bacterium [140; 141; 142]. Although females can lay eggs, the eggs never hatch. Over the past decade, _Wolbachia_-based intervention programs have focused primarily on reducing _Aedes_ species transmitting dengue virus in affected regions in India, Malaysia, China, Singapore, Australia, Brazil, and in the United States where, since 2017, the CI-based MosquitoMate ZAP pesticide has been permitted for use in at least 20 states [142]. Where data are available for the period surveyed, reductions in the incidence of dengue ranged from 40% in Kuala Lumpur, Malaysia, to 96% in Cairns, Australia [143; 144; 145; 146; 147; 148; 149; 150; 151; 152; 153].  
Although _Wolbachia_ is known to be an endosymbiont in _Culex_ and _Anopheles_ species, studies have not been conducted to determine the efficacy of the IIT in reducing natural populations of these mosquitoes or the impact on the incidence of viral and parasitic agents of diseases they transmit on a large geographical scale. It is known that suppression is mediated by _Wolbachia_ incompatibility in _Culex pipiens fatigans_, and there appears to be promise for controlling _Culex quinquefasciatus_ in the field [154; 155; 156; 157]. The use of _Wolbachia_ in mosquito control is also attractive because the intracellular bacterium can be transmitted vertically and spread horizontally among field populations. As several studies suggest that _Wolbachia_ can inhibit the proliferation of _Plasmodium falciparum_ in _Anopheles stephensi_ and _Anopheles gambiae_, and West Nile virus in _Culex quinquefasciatus_[158; 159; 160], targeted control utilizing the appropriate strains of _Wolbachia_ could be helpful in suppressing pathogen propagation in these mosquitoes.  
On the other hand, while the utility of _Wolbachia_ in controlling mosquito populations has been successful, there are concerns that may limit its fidelity and efficacy. Several studies have shown that _Wolbachia_ can enhance rather than suppress pathogen proliferation in insects, including the _Plasmodium_ parasite and West Nile virus, and even insect-specific flaviviruses that are not etiologic agents of human disease [161; 162; 163; 164; 165; 166; 167; 168; 169]. Considering climate change, globalization, and the geographical expansion of mosquitoes, it is reasonable that these apparently conflicting issues should be addressed adequately by a diversity of experts, including ecologists, before large-scale _Wolbachia_-based control programs become routine.