**12. Biological control**

Although, chemical use in the form of synthetic insecticides remains promising factor for the control of insect vectors; however, indiscriminate and overuse pose insecticide resistance issues [58]. Moreover, various health and environmental concerns make the use of insecticide questionable. Thus, it is imagined that in future only those techniques will be accepted which may overcome the problems related to chemical insecticides. Recently, non-chemical methods have been summed-up into "biopesticides"; meaning thereby simply to kill the pest using material originated from living things [59]. Hence, it necessitates to explore biological control agents like various predators and parasites, that is, viruses, fungi, bacteria, etc. to look for a potent agent for the development of safe control program. Various pathogens and predators have been reported to use against mosquitoes as biological control agents. Recently, in Vietnam, copepods were used to control larvae of *A. aegypti*. At local level, the control program was launched very successfully and showed good results [61, 62]. In addition, a bacterium *Wolbachia pipientis* which is an obligate intracellular bacterium and vertically transmitted from mother to their offsprings and causes cytoplasmic incompatibility. It has been reported to present in 60% populations of insects in field conditions. Wolbachia infects the gonads and ensures transmission to the next host generation and orchestrates various reproductive manipulations in host. The symbiont can also cause feminization of genetic males, parthenogenesis and male killing, depending on the host species [63]. Thus, via females the Wolbachia spreads in the host populations and ultimately hinders its increase in number in future. It is reported that Wolbachia infections spread upto 100 km per annum. The Wolbachia strains were manifested and manipulated successfully in 1967 in Burma against filariasis vectors, where Wolbachia infected male *Culex quinquefasciatus* were released in wild populations. In principle, Wolbachia infection affects the sperm and prevents the further reproduction as a measure of local mosquito population control [65].

The sterile insect technique (SIT) is widely tested strategy in insects; wherein, males are treated with either sterilizing chemicals or exposed to γ-irradiation producing random dominant lethal mutations; means only one locus containing the DNA damage can cause dominant effect in the form of lethality. The SIT males when mate with normal females results nonviable offsprings leading to elimination of the populations in successive generations [65]. Another approach is RIDL (release of insects carrying a dominant lethal mutation) which is an improved version of SIT using transgenic technique and specifically focuses on femalekilling. For instance, gene specifically expressing in the flight muscles were made transgenically expressed low and the resulting females in the offsprings would not be able to fly properly which causes its non-feeding on human blood meal which ultimately leads towards low fecundity [67]. Specific transgenic approaches have been proved successful also in pupae and adults [68, 69]. This RIDL techniques is being exploited and deployed by Oxitec® in Brazil and Malaysia and reproduced appreciable results [70]. Subsequently, *Bacillus thuringiensis*  *israelensis* (*Bti*), methoprene and the insect growth hormone are also proven to be quite effective against *Aedes albopictus* in the laboratory as well as in the field [57, 71–75].
