**Abstract**

Arthropods like mosquitoes are well-known vectors which are mainly involved in the transmission of pathogens to different human and vertebrate diseases. Most of the pathogens like viruses and nematodes are transmitted by mosquitoes. Controlling vector populations by using actinobacteria can be particularly very effective. Actinobacteria which contain also non filamentous forms of bacteria which produce a large number of biologically active secondary metabolites. Even though many antibiotics have been developed from actinobacteria, not much work have been conducted in the field of pest control. The actinobacteria and their metabolites effectively control mosquito populations and the transmission of diseases by them. The microbial metabolites have many advantages over synthetic chemicals because many of them are host-specific and safe for beneficial organisms. Due to this speciesspecific effect, microbial pesticides are more reliable to control mosquito populations. These types of metabolites have to be evaluated for the development of novel insecticides for vector control. Some studies have reported the mosquitocidal effects of actinobacterial metabolites like tetranectin, avermectins, spinosad, macrotetrolides, etc; they have less or no residual effect in the environment. This chapter focuses on the mosquitocidal effects of actinobacteria and their metabolites.

**Keywords:** Actinobacteria, *Streptomyces*, *Aedes aegypti*, *Culex quinquefasciatus*, *Anopheles stephensi*, vector-borne diseases, microbial pesticides

#### **1. Introduction**

Arthropods are the most important organisms in relation to humans and environment in many ways. Most insects are beneficial to environment, humans and other animals; some of them are dangerous to humans and mammals. Insects which act as vectors can cause several devastating diseases to human beings and other mammals. Mosquitoes are the most harmful vectors among hematophagous insects [1]. They transmit harmful pathogens which cause millions of death every year; they produce a great impact on public health, labour outputs and economics [2, 3]. Mosquitoes mainly transmit the diseases like *Japanese encephalitis*, filariasis, dengue, malaria, dengue haemorrhagic fever, yellow fever, Zika and chikungunya [4–7].

World Health Organization declared mosquito as the 'public enemy number one' in 1996 [8]. Millions of people are dying every year due to mosquito-borne diseases. Mosquitoes can grow in different aquatic habitats such as ponds, overhead tanks, brackish water, sewage waters, freshwater pools, paddy fields, and even in stagnant rainwater in small containers [9]. Mosquitoes are important etiological agents not only to human beings but also to other native faunas [10]. Mosquito-borne diseases

are becoming more extreme and spreading due to ecological and environmental changes like urbanization.

#### **1.1 The most common mosquitoes as disease vectors**

Five vector-borne diseases are considered as most dreadful diseases in India. They are malaria (transmitted by *Anopheles* spp.), dengue, chikungunya (*Aedes* spp.), filaria and *Japanese encephalitis*(*Culex* spp.) [11, 12].

#### *1.1.1 Aedes spp.*

The genus *Aedes* is the most important vector responsible for chikungunya and dengue, which are mainly found in the temperate regions of the world. Nearly 30–50% of the world population has been affected by dengue virus [13, 14]. *Aedes aegypti* is a tropical species that grows in fresh water in and around human dwelling areas. *Aedes polynesiensis* and *Aedes scutellaris* are in the western Pacific region and *Aedes mediovittatus* is in the Caribbean. *Aedes* is an important vector in Southeast Asia and it has spread to the Mediterranean rim, Americas, and western Africa [15, 16]. In 2006, several parts of southern India confirmed the re-emergence of chikungunya infection [17]. Chikungunya outbreak affected 1.25 million people from about 150 districts in eight states of India; the causative viral agent was spread by *Aedes aegypti* [18]. Mosquitoes not only transmit diseases to humans but also to other mammals like dogs, horses and cats. They cause diseases like West Nile fever, dog heartworm and Eastern equine encephalitis (EEE). Dog heartworm (*Dirofilaria immitis*) is a dreadful disease for canines.

#### *1.1.2 Anopheles spp.*

Malaria is transmitted by *Anopheles* spp. mostly in urban areas. *Anopheles* mosquitoes mainly breed in clean and rainwater storage amenities. Out of 59 Anopheline species in the world, nine occur in India as vectors. In Ethiopia, malaria is the main disease responsible for a large number of deaths. It is one of the significant interferences to financial enhancement as the important transmission time frames agree with top farming and collecting period [19–21]. In Orissa, a state which is located in the eastern part of India, a large number of malaria cases and malaria-related deaths were recorded [22]. Malaria outbreaks are common in Indonesia, India, Bangladesh, Myanmar, Thailand and Sri Lanka [23, 24]. In India, *Anopheles subpictus* was reported in the state of Rajasthan and it is identified to transmit malaria and filariasis [25, 26].

#### *1.1.3 Culex spp.*

*Culex* is a vector of many diseases and an important genus of mosquito which transmits diseases like filariasis, St. Louis encephalitis, *Japanese encephalitis* and avian West Nile fever. The adult *Culex* mosquito can size up to 0.16–0.4 inches [27]. It is a major house-dwelling mosquito in many tropical areas. *Culex* is an annoying mosquito to humans and main vector of filariasis in some countries. These mosquitoes mainly breed in polluted waters close to human residences. *Culex* mosquitoes are known to carry the nematode worm *Wuchereria bancrofti* which is responsible for causing lymphatic filariasis. More than 146 million people were affected all over the world [12, 28]. *Japanese encephalitis* virus (JEV) belongs to the family of *Flaviviridae* and is the primary pathogen of viral encephalitis. In earlier times, JEV was efficiently controlled primarily by vaccination [11, 29]. *Culex* spp.

#### *Metabolites from Actinobacteria for Mosquito Control DOI: http://dx.doi.org/10.5772/intechopen.106885*

are night-biting mosquitoes, with highest activities after 1 h of darkness. They are mainly exophilic and commonly stay indoors after feeding on blood. *Culex* bite causes sensitive responses like skin irritation, urticaria and angioedema [30].

With increasing human activities and climate change, several vector-borne diseases are emerging in the world. Humans are fighting to prevent mosquito-borne diseases for many centuries but still they are unable to find any definite way. To control mosquito-borne diseases we are following mainly two ways namely controlling mosquito population and protecting from bite. In eradication programmes, mosquitoes are killed at their immature and adult stage. Control of adult mosquitoes is mainly done in malaria control programmes, and larval control is done to eradicate filariasis, dengue and encephalitis [31–33]. In order to prevent mosquitoborne diseases, it is important to eradicate mosquito population for improving public health. Currently, eradication of mosquito programme is suffering because of the ever-increasing detrimental effects of synthetic chemicals on non-target organisms, development of pesticide resistance and environmental and public health concerns. The increased costs of insecticides and greater public concern over ecological pollution have required a continued search for alternative vector-control approaches, which would be naturally safer and specific in their action [12, 34–38]. Controlling of mosquito population at juvenile stages is done by direct application of insecticides in their breeding sites. Early insecticides such as DDT, BHC and methoxychlor were found to be effective in the beginning; after some years, due to the development of resistance by insect pests, their effectivity declined. Manmade chemicals such as chlorpyrifos, diflbenzuron, petroleum oils, pyriproxyfen, permethrin, malathion, methoprene, temephos and resmethrin are used to control mosquito population at the immature and adult stages [36, 39].

Applications of synthetic insecticides in the field have created a number of environmental problems, like resistance development in insect pests, environmental imbalance, and detrimental effects on animals. Repellents from synthetic chemicals have harmful impacts of toxic effects, undesirable effects like unpleasant odour and unpleasantly sticky skin; toxic reactions under some situations to different age groups, toxicity against the skin, nervous and immune systems usually occur when the product is used incorrectly or in the long term [40, 41]. Harmful effects of malathion are twitching of voluntary muscles, paralysis, ultimately death, incoordination, headaches, nausea, convulsions, blurred vision and pupil constriction, slowed heartbeat, respiratory depression, paralysis and coma [42]. Axonic poisons from pyrethroids cause toxicity to the nerve fibres which results in continuous nerve stimulation and suffering from headache, dizziness, nausea and diarrhoea. Different groups of pyrethroids like fenvalerate, sumithrin, d-trans allethrin and permethrin have some undesirable effects like disruption of hormonal pathways, reproductive dysfunction, developmental impairment and cancer [43].

Constant use of insecticides in the field and water bodies leads to serious hazards to the soil microorganisms and other beneficial organisms present in the environment. Highly sensitive reactions were observed when using malathion and carbendazim to *Hyphessobrycon erythrostigma*, *Colossoma macropomum*, *Nannostomus unifasciatus*, *Otocinclus affinis* and *Paracheirodon axelrodi*, one crustacean (*Macrobrachium ferreirai*), three insects (Hydrophilus sp., *Buenoa unguis*, and *Palustra laboulbeni*) and one freshwater snail (*Pomacea dilioides*) [44–46]. Thus, there is a continual need for developing biologically active molecules from natural resources which are toxic to insect pests but beneficial to environment. Insecticides derived from natural resources are generally preferred because of their less harmful nature to non-target organisms and innate biodegradability. Pesticides from natural sources are effective alternatives to such synthetic insecticides to control mosquito population [47–51]. In this chapter, the metabolites derived from actinobacteria

which are toxic to mosquitoes, beneficial to non-target organisms, and their role in eco-friendly mosquito control programmes at present and in the future are discussed.

## **2. Chemical insecticides in mosquito control**

Synthetic insecticides play an important role in controlling vector-borne diseases [52]. Methoprene is an important hormone that was first registered by EPA that acts as an insect growth-regulating hormone and inhibits the normal development of immature stages of insects. It mimics the insect growth hormone; it was successfully developed as a biorational insecticide based on understanding the physiology of insects [53–55]. Temephos is an organophosphate (OP) class of pesticides, and it was first registered by EPA in 1965. It was mainly used for controlling immature stages of mosquitoes and also other insect pests. Application of temephos is mainly on standing water, swamps, marshes, shallow ponds and intertidal zones to kill mosquito life stages [56]. Monomolecular films are prepared from renewable plant oils. Presently, two types of monomolecular surface film products Agnique® MMF and Agnique® MMF are available in the market for controlling the population of mosquitoes [57]. Using oils in vector control programme is the best way to control the population of insect pests. Oils are mainly derived from crude petroleum and several petroleum products. They act as contact poisons, with effective mosquitocidal efficiency [58]. Pyrethroid, resmethrin and chlorpyrifos have the ability to kill insects quickly mainly in mature stages, flying mosquitoes and other insect pests. Organophosphates and Malathion are mostly used for controlling both larvae and adults. DEET provides long-lasting protection against a wide range of insect pests, and it has been documented in several reports especially for preventing mosquito biting [59]. DEET is available in various commercial formulations such as lotions, gels, creams, aerosols, solutions, sticks, and impregnated towelettes [41]. Synthetic chemicals are preferred over natural because of their quick and strong efficacy to control vector population. However, chemicals derived from nature to control vectors are given preferences by government and non-government agencies to reduce the use of synthetic chemicals.

### **3. Ecofriendly management of mosquitoes**

Predatory organisms mostly act as the main agents that are hazardous to mosquitoes but favourable to human beings. Without insecticides, predators can control mosquito population to some extent. Dragonflies consume the larvae and bats, and birds eat adult mosquitoes. Electrified coils are used to control insect pest population. They do not release toxic chemicals into the environment, but they can kill beneficial insects also and may cause danger to children and pets (http://homeguides.sfgate.com/ecofriendly-mosquito-killer-lawn-81948.html). Larvivorous fishes have been widely used all over the world for controlling mosquito population. In 1905, larvivorous fish *Gambusia affinis* was purposely introduced from its native Texas to Hawaiian Islands, to Italy and Spain during1920s and later to 60 other countries [60]. *Poecilia reticulata*, a native of South America, was introduced to control malaria in British India and many other countries [61]. Sound traps which are used to control mosquitoes attract mosquitoes from long distances [62]. Using the lure and killing is the best method to control mosquitoes, especially in genus *Anopheles* and other arthropods [62, 63]. Balancing ecosystem is the most important thing in the living world. Every organism in the ecosystem is dependent on some other organism.
