Mosquitoes - The Main Important Group of Biting Dipterans

The main important group of biting Dipterans are the mosquitoes. Mosquitoes have long slender body, needle shaped mouth parts and legs. The wings sometimes have discernible patterns of scales. Some species of mosquitoes bite in the evening or morning and at night and some mosquitoes bite during the day time. (Rozendaal, 1997). Many tropical diseases such as filariasis, malaria, dengue, dengu haemorrhagic fever, Japanese encephalitis and yellow fever etc are transmitted by several species of mosquitoes. About 100 species among 3000 species of mosquitoes act as a vectors of human diseases (Rozendaal, 1997; Rahuman et al., 2008; Arivoli and Tennyson, 2012). Lymphatic filariasis is transmitted by different species of mosquitoes, namely, Culex, Anopheles, and Aedes mosquito species. Infection commonly occurs in childhood and cause hidden damage the lymphatic system. Lymph oedema elephantiasis and swelling of scrotum occur later in life and permanent disability of the patient is found. Patients suffer social, mental and financial losses contributing to stigma and poverty including physically. Worldwide 947 million people in 54 countries suffer by lymphatic filariasis and require chemotherapy to prevent this neglected disease.

In 2000 over 120 million people were infected, with about 40 million become disfigured and incapacitated by this dreadful disease. Globally, persons affected by lymphatic filariasis were 25 million men with hydrocele and over 15 million people with lymphoedema. Chronic disease manifestations are found in about 36 million people. Lymphatic filariasis is caused by nematodes (Family Filariodidea). There are 3 types of filarial worms: Wuchereria bancrofti (causing, 90% of the filariasis), Brugia malayi (causing most of the remainder of the cases), and Brugia timori (which also causes the diseases). The Immune system of an infected person becomes destroyed by adult worms. Adult worms produce millions of microfilaria which circulate in the blood stream of man. When mosquitoes ingest blood then microfilaria enter into mosquito’s body. Microfilaria transform into infective larvae within the mosquito. When infected mosquitoes bite people, mature microfilaria enters the lymphatic vessels of human body and develop into adult worms and thus a cycle of transmission become continuing (WHO, 2017). In 2000, WHO launched Global Programme to Eliminate Lymphatic Filariasis (GPELF).

In 2012, WHO reconfirmed the target date for achieving elimination of neglected disease, filariasis by 2020. WHO recommended mass drug administration (MDA) to stop the spread of infection for elimination of lymphatic filariasis (LF). MDA consist of a combined dose of 2 medicines given annually as a preventic chemotherapy measures and these medicines are 400 mg albendazole and ivermectin (150–200 mcg/kg) or with diethylcarbamazine citrate (DEC) (6 mg/kg). These medicines have a little effect on adult Wuchereria bancrofti but very much effective on microfilaria. From 2000-2015, 6.2 billion treatments were provided to more than 820 million people to prevent the spread of the disease in many places. Cambodia, Niue, Sri Lanka, Vanuatu, Maldives, and Cook Islands, have achieved the goal of elimination of filariasis. The WHO’s recommendation strategy of elimination of lymphatic filariasis have successfully implemented by thirteen additional countries. In 54 countries, chemotherapy is still now needed for eradication of the disease. (WHO, 2017).

In India, Wuchereria bancrofti and Brugia malayi are two causative agents of lymphatic filariasis. But 95% filariasis is caused by Wuchereria bancrofti and 5% by Brugia malayi parasite. Brugia malayi is prevalent in the states of Tamil Nadu, Andra Pradesh, Kerala, Odisha, West Bengal, Madhya Pradesh, and Assam. India alone accounts for 40% of the world disease burden (Michael et al., 1996). Seventeen states and six Union Territories in India were identified to be endemic with about 553 million people exposed to the risk of infection, and among them, about 146 million live in urban and the rest of the people live in rural areas. In India, about 31 million people are estimated to be the carriers of microfilaria and over 23 million people suffer from filarial disease manifestations (WHO, 2005). Highest endemicity has found in Bihar (over 17%) followed by Kerala (15.7%) and Uttar Pradesh (14.6%).10% endemicity has found in the states of Andhra Pradesh and Tamil Nadu. Lowest endemicity has found in Goa (less than 1%) followed by Lakshadweep (1.8%), Madhya Pradesh (above 3%) and Assam (about 5%). B. malayi is prevalent in the states of Kerala, Tamil Nadu, Andhra Pradesh, Orissa, Madhya Pradesh, Assam and West Bengal (Regu et al., 2005; National Vector Borne Disease Control Programme, 2010) Mosquito control is essential for the eradication of mosquito borne diseases, improving the environmental quality and public health. The major tool and technique for the controlling mosquitoes is the application of synthetic insecticides.

In the past, the control measures for mosquito vectors were based on the frequent and indiscriminate use of synthetic chemical-based insecticides viz., carbamates, organochlorines, organophosphates, and pyrethroids (Liu et al., 2006). Indiscriminate use of insecticides has resulted in the increased selection pressure on the mosquitoes leading to the development of insecticide resistance varieties among mosquitoes (Raghvendra, 2002; Kumar et al., 2012). Insecticide resistance variety in Culex quinquefasciatus against cyhalothrin, fenthion, and cypermethrin, temephos has been developed. The insecticide residues enter into the ecosystem through food chain. The ill-effects of insecticide usage have thus necessitated the need for research and development on environmentally safe, bio-degradable and indigenous methods for controlling mosquito species (Tikar et al., 2008). Thus, in recent years, use of many of the former synthetic insecticides for controlling of mosquito programme has been limited due to high cost of pesticides, concern of environment sustainability, lack of novel pesticides, adverse effect on human health and other animals, increase rate of biological magnification, their non biodegradable in nature, and insecticide resistance variety development (Brown, 1986; Russell, 2009).

As a result, Environmental Protection Act in 1969 has constructed a number of rules and regulations to check the application of chemical control agents in nature (Bhatt and Khanal, 2009). Since early times even before the discovery of synthetic insecticides, many herbal products have been used as natural insecticides. Botanicals such as Pyrethrum, Chrysanthemum, Derris, Quassia, Nicotine, Turpentine, Hellebore, Azadirachtin, etc. have been used as botanical insecticides in the pre-DDT era (Shaalan et al., 2005). One of the approaches for controlling of mosquito-borne diseases is the interruption of disease transmission by killing, using repellents or using larvicide for larval mortality in a large scale at the breeding centres of vectors. Currently, mosquito control strategies have failed because of the development of increasing insecticide resistance varieties (Brown, 1986; Georghion and Lagunestjida, 1991; WHO, 1992; Kelm et al., 1997; Su and Mulla, 1998; Gericke et al., 2002; Haegreaves et al., 2003). Various organophosphates (Temiphos and Fenthion) and insect growth regulators (Diflubenzuron and Methoprene) are widely used as larvicides for controling of mosquitoes (Rozendaal, 1997). These synthetic pesticides have caused the development of resistant variety of mosquitoes, imbalance of ecosystem and harm to mammals including humans (Georghiou and Langunes-tejeda et al., 1991).

The best alternative way for preventing these problems could be the use of botanical insecticides, which are degradable in nature and their source is renewable. Plants have co-evolved with insects with production of secondary metabolites for their chemical defence mechanisms. More than 2000 plant species have been identified which produce secondary metabolites with value of biological pest control programmes and among them 344 species has been unfolded with significant activity against mosquitoes (Remia and Logaswamy, 2009). Larvicidal, pupicidal, adulticidal, oviposition detterent activity, smoke toxicity or repellent activities from the plant species belonging different families viz., Asteraceae, Labiatae,Cladophoraceae, Miliaceae, Rutaceae Solanaceae, Oocystaceae, Caricaceae etc. have been identified (Shaalan et al., 2005; Rawani et al., 2012; Rajkumar et al., 2005; Singha et al., 2011). Even before the discovery of synthetic organic insecticides, more than 50 years ago, some herbal products viz., anabasine and lupinine , the alkaloids from Russian weed, Anabasis aphylla; nicotine from leaves of Nicotiana tabacum; rotenone from Derris eliptica and pyrethrums from Chrysanthemum cinererifolium flowers have been used as herbal insecticides for vector control because of low cost, biodegradable in nature, safe for environment etc (Campbell et al., 1993; Zubairi et al., 2004; Hartzell and Willcoxon, 1941)Hartzell and Willcoxon (1941) worked with 150 plant species to observe the toxicities against mosquito and several of them exhibited the efficacy.

Sarita et al. 2012 collected 15 plant species from local areas in New Delhi, India and obtained extracts of different solvents from different plants parts. Each extract was screened to explore its efficacy as a mosquito larvicidal agent against early fourth instars of dengue vector, Aedes aegypti. 10 plants showed larvicidal potential and further evaluation of the larvicidal efficacy of extracts established that the hexane leaf extract of Lantana camara to be most effective extract having a significant LC50 value of 30.71 ppm while the Phyllanthus emblica fruit extract was found to be least efficacy having an LC50 value of 298.93 ppm. Ranaweera, 1996 screened of some Srilankan plants to observe mosquito larvicidal activity and out of 53 tested plant species, 18 plants showed larvicidal activity against Culex quinquefasciatus mosquito species. Mondal et al., 2016 experimented on 32 plants species and out of them 8 plants showed larvicidal activity by crude extracts against Culex quinquefasciatus mosquito species. Amer and Mehlhorn (2006) showed repellency of forty one essential oil preparations against Aedes, Anopheles and Culex mosquitoes.

Jantal et al. (2003) evaluated 17 methanol extracts and 9 essential oil preparations of Malaysian plants for their larvicidal activities against Aedes aegypti.Roark, 1947 described about1200 plants species which possessed insecticidal potential. Sukumar et al., 1991 listed and discussed 344 plant species that only showed mosquitocidal activity. Ghosh et al., 2012 reviewed a large number of plants which have mosquitocidal efficacy. Insecticidal activity of plant extracts vary according to plant species, mosquito species, geographical varieties, plant part, methodology of extraction taken, and polarity of the solvents used during extraction. A wide range of plants from shrubs, herbs and large trees was used for extraction to obtain toxic phytochemicals to kill mosquitoes. Phytochemicals are extracted either from whole plant like small herbs or from different parts viz., leaves, fruites, barks, stems, roots etc of larger plants or trees. In all cases, the most toxic substances are used for mosquito control (Shaalan et al., 2005). The secondary metabolites, present in plants act as defence system against pest/ insect attacks. The presence of plant’s secondary metabolites viz., steroids, alkaloids, terpenoids, phenolics, flavanoids, etc act as moulting hormones, juvenile hormone mimics, antifeedants, oviposition deterrents, repellents, growth inhibitors, antimoulting hormones, attractants etc and these properties of secondary metabolites responsible for biological activity of plant extracts against target pest (Champagne et al., 1986).

The Annonaceae family consists of tree, shrubs or rarely lianus. The family comprises 108 genera (accepted) and near about 2400 known species. The plants of Annonaceae family mainly grow in the Tropics; nearabout 900 species grow in Neotropical; 450 species in Afrotropical; few species in temperate regions and the other species in Indomalayan. Annona reticulata Linn. belongs to the family Annonaceae. It is also known as Custard Apple, Sugar Apple, Sweet Apple, Ramphalam, Sitaphala, Sarifa etc. Its native land is South America and West Indies. It is widely distributed in India, Bangladesh, Pakistan and Thailand (Kaleem, 2006; Satyanarayana, 2013). It is a small deciduous and semi evergreen tree with 8 metres to 10 metres tall, spreading or rounded crown and trunk measures about 25-35 cm in diameter. The leaves are hairless, straight and pointed at the apex and wrinkled in some varieties, Leaves are narrow-lanceolate, alternating, and deciduous in nature, conspicuous veins and the leaves measures about10-20 cm long and 2-5cm wide. The flowers are yellow green in colour, fragrant in drooping clusters, slender, with 3 outer narrow, fleshy petals 2-3cm long which are never fully opened. The fruits vary in structure, like, spherical, heart-shaped, irregular or oblong and measuring about 8-16 cm in diameter. Ripe fruit is brown or yellowish, with red highlights and a varying degree of reticulation, depending upon the variety and skin is thin. The flesh is thick, somewhat granular and cream white in colour. There is a pointed central fibrous core which one is attached to the thick stem, extending from the midway through the fruit which is a speciality of fruit (Mahdeem, 1998; Duke, 1993).

In Ayurveda A. reticulata is used for the treatment of cancer, dysentery, epilepsy, cardiac problem, worm infestation, constipation, haemorrhage and also has antifertility, antitumour and aborfacient properties. (Kaleem, 2006). Ripe fruits are good tonic and sedative. It increases the blood, increases muscular strength, reduces burning sensation, lessens, tendency to biliousness and vomiting (Morton, 1987). A. reticulata leaves are used in the treatment of colic. Decoction of the leaves is used to cure malaria and syphilis (Duke, 1993). The root bark is use in toothache and roots of the plant are used in the form of a prepared decoction for fever (www.worldagroforestrycentre.org). Some people of Philippines use the warmed leaves for application over the abdomen for getting relief from indigestion of small childrens (http://www.stuartxchange.org). The plant is used as an anti-inflammatory agent in anti-stress, wound healing, anti-anxiety, spasmolytic and anti-mutagenic agent. Leaf and stem extract demonstrates positive chronotropic, inotropic, and spasmolytic activities (Anonymous, 1994). A decoction of leaves is used as a vermifuge and decoction of bark is used as tonic, treatment of diarrhoea and dysentery. Fragments of root bark are used to relieve toothache and roots decoction is used as febrifuge (Orwa et al., 2009). Ethanol extract of its roots has an inhibitory effect against Hela, A- 549, K-562, and MDA- MB human cancer cell lines (Suresh et al., 2011). Methanol extract of A. reticulata bark and its water fraction showed strong antioxidant activity and both the fraction showed significant hepatoprotection and anti-inflammatory response in both in vitro and in vivo studies (Kandimalla, 2016). Stem-bark extract of A. reticulata showed significant analgesic activity and significant anti-inflammatory activity against carrageenan and histamine induced paw edema (Reddy et al., 2011).

Chang et al., 1998 isolated new cytotoxic gamma-lactone acetogenin, cis-/trans-isomurisolenin, along with six known cytotoxic acetogenins, annoreticuin, annoreticuin-9-one, bullatacin, squamocin, cis-/trans-bullatacinone and cis-/trans-murisolinone from ethyl acetate extract of seeds of Annona reticulata and their structures were established by means of mass and related spectral experiments and some of which showed effective cytotoxicities against Hep. 2,2,15, CCM2, Hep. G2, KB and four cancer cell-lines. Study on Annona reticulata leaves resulted in the identification of nine compounds, a new triterpenoid, annonaretin which have significance effect on NO inhibition in most of LPS-activated mouse peritoneal macrophages (Thang et al., 2013). Bhalke and Chavan, 2011 investigated that analgesic and CNS depressant activity potency increases from ethyl acetate, methanol and petroleum ether extracts of Annona reticulata bark. The methanol leaf extract of A. reticulata L. possess antimicrobial (antifungal and antibacterial) activity and has also remarkable antioxidant activity. The present study was an attempt to unfold the mosquitocidal activity of phytochemicals of Annona reticulata L. plant against Culex quinquefasciatus mosquito species.