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Preliminary evaluation of mosquito larvicidal efficacy of plant extracts.

Key words Aedes albopictus--Culex quinquefasciatus--laboratory evaluation--mosquito larvicide--plant extracts

Mosquitoes are the most important single group of insects in terms of public health importance, which transmit a number of diseases, such as malaria, filariasis, dengue, Japanese encephalitis, etc. causing millions of deaths every year. Repeated use of synthetic insecticides for mosquito control has disrupted natural biological control systems and led to resurgences in mosquito populations. It has also resulted in the development of resistance (1), undesirable effects on non-target organisms and fostered environmental and human health concern (2), which initiated a search for alternative control measures. Plants are considered as a rich source of bioactive chemicals (3) and they may be an alternative source of mosquito control agents.

Natural products of plant origin with insecticidal properties have been tried in the recent past for control of variety of insect pests and vectors. Essential oils of leaf and bark of Cryptomeria japonica demonstrated high larvicidal activity against Aedes aegypti (Diptera: Culicidae) larvae (4). Insecticidal activity of plant essential oils has been well-described by Isman (5). Azadiractin, the active ingredient of neem has long been recognised for its mosquito larvicidal capability. The extracts of Murraya koenigii, Coriandrum sativam, Ferula asafetida and Trigonella foenum graceum were found to be effective and showed encouraging results against Ae. aegypti (6) and Culex (Diptera: Culicidae) mosquito larvae (7). It is also reported that many compounds with insecticidal potential have been isolated from the genus Piper--Pipercide, isolated from Piper negrum (black piper) has been found to be just as active against adjuki bean weevils as the pyrethroides (8). Phytochemicals derived from plant sources can act as larvicide, insect growth regulators, repellent and ovipositor attractant and have different activities observed by many researchers (9-11). However, insecticides of plant origin have been extensively used on agricultural pests and to a very limited extent, against insect vectors of public health importance.

Northeastern region of India is considered as a major biodiversity hot spot. The eastern Himalayas range, which extends all through the northern border of Assam, is a rich treasure house of many promising medicinal and aromatic plants. In the present communication, an attempt has been made to evaluate the mosquito larvicidal efficacy of methanol and ethanol extracts of different parts of five indigenous plants against Ae. albopictus (Diptera: Culicidae) and Culex quinquefasciatus larvae in laboratory conditions.

Plant materials were collected from the foothill forests of Sonitpur district, Assam bordering Arunachal Pradesh during April and May 2005. They were segregated as leaf, stem, bark, root and fruit/pericarp and air-dried in a shady place. Dried materials were ground in a table model grinder. The ground plant materials were dipped in solvents (methanol and ethanol) in tightly capped jars separately for 48 h. The solvents along with extracts were drained out, filtered and semisolid extracts were obtained in vacuum using rotary evaporator. The semisolid extracts were lyophilised to obtain solid extracts. Stock solutions of desired concentration were prepared in distilled water using 1 ppm teepol as emulsifying agent and subsequent dilutions were made as per requirement. Larvicidal bioassay was carried out as per standard WHO techniques in 500 ml glass beakers containing 250 ml of water and 25 numbers of late III or early IV instar mosquito larvae for various concentrations. Three different concentrations of each extract were tried out at a time with six replicates. One control was kept with each set of experiment and mortality was recorded after 24 h. Five sets of experiments were conducted for each extract. Tests were carried out under controlled laboratory conditions (temperature 27 [+ or -] 2[degrees]C) against laboratory reared Ae. albopictus and Cx. quinquefasciatus (Diptera: Culicidae) larvae. Values obtained were subjected to log probit regression analysis to obtain [LC.sub.50] and [LC.sub.90] values with 95% confidence limit (12).

The results showed that the larvicidal activity of methanol and ethanol extracts of five aromatic plant species against Ae. albopictus and Cx. quinquefasciatus larvae varied according to plant species (Tables 1 & 2). Methanol extract of Aristolochia saccata roots was found to be the most effective against Ae. albopictus larvae followed by ethanol extracts of A. saccata, Annona squamosa leaf and methanol extract of A. squamosa leaf respectively. [LC.sub.90] values of methanol extract of fruit/pericarp of Gymnopetelum cochinchinensis, bark of Caesalpinea species and ethanol extract of stem of Piper species were obtained at <200 ppm but methanol extract of seeds of G cochinchinensis and stem of Piper species gave at <358 ppm against Ae. albopictus larvae (Table 1).

Ethanol extract of leaf of A. squamosa was found to have the most promising larvicidal activity against Cx. quinquefasciatus larvae. Methanol and ethanol extracts of A. saccata (root), methanol extract of A. squamosa (leaf) showed [LC.sub.90] values at <100 ppm while methanol extract of G. cochinchinensis (fruit/ pericarp), methanol and ethanol extract of Piper species showed at <200 ppm and methanol extract of G. cochinchinensis (seed) showed at >302 ppm against Cx. quinquefasciatus larvae (Table 2).

Long before the advent of synthetic insecticides, plants and their derivatives were used to kill pest of agriculture, veterinary and public health. Sosan et al (13) reported larvicidal activities of essential oils of Ocimum gratissium, Cymbopogon citrus and Ageratum conyzoides against Ae. aegypti and achieved 100% mortality at 120, 200 and 300 ppm concentrations respectively. Similarly, it was reported that the essential oil of Ipomoea cairica Linn. possesses remark able larvicidal properties as it could produce 100% mortality in the larvae of Cx. tritaeniorhynchus, Ae. aegypti, An. stephensi and Cx. quinquefasciatus mosquitoes at concentrations ranging from 100 to 170 ppm (14). Dwivedi & Kawasara (15) found acetone extract of Lantana camara to be most effective against Cx. quinquefasciatus larvae at the dose of 1 ml/100 ml. Latha et al (16) reported Piper longum and Zingiber wightianum extracts at 80 mg/l causing complete mortality in Cx. quinquefasciatus and 60 mg/l for Cx. sitiens. In the present investigation [LC.sub.90] values of methanol and ethanol extracts of roots of A. saccata, leaf of A. squamosa and fruits/pericarp of G. cochinchinensis against Ae. albopictus and Cx. quinquefasciatus larvae ranged between 31.80 and 155 ppm. Studies with essential oil of Ocimum americans and O. gratissium showed [LC.sub.50] at 67 and 60 ppm respectively against Ae. aegypti larvae (17). In contrast, in the present study methanol and ethanol extracts of roots of A. saccata, leaf of A. squamosa and fruits/ pericarp of G cochinchinensis against Ae. albopictus and Cx. quinquefasciatus larvae showed [LC.sub.50] values between 6.96 and 57.4 ppm. Larvicidal activities of the plant extracts vary according to the plant species, the parts of the plant, the geographical location where the plants were grown and the application method.

Plant could be an alternative source for mosquito larvicides because they constitute a potential source of bioactive chemicals and generally free from harmful effects. Use of these botanical derivatives in mosquito control instead of synthetic insecticides could reduce the cost and environmental pollution. Further studies on identification of active compounds, toxicity and field trials are needed to recommend the active fraction of these plant extracts for development of eco-friendly chemicals for control of insect vectors.

Acknowledgement

The authors are thankful to Dr. S.N. Dube, Director, Defence Research Laboratory, Tezpur, Assam, India for extending necessary facilities, continuous support and guidance in the study.

Received: 22 October 2006

Accepted in revised form: 27 December 2006

References

(1.) Brown AWA. Insecticide resistance in mosquitoes: pragmatic review. J Am Mosq Control Assoc 1986; 2: 12340.

(2.) Hayes JB Jr, Laws ER Jr. Handbook of pesticide toxicology, v. 1. San Diego, CA: Academic Press 1991.

(3.) Wink M. Production and application of pytochemicals from an agricultural perspective. In: Van Beek TA, Breteler H, editors. Phytochemistry and agriculture. Oxford, UK: Clerendon Press 1993; p. 171-213.

(4.) Cheng SS, Chang HT, Chang ST, Tsai KH, Chen WJ. Bioactivity of selected plant essential oils against the yellow fever mosquito Aedes aegypti larvae. Biores Technol 2003; 89(1): 99-102.

(5.) Isman MB. Pesticides based on plant essential oils. Pesticide Outlook 1999; p. 68-72.

(6.) Harve G, Kamath V. Larvicidal activity of plant extracts used alone and in combination with known synthetic larvicidal agents against Aedes aegypti. Indian J Exptl Biol 2004; 42: 1216-9.

(7.) Desai ST. Potency of larvicidal properties of plant extracts against mosquito larvae under laboratory conditions (M.Sc. Dissertation submitted to Mumbai University Mumbai, India 2002).

(8.) Mwangi RW, Mukiama TK. Evaluation of Melia volkensi extract fractions as mosquito larvicides. J Am Mosq Control Assoc 1988; 4: 442-7.

(9.) Babu R, Murugan K. Interactive effect of neem seed kerna and neem gum extract on the control of Culex quinquefasciatus Say. Neem Newsletter 1998; i5(2): 9-11.

(10.) Venketachalam MR, Jebasan A. Repellent activity of Ferronia elephantum Corr. (Rutaceae) leaf extract against Aedes aegypti. Biores Technol 2001; 76(3): 287-8.

(11.) Venketachalam MR, Jebasan A. Larvicidal activity of Hydrocotyl javanica Thunb (Apiaceae) extract against Cx. quinquefasciatus. J Exptl Zool India 2001; 4(1): 99-101.

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(13.) Sosan MB, Adewoyin FB, Adewunmi CO. Larvicidal properties of three indigenous plant oils on the mosquito Aedes aegypti. Nigerian J Natl Prod Med 2001; 5: 30-3.

(14.) Thomas TG, Rao S, Lal S. Mosquito larvicidal properties of an indigenous plant, Ipomoea cairica Linn. Japanese J Infect Dis 2004; 57: 176-7.

(15.) Dwivedi SC, Karwasara K. Larvicidal activity of five plants extracts against Culex quinquefasciatus. Indian J Entomol 2003; 65(3): 335-8.

(16.) Latha C, Vijhayakumar PD, Velayudhan S, Joseph A. Biological activity of indigenous plant extracts as mosquito larvicides. Indian J Exptl Biol 1999; 37: 206-8.

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N.G. Das, D. Goswami & B. Rabha

Medical Entomology Division, Defence Research Laboratory, Tezpur, Assam, India

Corresponding author: Dr. N.G. Das, Medical Entomology Division, Defence Research Laboratory, Post Bag No. 2, Tezpur-784 001, India.

E-mail: ngdas_drdo@rediffmail.com; director_drl@yahoo.com
Table 1. Larvicidal efficacy of plant extracts against Ae.
albopictus larvae

Name of plant Part used Solvent used [LC.sub.50]

Aristolochia saccata Root Methanol 14.52
-do- Root Ethanol 17.30
Annona squamosa Leaf Methanol 20.26
-do- Leaf Ethanol 20.70
Gymnopetelum Fruit/Pericarp Methanol 50.67
 cochinchinensis
-do- Seed Methanol 100.42
Caesalpinea species Bark Methanol 53.66
Piper species Stem Methanol 144.22
-do- Stem Ethanol 76.35

Name of plant [LC.sub.90] Regression equation

Aristolochia saccata 42.68 Y = 2.5683 * X +2.0164
-do- 58.51 Y = 2.3633 * X +2.0721
Annona squamosa 86.59 Y = 1.9392 * X +2.4637
-do- 76.73 Y = 2.1991 * X +2.1020
Gymnopetelum 155.12 Y = 2.5821 * X +0.5927
 cochinchinensis
-do- 312.45 Y = 2.3014 * X +0.3481
Caesalpinea species 169.41 Y = 2.3429 * X +0.8638
Piper species 357.32 Y = 3.1826 * X -1.9688
-do- 180.42 Y = 3.2525 * X -1.1333

Table 2. Larvicidal efficacy of plant extracts against Cx.
quinquefasciatus larvae

Name of plant Part used Solvent used [LC.sub.50]

Aristolochia saccata Root Methanol 31.91
-do- Root Ethanol 19.83
Annona squamosa Leaf Methanol 17.70
-do- Leaf Ethanol 6.96
Gymnopetelum Fruit/pericarp Methanol 57.4
 cochinchinensis
-do- Seed Methanol 199.0
Caesalpinea species Bark Methanol 42.27
Piper species Stem Methanol 70.10
-do- Stem Ethanol 57.4

Name of plant [LC.sub.90] Regression equation

Aristolochia saccata 81.06 Y = 3.3086 * X -0.0062
-do- 60.44 Y = 2.5791 * X -1.6605
Annona squamosa 64.29 Y = 2.1180 * X +2.3457
-do- 31.80 Y = 1.9441 * X +3.3592
Gymnopetelum 108.3 Y = 4.1627 * X +2.3501
 cochinchinensis
-do- 301.6 Y = 1.7586 * X +11.0557
Caesalpinea species 207.13 Y = 1.7586 * X +2.0573
Piper species 113.90 Y = 5.669 * X +5.4992
-do- 108.3 Y = 4.1627 * X +2.3501
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Title Annotation:Short Research Communications
Author:Das, N.G.; Goswami, D.; Rabha, B.
Publication:Journal of Vector Borne Diseases
Date:Jun 1, 2007
Words:2012
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