Effect of stalk and leaf extracts from Euphorbiaceae species on Aedes aegypti (Diptera, Culicidae) larvae

Efeito dos extratos de caule e folha de espécies de Euphorbiaceae sobre larvas de Aedes aegypti (Diptera, Culicidae)

LARVICIDAL ACTIVTY

Effect of stalk and leaf extracts from Euphorbiaceae species on Aedes aegypti (Diptera, Culicidae) larvae

Efeito dos extratos de caule e folha de espécies de Euphorbiaceae sobre larvas de Aedes aegypti (Diptera, Culicidae)

Maria Goretti Araújo de Lima^I; Ismália Cassandra Costa Maia^I; Bruna Dantas de Sousa^I; Selene Maia de Morais^II; Sílvia Maria Freitas^III

^ICurso de Ciências Biológicas da Universidade Estadual do Ceará, Fortaleza, CE, Brasil

^IILaboratório de Produtos Naturais da Universidade Estadual do Ceará, Fortaleza, CE, Brasil

^IIIDepartamento de Estatística e Matemática Aplicada da Universidade Federal do Ceará, Fortaleza, CE, Brasil

^{Correspondence to}

SUMMARY

The objective of this study was to evaluate the larvicidal activity of essential oil aqueous solutions (hydrolates) obtained by steam distillation of stalks and leaves of Croton argyrophylloides, Croton nepetaefolius, Croton sonderianus and Croton zehntneri against Aedes aegypti larvae. Twenty-five larvae of third instar were placed in plastic beckers, containing the hydrolates (50 mL), in a four repetitions scheme. Water was used as control and the number of dead larvae was counted after 24 hours. The data obtained were submitted to Variance Analysis and Tukey test. Significant differences were observed among the hydrolates from different species and from different parts of each plant (p < 0.001). The hydrolates of stalk and leaf from C. nepetaefolius and C. zehntneri and leaf hydrolate of C. argyrophylloides presented 100% mortality against larvae. The compounds present in C. zenhtneri and C. nepetaefolius are oxygenated phenylpropanoids that are more soluble in water than the monoterpenes and sesquiterpenes detected in the oils of C. argyrophylloides and C. sonderianus. This study showed that all species analyzed presented compounds with larvicidal properties, with differences between each plant parts.

Keywords:Aedes aegypti, Hydrolates, Larvicidal activity, Euphorbiaceae, Croton.

RESUMO

O objetivo deste trabalho foi avaliar a atividade larvicida dos hidrolatos obtidos por destilação à vapor de caule e folha das espécies de Croton argyrophylloides, Croton nepetaefolius, Croton sonderianus e Croton zehntneri contra Aedes aegypti. Em cada bioensaio foram utilizadas 25 larvas de 3º estádio juntamente com 50 mL de cada hidrolato, dispostos em recipientes plásticos, num esquema de quatro repetições, utilizando-se como controle a água e avaliando-se a mortalidade com 24 horas de tratamento. Os dados foram submetidos à análise de variância e ao teste de Tukey. Verificou-se que houve diferença significativa tanto em relação aos hidrolatos das diferentes espécies vegetais, quanto em relação às diferentes partes de cada planta (p < 0,001). Os hidrolatos referentes ao caule e folha de C. nepetaefolius e C. zehntneri causaram 100% de mortalidade das larvas e diferiram das demais espécies, exceto da folha do C. argyrophylloides que apresentou o mesmo resultado. Os compostos presentes em C. zehntneri e C. nepetaefolius são fenil propanóides mais solúveis em água que os monoterpenos e sesquiterpenos detectados em C. argyrophylloides e C. sonderianus. Esta pesquisa evidenciou que todas as espécies testadas possuem compostos com propriedades larvicidas, com diferenças entre as partes da planta analisadas.

INTRODUCTION

Dengue fever is a viral infection transmitted by mosquitoes of genus Aedes and is considered one of the most important problems to the world public health. This disease presents high incidence in tropical and subtropical countries and it is estimated that approximately 1,3 billion people are at risk to be infected by the dengue fever virus¹⁹. A. aegypti is the principal insect responsible for dengue fever transmission in the tropical countries. In America, this insect promotes frequent epidemics and there was a spreading of the four serotypes of the virus in the continent⁵.

Several cases of resistance have been reported in the world for vector mosquito species, and particularly for the population of A. aegypti in Brazil. There are reports of occurrence of resistance to organophosphorates at least in eight cities of São Paulo State with detection of resistance against temephos^2,10.

The great diversity of plants in Brazil is represented by 550,000 species¹⁴ and studies with plant extracts show the expectation of finding substances with insecticide properties and simultaneously selective to be used in future formulas of commercial products. The hydrolates are aqueous solutions obtained as by-products of the essential oil steam distillation process, using a Clevenger type apparatus⁶. They contain as main constituents the most hydrophylic compounds present in the essential oils.

Various studies showed the activity of plant extracts against different species of mosquitoes^8,11,12 including A. aegypti^9,15,17. The present study aimed to determine and evaluate the larvicidal effect of hydrolates obtained from stalk and leaves of Croton argyrophylloides, Croton nepetaefolius, Croton sonderianus and Croton zehntneri against third instar larvae of A. aegypti.

MATERIAL AND METHODS

Plant species: The selected plants of this research were native species from Ceará State, situated in northeast of Brazil and were collected in Viçosa city. Voucher specimens were deposited in Prisco Bezerra Herbarium of Federal University of Ceará under the following numbers: for C. argyrophylloides Muell. Arg. (Marmeleiro prateado) - 32444, for C. nepetaefolius Baill (Marmeleiro sabiá) - 32448; C. sonderianus Muell. Arg. (Marmeleiro preto) - 32445 and for C. zehntneri Pax & Hoffm (Canela de cunhã) - 32446. The hydrolates were obtained from stalk and leaves of the plants.

Extraction of hydrolates: The part plants were submitted to steam distillation in a Clevenger-type apparatus⁶. The steam passes through a condenser and is collected into a separator. A biphasic mixture is formed by the essential oil in the superior phase and the aqueous phase, which is separated through decantation. The water that remains after the process of oil extraction is called hydrosol or hydrolate; it contains many bioactive compounds and the plant therapeutic properties⁷.

Essential oil analysis: The oils were analysed using a Hewlett-Packard 5971 GC/MS instrument employing the following conditions: column: Dimethylpolysiloxane DB-1 coated fused silica capillary column (30 mm x 0.25 mm); carrier gas: He (1 mL/min); injector temperature: 250 ºC; detector temperature: 200 ºC; column temperature: 35 ºC - 180 ºC at 4 ºC/min then 180 ºC-250 ºC at 10 ºC/min; mass spectra: electron impact 70 eV. The identification of the constituents was performed by computer library search, retention indices and visual interpretation of the mass spectra^1,7.

Bioassays: Larvae of A. aegypti were obtained from a five years old colony, maintained under controlled conditions, 27 - 30 ºC of temperature, 75 - 80% of relative humidity and the light-dark cycle at 12 hours of light followed by 12 hours of darkness. This colony belonged to the Laboratory of Entomology of the Endemic Diseases Unit from Health Secretary in Ceará State (NUEND/SESA). Third instar larvae were collected by direct pipeting from a previous flask and carefully washed. Then they were removed from water by filtration and 25 larvae were transferred to the test flask that contained the hydrolates (50 mL).

The control was distilled water, with an experimental design made totally at random, following a factorial scheme of 4 x 2 (hydrolates x plant parts), with four repetitions, comprising 100 larvae for each treatment.

The evaluation of mortality rate was performed 24 hours after the beginning of the experiment, verifying the number of dead larvae. The larvae were considered dead when they did not present movement and did not respond to stimulus with a Pasteur pipette. The environmental temperature and humidity were observed during the experiment, with variation between 27 ºC - 30 ºC.

Statistical analysis: The data were submitted to angular transformation¹³ to follow the conditions of normality of the distribution of responses and homogeneity of the variance among the treatments to enable the performance of Variance Analysis. Dunnet test to multiple comparisons was used between the plant parts.

RESULTS

The concentration of the leaf essential oil in each hydrolate differ: C. nepetaefolius - 8.3%, C. zehntneri - 7.8%, C. argyrophyloides - 4% and C. sonderianus - 4.6%. The stalk and leaves hydrolates of C. nepetaefolius and C. zehntneri induced 100% mortality to larvae. The hydrolates of C. argyrophyloides and C. sonderianus presented variations on larvicidal potential for different tested plant parts. The hydrolate of C. argyrophyloides stalk induced 54% mortality while the leaf hydrolate promoted 100% mortality. The hydrolate of C. sonderianus stalk induced 8% mortality while leaf hydrolate and promoted 52% of mortality rate to larvae (Fig. 1). Almost all treatments tested differed significantly (p < 0.001) to control, with exception for the hydrolate of C. sonderianus stalk, which promoted low mortality, and did not differ to group control, which presented no mortality to A. aegypti larvae (p > 0.05). C. sonderianus and C. argyrophylloides hydrolates showed statistic differences activities for stalk and leaf, suggesting that different active properties are distributed in these plant parts or the same active property is present in different concentrations. However, the stalk and leaf hydrolates of C. zehntneri and C. nepetaefolius did not present results with statistically significance, indicating the possibility that the active principle is distributed equally in the tested parts.

DISCUSSION

According to VIEIRA et al. (2001)¹⁸, terpenoids, especially lemonoids (tetranortriterpenes), are the major examples of insecticide substances, however simple monoterpenes also perform protection against insects in the plants, demonstrating good insecticide activity in experimental models. Various other compounds as diterpenes, nortriterpenes and sesquiterpenes are reported as phagoinhibitors and growth inhibitors (blocking the development of ecdyses) to many types of insects. Reports about the larvicidal action against A. aegypti of C. nepetaefolius, C. zehntneri, C. argyrophyloides and C. sonderianus, species used in this study, were not found in the literature. CARVALHO et al. (2003)³ demonstrated the larvicidal activity of pure and diluted hydrolate of Lippia sidoides Cham. and the principal component of leaf essential oil, thymol, against A. aegypti. The hydrolate induced mortality almost instantaneous to the larvae while thymol induced 100% mortality with 0.017% (w/v) of concentration at 1.5 hour of experiment. A study conducted with essential oil components revealed that the more active compounds against A. aegypti are phenylpropanoids and sesquiterpene alcohols¹⁶. The larvicidal activity of essential oils from Northeastern Brazilian plants showed good results for Ocimum americanum with LC₅₀ 67 ppm and Ocimum gratissimum LC₅₀ 60 ppm. The main components in these oils were E-methyl-cinnamate and eugenol both phenylpropanoid derivatives⁴.

The composition of the leaf essential oils of these Croton species is displayed in Table 1. The main constituents of C. zenhtneri oil was anethole and estragole and C. nepetaefolius presented as major components methyleugenol that are oxygenated compounds and explains the higher percentage of these oils in the respective hydrolates when compared to other two Croton species. C. argyrophylloides showed as main constituents the monoterpenes a-pinene and b-pinene, that are considered good larvicidal agents¹⁶. C. sonderianus presented the hydrocarbons a-pinene, b-phelandrene (monoterpenes) and trans-caryophyllene (sesquiterpenes) as main constituents. The hydrocarbons are lesser soluble in water than oxygenated compounds therefore the lower solubility of active ingredients also account to the differences in the activity of the hydrolates.

In conclusion, despite the compounds detected in the essential oils of these plant species, the hydrolates consist of a water solution that contains the most hydrophyllic compounds, which can be responsible for the mortality of A. aegypti larvae. The compounds present in C. zenhtneri and C. nepetaefolius are oxygenated phenylpropanoids that are more soluble in water than the monoterpenes and sesquiterpenes detected in the oils of C. argyrophylloides and C. sonderianus. The hydrolates in Brazilian essential oil producers are obtained in larger amounts in relation to the respective essential oils, therefore they represent an important and viable alternative, since they are produced in superior quantities through the same method of production.

ACKNOWLEDGEMENTS

The authors thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the scholarships and to Núcleo de Endemias da Secretaria de Saúde do Estado do Ceará for their collaboration in grain processing.

Received: 12 April 2005

Accepted: 9 May 2006

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Publication Dates

• Publication in this collection
  13 Sept 2006
• Date of issue
  Aug 2006

History

• Accepted
  09 May 2006
• Received
  12 Apr 2005