Electroantennographic responses of the Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) (Diptera: Psychodidae) to 1-octen-3-ol

Respostas eletroantenográficas de Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) (Diptera: Psychodidae) a 1-octen-3-ol

Abstracts

Octenol (1-octen-3-ol) is a kairomone used by haematophagous insects to locate their vertebrate hosts. However, effect of 1-octen-3-ol on Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) has never been studied. The present work evaluated the electrophysiological (EAG) responses of female L. (Lutzomyia) longipalpis. Air current, air pulse and solvent (hexane) pulse were used as control stimuli. The logarithmic concentrations of 1-octen-3-ol 10 a 10(6) etag/50µl of solvent were tested. Significant olfactory responses were observed in the concentration of 1-octen-3-ol from 10³ etag/50ul with the greatest response at concentration of 10(6) etag/50ul (-3,33mV). Dose-dependency was observed, as the concentration increased, so did the electrophysiological response. These results demonstrated, for the first time, that L. longipalpis, can detect the presence of 1-octen-3-ol in air current. The possible use of 1-octen-3-ol as kairomone for this species is discussed.

Insecta; chemoreception; olfaction; semiochemicals; visceral leishmaniasis

Octenol (1-octen-3-ol) é um cairomônio utilizado por vários grupos de insetos hematófagos para a localização de hospedeiros vertebrados. No entanto, o seu efeito sobre Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) nunca foi estudado. O presente trabalho avaliou as respostas eletroantenográficas (EAG) de fêmeas de L. longipalpis. Como estímulo controle utilizou-se corrente de ar, pulsos de ar e pulsos de solvente (hexano). As concentrações logarítmicas de 1-octen-3-ol testadas foram de 10 a 10(6) etag/50mil de solvente. Observaram-se respostas olfativas significativas de 1-octen-3-ol a partir de 10³etag/50mil, tendo a maior amplitude na concentração 10(6)etag/50mil (-3,33mV). Foi observada dose-dependência, ou seja, quanto maior a concentração, maior foi a resposta eletrofisiológica. Estes resultados demonstram, pela primeira vez que L. longipalpis pode detectar a presença do 1-octen-3-ol em corrente de ar. O possível uso de 1-octen-3-ol como cairomônio é discutido para a espécie.

Insecta; quimiorecepção; olfação; semioquímicos; leishmaniose visceral

ECOLOGY, BEHAVIOR AND BIONOMICS

Electroantennographic Responses of the Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) (Diptera: Psychodidae) to 1-octen-3-ol

ADSON L. SANT'ANA¹, ALVARO E. EIRAS¹ E REGINALDO R. CAVALCANTE ^1,2

¹ Depto. Parasitologia, Universidade Federal de Minas Gerais, ICB/UFMG,

Av. Presidente Antônio Carlos, 6627, Pampulha, 31270-901, Belo Horizonte, MG

²Depto. Parasitologia e Microbiologia, Universidade Federal do Piauí, CCS/UFPI

Campus Ininga, Teresina, PI

Neotropical Entomology 31(1): 013-017 (2002)

Respostas Eletroantenográficas de Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) (Diptera: Psychodidae) a 1-octen-3-ol

RESUMO ¾ Octenol (1-octen-3-ol) é um cairomônio utilizado por vários grupos de insetos hematófagos para a localização de hospedeiros vertebrados. No entanto, o seu efeito sobre Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) nunca foi estudado. O presente trabalho avaliou as respostas eletroantenográficas (EAG) de fêmeas de L. longipalpis. Como estímulo controle utilizou-se corrente de ar, pulsos de ar e pulsos de solvente (hexano). As concentrações logarítmicas de 1-octen-3-ol testadas foram de 10 a 10⁶hg/50ml de solvente. Observaram-se respostas olfativas significativas de 1-octen-3-ol a partir de 10³hg/50ml, tendo a maior amplitude na concentração 10⁶hg/50ml (-3,33mV). Foi observada dose-dependência, ou seja, quanto maior a concentração, maior foi a resposta eletrofisiológica. Estes resultados demonstram, pela primeira vez que L. longipalpis pode detectar a presença do 1-octen-3-ol em corrente de ar. O possível uso de 1-octen-3-ol como cairomônio é discutido para a espécie.

PALAVRAS-CHAVE: Insecta, quimiorecepção, olfação, semioquímicos, leishmaniose visceral.

ABSTRACT ¾ Octenol (1-octen-3-ol) is a kairomone used by haematophagous insects to locate their vertebrate hosts. However, effect of 1-octen-3-ol on Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) has never been studied. The present work evaluated the electrophysiological (EAG) responses of female L. (Lutzomyia) longipalpis. Air current, air pulse and solvent (hexane) pulse were used as control stimuli. The logarithmic concentrations of 1-octen-3-ol 10 a 10⁶hg/50µl of solvent were tested. Significant olfactory responses were observed in the concentration of 1-octen-3-ol from 10³hg/50ul with the greatest response at concentration of 10⁶hg/50ul (-3,33mV). Dose-dependency was observed, as the concentration increased, so did the electrophysiological response. These results demonstrated, for the first time, that L. longipalpis, can detect the presence of 1-octen-3-ol in air current. The possible use of 1-octen-3-ol as kairomone for this species is discussed.

KEY WORDS: Insecta, chemoreception, olfaction, semiochemicals, visceral leishmaniasis.

Kairomones are odors that benefit the receptor organism (ex: haematophagous insect) and are disadvantageous to the emitter (ex: host), in interspecific interactions (Nordland 1984). Kairomones (host-odor) are used by haematophagous insects in the process of searching and locating the host for blood feeding, following a sequence of behavior (Eiras 2001). The 1-octen-3-ol kairomone (octenol) is atractive for the tse-tse fly Glossina (Glossina) morsitans (Westwood) (Diptera: Glossinidae) and was identified from volatile compounds emanated from bovines (Hall et al. 1984). The attraction of the tse-tse fly and other haematophagous insects by 1-octen-3-ol baited traps was also reported for mosquitoes (Takken & Kline 1989, Kline et al. 1990, Becker et al. 1995), black fly (Atwood & Meisch 1993), screwworm (Cork 1994), tabanides (Hayes et al. 1993), and culicoides (Kline et al. 1994).

The sand fly Lutzomyia (Lutzomyia) longipalpis (Lutz & Neiva) (Diptera: Psychodidae) is a phlebotomine of great importance because it is the main vector of Leishmania chagasi (Cunha & Chagas), the etiological agent of the visceral leishmaniases in the New World. Only females possess the haematophagic behavior. It is a species of wide geographic distribution, comprising the North and South Americas, from Mexico to North-Eastern Argentina and Paraguay. The primary hosts and the main reservoirs of the parasite are foxes in the wild environment, and dogs in the peri-domestic habitat. L. longipalpis also feeds on pigs, cats, horses, birds, humans and opossums, and the feeding preference varies according to its environment (Dougherty et al. 1999).

The biology of L. longipalpis in its natural habitat is practically unknown due to its behavior and to the sites of development of the larval phase (Forattini 1973). Adults monitoring is performed by means of light traps, generally the CDC type (Sudia & Chamberlain 1962) or traps baited with birds or small mammals (Disney 1966). Several studies on development of attractants, such as sexual pheromones (Ward et al. 1990) or oviposition attractants (El-Naien & Ward 1991), have been carried out in the search for improving the efficiency and specificity of the traps used for monitoring. Up to the present, the use of 1-octen-3-ol as a possible attractant for L. longipalpis has not been published.

The electroantennographic (EAG) technique that consists in measuring electrical activities of the insect antennae in response to olfactory stimulus has already been used for decades to evaluate the sensitivity of the chemical receptors to semiochemicals. Up to the present, the effect of 1-octen-3-ol on the chemoreceptors of L. longipalpis is unknown. The objective of this research work was to evaluate the electrophysiological responses of L. longipalpis females' antennae to 1-octen-3-ol, aiming its use as possible kairomone in traps.

Materials and Methods

L. longipalpis Rearing. The insects were reared in laboratory and maintained in insectary at 25±1^oC, RH 80% and 12h photoperiod. The colony used was in the 26^th generation and was initiated in July 1996 with specimens obtained from an open rearing from Teresina County, State of Piaui, North of Brazil. The rearing technique used was based on the methodologies described by Young et al. (1981) and Modi & Tesh (1983).

Preparation of the Antennae for the Assays. The antennae used in the tests were obtained from two- to seven-day old females, fed on a honey solution. The insects were individually anesthetized at ¾20^oC for 2 min. The antennae were amputated at the base and at the tip using a micro-scalpel under stereomicroscope. The antennae were individually tested and each antennae tip was placed in the extremity of a microcapillary tube (10 ml) with the aid of a micro-handler. Each microcapillary tube contained a microelectrode and a KCL solution (0.1 N) in its interior (Van der Pers & Minks 1993). Three antennae were analyzed with five replications totaling 15 replications for each treatment, totalizing 135 observations.

Olfactory Stimuli. 1-octen-3-ol (Lancaster Synthesis, 98% purity) was diluted in hexane (Carlo Erba, HPLC degree of purity) to obtain logarithmic concentrations from 10 hg to 10⁶hg. Fifty micro-liters of the solution to be tested were than transferred to a 2 cm² filter paper, and after solvent evaporation, the filter paper was placed into a 15 cm Pasteur pipette.

Electroantennogram Response (EAG). Microelectrodes were connected to an amplifier and to a potentiometer (IDAC Box Model ID-01B, Synthec, the Netherlands), which records the potential of action in the antennae nerves (Van der Peers & Minks 1993). An air current was produced, purified and calibrated to a continuous flow of 5 ml/min., with 0.3 seconds of stimulus duration (Stimulus Controller C5-05, Synthec, the Netherlands). Data were stored in the EAG for Windows V2.6 program and than transferred to statistical programs (Systat 8.0) for linear regression analysis. Data received logarithmic transformation followed by ANOVA and Tukey test for means.

Results and Discussion

The EAG technique has been used for moths (Lepidoptera) (Van der Pers & Minks 1993), mosquitoes (Diptera: Culicidae) (Knols et al. 1997, Du & Millar 1999), Culicoides impuctatus (Goethwebuer) (Diptera: Ceratopogonidae) (Blackweel et al. 1996), aphids (Homoptera) (Park & Hardie 1998), and L. longipalpis (Dougherty et al. 1999). Electrophysiological techniques have been extensively used to identify host-odors (kairomones) for several haematophagous insects (Hall et al. 1984) and the screwworm (Cork 1994). However, little is known about the sensorial physiology of some groups of dipterans such as anopheline and mainly phlebotomine.

Some examples of electrophysiological graphs obtained during this study are shown in Fig. 1. The highest potential of action recorded was -3.33 mV in the concentration of 10⁶hg, and the lowest was 0.097 mV in the concentration of 10 hg.

The antennae response to the controls remained stable (mean variation of 0.16 ¾ 0.19 mV) with no significant differences among them (P=1.000). All concentrations were significantly different from the controls. No significant differences were observed among the concentrations of 10 hg to 10⁵ hg. However, significantly higher responses were observed only at 10⁶hg when compared with the lower concentrations of 10 hg and 10²hg (Fig. 2). The responses in the EAG for 1-octen-3-ol, which were able to significantly stimulate the chemoreceptors (or chemical receptors) present in the L. longipalpis antennae, occurred in a dose-dependent manner.

The regression analysis of the effect of 1-octen-3-ol concentrations (10² hg to 10⁶ hg) on the electrophysiological response (mV) indicated that the concentrations follow a linear pattern, in which the electrophysiological response is directly correlated to concentration (R² = 0.98; P<0.001) (Fig. 3).

The carbon dioxide is incontestably considered the most important kairomone among the haematophagous insects. Nevertheless its use is limited due to its high cost and the need of constant maintenance (Eiras 2001). The kairomone 1-octen-3-ol has shown evidences of attraction in traps for species of Glossinidae and zoophilic species of Muscidae, Tabanidae, Ceratopogonidae and Culicidae as well as some indications of effect in some species of Simulidae (Cheke & Garms 1987). Takken & Kline (1989) and Kline et al. (1994) reported that Culicoides furens (Poey) is attracted by carbon dioxide and by 1-octen-3-ol, and that the combination of both promoted a synergistic effect in traps. These studies used a relatively high rate of 1-octen-3-ol release (2-3mg/h). Gibson & Torr (1999) pointed out that there is no evidence of response in phlebotomine for 1-octen-3-ol. However, in the present work it was demonstrated that the L. longipalpis antennae possess chemoreceptors for this compound.

Dougherty et al. (1995) were the pioneers in carrying out research on electrophysiology and in detecting the ascoide sensilla in the L. longipalpis antennae, which are sensitive to sexual and oviposition pheromones. Dougherty et al. (1999) evaluated the behavioral and electrophysiological responses of L. longipalpis to different kairomones extracted from a primary host, the fox Vulpes vulpes. They found neural receptors in the ascoide sensilla of this insect antennae, which responded in a dose-dependent manner to synthetic extracts of odor glands of this canine. Sixty constituents such as ketones, alcohols, aldehydes, and carboxylic acids were also identified as olfactive stimulants.

Concerning visual response, Mellor et al. (1996) have demonstrated that the sensitive spectrum of L. longipalpis is similar to that of the tse-tse fly G. morsitans and the mosquito Aedes aegypti (Linnaeus). Temperature and relative humidity play an important role in locating the host (Nigam & Ward 1991) as well as do volatiles from the host (Hamilton & Ramsoondar 1994), carbon dioxide, hamster urine, and chicken uropygial gland (Nigam & Ward 1991). Killick-Kendrick et al. (1986) demonstrated that Phlebotomus ariasi (Tonnoir) (Diptera: Psychodidae) was attracted to human odors. Blackwell et al. (1996) observed electrophysiological and behavioral responses to 1-octen-3-ol in ceratopogonideans, and were able to increase the capture of these insects in the field by using this compound in relatively low dose (0.11 mg/day) as baits.

Olfactive and electrophysiological responses of a species of great parasitological importance such as L. longipalpis, as other phlebotomines, are scarcely investigated by researchers all over the world. In the present work it was demonstrated that chemical receptors for 1-octen-3-ol do exist and confer a special character of this semiochemical to this insect. These results demonstrate that L. longipalpis apparently detects the presence of 1-octen-3-ol in air currents. Further behavioral and field studies are needed in order to determine the orientation of L. longipalpis in response to 1-octen-3-ol aiming its possible use for detection and/or monitoring these vector insects.

Acknowledgements

The authors wish to thank CNPq, CAPES and IFS (Sweden) for the financial support.

Literature Cited

Received 10/04/2001. Accepted 10/12/2001.

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Publication Dates

• Publication in this collection
  15 Sept 2002
• Date of issue
  Mar 2002

History

• Accepted
  10 Dec 2001
• Received
  10 Apr 2001