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Effects of Water Color and Chemical Compoundson the Oviposition Behavior of Gravid Culex pipienspallens Females under Laboratory ConditionsAuthor(s): Jing Li, Tianfu Deng, Hongjie Li, Li Chen, and JianchuMoSource: Journal of Agricultural and Urban Entomology,26(1):23-30. 2009.Published By: South Carolina Entomological SocietyDOI: http://dx.doi.org/10.3954/1523-5475-26.1.23URL: http://www.bioone.org/doi/full/10.3954/1523-5475-26.1.23

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Effects of Water Color and Chemical Compounds on theOviposition Behavior of Gravid Culex pipiens pallens

Females under Laboratory Conditions1

Jing Li,2 Tianfu Deng,3 Hongjie Li,2 Li Chen,2 and Jianchu Mo2

J. Agric. Urban Entomol. 26(1): 23–30 (January 2009)

ABSTRACT Oviposition behavior is a plastic trait that can be affected by avariety of physical factors and chemical cues. The effects of water color andthree chemical compounds on the oviposition behavior of Culex pipiens pallens(Diptera: Culicidae) females were studied under laboratory conditions.Solutions of methylene blue (50 mg/L) and brilliant blue (50 mg/L and200 mg/L) attracted significantly more gravid C. pipiens pallens females thandid the distilled water control. Among the three chemical compounds tested,only 0.1 mg/L acetic acid solution showed significantly greater ovipositionattraction activity than the control solutions of distilled water or acetone(25 mg/L) in water. A mixture of 25 mg/L methylene blue plus 0.05 mg/L aceticacid attracted significantly more gravid females to lay eggs than did distilledwater, methylene blue solutions alone, or acetic acid solutions alone. A solutionof 25 mg/L methylene blue and 0.05 mg/L acetic acid might have potential foruse in traps for monitoring population densities of C. pipiens pallens.

KEY WORDS Culex pipiens pallens, gravid female, oviposition, dye,compound

The selection of an oviposition site is an important component of thebehavioral repertoire of mosquitoes (Diptera: Culicidae), and the correct choiceis crucial for the survival of progeny. The attractiveness of these sites toovipositing mosquitoes is dependent upon a number of physical, chemical, andbiological cues presented under natural conditions (Millar et al. 1994, Dhileepan1997, Olagbemiro et al. 1999, Geetha et al. 2003).

Water color has an important influence on the oviposition activity ofmosquitoes. Studies have shown that dyed water is more attractive to ovipositingmosquitoes than un-dyed water under both laboratory and field conditions(Williams 1962, Beehler & DeFoliart 1990, Beehler et al. 1993, Isoe et al. 1995).Black water was the most preferred oviposition site for the gravid Culexquinquefasciatus Say (Diptera: Culicidae) females (Frank 1985). Dhileepan(1997) demonstrated that black and red water were the most preferred

1Accepted for publication 27 January 2010.2 Urban Entomology Research Center, and Ministry of Agriculture Key Laboratory of Molecular Biology

of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, Zhejiang

310029, China.3 Department of Plant Protection, Henan Institute of Science and Technology, Xinxiang, Henan 453003,

China.

23

oviposition sites for gravid C. annulirostris Skuse and C. molestus Ficalbifemales, respectively.

Natural chemical cues also influence mosquito oviposition behavior (Geetha etal. 2003), and 3-methylindole was shown to be the most attractive chemical togravid Culex females under both laboratory and field conditions (Millar et al.1992, Mordue (Luntz) et al. 1992, Blackwell et al. 1993, Beehler et al. 1994). Inaddition, the influence of some fatty acids on the oviposition behaviors of C.quinquefasciatus and C. tarsalis Coquillett has also been evaluated underlaboratory condition (Hwang et al. 1980, 1982, 1984). However, chemical cues andwater color do not act independently in natural situations, as they typicallyinteract with other factors at the oviposition site for mosquito species (Dhileepan1997, Mboera et al. 1999, Olagbemiro et al. 2004).

Culex pipiens pallens Coquillett is an important disease vector widelydistributed in northern and central China. This species transmits lymphaticfilariasis, Japanese B encephalitis, and other viral diseases (Li et al. 2002, Tao etal. 2006). Since 2005, the Chinese government has monitored populationdensities of C. pipiens pallens by counting the average number of egg rafts inthe water containers of ovitraps (Service 1993). Thus, the ‘‘Mosq-ovitrap’’ (Lin etal. 2005) has become an important tool for monitoring mosquito densities inChina. However, because of lack of information on the oviposition site preferenceof female C. pipiens pallens, the monitoring of population dynamics of thismosquito has been unsatisfactory. The objective of this study was to study theeffects of water color and certain chemical compounds on the oviposition behaviorof gravid C. pipiens pallens females.

Methods and Materials

Mosquito rearing. Culex pipiens pallens was maintained in a rearing roomat 26uC, 65% RH, and L:D 14:10 h photoperiod. Larvae were reared in plasticbasins filled with dechlorinated tap water. Commercial rat food formulated withwheat flour, wheat bran, corn powder, soybean powder, fish meat powder, yeast,salt, and vitamins was provided as nutrient for mosquito larvae. Pupae werecollected and allowed to emerge in a gauze cage (35 3 35 3 35 cm). A diet of 5%sucrose solution was provided for the adults. Females were allowed to feed on theblood of a live mouse at the fifth day after emergence. Twenty-four hours afterblood feeding, the gravid females were used for experiments.

Chemical compounds. Methylene blue, acetic acid, and ethyl acetate werepurchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).Carmine, brilliant blue, fruit green, and tartrazine dye were purchased fromShanghai Dye Research Institute Co., Ltd. (Shanghai, China). Dimethyl disulfidewere purchased from Sigma-Aldrich Co., Ltd. (Shanghai, China).

Experiments. All laboratory experiments were carried out in a 190 cm 3

150 cm 3 140 cm mosquito net in the laboratory (26 6 1uC, 65 6 5% RH, and L:D14:10 photoperiod). Seventy-five gravid females were used for each experiment.The number of egg rafts laid by females in each beaker was recorded four daysafter the start of each experiment.

Experiment 1 was designed to assess the attractiveness of different coloredwater to gravid female mosquitoes. The dyes tested in this experiment weremethylene blue, carmine, brilliant blue, fruit green, and tartrazine. The

24 J. Agric. Urban Entomol. Vol. 26, No. 1 (2009)

concentrations of dyes in distilled water were 200, 50, 12.5, and 3.1 mg/L. Foreach of the three replicates, 21 beakers (100 ml) with 50 ml distilled water or dyesolution were placed equidistantly in a random pattern around the edge of themosquito net.

Experiment 2 was designed to assess the attractiveness of acetic acid, ethylacetate, and dimethyl disulfide to gravid female mosquitoes. The concentrationsof these compounds in distilled water were 100, 10, 1, 0.1, and 0.01 mg/L. Duringformulation, acetic acid was dissolved directly in distilled water, whereas ethylacetate and dimethyl disulfide were first dissolved in pure acetone and thendiluted with distilled water to the experimental concentrations. The finalconcentration of acetone in the formulated solutions was 25 mg/L, and awater:actone solution of this concentration was used as an additional control forthis experiment. For each of the eight replicates, 17 beakers (100 ml) with 50 mldistilled water (Control 1), 25 mg/L acetone solution (Control 2), or one of thecompound solutions were placed equidistantly in a random pattern around theedge of the mosquito net.

Experiment 3 was designed to assess the combined attractiveness of bluewater color and the acetic acid to gravid female mosquitoes. Methylene blue wasused as the colorant in distilled water at concentrations of 25 mg/L, 50 mg/L, and75 mg/L. Acetic acid in distilled water was used at concentrations of 0.05 mg/L,0.10 mg/L, and 0.50 mg/L. For each of the five replicates, 16 beakers with 50 ml ofa treatment solution were placed equidistantly in a random pattern around theedge of the mosquito net.

Statistical analyses. For all experiments, the number of egg rafts in eachbeaker was recorded and used for analysis. The data were analyzed with ANOVAand LSD by the DPSE software (Tang & Feng 2002) to detect any significantdifferences between treatments.

Results

Effect of water color on the oviposition behavior of gravidfemales. The water-color experiment showed that 50 mg/L of methylene bluesolution and 50 mg/L and 200 mg/L of brilliant blue solution were significantlypreferred by the gravid females of C. pipiens pallens compared with distilledwater (ANOVA: F 5 3.462, df 5 20, 42; P 5 0.0003) (Table 1). In this experiment,10.00 6 2.52 egg rafts were laid in 50 mg/L methylene blue solution, 8.67 6 2.33egg rafts in 200 mg/L brilliant blue solution, and 6.33 6 4.10 egg rafts in 50 mg/Lbrilliant blue solution (Table 1). No significant differences were observedbetween the other dye solutions and distilled water (P . 0.05, Table 1).

Effect of chemical compounds on the oviposition behavior ofgravid females. Among the three compounds tested, only 0.1 mg/L of aceticacid solution significantly attracted more gravid C. pipiens pallens females tooviposit than did the controls of distilled water or 25 mg/L acetone solution (F 5

3.715; df 5 16, 119; P 5 0.0001). There were no significant differences among theother compounds and control solutions (P . 0.05, Table 2).

Combined effect of color and compound on the oviposition behaviorof gravid females. Results indicated that combinations of methylene blue withacetic acid had a significant effect on the oviposition behavior of C. pipienspallens females (F 5 4.595; df 5 15, 64; P 5 0.0001). The mixture of 25 mg/L

LI et al.: Oviposition cues for Culex 25

methylene blue and 0.05 mg/L acetic acid induced the most C. pipiens pallensfemales to lay eggs. Significantly more egg rafts were laid by females in thissolution than in distilled water, in methylene blue-water alone, or in acetic acidsolution alone (Table 3). However, there were no significant differences inoviposition between this mixture and six of the eight other mixtures of methyleneblue and acetic acid, and only two mixtures of these materials (75 mg/Lmethylene blue + 0.10 mg/L acetic acid and 50 mg/L methylene blue + 0.50 mg/Lacetic acid) attracted significantly fewer egg rafts. Also for this experiment, therewere no significant differences between distilled water, methylene blue solutionalone, or acetic acid solution alone (P . 0.05) (Table 3).

Discussion

Water color is an important factors influencing oviposition behavior of femalemosquitoes. Our study showed that Culex pipiens pallens females laidsignificantly more eggs in dark blue water (50 mg/L of methylene blue solution,or 50 mg/L and 200 mg/L of brilliant blue solution) than in distilled water. Thisbehavior has also been shown for C. tarsalis, C. quinquefasciatus, C.annulirostris, and C. molestus (Beehler & DeFoliart 1990, Yap et al. 1995,

Table 1. Number of egg rafts laid by C. pipiens pallens females in watercolored by different dyes.

DyeDye concentration indistilled water (mg/L)

Number of egg rafts(Mean 6 SE)a

Methylene blue 200 1.33 6 0.88 de50 10.00 6 2.52 a12.5 1.33 6 0.67 de3.1 1.67 6 0.33 cde

Brilliant blue 200 8.67 6 2.33 ab50 6.33 6 4.10 abc12.5 0.67 6 0.33 de3.1 2.00 6 1.15 cde

Carmine 200 5.33 6 2.19 bcd50 3.33 6 0.33 cde12.5 3.00 6 1.00 cde3.1 2.67 6 1.20 cde

Fruit green 200 3.33 6 0.88 cde50 2.00 6 1.15 cde12.5 1.33 6 0.33 de3.1 1.00 6 0.58 de

Tartrazine 200 0.67 6 0.33 de50 1.00 6 0.58 de12.5 1.33 6 0.88 de3.1 0.00 6 0.00 e

Distilled water 0 1.33 6 0.88 de

aMeans in the same column followed by different letters are significantly different (P , 0.05, ANOVA).

26 J. Agric. Urban Entomol. Vol. 26, No. 1 (2009)

Dhileepan 1997). Beehler et al. (1993) suggested that dark colors attract moregravid C. quinquefasciatus because females respond to the increased opticaldensity of the dyed water rather than to the volatile components of the dye.

Hwang et al. (1980, 1982, 1984) reported that small chain aliphatic acids (e.g.,acetic, propionic, isobutyric, butyric acids), homologues of C5 to C13 and C16 to C22

fatty acids, elicited negative oviposition activity when tested for C. quinquefas-ciatus, C. tarsalis, and Aedes aegypti (L.). However, a recent study showed thatlarger chain fatty acids of C12 to C18 isolated from the egg cuticle of A. aegyptiexhibited oviposition activity at one of three concentrations (1, 10 and 100 mg/L)tested (Ganesan et al. 2006). In our study, acetic acid exhibited significantlystronger attractiveness to the gravid C. pipiens pallens females at 0.1 mg/Lconcentration compared with distilled water.

There have been few studies on the effects of esters of fatty acids on theoviposition behavior of mosquitoes (Perry & Fay 1967, Ganesan et al. 2006).However, the current study showed that 10 mg/L and 0.1 mg/L of ethyl acetatewater solution had significantly higher attractive activity to gravid C. pipienspallens females compared with distilled water. Torres-Estrada et al. (2007)suggested that ethyl acetate in the extract of Spirogyra majuscula Kutzing algae(Zygnemataceae) might also be involved in attraction of gravid Anophelespseudopunctipennis Theobald (Diptera: Culicidae) females to oviposition sites.

Table 2. Number of egg rafts laid by C. pipiens pallens females in watersolutions with three chemical compounds.

ChemicalCompound

Compound concentrationin distilled water (mg/L)

Number of egg rafts(Mean 6 SE)a

Acetic acid 100 0.25 6 0.16 c10 1.25 6 0.37 bc1 1.37 6 0.46 bc0.1 7.12 6 1.94 a0.01 1.87 6 0.69 bc

Ethyl acetate 100 3.00 6 0.82 b10 1.12 6 0.23 bc1 1.75 6 0.65 bc0.1 2.62 6 1.25 bc0.01 1.50 6 0.38 bc

Dimethyl disulfide 100 2.25 6 0.73 bc10 3.62 6 0.75 bc1 3.37 6 0.86 b0.1 2.00 6 0.98 bc0.01 1.00 6 0.27 bc

Control 1b 0 1.25 6 0.31 bcControl 2c 0 1.75 6 0.73 bc

aMeans in the same column followed by different letters are significantly different (P , 0.05, ANOVA).bDistilled water.cDistilled water plus 25 mg/L acetone.

LI et al.: Oviposition cues for Culex 27

However, in our study, ethyl acetate water solution was not attractive to gravidC. pipiens pallens females.

Hog waste lagoons and other animal waste sites are common places in whichCulex mosquitoes are produced (O’Meara & Evans 1983). Dimethyl disulfide wasdemonstrated to be a component in hog lagoon odors (Zahn et al. 2001). Trexler etal. (2003) reported that dimethyl disulfide did not elicit the oviposition responseof Aedes albopictus (Skuse) (Diptera: Culicidae) in laboratory bioassay and infield trial. Similarly, in our study, C. pipiens pallens females also did not show asignificant preference to dimethyl disulfide solution compared with the controlsolutions.

Interactions between chemical attractants and physical cues have beendocumented as affecting the ovipositional behavior of some mosquito species(Beehler et al. 1993, Mboera et al. 1999, Olagbemiro et al. 2004). Beehler et al.(1993) reported that gravid C. quinquefasciatus females used both visual andchemical cues in the selection of an oviposition site, and water dyed with inkacted synergistically with a five-component chemical attractant mixture (3-methylindole, indole, 4-methylphenol, 4-ethylphenol, and phenol) under labora-tory conditions. In our study, most of the mixtures of methylene blue and aceticacid induced a significant ovipositional response by C. pipiens pallens females.The solution of 25 mg/L methylene blue and 0.05 mg/L acetic acid was especiallyattractive and induced the most females to lay eggs. This solution could be ofpotential use in traps for monitoring population densities of C. pipiens pallens inthe field.

Table 3. Number of egg rafts laid by C. pipiens pallens females in mixedwater solutions of methylene blue and acetic acid.

SolutionNumber of egg rafts

(Mean 6 SE)a

75 mg/L methylene blue 0.40 6 0.24 c50 mg/L methylene blue 2.00 6 0.63 c25 mg/L methylene blue 1.20 6 0.37 c0.50 mg/L acetic acid 0.40 6 0.24 c0.10 mg/L acetic acid 3.00 6 1.41 bc0.05 mg/L acetic acid 1.40 6 0.60 c75 mg/L methylene blue + 0.50 mg/L acetic acid 4.60 6 1.08 abc75 mg/L methylene blue + 0.10 mg/L acetic acid 1.40 6 0.93 c75 mg/L methylene blue + 0.05 mg/L acetic acid 3.40 6 0.98 abc50 mg/L methylene blue + 0.50 mg/L acetic acid 2.40 6 1.17 bc50 mg/L methylene blue + 0.10 mg/L acetic acid 5.20 6 2.54 abc50 mg/L methylene blue + 0.05 mg/L acetic acid 6.20 6 1.50 abc25 mg/L methylene blue + 0.50 mg/L acetic acid 3.60 6 0.93 abc25 mg/L methylene blue + 0.10 mg/L acetic acid 9.40 6 3.53 ab25 mg/L methylene blue + 0.05 mg/L acetic acid 10.20 6 1.32 aDistilled water 0.80 6 0.59 c

aMeans in the same column followed by different letters are significantly different (P , 0.05, ANOVA).

28 J. Agric. Urban Entomol. Vol. 26, No. 1 (2009)

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