Flight Capacity of Adult Culex pipiens pallens (Diptera: Culicidae) in Relation to Gender and Day-Age Author(s): Jianxin Cui, Shujuan Li, Ping Zhao, and Fumin Zou Source: Journal of Medical Entomology, 50(5):1055-1058. Published By: Entomological Society of America URL: http://www.bioone.org/doi/full/10.1603/ME12078
BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research.
VECTOR CONTROL, PEST MANAGEMENT, RESISTANCE, REPELLENTS
Flight Capacity of Adult Culex pipiens pallens (Diptera: Culicidae) in Relation to Gender and Day-Age JIANXIN CUI,1,2 SHUJUAN LI,3 PING ZHAO,4
AND
FUMIN ZOU1
J. Med. Entomol. 50(5): 1055Ð1058 (2013); DOI: http://dx.doi.org/10.1603/ME12078
ABSTRACT Culex pipiens pallens (L.) is the most common mosquito in houses of central and northern China. It is the primary vector of lymphatic Þlariasis and Japanese encephalitis. The ßight range of mosquitoes is an important factor predicting the risk area of transmission of mosquito-borne pathogens to vertebrate hosts. The ßight performance of Cx. pipiens pallens was measured with a 26-channel computer-monitored ßight-mill system. We found that females had longer ßight capability than males for total ßight distance (TFD) and total ßight duration (TFDr), and females ßew faster than males based on mean ßight velocity. No signiÞcant difference in ßight capability was found between different age-groups in males. However, certain age-groups of females showed signiÞcant differences in TFDr and TFD. SpeciÞcally, TFD and TFDr tended to be shortest for 5- and 6-d-old females. These signiÞcant differences in ßight capability between ages and genders provide insights to determine the size of operational area to achieve effective control of Cx. pipiens pallens and minimize the risk of the related mosquito-borne epidemic diseases of lymphatic Þlariasis and Japanese encephalitis. KEY WORDS ßight capacity, Culex pipiens pallens, day-age, mosquito, dispersal
Culex pipiens pallens (L.) is the most common mosquito in houses of central and northern China. It is the primary vector of lymphatic Þlariasis and Japanese encephalitis (Li et al. 2002). The adult females are primarily avian feeders but also consume blood from humans and other mammals (Tanaka et al. 1979). The blood-sucking activities of female Cx. pipiens pallens often occur 3Ð5 d after adult emergence (Liu et al. 1994, Ma et al. 1998). The earliest oviposition of gravid mosquitoes occurs at the third day after blood-sucking, whereas the peak time for oviposition comes 1 d later. The ßight range of mosquitoes is an important factor in predicting the risk area of transmission of mosquito-borne pathogens to vertebrate hosts. Different sizes of operational area are recommended for vector control based on the dispersal ability of vector mosquitoes (World Health Organization [WHO] 1986). The ßight ability of Culex mosquitoes has been extensively studied. Tsuda et al. (2008) used a markÐ releaseÐrecapture method and found that female adults of Cx. pipiens pallens could disperse 470, 287, 326, and 517 m on days 1, 2, 3, and 4, respectively, after release. They estimated that the maximum ßight distance of this species was 1,217 m based on the rela1 Department of Plant Protection, Henan Institute of Science and Technology, Xinxiang, Henan 453003, China. 2 Corresponding author, e-mail: [email protected]. 3 Maricopa Agricultural Center, University of Arizona, 37860 West Smith-Enke Rd., Maricopa, AZ 85138-3010. 4 Division of Life Science, College of the Environmental and Life Science, Kaili University, Kaili, Guizhou 556011, China.
tionship between distance from the release site to the collection site and the total number of recaptures per trap. The estimated mean and 99th percentile of dispersal distance for Culex erraticus was 970 and 3,210 m, respectively, per gonotrophic cycle (Estep et al. 2010). Morris et al. (1991) found that the mean dispersal distance for this same species was 730 m, and the maximum dispersal range was 1,400 Ð2,200 m. The study reported herein was conducted to evaluate ßight capacity of Cx. pipiens pallens by using ßight mills. It provides insights to determine the size of operational area to achieve effective control of Cx. pipiens pallens and minimize the risk of related mosquito-borne epidemic diseases. Materials and Methods Mosquitoes. Cx. pipiens pallens colony used in this study had been reared on artiÞcial diet in the laboratory for 3 yr at the Henan Institute of Science and Technology (N 35.18⬚, E 113.52⬚). Larvae were reared on a mixture of wheat bran and maize ßour. Adult mosquitoes within 12 h after emergence were placed in a cage with a volume ⬇0.1 m3. Each cage contained ⬇200 mosquitoes of mixed gender. The diet for adult mosquitoes was 5% sucrose solution (wt:vol). Adult male and female insects of 1Ð10 d of age and females of 15, 20, and 25 d of age were assayed. Ten to 23 mosquitoes were assayed for each combination of age and gender (1 d, 么 n ⫽ 10, 乆 n ⫽ 10; 2 d, 么 n ⫽ 10, 乆 n ⫽ 15; 3 d, 么 n ⫽ 13, 乆 n ⫽ 11; 4 d, 么 n ⫽ 10, 乆 n ⫽ 13; 5 d, 么 n ⫽ 10, 乆 n ⫽ 17; 6 d, 么 n ⫽ 10, 乆 n ⫽
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Fig. 1. Mean (black bar) ⫹ SD (gray bar) of ßight parameters for respective combinations of Culex pipiens pallens gender and age; (A and D) total ßight distance; (B and E) total ßight duration; and (C and F) ßight velocity. Different letters indicate signiÞcant difference between means within a plot by using the TukeyÐKramer test.
23; 7 d, 么 n ⫽ 15, 乆 n ⫽ 15; 8 d, 么 n ⫽ 11, 乆 n ⫽ 10; 9 d, 么 n ⫽ 10, 乆 n ⫽ 10; 10 d, 么 n ⫽ 11, 乆 n ⫽ 10; 15 d, 乆 n ⫽ 13; 20 d, 乆 n ⫽ 10; and 25 d, 乆 n ⫽ 15). Because males have a shorter adult life span than females, males were not assayed at ages ⬎10 d. Flight Mill Assays. The ßight performance of Cx. pipiens pallens was measured with a 26-channel computer-monitored ßight-mill system (Beerwinkle et al. 1995, Cheng et al. 2002). The arm of a ßight mill was a 10-cm-long (0.02-cm-diameter) metal wire, thus the distance of one complete revolution was 0.63 m. Insects were anesthetized brießy with ether, and a small tether was attached to their pronotum with cyanoacrylate Super Glue (502 Glue, Dongguan, Guangdong, China) at one end of the ßight mill arm. The opposing end of the arm was dipped in melted parafÞn until the mill was balanced. The ßight mill was positioned in a room with temperature ranging from 18 to 22⬚C and relative humidity from 40 to 50%. The photoperiod was following natural changes in late summer (14:10 [L:D]). A light intensity of 150 lux during daytime was maintained. Flight assays of 22 h in duration were conducted beginning at 1400 h and ending at 1200 h the next day. No water or nutriment was provided to the adult insects during the ßight periods. Statistical Analyses. Flight mill data were processed by using Matlab software. For each tethered insect, total ßight distance (TFD), total ßight duration (TFDr), and mean ßight velocity (MFV) were calculated. During an assay, ßight was considered halted if no data were captured for ⬎60 s. Periods during which ßight was halted were excluded from calculations of TFDr, and individuals with TFD ⬍20 m during the 22-h assay were also excluded. Unbalanced multiway analysis of variance including data on 15-, 20-, and 25-d-old females was performed to analyze the effect of age, gender, and age by gender interactions on ßight performance of Cx. pipiens pallens, with TukeyÐ Kramer test to separate the means.
Results In total, 172 females and 110 males of Cx. pipiens pallens were examined and analyzed for ßight performance in this study. The ßight capacity of these mosquitoes, as indicated by estimates of TFD, TFDr, and MFV, is shown in Fig. 1. Total Flight Distance. The mean TFD for males during the 22-h ßight period was 869.0 ⫾ 188.4 m, ⬇977.4 m shorter than that of females. The mean TFD for females was 1,846.4 ⫾ 129.6 m, with a 95% CI of 519.2Ð1,435.6 m. There was a signiÞcant difference for TFD between the genders of Cx. pipiens pallens (F ⫽ 21.03; df ⫽ 1, 259; P ⬍ 0.01). For female mosquitoes, there was a signiÞcant difference for TFD among the 13 different age-groups (F ⫽ 2.51; df ⫽ 12, 159; P ⬍ 0.01; Fig. 1). The TukeyÐKramer test for TFD of female mosquitoes indicated 7-d-old female mosquitoes ßew farther than 6- and 5-d-old insects. Other agegroup pairs of female mosquitoes showed no statistical difference for TFD. The mean TFD for 7-d-old females was 2,557.4 m longer than that of 6-d-old females, with a 95% CI of 235.9 Ð 4,878.9 m for this difference. Seven-day-old females also ßew 2,529.4 m farther than 5-d-old females, with a 95% CI of 51.4 Ð 2,529.4 m. There were no differences among different age-groups for male mosquitoes (F ⫽ 1.20; df ⫽ 9, 100; P ⫽ 0.30). Presence of an age effect for females and absence of a similar effect for males were reßected in the signiÞcant interaction between gender and age (F ⫽ 2.11; df ⫽ 9, 100; P ⬍ 0.05). Total Flight Duration. The mean TFDr for male mosquitoes was 5,672.1 ⫾ 953.8 s, and the mean TFDr for female mosquitoes was 8,960.1 ⫾ 706.8 s, with a 95% CI of 967.8 Ð5,608.2 s. There was a signiÞcant difference for TFDr between females and males (F ⫽ 7.74; df ⫽ 1, 259; P ⬍ 0.01), with females exhibiting a longer average ßight duration. There was also a signiÞcant difference for TFDr among different age-groups of
CUI ET AL.: FLIGHT CAPACITY OF ADULT Cx. pipiens pallens
September 2013
both genders combined (F ⫽ 2.54; df ⫽ 12, 259; P ⬍ 0.01). By one-way analysis of variance analysis for female mosquitoes, there was a signiÞcant difference for TFDr among different age-groups (F ⫽ 2.47; df ⫽ 12, 159; P ⬍ 0.01; Fig. 1). With TukeyÐKramer test, mean TFDr of 6-d-old female mosquitoes (19,34.73 ⫾ 398.72 s) was signiÞcantly shorter when compared with 2-d-old females (14,884.96 ⫾ 5,612.67 s) and 20d-old females (17,090.84 ⫾ 4,266.23 s). Although the gender by age interaction was not signiÞcant (F ⫽ 1.08; df ⫽ 9, 259; P ⫽ 0.37), differences in TFDr among male ages were not large enough to be statistically demonstrated (F ⫽ 0.68; df ⫽ 9, 100; P ⫽ 0.73). Mean Flight Velocity. The mean MFV for male mosquitoes was 0.28 ⫾ 0.17 m/s, and the mean MFV for female mosquitoes was 0.33 ⫾ 0.19 m/s. There was a signiÞcant difference for MFV between females and males (F ⫽ 4.84; df ⫽ 1, 259; P ⬍ 0.05). For both genders combined, there was no signiÞcant difference for MFV among different age-groups (F ⫽ 1.11; df ⫽ 12, 259; P ⫽ 0.35). However, the signiÞcant gender by age interaction (F ⫽ 2.59; df ⫽ 9, 259; P ⬍ 0.01) indicated the effect of age on ßight velocity differed between the two genders. Despite this interaction, examination of the age effect within genders failed to demonstrate signiÞcant age effects on MFV (female, F ⫽ 1.68; df ⫽ 12, 159; P ⫽ 0.08; male, F ⫽ 1.90; df ⫽ 9, 100; P ⫽ 0.06). Discussion The autogeny of Cx. pipiens pallens has been veriÞed by previous studies (Wang et al. 1993, Vinogradova 2000, Hai et al. 2007, Strickman and Fonseca 2012). For this reason, although the mosquitoes used in this study were not served with bloodmeals, they could still undergo the general behavioral and physiological processes associated with egg production. Our study found that the 4-d-old adult females had a peak potential to travel a mean distance of 2,671.1 ⫾ 585.6 m in tethered ßight, with a 95% CI of 1,891.0 Ð 4,456.3 m. This peak ßight potential takes place near the time of the Þrst blood-sucking activity of ungravid adult female mosquitoes. Therefore, it is signiÞcant to evaluate the risk area for the Þrst blood-sucking activities to minimize the transmission of pathogens by Cx. pipiens pallens. The results in this study showed the ßight potential of 5- and 6-d-old adult female mosquitoes stayed at the lowest level, both below the level of 1-d-old mosquitoes, which happened at the same time as the developmental and maturing period of ovaries in the female. The egg rafts were observed in the rearing cages, which was consistent with the results from Strickman and Fonseca (2012). Based on Strickman and Fonseca (2012); 95% of female mosquitoes in their study had the ability to oviposit fertilized eggs without a previous bloodmeal. These biological facts suggest presence of a large egg clutch may explain the short ßight distances of 5- and 6-d-old adult females. The 7-d-old adult female mosquitoes had a second peak ßight potential with a mean of TFD at 3,173.6 ⫾ 545.2 m, with a 95% CI of 1,891.0 Ð 4,456.3 m. This peak
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ßight potential is important not only to determine the oviposition range of gravid female mosquitoes, but also to evaluate the scale of the second blood-sucking activity of female mosquitoes. The females of 20 d of age exhibited the maximum potential for ßight capacity, with a mean TFD of 3,181.5 ⫾ 667.7 m, and a 95% CI of 1,295.3Ð5,067.7 m. This peak ßight potential would be important to evaluate the scale of the second bloodsucking activity of female mosquitoes in transmission of lymphatic Þlariasis to human hosts. Our estimates of the ßight capacity of Cx. pipiens pallens are also useful in determining control strategies for other mosquitoborne diseases, such as Japanese encephalitis, or meningoencephalitis caused by West Nile virus. Adults of a given egg raft of Cx. pipiens pallens emerge over 5Ð 6 d, and the male mosquitoes account for 92% of all individuals emerging on the Þrst day. Female mosquitoes are predominant on the second and third day of emergence, accounting for 62.2 and 71.8%, respectively (Ma and Wang 1998). In our study, we found that 5-d-old male mosquitoes possess the maximum ßight potential, whereas 4- and 3-d-old female mosquitoes exhibit the Þrst potential ßight peak. These results are consistent with the mosquito life history during the mating season. When considering the ßight velocity of the male mosquito, the results show that male mosquitoes exhibited the maximum ßight velocity at 6 d of age, with a slightly slower ßight speed at 5 d of age. In general, the male mosquitoes choose the Þfth day after emergence as the best time to mate with the female, and the sixth day after emergence as the second best choice. The best mating time for female mosquitoes occurs on the third or fourth day after emergence when the ßight capacity (MFV and TFD) is maximal. Our results may suggest a possible hypothesis regarding the biological implications of female mating: the maximal ßight duration on day 4 of female adult age may reßect a selective advantage of mating with a different patriarchal line, whereas the slightly lower ßight duration on day 3 of age may ensure mating when population levels are low and raft-mates are predominantly available. Mean of ßight capacity of male mosquitoes at 5 d of age is clearly weaker than that of female mosquitoes at 3 or 4 d of age on both TFD and MFV. This indicates that the female mosquitoes exert sexual selection pressure on male mosquitoes, where only the best ßiers likely intercept the female mosquito in ßight. Liu et al. (1994) found that one male mosquito of Cx. pipiens pallens can mate with Þve females on average, and in some extreme cases, the number of mating partners could reach eight. Based on the report of Kong and Liang (2006), the sex ratio within a swarm of Cx. pipiens pallens can as skewed as 30 Ð50:1 (male:female). These studies also showed severe competition in the sexual selection among male mosquitoes in the mating season. Acknowledgments We thank Dale Spurgeon and Al Fournier for their suggestions and comments. We thank two anonymous reviewers
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for helpful comments on earlier drafts of this manuscript. We also appreciate the special funding support of Henan Institute of Science and Technology.
References Cited Beerwinkle, K. R., J. D. Lopez, D. Cheng, P. D. Lingren, and R. W. Meola. 1995. Flight potential of feral Helicoverpa zea (Lepidoptera: Noctuidae) males measured with a 32-channel, computer-monitored, ßight-mill system. Environ. Entomol. 24: 1122Ð1130. Cheng, D., Z. Tian, H. Li, J. Sun, and J. Chen. 2002. Inßuence of temperature and humidity on the ßight capacity of Sitobion avenae. Acta Entomol. Sin. 45: 80 Ð 85. Estep, L. K., N. D. Burkett–Cadena, G. E. Hill, R. S. Unnasch, and T. R. Unnasch. 2010. Estimation of dispersal distances of Culex erraticus in a focus of eastern equine encephalitis virus in the southeastern United States. J. Med. Entomol. 47: 977Ð986. Hai, X. P., W. X. Shang, and Z. S. Zhan. 2007. Autogenic research on Culex pipiens pallens, Coquillett. Med. Ani. Prev. 23: 841. Kong, L., and Q. Liang. 2006. Observations on the ecological biology of Culex pipiens pallens in the region along the bank of Qi River. Chin. J. Vect. Biol. Control 17: 329 Ð330. Li, X., L. Sun, and C. L. Zhu. 2002. Biotic characteristics in the deltamethrin-susceptible and resistant strains of Culex pipiens pallens (Diptera-culicidae) in China. Appl. Entomol. Zool. 37: 21Ð24. Liu, X., Y. Hu, and C. Sun. 1994. Laboratory studies on the biology of Culex pipiens pallens. Chin. J. Vect. Biol. Control 5: 6 Ð 8.
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Ma, X., and H. Wang. 1998. Observations on the biological features of Culex pipiens pallens. Chin. J. Health Lab. Technol. 8: 316 Ð317. Ma, Z., K. Pan, Y. Huang, and S. Chen. 1998. Observational study on the biological features of laboratory Culex pipiens pallens. Chin. J. Zoonoses 14: 51Ð57. Morris, C. D., V. L. Larson, and D. B. Lounibos. 1991. Measuring mosquito dispersal for control programs. J. Am. Mosq. Control Assoc. 7: 608 Ð 615. Strickman, D., and D. M. Fonseca. 2012. Autogeny in Culex pipiens complex mosquitoes from the San Francisco Bay area. Am. J. Trop. Med. Hyg. 87: 19 Ð26. Tanaka, K., K. Mizusawa, and E. S. Saugstad. 1979. A review of the adult and larval mosquitoes of Japan (including the Ryukyu archipelago and the Ogasawara Island) and Korea (Diptera: Culicidae). Contrib. Am. Entomol. Inst. 16: 1Ð987. Tsuda, Y., O. Komagata, S. Kasai, T. Hayashi, N. Nihei, K. Saito, M. Mizutani, M. Kunida, M. Yoshida, and M. Kobayashi. 2008. A mark-release-recapture study on dispersal and ßight distance of Culex pipiens pallens in an urban area of Japan. J. Am. Mosq. Control Assoc. 24: 339 Ð343. Vinogradova, E. B. 2000. Culex pipiens pipiens mosquitoes: taxonomy, distribution, ecology, physiology, genetics, applied importance and control. Pensoft Publishers, Moscow, Russia. Wang, L. Z., Y. C. Cao, and C. M. Liu. 1993. Autogeny of Culex pipiens pallens in Shen Yang area, China. Chin. J. Vect. Biol. Control 4: 252Ð253. (WHO) World Health Organization. 1986. Mosquito ßight ranges. Wkly. Epidemiol. Rec. 61: 279. Received 30 March 2012; accepted 1 July 2013.
BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research.
VECTOR CONTROL, PEST MANAGEMENT, RESISTANCE, REPELLENTS
Flight Capacity of Adult Culex pipiens pallens (Diptera: Culicidae) in Relation to Gender and Day-Age JIANXIN CUI,1,2 SHUJUAN LI,3 PING ZHAO,4
AND
FUMIN ZOU1
J. Med. Entomol. 50(5): 1055Ð1058 (2013); DOI: http://dx.doi.org/10.1603/ME12078
ABSTRACT Culex pipiens pallens (L.) is the most common mosquito in houses of central and northern China. It is the primary vector of lymphatic Þlariasis and Japanese encephalitis. The ßight range of mosquitoes is an important factor predicting the risk area of transmission of mosquito-borne pathogens to vertebrate hosts. The ßight performance of Cx. pipiens pallens was measured with a 26-channel computer-monitored ßight-mill system. We found that females had longer ßight capability than males for total ßight distance (TFD) and total ßight duration (TFDr), and females ßew faster than males based on mean ßight velocity. No signiÞcant difference in ßight capability was found between different age-groups in males. However, certain age-groups of females showed signiÞcant differences in TFDr and TFD. SpeciÞcally, TFD and TFDr tended to be shortest for 5- and 6-d-old females. These signiÞcant differences in ßight capability between ages and genders provide insights to determine the size of operational area to achieve effective control of Cx. pipiens pallens and minimize the risk of the related mosquito-borne epidemic diseases of lymphatic Þlariasis and Japanese encephalitis. KEY WORDS ßight capacity, Culex pipiens pallens, day-age, mosquito, dispersal
Culex pipiens pallens (L.) is the most common mosquito in houses of central and northern China. It is the primary vector of lymphatic Þlariasis and Japanese encephalitis (Li et al. 2002). The adult females are primarily avian feeders but also consume blood from humans and other mammals (Tanaka et al. 1979). The blood-sucking activities of female Cx. pipiens pallens often occur 3Ð5 d after adult emergence (Liu et al. 1994, Ma et al. 1998). The earliest oviposition of gravid mosquitoes occurs at the third day after blood-sucking, whereas the peak time for oviposition comes 1 d later. The ßight range of mosquitoes is an important factor in predicting the risk area of transmission of mosquito-borne pathogens to vertebrate hosts. Different sizes of operational area are recommended for vector control based on the dispersal ability of vector mosquitoes (World Health Organization [WHO] 1986). The ßight ability of Culex mosquitoes has been extensively studied. Tsuda et al. (2008) used a markÐ releaseÐrecapture method and found that female adults of Cx. pipiens pallens could disperse 470, 287, 326, and 517 m on days 1, 2, 3, and 4, respectively, after release. They estimated that the maximum ßight distance of this species was 1,217 m based on the rela1 Department of Plant Protection, Henan Institute of Science and Technology, Xinxiang, Henan 453003, China. 2 Corresponding author, e-mail: [email protected]. 3 Maricopa Agricultural Center, University of Arizona, 37860 West Smith-Enke Rd., Maricopa, AZ 85138-3010. 4 Division of Life Science, College of the Environmental and Life Science, Kaili University, Kaili, Guizhou 556011, China.
tionship between distance from the release site to the collection site and the total number of recaptures per trap. The estimated mean and 99th percentile of dispersal distance for Culex erraticus was 970 and 3,210 m, respectively, per gonotrophic cycle (Estep et al. 2010). Morris et al. (1991) found that the mean dispersal distance for this same species was 730 m, and the maximum dispersal range was 1,400 Ð2,200 m. The study reported herein was conducted to evaluate ßight capacity of Cx. pipiens pallens by using ßight mills. It provides insights to determine the size of operational area to achieve effective control of Cx. pipiens pallens and minimize the risk of related mosquito-borne epidemic diseases. Materials and Methods Mosquitoes. Cx. pipiens pallens colony used in this study had been reared on artiÞcial diet in the laboratory for 3 yr at the Henan Institute of Science and Technology (N 35.18⬚, E 113.52⬚). Larvae were reared on a mixture of wheat bran and maize ßour. Adult mosquitoes within 12 h after emergence were placed in a cage with a volume ⬇0.1 m3. Each cage contained ⬇200 mosquitoes of mixed gender. The diet for adult mosquitoes was 5% sucrose solution (wt:vol). Adult male and female insects of 1Ð10 d of age and females of 15, 20, and 25 d of age were assayed. Ten to 23 mosquitoes were assayed for each combination of age and gender (1 d, 么 n ⫽ 10, 乆 n ⫽ 10; 2 d, 么 n ⫽ 10, 乆 n ⫽ 15; 3 d, 么 n ⫽ 13, 乆 n ⫽ 11; 4 d, 么 n ⫽ 10, 乆 n ⫽ 13; 5 d, 么 n ⫽ 10, 乆 n ⫽ 17; 6 d, 么 n ⫽ 10, 乆 n ⫽
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Fig. 1. Mean (black bar) ⫹ SD (gray bar) of ßight parameters for respective combinations of Culex pipiens pallens gender and age; (A and D) total ßight distance; (B and E) total ßight duration; and (C and F) ßight velocity. Different letters indicate signiÞcant difference between means within a plot by using the TukeyÐKramer test.
23; 7 d, 么 n ⫽ 15, 乆 n ⫽ 15; 8 d, 么 n ⫽ 11, 乆 n ⫽ 10; 9 d, 么 n ⫽ 10, 乆 n ⫽ 10; 10 d, 么 n ⫽ 11, 乆 n ⫽ 10; 15 d, 乆 n ⫽ 13; 20 d, 乆 n ⫽ 10; and 25 d, 乆 n ⫽ 15). Because males have a shorter adult life span than females, males were not assayed at ages ⬎10 d. Flight Mill Assays. The ßight performance of Cx. pipiens pallens was measured with a 26-channel computer-monitored ßight-mill system (Beerwinkle et al. 1995, Cheng et al. 2002). The arm of a ßight mill was a 10-cm-long (0.02-cm-diameter) metal wire, thus the distance of one complete revolution was 0.63 m. Insects were anesthetized brießy with ether, and a small tether was attached to their pronotum with cyanoacrylate Super Glue (502 Glue, Dongguan, Guangdong, China) at one end of the ßight mill arm. The opposing end of the arm was dipped in melted parafÞn until the mill was balanced. The ßight mill was positioned in a room with temperature ranging from 18 to 22⬚C and relative humidity from 40 to 50%. The photoperiod was following natural changes in late summer (14:10 [L:D]). A light intensity of 150 lux during daytime was maintained. Flight assays of 22 h in duration were conducted beginning at 1400 h and ending at 1200 h the next day. No water or nutriment was provided to the adult insects during the ßight periods. Statistical Analyses. Flight mill data were processed by using Matlab software. For each tethered insect, total ßight distance (TFD), total ßight duration (TFDr), and mean ßight velocity (MFV) were calculated. During an assay, ßight was considered halted if no data were captured for ⬎60 s. Periods during which ßight was halted were excluded from calculations of TFDr, and individuals with TFD ⬍20 m during the 22-h assay were also excluded. Unbalanced multiway analysis of variance including data on 15-, 20-, and 25-d-old females was performed to analyze the effect of age, gender, and age by gender interactions on ßight performance of Cx. pipiens pallens, with TukeyÐ Kramer test to separate the means.
Results In total, 172 females and 110 males of Cx. pipiens pallens were examined and analyzed for ßight performance in this study. The ßight capacity of these mosquitoes, as indicated by estimates of TFD, TFDr, and MFV, is shown in Fig. 1. Total Flight Distance. The mean TFD for males during the 22-h ßight period was 869.0 ⫾ 188.4 m, ⬇977.4 m shorter than that of females. The mean TFD for females was 1,846.4 ⫾ 129.6 m, with a 95% CI of 519.2Ð1,435.6 m. There was a signiÞcant difference for TFD between the genders of Cx. pipiens pallens (F ⫽ 21.03; df ⫽ 1, 259; P ⬍ 0.01). For female mosquitoes, there was a signiÞcant difference for TFD among the 13 different age-groups (F ⫽ 2.51; df ⫽ 12, 159; P ⬍ 0.01; Fig. 1). The TukeyÐKramer test for TFD of female mosquitoes indicated 7-d-old female mosquitoes ßew farther than 6- and 5-d-old insects. Other agegroup pairs of female mosquitoes showed no statistical difference for TFD. The mean TFD for 7-d-old females was 2,557.4 m longer than that of 6-d-old females, with a 95% CI of 235.9 Ð 4,878.9 m for this difference. Seven-day-old females also ßew 2,529.4 m farther than 5-d-old females, with a 95% CI of 51.4 Ð 2,529.4 m. There were no differences among different age-groups for male mosquitoes (F ⫽ 1.20; df ⫽ 9, 100; P ⫽ 0.30). Presence of an age effect for females and absence of a similar effect for males were reßected in the signiÞcant interaction between gender and age (F ⫽ 2.11; df ⫽ 9, 100; P ⬍ 0.05). Total Flight Duration. The mean TFDr for male mosquitoes was 5,672.1 ⫾ 953.8 s, and the mean TFDr for female mosquitoes was 8,960.1 ⫾ 706.8 s, with a 95% CI of 967.8 Ð5,608.2 s. There was a signiÞcant difference for TFDr between females and males (F ⫽ 7.74; df ⫽ 1, 259; P ⬍ 0.01), with females exhibiting a longer average ßight duration. There was also a signiÞcant difference for TFDr among different age-groups of
CUI ET AL.: FLIGHT CAPACITY OF ADULT Cx. pipiens pallens
September 2013
both genders combined (F ⫽ 2.54; df ⫽ 12, 259; P ⬍ 0.01). By one-way analysis of variance analysis for female mosquitoes, there was a signiÞcant difference for TFDr among different age-groups (F ⫽ 2.47; df ⫽ 12, 159; P ⬍ 0.01; Fig. 1). With TukeyÐKramer test, mean TFDr of 6-d-old female mosquitoes (19,34.73 ⫾ 398.72 s) was signiÞcantly shorter when compared with 2-d-old females (14,884.96 ⫾ 5,612.67 s) and 20d-old females (17,090.84 ⫾ 4,266.23 s). Although the gender by age interaction was not signiÞcant (F ⫽ 1.08; df ⫽ 9, 259; P ⫽ 0.37), differences in TFDr among male ages were not large enough to be statistically demonstrated (F ⫽ 0.68; df ⫽ 9, 100; P ⫽ 0.73). Mean Flight Velocity. The mean MFV for male mosquitoes was 0.28 ⫾ 0.17 m/s, and the mean MFV for female mosquitoes was 0.33 ⫾ 0.19 m/s. There was a signiÞcant difference for MFV between females and males (F ⫽ 4.84; df ⫽ 1, 259; P ⬍ 0.05). For both genders combined, there was no signiÞcant difference for MFV among different age-groups (F ⫽ 1.11; df ⫽ 12, 259; P ⫽ 0.35). However, the signiÞcant gender by age interaction (F ⫽ 2.59; df ⫽ 9, 259; P ⬍ 0.01) indicated the effect of age on ßight velocity differed between the two genders. Despite this interaction, examination of the age effect within genders failed to demonstrate signiÞcant age effects on MFV (female, F ⫽ 1.68; df ⫽ 12, 159; P ⫽ 0.08; male, F ⫽ 1.90; df ⫽ 9, 100; P ⫽ 0.06). Discussion The autogeny of Cx. pipiens pallens has been veriÞed by previous studies (Wang et al. 1993, Vinogradova 2000, Hai et al. 2007, Strickman and Fonseca 2012). For this reason, although the mosquitoes used in this study were not served with bloodmeals, they could still undergo the general behavioral and physiological processes associated with egg production. Our study found that the 4-d-old adult females had a peak potential to travel a mean distance of 2,671.1 ⫾ 585.6 m in tethered ßight, with a 95% CI of 1,891.0 Ð 4,456.3 m. This peak ßight potential takes place near the time of the Þrst blood-sucking activity of ungravid adult female mosquitoes. Therefore, it is signiÞcant to evaluate the risk area for the Þrst blood-sucking activities to minimize the transmission of pathogens by Cx. pipiens pallens. The results in this study showed the ßight potential of 5- and 6-d-old adult female mosquitoes stayed at the lowest level, both below the level of 1-d-old mosquitoes, which happened at the same time as the developmental and maturing period of ovaries in the female. The egg rafts were observed in the rearing cages, which was consistent with the results from Strickman and Fonseca (2012). Based on Strickman and Fonseca (2012); 95% of female mosquitoes in their study had the ability to oviposit fertilized eggs without a previous bloodmeal. These biological facts suggest presence of a large egg clutch may explain the short ßight distances of 5- and 6-d-old adult females. The 7-d-old adult female mosquitoes had a second peak ßight potential with a mean of TFD at 3,173.6 ⫾ 545.2 m, with a 95% CI of 1,891.0 Ð 4,456.3 m. This peak
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ßight potential is important not only to determine the oviposition range of gravid female mosquitoes, but also to evaluate the scale of the second blood-sucking activity of female mosquitoes. The females of 20 d of age exhibited the maximum potential for ßight capacity, with a mean TFD of 3,181.5 ⫾ 667.7 m, and a 95% CI of 1,295.3Ð5,067.7 m. This peak ßight potential would be important to evaluate the scale of the second bloodsucking activity of female mosquitoes in transmission of lymphatic Þlariasis to human hosts. Our estimates of the ßight capacity of Cx. pipiens pallens are also useful in determining control strategies for other mosquitoborne diseases, such as Japanese encephalitis, or meningoencephalitis caused by West Nile virus. Adults of a given egg raft of Cx. pipiens pallens emerge over 5Ð 6 d, and the male mosquitoes account for 92% of all individuals emerging on the Þrst day. Female mosquitoes are predominant on the second and third day of emergence, accounting for 62.2 and 71.8%, respectively (Ma and Wang 1998). In our study, we found that 5-d-old male mosquitoes possess the maximum ßight potential, whereas 4- and 3-d-old female mosquitoes exhibit the Þrst potential ßight peak. These results are consistent with the mosquito life history during the mating season. When considering the ßight velocity of the male mosquito, the results show that male mosquitoes exhibited the maximum ßight velocity at 6 d of age, with a slightly slower ßight speed at 5 d of age. In general, the male mosquitoes choose the Þfth day after emergence as the best time to mate with the female, and the sixth day after emergence as the second best choice. The best mating time for female mosquitoes occurs on the third or fourth day after emergence when the ßight capacity (MFV and TFD) is maximal. Our results may suggest a possible hypothesis regarding the biological implications of female mating: the maximal ßight duration on day 4 of female adult age may reßect a selective advantage of mating with a different patriarchal line, whereas the slightly lower ßight duration on day 3 of age may ensure mating when population levels are low and raft-mates are predominantly available. Mean of ßight capacity of male mosquitoes at 5 d of age is clearly weaker than that of female mosquitoes at 3 or 4 d of age on both TFD and MFV. This indicates that the female mosquitoes exert sexual selection pressure on male mosquitoes, where only the best ßiers likely intercept the female mosquito in ßight. Liu et al. (1994) found that one male mosquito of Cx. pipiens pallens can mate with Þve females on average, and in some extreme cases, the number of mating partners could reach eight. Based on the report of Kong and Liang (2006), the sex ratio within a swarm of Cx. pipiens pallens can as skewed as 30 Ð50:1 (male:female). These studies also showed severe competition in the sexual selection among male mosquitoes in the mating season. Acknowledgments We thank Dale Spurgeon and Al Fournier for their suggestions and comments. We thank two anonymous reviewers
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for helpful comments on earlier drafts of this manuscript. We also appreciate the special funding support of Henan Institute of Science and Technology.
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