SHORT COMMUNICATION
Use of an Aquatic Light Trap for Monitoring Larval Populations of Culex quinquefasciatus (Diptera: Culicidae) JEFFREY BEEHLER AND JAMES WEBB, JR.1 Department of Entomology, University of California, Riverside, California 92521
KEY WORDS
Insecta, aquatic light trap, Culex quinquefasciatus, larval sampling
THE 350-ML DIPPER is the most common sampling tool for mosquito larvae; however, a major problem with its use is a lack of standardization. There are several different methods for dipping mosquito larvae, all of which may give different results (Service 1976). Even different individuals taking samples from the same container with the same number of larvae may get significantly different estimates of abundance using a dipper (Shogaki & Makiya 1970). For these reasons, aquatic light traps have been evaluated for sampling mosquito larvae. These traps usually consist of an inverted funnel placed under the surface of the water with a light source to attract the larvae into a chamber. A small electric bulb (Hungerford et al. 1955, Husbands 1967, Weber 1985), chemical light (Service 1983, 1984), or radioactive betalights (Service et al. 1984) have been used as a light source. An aquatic light trap using a Cyalume (American Cyanamid Co., Milton, FL) light stick for illumination has been used to collect mosquito larvae in small pools and in marsh ecosystems (J. W., unpublished data). In outdoor tests conducted in small pools, blue, green, yellow and white Cyalume light sticks attracted fourth-instar Culex quinquefasciatus Say to submerged traps. Red light sticks were not effective. In the field, blue, yellow, and white light sticks attracted Culex tarsalis Coquillett and some Culex erythrothorax Dyar larvae. Service et al. (1983) con1 Orange County Vector Control District, P.O. Box 87, Santa Ana, Calif. 92702.
ducted field studies in which large numbers of larvae and pupae were recovered from ponds that contained high larval Culex thalassius (Theobald) populations using underwater light traps containing Cyalume light sticks. The purpose of the present study was to determine the effect of trap position and light source color in attracting mosquito larvae. We compared the placement of traps with the opening of the entrance funnel at the surface of the water with traps in which the entrance funnels were submerged. The color of the chemical light source on the efficacy of the surface traps also was considered. Materials and Methods Trap Design. The aquatic light trap (Bioquip Products, Gardena, CA) is constructed of acrylonitrile butarine styrene plastic and measures 21 cm in height and 26 cm in width. The exterior of the trap is black and the interior is white. Four clear plastic funnels (10 cm diameter) are inverted in the side ports of the trap. Because the trap has approximately the same specific gravity as water, it must be weighted to rest on the bottom of the habitat. Traps may also be used near the surface of the water by removing the weights. A Cyalume light stick provided illumination for the trap. Blue, yellow, and white light sticks were tested. Blue light sticks have a mean light emission at «450 nm, yellow at 550 nm, and white at 450,550, and 600 nm. Yellow light sticks
0022-2585/92/0898-0900$02.00/0 © 1992 Entomological Society of America
Downloaded from http://jme.oxfordjournals.org/ by guest on May 20, 2016
J. Med. Entomol. 29(5): 898-900 (1992) ABSTRACT An aquatic light trap was evaluated in wading pools placed in a greenhouse as a method of sampling populations of mosquito larvae. Three replicated experiments examined the effect of the color of a Cyalume light source and the vertical placement of the trap within the water column. Traps placed with the entrance funnel opening at the surface of the water collected significantly more fourth-instar Culex quinquefasciatus than did those with the entrance submerged. When traps were placed near the surface of the water, those with blue, yellow, and white light sticks, as well as unlighted control traps, collected approximately die same number of larvae. Therefore, a small change in trap position was more important than the presence of a light source in the effectiveness of this aquatic light trap as a sampling device for mosquito larvae.
September 1992 BEEHLER & WEBB: AQUATIC LIGHT TRAP FOR C. quinquefasciatus LARVAE 899
Downloaded from http://jme.oxfordjournals.org/ by guest on May 20, 2016
360 (34%) Cx. quinquefasciatus larvae were captured by the traps. Of these larvae, 91 (74%) were collected from traps with openings at the surface of the water. A back-transformed mean of 15.2 larvae per trap per night were collected in traps with the funnel opening on the surface, whereas traps with funnels placed below the surface of the water collected a mean of 5.3 larvae per trap. The ANOVA of the square root-transformed data showed that the traps were more attractive to larvae when placed with the opening at the surface of the water (F = 21.1; df = 1, 10; P < 0.001). In experiment 2, when all traps were placed at the surface using four different-colored light sticks and a control trap containing no light stick, 231 of the 720 larvae (32%) were recovered. The traps with blue, yellow, white, and no light sticks collected a back-transformed mean of 9.7, 10.0, 8.5, and 11.5 larvae per trap per night, respectively. The ANOVA of the square roottransformed data showed that there was no significant difference among traps (F = 0.15; df = 3, 20; P > 0.20). In experiment 3, traps were placed at the surface of the water, comparing illuminated (yellow light sticks) and unlighted control traps. In this experiment, 149 of 360 larvae (41%) were recovered. A back-transformed mean of 13.7 larvae were collected from traps that were illuminated, and 11.2 larvae per trap per night were collected from traps that were not illuminated. The ANOVA of the square root-transformed data showed that there was no significant difference in the number of larvae collected from lighted or unlighted traps (F = 1.05; df = 1, 10; P = 0.18). In conclusion, aquatic light traps placed with the opening of the funnel at the surface of the water collected significantly more Cx. quinquefasciatus larvae than those placed with the openings under the surface of the water. A difference of only a few centimeters resulted in significantly higher trap catches. Both lighted and unlighted traps placed with the funnel opening at the surface of the water were equally effective in attracting larvae. Mosquito larvae are generally contagious in distribution (Service 1976), and Culex larvae tend to cluster along edges of the aquatic habitat (Walton et al. 1990). This movement across open water to habitat edges provided by these traps could account for much of the catch by traps placed with the funnels at the surface of the water. Most of the larvae recovered at the conclusion of each experiment were distributed along the pool edge. Movement toward a water—structure interface could account for the higher trap catches in traps with the enResults and Discussion trance funnel at the surface of the water rather any attractancy from the light sticks, as was In experiment 1, comparing the traps placed than previously assumed. Our data show that surface on the bottom of the pools with traps with funnel traps collected the largest number of larvae in openings at the surface of the water, 123 of provide 12 h of illumination, whereas the other sticks provided 8 h. Experiments. Experiments using aquatic light traps were conducted in a greenhouse using pools (1.5 m diameter) filled to a depth of 15 cm with tap water. Pools were separated by a distance of at least 3.6 m. In each test, 30 laboratoryreared fourth-instar Cx. quinquefasciatus were placed in the water at the edge of the pool. At the conclusion of each test, larvae that were not captured in the trap were removed with an aquarium net. Tap water was replaced at the conclusion of each experiment. Experiment 1 examined the importance of the placement of the trap funnel opening relative to the surface of the water in attracting larvae. Two traps containing a yellow Cyalume light stick were placed on the bottom at the center of two pools, and two traps (also containing yellow light sticks) that were supported on metal pans (20 by 20 by 5 cm) (to bring the entrance funnels to the water surface) were placed in the center of two additional pools. The tests began at 1800 hours (PST) with the placement of the trap and the addition of the test larvae. At 0800 hours the following morning, the traps were removed from the water and the number of larvae in each trap was counted. The test was replicated for three nights for a total of six trap-nights per treatment. Data were transformed to VA, an appropriate transformation when the sample variance is proportional to the mean (Snedecor & Cochran 1989), and were analyzed using analysis of variance (ANOVA). In experiment 2, traps with different-colored light sticks and an untreated control trap (all placed with funnel openings at the surface of the water) were compared. A trap with either a blue, yellow, white, or no light stick was randomly assigned to one of four pools. The traps and larvae were placed at 2200 hours and removed at 0800 hours the following morning. The yellow light sticks provided light for 12 h, whereas the other sticks provided only 8 h of illumination, so tests were initiated 4 h later. The comparison was replicated six times. Data were again transformed (Vx) and analyzed using ANOVA. In experiment 3, four traps were placed on metal pans in four pools, bringing their funnels to the water level. Two traps were illuminated with yellow light sticks and two were unilluminated controls. The test began at 1800 hours and was concluded at 0800 hours the following morning. Experiments were replicated six times. Data again were transformed (VA) and analyzed using ANOVA.
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JOURNAL OF MEDICAL ENTOMOLOGY
pool tests regardless of the presence of a light source. The Cyalume-lighted underwater light trap effectively captured mosquitoes in low-density situations where they could not be recovered by dipping (J. W., unpublished data). Changes in trap placement may improve the trap's sensitivity in man-made impoundments such as sewage ponds, aquaculture ponds, and urban water management holding ponds where larval density is low. Acknowledgment
References Cited Hungerford, H. B., P. L. Spangler & N. A. Walker. 1955. Sub-aquatic light traps for insects and other organisms. Trans. Kans. Acad. Sci. 58: 387-407. Husbands, R. C. 1967. A subsurface light trap for
sampling aquatic insect populations. Calif. Vector Views 14: 81-82. Service, M. W. 1976. Mosquito ecology: field sampling methods. Wiley, New York. 1983. Chemical light traps for the collection of mosquito larvae. Proc. Fla. Antimosq. Assoc. 54: 29-^30. 1984. Evaluation of sticky light traps for sampling mosquito larvae. Entomol. Exp. Appl. 35: 27-32. Service, M. W., S. Sulaiman & R. Esena. 1983. A chemical light trap for mosquito larvae (Diptera: Culicidae). J. Med. Entomol. 20: 659-663. Shogaki, Y. & K. Makiya. 1970. An improved device for quantitative sampling of mosquito larvae. Jpn. J. Sanit. Zool. 21: 172-179. Snedecor, G. W. & W. G. Cochran. 1989. Statistical methods. Iowa State University Press, Ames. Walton, W. E., E. T. Schreiber & M. S. Mulla. 1990. Distribution of Culex tarsalis larvae in a freshwater marsh in Orange County, California. J. Am. Mosq. Control Assoc. 6: 539-543. Weber, R. G. 1985. An aquatic light trap for possible use in mosquito larvae surveillance. Proc. N.J. Mosq. Control Assoc. 72: 122-125. Received for publication 26 August 1991; accepted 14 April 1992.
Downloaded from http://jme.oxfordjournals.org/ by guest on May 20, 2016
Lisa Fry, Department of Entomology, University of California, Riverside, provided greenhouse space for this study. In addition, the authors thank M. S. Mulla, also of the Department of Entomology, for his critical reading of the manuscript.
Vol. 29, no. 5
Use of an Aquatic Light Trap for Monitoring Larval Populations of Culex quinquefasciatus (Diptera: Culicidae) JEFFREY BEEHLER AND JAMES WEBB, JR.1 Department of Entomology, University of California, Riverside, California 92521
KEY WORDS
Insecta, aquatic light trap, Culex quinquefasciatus, larval sampling
THE 350-ML DIPPER is the most common sampling tool for mosquito larvae; however, a major problem with its use is a lack of standardization. There are several different methods for dipping mosquito larvae, all of which may give different results (Service 1976). Even different individuals taking samples from the same container with the same number of larvae may get significantly different estimates of abundance using a dipper (Shogaki & Makiya 1970). For these reasons, aquatic light traps have been evaluated for sampling mosquito larvae. These traps usually consist of an inverted funnel placed under the surface of the water with a light source to attract the larvae into a chamber. A small electric bulb (Hungerford et al. 1955, Husbands 1967, Weber 1985), chemical light (Service 1983, 1984), or radioactive betalights (Service et al. 1984) have been used as a light source. An aquatic light trap using a Cyalume (American Cyanamid Co., Milton, FL) light stick for illumination has been used to collect mosquito larvae in small pools and in marsh ecosystems (J. W., unpublished data). In outdoor tests conducted in small pools, blue, green, yellow and white Cyalume light sticks attracted fourth-instar Culex quinquefasciatus Say to submerged traps. Red light sticks were not effective. In the field, blue, yellow, and white light sticks attracted Culex tarsalis Coquillett and some Culex erythrothorax Dyar larvae. Service et al. (1983) con1 Orange County Vector Control District, P.O. Box 87, Santa Ana, Calif. 92702.
ducted field studies in which large numbers of larvae and pupae were recovered from ponds that contained high larval Culex thalassius (Theobald) populations using underwater light traps containing Cyalume light sticks. The purpose of the present study was to determine the effect of trap position and light source color in attracting mosquito larvae. We compared the placement of traps with the opening of the entrance funnel at the surface of the water with traps in which the entrance funnels were submerged. The color of the chemical light source on the efficacy of the surface traps also was considered. Materials and Methods Trap Design. The aquatic light trap (Bioquip Products, Gardena, CA) is constructed of acrylonitrile butarine styrene plastic and measures 21 cm in height and 26 cm in width. The exterior of the trap is black and the interior is white. Four clear plastic funnels (10 cm diameter) are inverted in the side ports of the trap. Because the trap has approximately the same specific gravity as water, it must be weighted to rest on the bottom of the habitat. Traps may also be used near the surface of the water by removing the weights. A Cyalume light stick provided illumination for the trap. Blue, yellow, and white light sticks were tested. Blue light sticks have a mean light emission at «450 nm, yellow at 550 nm, and white at 450,550, and 600 nm. Yellow light sticks
0022-2585/92/0898-0900$02.00/0 © 1992 Entomological Society of America
Downloaded from http://jme.oxfordjournals.org/ by guest on May 20, 2016
J. Med. Entomol. 29(5): 898-900 (1992) ABSTRACT An aquatic light trap was evaluated in wading pools placed in a greenhouse as a method of sampling populations of mosquito larvae. Three replicated experiments examined the effect of the color of a Cyalume light source and the vertical placement of the trap within the water column. Traps placed with the entrance funnel opening at the surface of the water collected significantly more fourth-instar Culex quinquefasciatus than did those with the entrance submerged. When traps were placed near the surface of the water, those with blue, yellow, and white light sticks, as well as unlighted control traps, collected approximately die same number of larvae. Therefore, a small change in trap position was more important than the presence of a light source in the effectiveness of this aquatic light trap as a sampling device for mosquito larvae.
September 1992 BEEHLER & WEBB: AQUATIC LIGHT TRAP FOR C. quinquefasciatus LARVAE 899
Downloaded from http://jme.oxfordjournals.org/ by guest on May 20, 2016
360 (34%) Cx. quinquefasciatus larvae were captured by the traps. Of these larvae, 91 (74%) were collected from traps with openings at the surface of the water. A back-transformed mean of 15.2 larvae per trap per night were collected in traps with the funnel opening on the surface, whereas traps with funnels placed below the surface of the water collected a mean of 5.3 larvae per trap. The ANOVA of the square root-transformed data showed that the traps were more attractive to larvae when placed with the opening at the surface of the water (F = 21.1; df = 1, 10; P < 0.001). In experiment 2, when all traps were placed at the surface using four different-colored light sticks and a control trap containing no light stick, 231 of the 720 larvae (32%) were recovered. The traps with blue, yellow, white, and no light sticks collected a back-transformed mean of 9.7, 10.0, 8.5, and 11.5 larvae per trap per night, respectively. The ANOVA of the square roottransformed data showed that there was no significant difference among traps (F = 0.15; df = 3, 20; P > 0.20). In experiment 3, traps were placed at the surface of the water, comparing illuminated (yellow light sticks) and unlighted control traps. In this experiment, 149 of 360 larvae (41%) were recovered. A back-transformed mean of 13.7 larvae were collected from traps that were illuminated, and 11.2 larvae per trap per night were collected from traps that were not illuminated. The ANOVA of the square root-transformed data showed that there was no significant difference in the number of larvae collected from lighted or unlighted traps (F = 1.05; df = 1, 10; P = 0.18). In conclusion, aquatic light traps placed with the opening of the funnel at the surface of the water collected significantly more Cx. quinquefasciatus larvae than those placed with the openings under the surface of the water. A difference of only a few centimeters resulted in significantly higher trap catches. Both lighted and unlighted traps placed with the funnel opening at the surface of the water were equally effective in attracting larvae. Mosquito larvae are generally contagious in distribution (Service 1976), and Culex larvae tend to cluster along edges of the aquatic habitat (Walton et al. 1990). This movement across open water to habitat edges provided by these traps could account for much of the catch by traps placed with the funnels at the surface of the water. Most of the larvae recovered at the conclusion of each experiment were distributed along the pool edge. Movement toward a water—structure interface could account for the higher trap catches in traps with the enResults and Discussion trance funnel at the surface of the water rather any attractancy from the light sticks, as was In experiment 1, comparing the traps placed than previously assumed. Our data show that surface on the bottom of the pools with traps with funnel traps collected the largest number of larvae in openings at the surface of the water, 123 of provide 12 h of illumination, whereas the other sticks provided 8 h. Experiments. Experiments using aquatic light traps were conducted in a greenhouse using pools (1.5 m diameter) filled to a depth of 15 cm with tap water. Pools were separated by a distance of at least 3.6 m. In each test, 30 laboratoryreared fourth-instar Cx. quinquefasciatus were placed in the water at the edge of the pool. At the conclusion of each test, larvae that were not captured in the trap were removed with an aquarium net. Tap water was replaced at the conclusion of each experiment. Experiment 1 examined the importance of the placement of the trap funnel opening relative to the surface of the water in attracting larvae. Two traps containing a yellow Cyalume light stick were placed on the bottom at the center of two pools, and two traps (also containing yellow light sticks) that were supported on metal pans (20 by 20 by 5 cm) (to bring the entrance funnels to the water surface) were placed in the center of two additional pools. The tests began at 1800 hours (PST) with the placement of the trap and the addition of the test larvae. At 0800 hours the following morning, the traps were removed from the water and the number of larvae in each trap was counted. The test was replicated for three nights for a total of six trap-nights per treatment. Data were transformed to VA, an appropriate transformation when the sample variance is proportional to the mean (Snedecor & Cochran 1989), and were analyzed using analysis of variance (ANOVA). In experiment 2, traps with different-colored light sticks and an untreated control trap (all placed with funnel openings at the surface of the water) were compared. A trap with either a blue, yellow, white, or no light stick was randomly assigned to one of four pools. The traps and larvae were placed at 2200 hours and removed at 0800 hours the following morning. The yellow light sticks provided light for 12 h, whereas the other sticks provided only 8 h of illumination, so tests were initiated 4 h later. The comparison was replicated six times. Data were again transformed (Vx) and analyzed using ANOVA. In experiment 3, four traps were placed on metal pans in four pools, bringing their funnels to the water level. Two traps were illuminated with yellow light sticks and two were unilluminated controls. The test began at 1800 hours and was concluded at 0800 hours the following morning. Experiments were replicated six times. Data again were transformed (VA) and analyzed using ANOVA.
900
JOURNAL OF MEDICAL ENTOMOLOGY
pool tests regardless of the presence of a light source. The Cyalume-lighted underwater light trap effectively captured mosquitoes in low-density situations where they could not be recovered by dipping (J. W., unpublished data). Changes in trap placement may improve the trap's sensitivity in man-made impoundments such as sewage ponds, aquaculture ponds, and urban water management holding ponds where larval density is low. Acknowledgment
References Cited Hungerford, H. B., P. L. Spangler & N. A. Walker. 1955. Sub-aquatic light traps for insects and other organisms. Trans. Kans. Acad. Sci. 58: 387-407. Husbands, R. C. 1967. A subsurface light trap for
sampling aquatic insect populations. Calif. Vector Views 14: 81-82. Service, M. W. 1976. Mosquito ecology: field sampling methods. Wiley, New York. 1983. Chemical light traps for the collection of mosquito larvae. Proc. Fla. Antimosq. Assoc. 54: 29-^30. 1984. Evaluation of sticky light traps for sampling mosquito larvae. Entomol. Exp. Appl. 35: 27-32. Service, M. W., S. Sulaiman & R. Esena. 1983. A chemical light trap for mosquito larvae (Diptera: Culicidae). J. Med. Entomol. 20: 659-663. Shogaki, Y. & K. Makiya. 1970. An improved device for quantitative sampling of mosquito larvae. Jpn. J. Sanit. Zool. 21: 172-179. Snedecor, G. W. & W. G. Cochran. 1989. Statistical methods. Iowa State University Press, Ames. Walton, W. E., E. T. Schreiber & M. S. Mulla. 1990. Distribution of Culex tarsalis larvae in a freshwater marsh in Orange County, California. J. Am. Mosq. Control Assoc. 6: 539-543. Weber, R. G. 1985. An aquatic light trap for possible use in mosquito larvae surveillance. Proc. N.J. Mosq. Control Assoc. 72: 122-125. Received for publication 26 August 1991; accepted 14 April 1992.
Downloaded from http://jme.oxfordjournals.org/ by guest on May 20, 2016
Lisa Fry, Department of Entomology, University of California, Riverside, provided greenhouse space for this study. In addition, the authors thank M. S. Mulla, also of the Department of Entomology, for his critical reading of the manuscript.
Vol. 29, no. 5
