2009 SOUTHEASTERN NATURALIST 8(4):733–738 Comparing Chemiluminescent and LED Light for Trapping Water Mites and Aquatic Insects Andrea J. Radwell1,* and Nicholas B. Camp2 Abstract - This research compared the effectiveness of red, yellow, green, and blue chemiluminescent candles and white light from an LED source in capturing water mites and aquatic insects in a macrophyte bed of a small reservoir. We sought to compare the abundance of organisms captured and to determine whether specific taxa showed a preference for certain colors. A total of 2974 organisms in 19 taxa were collected including 7 water mite genera and 12 other invertebrate taxa. The abundance of Hydrachnida (water mites) in the traps was greater than all other taxa combined. The dominant insect taxa collected were Ephemeroptera and Odonata. No statistically significant inter-taxon preferences for color were found, but overall there was a greater attraction to yellow, green, or white light than to red and blue light. Since white light from the reusable LED source performed as well as yellow or green disposable chemiluminescent candles that are typically used in aquatic traps, submersible LED fl ashlights could be considered a suitable alternative. Introduction Abundant and diverse assemblages of lentic invertebrate species can be found in pools, backwaters, and margins of rivers and streams and in the littoral zone of small lakes and reservoirs. A 1-m2 area of substrate from littoral macrophyte beds in eutrophic lakes may contain as many as 2000 juvenile and adult water mites (Acari: Hydrachnida; Smith et al. 2001). Water mites and insects have a complex ecological relationship that includes parasitism and predation, and together they form one of the most abundant invertebrate groups in lentic habitats. While nets have been effectively used to collect lentic invertebrates, they present certain disadvantages, particularly when macrophyte beds are the habitat of interest. Wading through the sampling area may result in dispersal of organisms and damage to vegetation. Because collection of water mites and early instars of insects requires nets with fine mesh, clogging is often a problem. Samples collected using nets often include substantial amounts of plant material and detritus that make sorting difficult. Light trapping is an alternative that eliminates some limitations of collecting with nets in lentic habitats and can be useful in areas that are not easily accessible. Most studies of the preference of various insect taxa for particular colors in light traps have been done in terrestrial environments. Barker et al. (1997) demonstrated that yellow and white consistently attracted more 1Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701. 234 Sunrise Place, Cabot, AR 72023. *Corresponding author - aradwell@uark.edu. 734 Southeastern Naturalist Vol. 8, No. 4 organisms than darker colors, such as blue, and hypothesized that herbivorous insects are more attracted to yellow because it is the peak reflectance of plants. Yellow was also found to be more attractive to pollen beetles (Nitidulidae; Blight and Smart 1999), and lime green, spring green, and yellow were shown to be most effective in collecting the majority of Bemisia argentifolii Bellows and Perring (Silverleaf Whitefly; Aleyrodidae) and leafhopper species (Cicadellidae) (Chu 2000). White was more attractive to Palpita unionalis (Hübn) (Jasmine Moth; Pyralidae) when compared to yellow (Athanassiou et al. 2004). Research on the effect of color in light-trapping in aquatic habitats is limited. Hungerford et al. (1955) were among the first to report on the effectiveness of submerged light traps, and they established the usefulness of this method for the capture of various freshwater invertebrate taxa. In a comparison of lit and unlit traps, Pieczynski (1962) demonstrated a strong affinity of water mites to light and suggested the usefulness of traps for studying species that are rare but have a strong response to light. Barr (1979) compared dipnets and traps baited with yellow-green luminescent light for trapping water mites and found that light traps often collected more individuals than dipnets, although the choice of yellow-green rather than red or blue was not explained. The utility of submersible light emitting diode (LED) fl ashlights in aquatic light traps has not been reported. The goal of our research was to compare the effectiveness of red, yellow, green, and blue chemiluminescent candles and a LED fl ashlight (white light) in capturing water mites and aquatic insects in a macrophyte bed of a small reservoir. We sought to compare the abundance of organisms captured and to determine whether specific taxa showed a preference for certain colors. Field-site Description The experiment was conducted in Lake Leatherwood, Eureka Springs, Carroll County, AR. Lake Leatherwood is a 34-ha impoundment of Leatherwood Creek completed in 1944 by the Civilian Conservation Corps. A 28-m2 macrophyte bed with a depth of 50 to 82 cm was selected for submersion of light traps. The predominant macrophytes were Potamogeton nodosus Poir. (Pondweed; Potamogetonaceae) and Ceratophyllum demersum L. (Coontail; Ceratophyllaceae). Methods Bioquip™ light traps (model #2821) were positioned at dusk and retrieved at dawn each day for 9 consecutive days (27 Aug–5 Sept 2007). Two Ameriglo ™ chemiluminescent candles of red, yellow, green, or blue were placed in four traps with one color per trap, and a fifth trap contained a submersible Underwater Kinetics™ light emitting diode (LED) fl ashlight (model 09102) powered by two AAA batteries. The traps were placed at least 1 m apart, and 2009 A.J. Radwell and N.B. Camp 735 the position of the colors relative to each other was randomly assigned each day. Water and air temperature were measured each day at dawn. To retrieve each sample, the trap was lifted from the bottom of the lake and placed, while remaining submerged, into a large 250-μm mesh net to prevent fl ushing of organisms back into the lake. The funnels on each side of the trap were removed to wash out organisms while it was in the submerged net. The trap was then removed from the net, and the net was pulled from the water. The contents of the net were placed in a 1-L container of lake water. In the laboratory, each sample was placed in a large white tray and live organisms were collected using a pipette. Water mites were placed in modified Koenike’s solution (50% glycerine, 10% glacial acetic acid, and 40% water), and insects were placed in 70% ethanol. Water mites were identified to genus, and insects were identified to family. One-way ANOVA was used to determine whether there were signifi- cant differences in attraction to red, yellow, green, blue, or white light. The response of all organisms combined and that of major taxa including Hydrachnida, Insecta, Ephemeroptera, Odonata, and the water mite genus Arrenurus were analyzed. When ANOVA results were significant (α = 0.05), least signifi- cant difference tests were used to determine specific differences. Results No spates or other notable weather events occurred during the sampling period. Air temperature was 24 ± 2 ºC and water temperature was 28 ± 1 ºC. The chemiluminescent candles continued to emit light until the traps were retrieved, although the blue candles were nearly extinguished by sunrise. The LED light provided consistent light each night. A total of 2974 organisms were collected representing 7 water mite genera and 12 other invertebrate taxa (Table 1). Water mites were more abundant than insects in the traps, and the water mite genus Arrenurus was the most abundant taxon, accounting for more than half of the total organisms. Baetid mayfl ies were the most common insects. Very high densities of ostracodes, cladocerans, and copepods were present in both the water column and the traps. Since it was not possible to differentiate between those collected from the water column while retrieving the traps and those that had been attracted to the traps, no effort was made to analyze the response of these organisms. In contrast, insects and mites were not apparent in the water column. While some may have been captured in the retrieval process, the assumption was made that their numbers were not large enough to infl uence the outcome of the experiment. Of the 19 taxa, more organisms were attracted to yellow, green, and white light than red or blue light (P < 0.0001, Fig. 1). Water mites were more attracted to yellow, green, and white than red or blue (P = < 0.0001). When data for the predominant water mite Arrenurus were analyzed separately, yellow, green, and white light captured more than red, but only green and white captured more than red or blue (P = 0.0009). Yellow, green, and white 736 Southeastern Naturalist Vol. 8, No. 4 attracted more insects than blue, but only green attracted more than red (P = 0.0058). Ephemeroptera and Odonata, when analyzed separately, did not produce significant results (P = 0.0563 and 0.1816, respectively). Discussion Light-trapping provided a convenient and effective method for obtaining information on the diversity of aquatic organisms in the lentic community of a small reservoir. The study addressed only the response of invertebrate taxa that are attracted to various colors or white light rather than the affinity of various taxa for traps or light in general; thus, the observed community composition may not refl ect the actual composition of the aquatic community. The method was particularly effective for capturing water mites, an invertebrate group that has received relatively less attention than insects in studies of freshwater communities. The response of both water mites and aquatic insects to color was consistent with earlier research on insects in terrestrial ecosystems that found yellow, green, and white to be more attractive than red or blue. Table 1. Total number of organisms by taxon collected from Lake Leatherwood, Carroll County, AR, 27 Aug–5 Sept 2007 in aquatic light traps baited with chemiluminescent candles and LED white light. Order/Family Genus Red Yellow Green Blue White Total Hydrachnida Lebertiidae Lebertia 13 25 46 24 24 132 Limnesiidae Limnesia 10 21 47 11 34 123 Hygrobatidae Atractides 2 3 0 3 2 10 Unionicolidae Neumania 16 82 70 11 34 213 Aturidae Albia 0 1 7 6 6 20 Mideopsidae Mideopsis 15 39 45 23 35 157 Arrenuridae Arrenurus 152 344 421 239 402 1558 Coleoptera Dytiscidae 3 8 18 5 10 44 Diptera Chironomidae 2 4 1 2 7 16 Ephemeroptera Baetidae 22 104 121 23 75 345 Caenidae 17 26 30 13 23 109 Ephemerellidae 5 7 2 1 18 33 Plecoptera Nemouridae 3 2 3 1 2 11 Zygoptera Coenagrionidae 18 4 20 4 16 62 Lestidae 2 1 1 0 4 8 Anisoptera Libellulidae 3 5 6 4 5 23 Gomphidae 10 11 14 7 9 51 Hemiptera Corixidae 1 0 0 2 0 3 Other (Amphipoda) 14 4 17 6 15 56 Total 308 691 869 385 721 2974 2009 A.J. Radwell and N.B. Camp 737 The LED fl ashlight proved as effective as the yellow or green chemiluminescent candles; thus, it could be considered a suitable substitute for disposable candles. The AAA batteries required replacement each day, but Figure 1. Attraction of taxa to aquatic light trap color (ANOVA). Error bars represent 95% confidence intervals. Specific differences were determined using least signifi- cant difference tests when ANOVA was significant (α = 0.05). Results that share the same letter were not found to be significantly different. 738 Southeastern Naturalist Vol. 8, No. 4 rechargeable batteries offer a cost-effective alternative. The fl ashlight used for this experiment was of relatively low intensity, yet it performed well compared to the chemiluminescent candles. Further research is needed to determine whether a LED light source of higher intensity or other sources of light (e.g., halogen or UV light) would be even more effective in attracting invertebrates in aquatic habitats. Acknowledgments We wish to acknowledge contributions to this research from the University of Arkansas, Fayetteville, including the Honors College, for financial and academic support; Jeff Velie, from the Agricultural Statistics Laboratory, for assistance with statistical analyses; and Scott Longing, from Soil, Water and Environmental Science, for his expertise in the taxonomy of insects. Eureka Springs Parks and Recreation provided access to Lake Leatherwood and cooperated in the effort to assure that the study site was not disturbed during the collection period. The willingness of Arthur V. Brown and Janice Hinsey to provide suggestions for improving the manuscript is appreciated. Literature Cited Athanassiou, C.G., N.G. Kavallieratos, and B.E. Mazomenos. 2004. Effect of trap type, trap color, trapping location, and pheromone dispenser on captures of male Palpita unionalis (Lepidoptera: Pyralidae). Journal of Economic Entomology 97(2):321–329. Barker, A.M., K.J. Sanbrooke, and N.J. Aebischer. 1997. The water-trap colour preferences of farmland sawfl ies. Entomologia Experimentalis et Applicata 85(1):83–86. Barr, D. 1979. Water mites (Acari, Parasitengona) sampled with chemiluminescent bait in underwater traps. International Journal of Acarology 5:187–194. Blight, M.M., and L.E. Smart. 1999. Infl uence of visual cues and isothiocyanate lures on capture of the pollen beetle, Meligethes aeneus in field traps. Journal of Chemical Ecology 25(7):1501–1516. Chu, C. 2000. Use of CC traps with different trap base colors for Silverleaf Whitefl ies (Homoptera: Aleyrodidae), thrips (Thysanoptera: Thripidae), and leafhoppers (Homoptera: Cicadellidae). Journal of Economic Entomology 93(4):1329–1337. Hungerford H., P.J. Spangler, and N.A. Walker. 1955. Subaquatic light traps for insects and other animal organisms. Transactions of the Kansas Academy of Science 58(3):387–407. Pieczynski, E. 1962. Notes on the use of light traps for water mites (Hydracarina). 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