Increasing Horse Fly (Diptera: Tabanidae) Catch in Canopy Traps by ...

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Increasing Horse Fly (Diptera: Tabanidae) Catch in Canopy Traps by Reducing Ultraviolet Light Reflectance LAWRENCE J. HRIBAR, DANIEL J. LEPRINCE, AND LANE D. FOIL Department of Entomology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803

J. Med. Entomol. 28(6): 874-877 (1991) ABSTRACT Application of UV Killer, a commercially available product which reduced ultraviolet reflectance from cloth fabrics, increased the catch of tabanids in canopy traps by 24% and in CO2-baited traps by 30%. Catch decreased as ultraviolet reflectance increased during the experiment. KEY WORDS

Insecta, Tabanidae, ultraviolet reflectance, canopy trap design

ULTRAVIOLET (UV) LIGHT, either direct or reflect-

ed, attracts many insect species (Menzel 1979). For example, UV reflectance patterns on flowers are visible to Hymenoptera, and these patterns may be used by insects to locate food (Daumer 1958). Anthony (1959) collected 23 species of Tabanidae in a UV trap; the majority of the flies that were attracted to UV light were males. However, Allen & Stoffolano (1986a) used various pigments to show that substrates with low UV reflectance attracted more host-seeking female Tabanus nigrovittatus Macquart than did those with higher UV reflectance. Certain vertebrate game species (e.g., deer) also have been reported to detect reflected UV (Kroll 1991), and a commercial product, UV Killer, has been introduced to reduce UV reflectance from hunting clothes. The identity of the primary UVabsorbing pigments in UV Killer is proprietary information and is unknown to the authors. UV brighteners are used with dyes during the manufacturing process of cloth and are present in most laundry detergents (Mandile 1990). Because UV reflectance affects horse fly host-seeking behavior (Allen & Stoffolano 1986a), the effect of UV Killer on the catch of tabanids in canopy traps was investigated. Materials and Methods This experiment was conducted at the Thistlethwaite Wildlife Management Area (WMA) [30°39'N, 92°00'W], «10 km north of the town of Washington, St. Landry Parish, La. On 12 June 1990, two clusters of four canopy traps each were placed 3.4 km apart on the grounds of the WMA. Each of the four sides of the canopy traps was made from two panels; a lower panel of black poplin cloth and an upper panel of nylon screen. The poplin of two traps per cluster was sprayed with

one bottle («532 ml) of UV Killer (Atsko, Orangeburg, S.C.), each according to label instructions. All traps were baited with « 5 kg of dry ice suspended in black muslin bags, except for 6 d when the traps were run without dry ice. Traps were baited between 1000 and 1200 hours (CDST) for 21 d between 12 June and 13 July 1990, and flies were removed «24 h later. Differences between treated and untreated traps were tested for traps pooled over clusters. Comparisons were made between baited and unbaited, treated traps. Finally, data for baited and unbaited traps were pooled by treatment. There is ample evidence that carbon dioxide bait increases the effectiveness of canopy traps (Roberts 1976, Leprince & Jolicoeur 1986, Leprince 1989, Leprince & Bigras-Poulin 1990), so interactions between CO2 bait and UV Killer were examined. Data were transformed by X' = (X + 3/8)1'2 (Kihlberg et al. 1972) and were subjected to analysis of variance by the GLM procedure (SAS Institute 1985). Differences between main effects were compared by orthogonal contrasts. Changes in numbers of flies captured over time by treated and untreated, baited traps were examined by regression analysis (SAS Institute 1985). Regressions were compared by a t test of the slopes at the 0.05 level of significance (Zar 1984). Results are reported as backtransformed mean number of flies per trap per day. Diversity of catch was also investigated. Shannon diversity indices were calculated for all bait-treatment combinations. Differences between Shannon diversity indices were compared by Hutcheson's two-tailed f-test (Hutcheson 1970) at the 0.05 level of significance between treated and untreated traps with CO2 and between treated and untreated traps without CO2. After the conclusion of the trapping study, changes in UV reflectance of the treated poplin material caused by weathering effects were ex-

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HRIBAR ET AL.: HORSE FLIES IN ULTRAVIOLET LIGHT

amined. A swatch of fabric (60 by 60 cm) was pinned to a canopy trap at the WMA. A subsample of fabric was removed before treatment. The remainder of the fabric was treated with UV Killer, and another subsample was removed immediately after the fabric had dried. Subsamples were taken weekly for 4 wk. All subsamples were wrapped in aluminum foil and returned to the laboratory. A Perkin-Elmer LS-5B luminescence fluorospectrometer was used to detect changes in UV reflectance. Fluorospectrometer readings were compared with the weekly total catch of flies in treated, baited traps by correlation analysis. Results and Discussion A total of 12,288 flies in five genera were collected: Chrysops spp., Chlorotabanus crepuscularis (Bequaert), Leucotabanus annulatus (Say), Tabanus americanus Forster, T. atratus F., T. equalis Hine, T. fuscicostatus Hine, T. limbatinevris Macquart, T. lineola F., T. molestus Say, T. pallidescens Philip, T. proximus Walker, T. trimaculatus Palisot de Beauvois, T. turbidus Wiedemann, T. wilsoni Pechuman, and Whitneyomyia beatifica atricorpus Philip. T. fuscicostatus (63%) and T. lineola (16.8%) were the species most commonly collected. Analysis of variance revealed that differences between traps were attributable to baiting with CO2 (F = 49.83; df = 1, 216; P < 0.0001) and treatment with UV Killer (F = 6.10; df = 1, 216; P < 0.01). There was no significant treatment x baiting interaction (F = 1.97; df = 1, 216; P > 0.1). When all traps were considered together by treatment without regard to carbon dioxide bait, treated traps captured 1.24 times more total flies than did untreated traps (60.1 versus 48.6 flies per trap per day, F = 5.09; df = 1, 216; P < 0.02). Traps that were treated with UV Killer and baited with CO2 collected 1.30 times as many flies as did traps that were baited only (78.4 versus 60.4fliesper trap per day (F = 4.35; df = 1, 216; P < 0.03)). The number of flies captured per trap per day by treated traps (Y = 256.55 - 7.88X, df = 19VR2 = 0.689, P < 0.0001) and untreated traps (Y = 120.20 - 2.79X, df = 19, R2 = 0.508, P < 0.0004) decreased as a function of time (Fig. 1). The slopes of these regressions were different (t = 237.84, df = 36, P < 0.001), indicating that catch size decreased more rapidly in treated than untreated traps. The greatest difference in the number of flies captured per day in treated, baited traps and untreated, baited traps was observed before day 19. After this time, there were only slight differences in numbers of flies collected, and on some days, untreated traps actually collected more flies than treated traps. Treatment of canopy traps with UV Killer did not affect catch diversity between baited traps (t = 0.86, df = 733, P > 0.05) or unbaited traps (t =

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0.28, df = 733, P > 0.05). There were differences for individual species catches between treated and untreated traps. There was a 4-fold difference in the number of T. fuscicostatus captured, a 12-fold difference in catch of T. limbatinevris, and a 23fold difference in the catch of T. lineola. However, the different responses of these species did not significantly change the diversity of catch. Treatment of the poplin fabric decreased reflectance from 0.85 units of fluorescence pretreatment to 0.17 units of fluorescence immediately after treatment with UV Killer. However, fluorescence increased over time: 1 wk, 0.18; 2 wk, 0.28; 3 wk, 0.49; and 4 wk, 0.60. These readings were correlated inversely with weekly total catch of flies in treated, baited traps (r = —0.89). Although no causeand-effect relationship can be inferred from this correlation, the catch of flies did decrease as UV reflectance increased over the experimental period. Some horse flies are known to have two maxima of sensitivity to light, one in the ultraviolet and the other in the blue-green; e.g., Hybomitra ciureai (Seguy) (reported as H. schineri Lyneborg) and T. bromius L. (Mazokhin-Porshnyakov et al. 1975), and T. nigrovittatus (Allen & Stoffolano 1986a). Allen & Stoffolano (1986a) found that surfaces with high UV reflectance were avoided by T. nigrovittatus, and that the majority of flies were captured when reflectance of UV was only 8%. MazokhinPorshnyakov (1969) noted that the sun was the only major source of UV in nature; it was speculated that high UV reflectance indicated "room to fly" and that low UV reflectance indicated "presence of an object." If an object contrasts sufficiently with its background, horse flies may be prone to attack it (Allen & Stoffolano 1986b,c). In our study, traps that were treated with UV Killer and baited with dry ice captured the most flies. Although the overall catch increased only by a factor of 1.3, on individual days there was as much as a 7-fold difference between treated and untreated baited traps (Fig. 1). Most of the difference was observed in the first 2 wk after treatment. During the 27-d experiment, the baited, treated traps caught more horse flies than the baited, untreated traps on 15 occasions, whereas the converse occurred on only five occasions. Four of the five times that the untreated traps caught more flies occurred after day 19. Based upon current understanding of tabanid host-seeking behavior, the reduced differences between treated and untreated traps in the latter part of the experiment could be attributed to a reduction of the differences in the UV reflectance relative to background (Allen & Stoffolano 1986a). In this study, we made no attempt to determine whether or not variation occurred in UV reflection among the trap sites. Rain fell on only 2 d during the experiment: 6.33 mm fell on 3 July (day 22) and 15.21 mm on 5 July (day 24). Therefore, thefluctuationsin tabanid catch were not attributable to rainfall. When baited and unbaited traps were pooled,

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Experiment Day Fig. 1. Mean catch in CO2-baited canopy traps regressed as a function of time after treatment or no treatment with UV Killer. traps treated with UV Killer collected more flies than did untreated traps. Using UV Killer in conjunction with carbon dioxide bait results in a greater number of flies captured per day per trap. If large numbers of flies must be field-collected (e.g., during studies of disease transmission, population dynamics, or physiology), the use of compounds to reduce trap UV reflectance could reduce significantly the amount of time or number of traps required to obtain a suitable number of flies. The traps used in this study were already highly effective for trapping tabanids, perhaps because the black portion of these traps has low UV reflectance. Therefore, the increase in catch attributed to UV Killer emphasizes the importance of UV reflectance in tabanid host-seeking behavior. Acknowledgment We thank the staff of the Louisiana Department of Wildlife and Fisheries, District 6, and the Thistlethwaite heirs for permitting the use of the facilities at the Thistlethwaite Wildlife Management area. We thank Kurt von Besser (Atsko, Orangeburg, S.C.) for furnishing the UV Killer used in this study. Bob Talmadge (Department of Zoology & Physiology, Louisiana State University) assisted with fluorospectroscopy. Eric Chris, Douglas Coleman, Jennifer Font, Keith Middlebrook, Robert Myers, Andrew Pecquet, Curtis Pool, and Philip Say provided technical assistance. This study was supported in part by USDA grant 89-34103-4251 and has been ap-

proved for publication by the director of the Louisiana Agriculture Experiment Station as manuscript number 90-17-4539.

References Cited Allen S. A. & J. G. Stoffolano, Jr. 1986a. The effects of hue and intensity on visual attraction of adult Tabanus nigrovittatus (Diptera: Tabanidae). J. Med. Entomol. 23: 83-91. 1986b. Effects of background and contrast on visual attraction and orientation of Tabanus nigrovittatus (Diptera: Tabanidae). Environ. Entomol. 15: 689694. 1986c. The importance of pattern in visual attraction of Tabanus nigrovittatus Macquart (Diptera: Tabanidae). Can. J. Zool. 64: 2273-2278. Anthony, D. W. 1959. Tabanidae attracted to an ultraviolet light trap. Fla. Entomol. 43: 77-80. Daumer, K. 1958. Blumenfarben, wie sie die Bienen sehen. Z. Vgl. Physiol. 41: 49-110. Hutcheson, K. 1970. A test for comparing diversities based on the Shannon formula. J. Theor. Biol. 29: 151-154. Kihlberg, J. K., J. H. Herson, & W. E. Schulz. 1972. Square root transformation revisited. J. R. Stat. Soc. Ser. C. Appl. Stat. 21: 76-81. Kroll, J. C. 1991. A practical guide to producing and harvesting white-tailed deer. Steven F. Austin University Press, Nacogdoches, Tex. Leprince, D. J. 1989. Gonotrophic status, sperm presence and sugar feeding patterns in southwestern Que-

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bee tabanid populations. J. Am. Mosq. Control Assoc. 5: 383-386. Leprince, D. J. & M. Bigras-Poulin. 1990. Gonotrophic status, follicular development, sperm presence, and sugar feeding patterns in Hybomitra lasiophthalma (Macquart) populations (Diptera: Tabanidae). J. Med. Entomol. 27: 31-35. Leprince, D. J. & P. Jolicoeur. 1986. Response to carbon dioxide of Tabanus quinquevittatus Wiedemann females (Diptera: Tabanidae) in relation to relative abundance, parity, follicle development, and sperm and fructose presence. Can. Entomol. 118: 1273-1277. Mandile, T. 1990. Now they see you . . . now they don't. Outdoor Life July 1990. pp. 80-90. Mazokhin-Porshnyakov, G. A. 1969. Insect vision. Plenum, New York. Mazokhin-Porshnyakov, C. A., A. D. Cherkasov, O. V.

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Burakova & T. M. Vishnevskaya. 1975. On the color vision of Tabanidae (Diptera). Zool. Zh. 54: 1574-1576 (In Russian, English summary). Menzel, R. 1979. Spectral sensitivity and color vision in invertebrates, pp. 501-580. In H. Autrum [ed.], Handbook of sensory physiology, vol. 7, no. 6A. Springer, New York. Roberts, R. H. 1976. The comparative efficiency of six trap types for the collection of Tabanidae (Diptera). Mosq. News 36: 530-535. SAS Institute. 1985. SAS users guide: statistics, version 5 ed. SAS Institute, Cary, N.C. Zar, J. H. 1984. Biostatistical analysis, 2nd ed. Prentice Hall, Englewood Cliffs, N.J. Received for publication 15 January 1991; accepted 29 May 1991.