SHORT COMMUNICATION
Similar Reproductive Status and Body Size of Horse Flies (Diptera: Tabanidae) Attracted to Carbon Dioxide-Baited Canopy Traps and a Jersey Bullock D. J. LEPRINCE, L. J. HRIBAR,1 AND L. D. FOIL Department of Entomology, 402 Life Sciences Building, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803
KEY WORDS Tabanus spp., attractants, reproductive status
to be major pests of ungulates worldwide. Livestock production losses from tabanid attack are attributed to annoyance and blood losses (Drummond 1987) and transmission of pathogenic agents (Foil 1989). The use of silhouette traps (Thorsteinson et al. 1964, Catts 1970) rather than animal baits is more economical and has facilitated studies on the temporal and spatial distribution of tabanid populations. Quantity and proportions of Tabanus species collected from cattle and caught in carbon dioxide-baited canopy traps has been observed to differ in Louisiana (L.D.F., unpublished data). These differences could be attributed to interspecific variations in the response of tabanids to chemical (i.e., carbon dioxide) (Roberts 1971, Leprince 1989) and visual attractants, efficiency of the trapping technique, or intraspecific variation in the response of tabanids to trapping methods as influenced by the reproductive status of individuals flies. The reproductive status of tabanids caught in canopy traps alone was not different from flies caught in canopy traps baited with carbon dioxide (Leprince & Jolicoeur 1986; Leprince & Bigras-Poulin 1988, 1990). However, similar studies comparing flies caught in traps and attracted to animals have not been conducted. The objective of our study was to determine if wing length, parity, stage of follicular
TABANIDS ARE CONSIDERED
1 Current address: Florida Medical Entomology Laboratory, 200 9th St. SE, Vero Beach, FL 32962.
development in terminal follicles, sperm presence, prevalence of individuals retaining eggs, and the number of eggs retained by female tabanids differed between flies collected from Jersey bullocks and from canopy traps baited with carbon dioxide. Materials and Methods Sampling Site and Collection Procedures. Collections were made daily from 12 to 15 June 1990 at different sites on the Thistlethwaite Wildlife Management Area (WMA) located in central Louisiana (Foil et al. 1989). Female horse flies were collected every 3-4 h from one stanchioned Jersey bullock and from four to eight canopy traps (Hribar et al. 1991) baited with 4-7 kg of dry ice. Traps were placed >50 m apart along a transect parallel to the wood's edge; eight traps were used on the first day and four traps were used on the next 3 d. One stanchioned Jersey bullock was placed >50 m from the end of the trap line for 3-4 h, then rotated to the other end of the trap line for an equal period of time. Flies were not collected during the first 10 min after arrival at the bullock bait to reduce the bias of flies attracted by the locomotion of the animal and research personnel. Flies were caught individually from the bullock in 30 ml transparent plastic cups, while blood-feeding, then stored in an ice chest. These flies were sorted to species and preserved in vials containing a
0022-2585/92/1056-1059$02.00/0 © 1992 Entomological Society of America
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
J. Med. Entomol. 29(6): 1056-1059 (1992) ABSTRACT The reproductive status and body size of four Tabanus species collected from canopy traps baited with carbon dioxide and from a Jersey bullock were compared. Parity rates, sperm prevalence, stage of follicular development in terminal follicles of parous females, prevalence of females retaining eggs, average number of eggs retained in parous flies, and the body size of parous females did not differ significantly between sampling methods. Based on the presence of nulliparous host-seeking flies, Tabanus pallidescens Philip and T. wilsoni Pechuman can be added to the list of tabanids found to be anautogenous.
November 1992
LEPRINCE ET AL.: TABANID REPRODUCTIVE STATUS AND ATTRACTANTS
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Table 1. Summary of statistics for parous Tabanus spp. Species
n
%FD
%EGG
No. EGGS ± SD
n
T. fuscicostatus T. lineola T. pallidescens T. wilsoni
137 253 259 259
31.3 25.7 27.8 31.3
10.2 19.0 25.9 15.1
10.1 ± 27.2 4.35 ± 9.61 23.7 ± 50.4 3.12 ± 3.79
92 105 84 177
Wings ± SD 8.90 ± 9.71 ± 9.65 ± 9.60 ±
0.40 0.58 0.51 0.43
FD, flies with stage of follicular development equal to or greater than stage II; EGG, flies retaining eggs; EGGS, eggs retained; wing, mean wing length (mm).
Results During the first 2 d of the experiment, 4,077 flies were collected, 89.2% in carbon dioxidebaited canopy traps and 10.8% from the bullock. The percentage species composition of flies collected from traps and the bullock was 55.1 and 31.1% for Tabanus fuscicostatus Hine, 30.3 and 24.5% for Tabanus lineola F., 10.9 and 19.5% for Tabanus pallidescens Philip, and 3.7 and 24.9% for T. wilsoni, respectively. The relative percentages of the four species were significantly different between collection methods (y2 = 365.7, df = 3, P < 0.05). The proportion of T. fuscicostatus
was higher in trap catches, whereas T. wilsoni was more prevalent on the bullock. In total, 1,184 flies belonging to T. fuscicostatus (22.9%), T. lineola F. (22.1%), T. pallidescens Philip (27.6%), and T. wilsoni (27.4%) were dissected; 55.6% of the dissected flies were collected from the bullock. Parous flies represented 77% of all flies dissected, and >98% of the flies dissected were inseminated. Sperm presence was similar in nulliparous and parous females (data not shown). No statistical differences in parity rates or insemination of flies collected in traps and on the bullock were detected within the four species ( / ^ 1.45, df = 1, P > 0.05). Parity rates and percentage of inseminated females were 50.1 and 98.5% for T. fuscicostatus, 96.6 and 98.5% for T. lineola, 79.2 and 99.4% for T. pallidescens, and 79.9 and 99.4% for T. wilsoni, respectively. Stage II follicular development was recorded for 99% of the nulliparous flies and 29% of the parous flies. No nulliparous flies had terminal follicles beyond stage II. Because of the higher prevalence of parous flies and the greater variation in the stages of follicular development in parous flies, ^ tests were performed on parous flies of the different Tabanus species. The proportion of parous females with follicular development at stage II and beyond did not vary significantly within species between flies collected from traps and bullocks (P > 0.05) (Table 1). Similarly, the proportion of parous females retaining eggs and the number of eggs retained did not vary significantly within species between collection methods (P > 0.05) (Table 1). The wing length of 458 parous flies collected from traps and bullocks did not vary significantly within species (t test, P > 0.05) (Table 1).
Discussion The relative abundance of tabanid species differed between carbon dioxide-baited canopy traps and the bovine host, but that variation was unrelated to intraspecific differences in the reproductive status of the flies. Discrepancies in the relative abundance of horse fly species between trapping methods could be attributed to
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
10% formalin solution within 2 h of their collection. Flies were removed from canopy traps every 2 h, placed in plastic bags (Nasco WhirlPak; Lenexa, Kansas), and preserved in 10% formalin solution. Reproductive Status and Body Size. Dissection procedures and reproductive categories for parity, stage of follicular development in terminal follicles, sperm presence, and egg presence have been described by Leprince & Lewis (1986). Wing length, an index of body size, was measured for females that had undamaged wings using the technique described by Leprince & Bigras-Poulin (1988). All Tabanus wilsoni Pechuman specimens collected during this study were dissected. For the other three species, a similar number of flies per treatment was dissected by day until the number of flies exceeded 125 per treatment. Statistical Analyses. Chi-square tests and 2-tailed Fisher's exact test were applied to 2 x 2 and 2 x 4 contingency tables to assess the homogeneity of the proportions obtained. Fisher's exact test (two-tailed) was used to analyze sperm prevalence data because of small cell frequencies. The number of eggs retained by parous flies did not have a normal distribution, and the nonparametric Wilcoxon rank sum test was used to compare number of eggs retained by treatments within species using the SAS procedure NPAR1WAY (SAS Institute 1988). A t test (SAS Institute 1988) was used to compare average wing length of different tabanids species between treatments.
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baited canopy traps and the Jersey bullock must be accounted for by parameters other than the reproductive status of the flies. Further research is needed to determine the extent to which visual and olfactory components of carbon dioxidebaited canopy traps and bovine hosts contribute to the attractancy to host-seeking tabanids. Acknowledgments We are grateful to Kerney Sonnier and his staff (Louisiana Department of Wildlife and Fisheries, District 6) and the Thistlethwaite heirs for allowing us to use the facilities at the Thistlethwaite Wildlife Management Area. We also thank E. Chris, D. Coleman, A. Pecquet, and P. Roach for their technical assistance. This paper was supported in part by USDA grant 89-34103-4251 and approved for publication by the Director, Louisiana Agricultural Experiment Station, as manuscript 9217-6008.
References Cited Catts, E. P. 1970. A canopy trap for collecting Tabanidae. Mosq. News 30: 472-474. Drummond, R. O. 1987. Economic aspects of ectoparasite of cattle in North America, pp. 9-24. In W.D.H. Leaning & J. Guerrero [eds], The economic impact of parasitism in cattle. 23rd World Veterinary Congress, 19 August 1987, Montreal, Quebec, Canada. Foil, L. D. 1989. Tabanids as vectors of disease agents. Parasitol. Today 5: 88-96. Foil, L. D., D. J. Leprince & G. E. Church. 1989. Changes in the parity rate of Tabanus fuscicostatus (Diptera: Tabanidae) populations associated with controlling available hosts. J. Med. Entomol. 28: 663-667. Hribar, L. J., D. J. LePrince & L. D. Foil. 1991. Design for a canopy trap for collecting horse flies (Diptera: Tabanidae). J. Am. Mosq. Control Assoc. 7: 657-659. LePrince, D. J. 1989. Gonotrophic status, sperm presence and sugar feeding patterns in southwestern Quebec tabanid (Diptera) populations. J. Am. Mosq. Control Assoc. 5: 383-386. LePrince, D. J. & M. Bigras-Poulin. 1988. Seasonal variation in body size, parity, and fecundity of hostseeking Tabanus quinquevittatus females (Diptera: Tabanidae). J. Med. Entomol. 25: 105-110. 1990. Gonotrophic status, follicular development, sperm presence, and sugar-feeding patterns in a Hybomitra lasiophthalma population (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. LePrince, D. J. & D. J. Lewis. 1986. Sperm presence and sugar feeding patterns in nulliparous and parous Tabanus quinquevittatus Wiedemann (Diptera: Tabanidae) in southwestern Quebec. Ann. Entomol. Soc. Am. 79: 912-917. LePrince, D. J. & A. Maire. 1990. Parity, stage of follicular development, and sperm presence in
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
interspecific variations in the response to chemical and visual cues of the trapping device influencing the trapping radius. The efficiency of the trapping technique in terms of number and diversity of flies attracted versus number of flies collected may also contribute to the disparity in relative abundance. The experiment was conducted when populations of T. lineola, T. pallidescens, and T. tvilsoni were decreasing, whereas populations of T.fuscicostatus were increasing (Leprince et al. 1991), perhaps accounting for high parity rates in the first three species and low parity rates in T. fuscicostatus. No host-seeking nulliparous flies had terminal follicles beyond stage II, indicating ovarian diapause which is characteristic of anautogenous flies (Spielman 1971). Anautogeny has been reported for T. fuscicostatus and T. lineola in North America (Foil et al. 1989, Leprince 1989), but this is the first report of anautogeny for T. pallidescens and T. wilsoni. Sperm prevalence was high (96%) among flies collected, indicating that mating occurs before host-seeking in Louisiana. In a previous study in the same area, sperm prevalence in T. fuscicostatus females was 98.0%, and no differences were detected between nulliparous and parous flies (Foil et al. 1989). Sperm prevalence in horse flies in Louisiana is higher than that reported for more temperate and subarctic areas in North America (Leprince & Lewis 1986, Leprince 1989, Leprince & Bigras-Poulin 1990, Leprince & Maire 1990), suggesting that climatic conditions may be more conducive to pairing and insemination in subtropical areas. The prevalence of females retaining eggs (10%) in T. fuscicostatus was similar (10%) to a previous report for that species in the same area (Foil et al. 1989). More than 25% of the parous flies of T. pallidescens retained eggs, which is a higher proportion than previously reported for any other tabanid species (Leprince & Lewis 1986, Leprince 1989, Leprince & BigrasPoulin 1990, Leprince & Maire 1990). Egg retention was not a reliable estimate of parity for tabanids. The reproductive status and wing length of flies did not vary between the two collection methods. In previous studies, the reproductive status (parity rates, prevalence of sperm and fructose, stage of terminal follicle development within nullipars or pars) of Tabanus quinquevittatus Wiedemann and Hybomitra lasiophthalma (Macquart) did not vary significantly between unbaited and carbon dioxide-baited canopy traps (Leprince & Jolicoeur 1986, Leprince & BigrasPoulin 1990). Response to carbon dioxide also was unrelated to the wing length of T. quinquevittatus females (Leprince & Bigras-Poulin 1988). Differences in the relative abundance of tabanid species collected from carbon dioxide-
Vol. 29, no. 6
November 1992
LEPRINCE ET AL.: TABANID REPRODUCTIVE STATUS AND ATTRACTANTS
hemiarctic host-seeking Hybomitra populations (Diptera: Tabanidae). J. Med. Entomol. 27: 835838. LePrince, D. J., L. J. Hribar, R. T. Bessin & L. D. Foil. 1991. Seasonal patterns of abundance of horse flies (Diptera: Tabanidae) from two locations in southern Louisiana. Proc. LA Acad. Sci. 54: 10-18. Roberts, R. H. 1971. Effects of the amount of CO 2 on the collection of Tabanidae in Malaise traps. Mosq. News 31: 150-154.
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SAS Institute. 1988. SAS/STAT user's guide, release 6.03 ed. SAS Institute, Cary, NC. Spielman, A. 1971. Bionomics of autogenous mosquitoes. Annu. Rev. Entomol. 16: 231-248. Thorsteinson, A. J., G. B. Bracken & W. Hanec. 1964. The Manitoba horse fly trap. Can. Entomol. 96: 166. Received for publication 19 February 1992; accepted 22 June 1992.
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
Similar Reproductive Status and Body Size of Horse Flies (Diptera: Tabanidae) Attracted to Carbon Dioxide-Baited Canopy Traps and a Jersey Bullock D. J. LEPRINCE, L. J. HRIBAR,1 AND L. D. FOIL Department of Entomology, 402 Life Sciences Building, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803
KEY WORDS Tabanus spp., attractants, reproductive status
to be major pests of ungulates worldwide. Livestock production losses from tabanid attack are attributed to annoyance and blood losses (Drummond 1987) and transmission of pathogenic agents (Foil 1989). The use of silhouette traps (Thorsteinson et al. 1964, Catts 1970) rather than animal baits is more economical and has facilitated studies on the temporal and spatial distribution of tabanid populations. Quantity and proportions of Tabanus species collected from cattle and caught in carbon dioxide-baited canopy traps has been observed to differ in Louisiana (L.D.F., unpublished data). These differences could be attributed to interspecific variations in the response of tabanids to chemical (i.e., carbon dioxide) (Roberts 1971, Leprince 1989) and visual attractants, efficiency of the trapping technique, or intraspecific variation in the response of tabanids to trapping methods as influenced by the reproductive status of individuals flies. The reproductive status of tabanids caught in canopy traps alone was not different from flies caught in canopy traps baited with carbon dioxide (Leprince & Jolicoeur 1986; Leprince & Bigras-Poulin 1988, 1990). However, similar studies comparing flies caught in traps and attracted to animals have not been conducted. The objective of our study was to determine if wing length, parity, stage of follicular
TABANIDS ARE CONSIDERED
1 Current address: Florida Medical Entomology Laboratory, 200 9th St. SE, Vero Beach, FL 32962.
development in terminal follicles, sperm presence, prevalence of individuals retaining eggs, and the number of eggs retained by female tabanids differed between flies collected from Jersey bullocks and from canopy traps baited with carbon dioxide. Materials and Methods Sampling Site and Collection Procedures. Collections were made daily from 12 to 15 June 1990 at different sites on the Thistlethwaite Wildlife Management Area (WMA) located in central Louisiana (Foil et al. 1989). Female horse flies were collected every 3-4 h from one stanchioned Jersey bullock and from four to eight canopy traps (Hribar et al. 1991) baited with 4-7 kg of dry ice. Traps were placed >50 m apart along a transect parallel to the wood's edge; eight traps were used on the first day and four traps were used on the next 3 d. One stanchioned Jersey bullock was placed >50 m from the end of the trap line for 3-4 h, then rotated to the other end of the trap line for an equal period of time. Flies were not collected during the first 10 min after arrival at the bullock bait to reduce the bias of flies attracted by the locomotion of the animal and research personnel. Flies were caught individually from the bullock in 30 ml transparent plastic cups, while blood-feeding, then stored in an ice chest. These flies were sorted to species and preserved in vials containing a
0022-2585/92/1056-1059$02.00/0 © 1992 Entomological Society of America
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
J. Med. Entomol. 29(6): 1056-1059 (1992) ABSTRACT The reproductive status and body size of four Tabanus species collected from canopy traps baited with carbon dioxide and from a Jersey bullock were compared. Parity rates, sperm prevalence, stage of follicular development in terminal follicles of parous females, prevalence of females retaining eggs, average number of eggs retained in parous flies, and the body size of parous females did not differ significantly between sampling methods. Based on the presence of nulliparous host-seeking flies, Tabanus pallidescens Philip and T. wilsoni Pechuman can be added to the list of tabanids found to be anautogenous.
November 1992
LEPRINCE ET AL.: TABANID REPRODUCTIVE STATUS AND ATTRACTANTS
1057
Table 1. Summary of statistics for parous Tabanus spp. Species
n
%FD
%EGG
No. EGGS ± SD
n
T. fuscicostatus T. lineola T. pallidescens T. wilsoni
137 253 259 259
31.3 25.7 27.8 31.3
10.2 19.0 25.9 15.1
10.1 ± 27.2 4.35 ± 9.61 23.7 ± 50.4 3.12 ± 3.79
92 105 84 177
Wings ± SD 8.90 ± 9.71 ± 9.65 ± 9.60 ±
0.40 0.58 0.51 0.43
FD, flies with stage of follicular development equal to or greater than stage II; EGG, flies retaining eggs; EGGS, eggs retained; wing, mean wing length (mm).
Results During the first 2 d of the experiment, 4,077 flies were collected, 89.2% in carbon dioxidebaited canopy traps and 10.8% from the bullock. The percentage species composition of flies collected from traps and the bullock was 55.1 and 31.1% for Tabanus fuscicostatus Hine, 30.3 and 24.5% for Tabanus lineola F., 10.9 and 19.5% for Tabanus pallidescens Philip, and 3.7 and 24.9% for T. wilsoni, respectively. The relative percentages of the four species were significantly different between collection methods (y2 = 365.7, df = 3, P < 0.05). The proportion of T. fuscicostatus
was higher in trap catches, whereas T. wilsoni was more prevalent on the bullock. In total, 1,184 flies belonging to T. fuscicostatus (22.9%), T. lineola F. (22.1%), T. pallidescens Philip (27.6%), and T. wilsoni (27.4%) were dissected; 55.6% of the dissected flies were collected from the bullock. Parous flies represented 77% of all flies dissected, and >98% of the flies dissected were inseminated. Sperm presence was similar in nulliparous and parous females (data not shown). No statistical differences in parity rates or insemination of flies collected in traps and on the bullock were detected within the four species ( / ^ 1.45, df = 1, P > 0.05). Parity rates and percentage of inseminated females were 50.1 and 98.5% for T. fuscicostatus, 96.6 and 98.5% for T. lineola, 79.2 and 99.4% for T. pallidescens, and 79.9 and 99.4% for T. wilsoni, respectively. Stage II follicular development was recorded for 99% of the nulliparous flies and 29% of the parous flies. No nulliparous flies had terminal follicles beyond stage II. Because of the higher prevalence of parous flies and the greater variation in the stages of follicular development in parous flies, ^ tests were performed on parous flies of the different Tabanus species. The proportion of parous females with follicular development at stage II and beyond did not vary significantly within species between flies collected from traps and bullocks (P > 0.05) (Table 1). Similarly, the proportion of parous females retaining eggs and the number of eggs retained did not vary significantly within species between collection methods (P > 0.05) (Table 1). The wing length of 458 parous flies collected from traps and bullocks did not vary significantly within species (t test, P > 0.05) (Table 1).
Discussion The relative abundance of tabanid species differed between carbon dioxide-baited canopy traps and the bovine host, but that variation was unrelated to intraspecific differences in the reproductive status of the flies. Discrepancies in the relative abundance of horse fly species between trapping methods could be attributed to
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
10% formalin solution within 2 h of their collection. Flies were removed from canopy traps every 2 h, placed in plastic bags (Nasco WhirlPak; Lenexa, Kansas), and preserved in 10% formalin solution. Reproductive Status and Body Size. Dissection procedures and reproductive categories for parity, stage of follicular development in terminal follicles, sperm presence, and egg presence have been described by Leprince & Lewis (1986). Wing length, an index of body size, was measured for females that had undamaged wings using the technique described by Leprince & Bigras-Poulin (1988). All Tabanus wilsoni Pechuman specimens collected during this study were dissected. For the other three species, a similar number of flies per treatment was dissected by day until the number of flies exceeded 125 per treatment. Statistical Analyses. Chi-square tests and 2-tailed Fisher's exact test were applied to 2 x 2 and 2 x 4 contingency tables to assess the homogeneity of the proportions obtained. Fisher's exact test (two-tailed) was used to analyze sperm prevalence data because of small cell frequencies. The number of eggs retained by parous flies did not have a normal distribution, and the nonparametric Wilcoxon rank sum test was used to compare number of eggs retained by treatments within species using the SAS procedure NPAR1WAY (SAS Institute 1988). A t test (SAS Institute 1988) was used to compare average wing length of different tabanids species between treatments.
1058
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baited canopy traps and the Jersey bullock must be accounted for by parameters other than the reproductive status of the flies. Further research is needed to determine the extent to which visual and olfactory components of carbon dioxidebaited canopy traps and bovine hosts contribute to the attractancy to host-seeking tabanids. Acknowledgments We are grateful to Kerney Sonnier and his staff (Louisiana Department of Wildlife and Fisheries, District 6) and the Thistlethwaite heirs for allowing us to use the facilities at the Thistlethwaite Wildlife Management Area. We also thank E. Chris, D. Coleman, A. Pecquet, and P. Roach for their technical assistance. This paper was supported in part by USDA grant 89-34103-4251 and approved for publication by the Director, Louisiana Agricultural Experiment Station, as manuscript 9217-6008.
References Cited Catts, E. P. 1970. A canopy trap for collecting Tabanidae. Mosq. News 30: 472-474. Drummond, R. O. 1987. Economic aspects of ectoparasite of cattle in North America, pp. 9-24. In W.D.H. Leaning & J. Guerrero [eds], The economic impact of parasitism in cattle. 23rd World Veterinary Congress, 19 August 1987, Montreal, Quebec, Canada. Foil, L. D. 1989. Tabanids as vectors of disease agents. Parasitol. Today 5: 88-96. Foil, L. D., D. J. Leprince & G. E. Church. 1989. Changes in the parity rate of Tabanus fuscicostatus (Diptera: Tabanidae) populations associated with controlling available hosts. J. Med. Entomol. 28: 663-667. Hribar, L. J., D. J. LePrince & L. D. Foil. 1991. Design for a canopy trap for collecting horse flies (Diptera: Tabanidae). J. Am. Mosq. Control Assoc. 7: 657-659. LePrince, D. J. 1989. Gonotrophic status, sperm presence and sugar feeding patterns in southwestern Quebec tabanid (Diptera) populations. J. Am. Mosq. Control Assoc. 5: 383-386. LePrince, D. J. & M. Bigras-Poulin. 1988. Seasonal variation in body size, parity, and fecundity of hostseeking Tabanus quinquevittatus females (Diptera: Tabanidae). J. Med. Entomol. 25: 105-110. 1990. Gonotrophic status, follicular development, sperm presence, and sugar-feeding patterns in a Hybomitra lasiophthalma population (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. LePrince, D. J. & D. J. Lewis. 1986. Sperm presence and sugar feeding patterns in nulliparous and parous Tabanus quinquevittatus Wiedemann (Diptera: Tabanidae) in southwestern Quebec. Ann. Entomol. Soc. Am. 79: 912-917. LePrince, D. J. & A. Maire. 1990. Parity, stage of follicular development, and sperm presence in
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
interspecific variations in the response to chemical and visual cues of the trapping device influencing the trapping radius. The efficiency of the trapping technique in terms of number and diversity of flies attracted versus number of flies collected may also contribute to the disparity in relative abundance. The experiment was conducted when populations of T. lineola, T. pallidescens, and T. tvilsoni were decreasing, whereas populations of T.fuscicostatus were increasing (Leprince et al. 1991), perhaps accounting for high parity rates in the first three species and low parity rates in T. fuscicostatus. No host-seeking nulliparous flies had terminal follicles beyond stage II, indicating ovarian diapause which is characteristic of anautogenous flies (Spielman 1971). Anautogeny has been reported for T. fuscicostatus and T. lineola in North America (Foil et al. 1989, Leprince 1989), but this is the first report of anautogeny for T. pallidescens and T. wilsoni. Sperm prevalence was high (96%) among flies collected, indicating that mating occurs before host-seeking in Louisiana. In a previous study in the same area, sperm prevalence in T. fuscicostatus females was 98.0%, and no differences were detected between nulliparous and parous flies (Foil et al. 1989). Sperm prevalence in horse flies in Louisiana is higher than that reported for more temperate and subarctic areas in North America (Leprince & Lewis 1986, Leprince 1989, Leprince & Bigras-Poulin 1990, Leprince & Maire 1990), suggesting that climatic conditions may be more conducive to pairing and insemination in subtropical areas. The prevalence of females retaining eggs (10%) in T. fuscicostatus was similar (10%) to a previous report for that species in the same area (Foil et al. 1989). More than 25% of the parous flies of T. pallidescens retained eggs, which is a higher proportion than previously reported for any other tabanid species (Leprince & Lewis 1986, Leprince 1989, Leprince & BigrasPoulin 1990, Leprince & Maire 1990). Egg retention was not a reliable estimate of parity for tabanids. The reproductive status and wing length of flies did not vary between the two collection methods. In previous studies, the reproductive status (parity rates, prevalence of sperm and fructose, stage of terminal follicle development within nullipars or pars) of Tabanus quinquevittatus Wiedemann and Hybomitra lasiophthalma (Macquart) did not vary significantly between unbaited and carbon dioxide-baited canopy traps (Leprince & Jolicoeur 1986, Leprince & BigrasPoulin 1990). Response to carbon dioxide also was unrelated to the wing length of T. quinquevittatus females (Leprince & Bigras-Poulin 1988). Differences in the relative abundance of tabanid species collected from carbon dioxide-
Vol. 29, no. 6
November 1992
LEPRINCE ET AL.: TABANID REPRODUCTIVE STATUS AND ATTRACTANTS
hemiarctic host-seeking Hybomitra populations (Diptera: Tabanidae). J. Med. Entomol. 27: 835838. LePrince, D. J., L. J. Hribar, R. T. Bessin & L. D. Foil. 1991. Seasonal patterns of abundance of horse flies (Diptera: Tabanidae) from two locations in southern Louisiana. Proc. LA Acad. Sci. 54: 10-18. Roberts, R. H. 1971. Effects of the amount of CO 2 on the collection of Tabanidae in Malaise traps. Mosq. News 31: 150-154.
1059
SAS Institute. 1988. SAS/STAT user's guide, release 6.03 ed. SAS Institute, Cary, NC. Spielman, A. 1971. Bionomics of autogenous mosquitoes. Annu. Rev. Entomol. 16: 231-248. Thorsteinson, A. J., G. B. Bracken & W. Hanec. 1964. The Manitoba horse fly trap. Can. Entomol. 96: 166. Received for publication 19 February 1992; accepted 22 June 1992.
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
