Oviposition Habits of Simulium kawamurae (Diptera: Simuliidae), with Reference to Seasonal Changes in Body Size and Fecundity MINORU BABAi Division of Medical Zoology, Medical College of Oita, Hazama, Oita 879-55, Japan
KEY WORDS Insecta, Simulium kawamurae, oviposition habits, body size
BLACK FLIES are distributed widely from mountain to lowland areas, and segregate their preimaginal habitats among species. Knowledge of their oviposition ecology is essential, not only for understanding the mechanisms of habitat segregation, but also for planning population control methods. The oviposition habits of Japanese black flies have been studied infrequently except for Simulium aokii (Takahasi) (Ogata 1954) and Prosimulium kiotoense Shiraki (Baba & Takaoka 1991). Selection of the type and site of oviposition, which must differ among species, will affect directly the survival of eggs and subsequent stages, because preimaginal simuliids begin to develop at or near the site of oviposition. In this article, oviposition site selection and egg-laying habits of Simulium kawamurae Matsumura were studied together with seasonal changes in body size and the number of ovarioles of females. This multivoltine species breeds in the most swiftly flowing sections of mountain streams. Although its seasonal population trend is unknown, larvae and pupae are found throughout the year and five generations per year are expected in southwestern Japan (Anonymous 1955; unpublished observation). S. kawamurae is taxonomically very close to S.japonicum Matsumura, a known human-biter and pest of domestic animals (Ogata 1955, Ono 1970, Takaoka 1977). The adult females of both species are mor1 Current address: Kitakyushu Museum of Natural History, Yahatahigashiku, Kitakyushu 805, Japan.
phologically indistinguishable except by differences in the pharyngeal armature (Anonymous 1955). Because the biting habits of S. kawamurae have not been reported, it is possible that this species has been mixed with S. japonicum where populations are sympatric. Materials and Methods Field studies were made at Tsuchiiwa (32° 50' N 131° 25' E, 350-370 m above sea level) at the upper reaches of the Okutake River, a tributary of the Ono River, Oita Prefecture, Kyushu Island, Japan (Fig. 1). Oviposition was observed at two sites. Site A was on a tributary of the Okutake River ~5 m wide, which consisted of a series of rapids and small pools. The stream bed was rocks, pebbles, or sandy soil. Vegetation of the stream side was well developed and overhung the water. Site B was on the main Okutake River, 5-20 m wide, with substrata of unbroken or large pieces of rock outcrop. These two sites were ==100 m apart. Observations for 2—4 d were made bimonthly between May and October 1988 at site A, and between October 1988 and April 1989 at site B. The number of females swarming at the oviposition site was counted, and illumination was recorded at time intervals of 30-, 15-, or 5-min duration, selecting the shorter intervals during active oviposition. Air temperature was measured at irregular intervals. Pupae and pupal exuviae were collected six times at site A between June and October and
0022-2585/92/0603-0610S02.00/0 © 1992 Entomological Society of America
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J. Med. Entomol. 29(4): 603-610 (1992) ABSTRACT Oviposition habits and seasonal changes in wing length, head width, and number of ovarioles of Simulium kawamurae Matsumura were investigated in Kyushu Island, Japan. Gravid flies swarmed over turbulent water and laid eggs on rock surfaces in the splash zone. Large, irregular egg masses often resulted from the mass oviposition by many females within the same small area. Oviposition occurred at dusk during springsummer, shifting to earlier periods during autumn—winter. Fecundity increased linearly as a function of body size (i.e., both with the cube of wing length and of head width, showing a better fit with the latter). Spring flies had a larger mean body size and fecundity than both summer and autumn flies. Winter flies had wings as long as spring flies, but their head widths and fecundity were comparable to summer-autumn individuals. This indicated seasonal variation in the relative proportion of body structures.
604
Vol. 29, no. 4
JOURNAL OF MEDICAL ENTOMOLOGY
measured to the nearest 0.01 mm by using calipers or an ocular micrometer.
Results
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
Species Composition. In total, 386 and 178 pupae collected at sites A and B, respectively, were identified to species (Fig. 1). At site A, S. rufibasis Brunetti was dominant (69.8%), followed by S. japonicum (24.4%) and S. suzukii Rubtsov (4.7%). S. kawamurae (0.5%) was a minor species at this site, and S. subcostatum (Takahasi) (0.3%) and S. aokii (0.3%) were collected sporadically. In contrast, there were only two species, S. japonicum and S. kawamurae, at site B and the latter included 94.4% of the pupae collected. Larvae were reared successfully from eggs of three of eight females collected at site A during May 1988, and from those of 2 of 16 flies captured at site B during April 1989. They were identified as S. kawamurae based on the boot-shaped cocoon and six short and widely spread pupal gill filaments. Oviposition Behavior. Three intensely used Species \ oviposition sites were recognized, one at site A composition and two at site B (Ba and Bb). The latter two sites were =7 m apart. Many gravid females aggreFig. 1. Map of the study area showing oviposition gated at the "white" turbulent water (oviposition sites (A, B) and species composition of pupae, j , Sim- swarm). Females landed on rock surfaces in the ulium japonicum; k, S. kawamurae; r, S. rufibasis; sz, splash zone, and selected appropriate oviposiS. suzukii; sb, S. subcostatum; a, S. aokii. Location of the study area on Kyushu Island, Japan, is shown as a tion sites that were protected from direct splash (i.e., shallow concavities and sheltered bases of solid circle on the inset. ridges on the rock surface). Flies repeated flying, landing, searching, and ovipositing, because they were often disturbed by spray during the four times at site B between August and Decem- course of this sequence. Eggs were laid individber 1988 to determine the species composition, ually on the rock surface from the water line to 60 because S. kawamurae and S. japonicum oc- cm above it without a consistent pattern, often curred sympatrically in the study area and were tightly adhering to one another by a gelatinous easily distinguishable as pupae. Collections matrix. Large egg masses frequently were were made within =50 m (site A) or —10 m (site formed by mass oviposition of many females. For B) downstream from the oviposition site. example, =450 cm2 of rock surface was covered Gravid females were captured at oviposition with newly laid eggs on the evening of 27 April sites by a sweep net and allowed to lay eggs in 1989. Assuming that an egg batch deposited by a polystyrene tubes (1.5 by 10.7 cm), each contain- female covered 0.25 cm2 (5 by 5 mm), the numing a strip of paper and a small amount of water. ber of participants was estimated as 1,800 feEggs were incubated and some of the hatched males. larvae were reared by the stir-bar system (Baba & Eggs were whitish in appearance immediately Takaoka 1989) for species identification. Twenty after oviposition and tanned in 12 h. Eggs were eggs were measured to the nearest 1 (xm with the subtriangular in shape in lateral view, and averaid of an ocular micrometer (OSM-D2, Olym- aged 292 ± 7.8 fim long by 166 ± 6.9 /xm wide pus). (x ± SD, n = 20). The number of ovarioles was counted in feOviposition Activity. Oviposition activity durmales that laid eggs in the laboratory or emerged ing June at site A typically increased after 1900 from field-collected pupae during May 1988 and hours when illumination decreased to
KEY WORDS Insecta, Simulium kawamurae, oviposition habits, body size
BLACK FLIES are distributed widely from mountain to lowland areas, and segregate their preimaginal habitats among species. Knowledge of their oviposition ecology is essential, not only for understanding the mechanisms of habitat segregation, but also for planning population control methods. The oviposition habits of Japanese black flies have been studied infrequently except for Simulium aokii (Takahasi) (Ogata 1954) and Prosimulium kiotoense Shiraki (Baba & Takaoka 1991). Selection of the type and site of oviposition, which must differ among species, will affect directly the survival of eggs and subsequent stages, because preimaginal simuliids begin to develop at or near the site of oviposition. In this article, oviposition site selection and egg-laying habits of Simulium kawamurae Matsumura were studied together with seasonal changes in body size and the number of ovarioles of females. This multivoltine species breeds in the most swiftly flowing sections of mountain streams. Although its seasonal population trend is unknown, larvae and pupae are found throughout the year and five generations per year are expected in southwestern Japan (Anonymous 1955; unpublished observation). S. kawamurae is taxonomically very close to S.japonicum Matsumura, a known human-biter and pest of domestic animals (Ogata 1955, Ono 1970, Takaoka 1977). The adult females of both species are mor1 Current address: Kitakyushu Museum of Natural History, Yahatahigashiku, Kitakyushu 805, Japan.
phologically indistinguishable except by differences in the pharyngeal armature (Anonymous 1955). Because the biting habits of S. kawamurae have not been reported, it is possible that this species has been mixed with S. japonicum where populations are sympatric. Materials and Methods Field studies were made at Tsuchiiwa (32° 50' N 131° 25' E, 350-370 m above sea level) at the upper reaches of the Okutake River, a tributary of the Ono River, Oita Prefecture, Kyushu Island, Japan (Fig. 1). Oviposition was observed at two sites. Site A was on a tributary of the Okutake River ~5 m wide, which consisted of a series of rapids and small pools. The stream bed was rocks, pebbles, or sandy soil. Vegetation of the stream side was well developed and overhung the water. Site B was on the main Okutake River, 5-20 m wide, with substrata of unbroken or large pieces of rock outcrop. These two sites were ==100 m apart. Observations for 2—4 d were made bimonthly between May and October 1988 at site A, and between October 1988 and April 1989 at site B. The number of females swarming at the oviposition site was counted, and illumination was recorded at time intervals of 30-, 15-, or 5-min duration, selecting the shorter intervals during active oviposition. Air temperature was measured at irregular intervals. Pupae and pupal exuviae were collected six times at site A between June and October and
0022-2585/92/0603-0610S02.00/0 © 1992 Entomological Society of America
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
J. Med. Entomol. 29(4): 603-610 (1992) ABSTRACT Oviposition habits and seasonal changes in wing length, head width, and number of ovarioles of Simulium kawamurae Matsumura were investigated in Kyushu Island, Japan. Gravid flies swarmed over turbulent water and laid eggs on rock surfaces in the splash zone. Large, irregular egg masses often resulted from the mass oviposition by many females within the same small area. Oviposition occurred at dusk during springsummer, shifting to earlier periods during autumn—winter. Fecundity increased linearly as a function of body size (i.e., both with the cube of wing length and of head width, showing a better fit with the latter). Spring flies had a larger mean body size and fecundity than both summer and autumn flies. Winter flies had wings as long as spring flies, but their head widths and fecundity were comparable to summer-autumn individuals. This indicated seasonal variation in the relative proportion of body structures.
604
Vol. 29, no. 4
JOURNAL OF MEDICAL ENTOMOLOGY
measured to the nearest 0.01 mm by using calipers or an ocular micrometer.
Results
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
Species Composition. In total, 386 and 178 pupae collected at sites A and B, respectively, were identified to species (Fig. 1). At site A, S. rufibasis Brunetti was dominant (69.8%), followed by S. japonicum (24.4%) and S. suzukii Rubtsov (4.7%). S. kawamurae (0.5%) was a minor species at this site, and S. subcostatum (Takahasi) (0.3%) and S. aokii (0.3%) were collected sporadically. In contrast, there were only two species, S. japonicum and S. kawamurae, at site B and the latter included 94.4% of the pupae collected. Larvae were reared successfully from eggs of three of eight females collected at site A during May 1988, and from those of 2 of 16 flies captured at site B during April 1989. They were identified as S. kawamurae based on the boot-shaped cocoon and six short and widely spread pupal gill filaments. Oviposition Behavior. Three intensely used Species \ oviposition sites were recognized, one at site A composition and two at site B (Ba and Bb). The latter two sites were =7 m apart. Many gravid females aggreFig. 1. Map of the study area showing oviposition gated at the "white" turbulent water (oviposition sites (A, B) and species composition of pupae, j , Sim- swarm). Females landed on rock surfaces in the ulium japonicum; k, S. kawamurae; r, S. rufibasis; sz, splash zone, and selected appropriate oviposiS. suzukii; sb, S. subcostatum; a, S. aokii. Location of the study area on Kyushu Island, Japan, is shown as a tion sites that were protected from direct splash (i.e., shallow concavities and sheltered bases of solid circle on the inset. ridges on the rock surface). Flies repeated flying, landing, searching, and ovipositing, because they were often disturbed by spray during the four times at site B between August and Decem- course of this sequence. Eggs were laid individber 1988 to determine the species composition, ually on the rock surface from the water line to 60 because S. kawamurae and S. japonicum oc- cm above it without a consistent pattern, often curred sympatrically in the study area and were tightly adhering to one another by a gelatinous easily distinguishable as pupae. Collections matrix. Large egg masses frequently were were made within =50 m (site A) or —10 m (site formed by mass oviposition of many females. For B) downstream from the oviposition site. example, =450 cm2 of rock surface was covered Gravid females were captured at oviposition with newly laid eggs on the evening of 27 April sites by a sweep net and allowed to lay eggs in 1989. Assuming that an egg batch deposited by a polystyrene tubes (1.5 by 10.7 cm), each contain- female covered 0.25 cm2 (5 by 5 mm), the numing a strip of paper and a small amount of water. ber of participants was estimated as 1,800 feEggs were incubated and some of the hatched males. larvae were reared by the stir-bar system (Baba & Eggs were whitish in appearance immediately Takaoka 1989) for species identification. Twenty after oviposition and tanned in 12 h. Eggs were eggs were measured to the nearest 1 (xm with the subtriangular in shape in lateral view, and averaid of an ocular micrometer (OSM-D2, Olym- aged 292 ± 7.8 fim long by 166 ± 6.9 /xm wide pus). (x ± SD, n = 20). The number of ovarioles was counted in feOviposition Activity. Oviposition activity durmales that laid eggs in the laboratory or emerged ing June at site A typically increased after 1900 from field-collected pupae during May 1988 and hours when illumination decreased to
