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Newly emerged nulliparous Culicoides imicola Kieffer (Diptera: Ceratopogonidae) with pigmented abdomen
Veterinary Parasitology 160 (2009) 356–358
Contents lists available at ScienceDirect
Veterinary Parasitology journal homepage: www.elsevier.com/locate/vetpar
Short communication
Newly emerged nulliparous Culicoides imicola Kieffer (Diptera: Ceratopogonidae) with pigmented abdomen Yehuda Braverman a, Kosta Mumcuoglu b,* a b
Koret School of Veterinary Medicine, Hebrew University, Rehovot, Israel Department of Parasitology, Hebrew University–Hadassah Medical School, POB 12272, Jerusalem 91120, Israel
A R T I C L E I N F O
A B S T R A C T
Article history: Received 24 September 2008 Received in revised form 17 November 2008 Accepted 18 November 2008
The method of segregating nulliparous and parous females of Culicoides spp. based on the presence of burgundy-red pigment inside the abdominal wall of parous Culicoides midges, is used worldwide. Out of 320 females of Culicoides imicola trapped by emergence traps, set over an artificial breeding site for 10 and 24 days, 73 (22.8%) showed a red-pigmentation despite the fact that they were nulliparous. This finding indicated that 23% of the ‘‘parous’’ females that are examined for the presence of arboviruses and other pathogens or for agegrading purposes, are actually old nulliparous females, which had no chance of acquiring pathogens. This bias in parous rate distorts upward the calculation of vectorial capacity. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Pigmentation Nulliparous Parous Culicoides imicola Breeding
1. Introduction Dyce’s (1969) method of segregating nulliparous (females, which do not have follicular relics and did not develop egg) and parous (females, which have follicular relics and did lay at least one batch of eggs) of Culicoides spp. based on the presence of burgundy-red pigment inside the abdomen wall of parous midges is used worldwide, especially in selecting female specimens for arbovirus or any other pathogen isolation and/or identification (Nelson and Scrivani, 1972; Mullens et al., 2006; Lysk, 2007). This method is also used for the analysis of population age structure (Braveman et al., 1985; Venter and Hermanides, 2006). Linely and Braverman (1984, 1986) assumed that the pigments are ommochromes synthesized inside the epithelial tissue during egg development as local waste products. The pigment accumulates with age and completion of gonotrophic cycles. There is however, a wide range of pigment intensity in the various species and within individuals of different ages of the same species. In some
* Corresponding author. Tel.: +972 2 675 8093; fax: +972 2 675 7425. E-mail address: [email protected] (K. Mumcuoglu). 0304-4017/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2008.11.016
species with dark abdomens, e.g., Culicoides circumscriptus Kieffer, Culicoides newsteadi Austen and Culicoides univitattus Vimmer the pigment is weakly visible. According to Dyce (1969) his method of age grading Culicoides is not applicable to blood-engorged females when the gut contents darken the abdomen or when females show advanced follicular development. When Dyce (1969) tested his method on females of Culicoides variipennis occidentalis Wirth and Jones in California, found only one empty unpigmented and nulliparous female, while the remainder were strongly pigmented and prior to dissection were classified as empty and parous. On dissection, however, all 26 were found to be nulliparous. The aim of this study was to determine the rate of pigmented females of Culicoides imicola that hatched inside an emergence trap, situated over an artificial breeding site, despite the fact that these nulliparous females had no chance to take a blood meal and lay eggs. 2. Materials and methods An artificial breeding site for C. imicola exposed entirely to the summer sun (Fig. 1) was formed at the yard edge of a cowshed at the Kimron Veterinary Institute, Bet Dagan
Y. Braverman, K. Mumcuoglu / Veterinary Parasitology 160 (2009) 356–358
357
Table 1 Culicoides imicola trapped in emergence traps situated over an artificial breeding site. Date of trapping
No. (%) of C. imicola in the total catch
No. of C. imicola males
No. of C. imicola females
No. (%) of pigmented nulliparous females of C. imicola
24.06–04.07 04.07–29.07
266 (33) 336 (77)
93 189
173 147
62 (35.8%) 11 (7.5%)
Total
602 (38)
282
320
73 (22.8%)
(328000 N 348 500 E) at the coastal plain near Tel Aviv. Israel’s climate is Mediterranean in the north and arid in the south. In summer the entire area is dominated by a subtropical high that brings cloudless skies and no precipitation. Average summer temperature at the coastal plain in August is 24–26 8C with 70% relative humidity (Orni and Efrat, 1973). The water source was a water faucet installed on the fence that was adjusted to drip slightly. During the 4 months of experiment (June–September) the crumbled dusty dry cow manure became covered with algae and initially became a fertile breeding site for C. imicola. Later (August, September) it turned to a puddle and was too wet for C. imicola to breed and species such as C. circumscriptus became dominant. Two emergence traps, previously described by Braverman (1970) were used in June and July for collecting the adult C. imicola, while a third one was added during August and September. The design of the emergence trap and its submerged position inside the breeding site, does not enable escape of the emerged insects or infiltration of insects from the outside. The hatched and emerging midges were placed in 70% ethanol and glycerin (1:1, v/v) inside the jars of the emergence traps. A dissecting microscope was used to identify and segregate the pigmented and non-pigmented specimens. 3. Results and discussion Table 1 shows that out of 320 trapped C. imicola females 73 (22.8%) were pigmented nulliparous. No pigmented females of other Culicoides spp. were collected in the
emergence traps. The most suitable conditions for breeding C. imicola prevailed between 4 July and 29 July, i.e., rotting organic matter, saturated with water. Other Culicoides spp. that bred in sites, which turned to be too wet for C. imicola were C. circumscriptus, Culicoides puncticollis Becker, Culicoides cataneii Clastrier and Culicoides schultzei gp. These species seem to not compete on the breeding site with C. imicola, as they breed in the parts covered with water layers. As the emergence traps were not emptied daily, it could be assumed that some of the females that were not attracted by the light of the collecting jar, were held for 10 and 24 days, and survived for a few days inside the emergence traps due to the high humidity, continued to develop their eggs to the stage when the ommochromes were deposited in the epithelium and the red pigment seen in their abdomens was the result of aging inside the emergence trap. Hundreds of samples of C. imicola breeding site material that were taken during many years for breeding in the laboratory, where the emerged adults were collected within 24–48 h, pigmented specimens could never be observed (unpublished results). This fact supports the argument that pigmentation in nulliparous C. imicola occurs only in old females. These finding are in agreement with the results of Dyce (1969) about pigmented nulliparous Culicoides victoriae Macfie and Culicoides marmoratus Skuse in Australia and C. variipennis occidentalis in California. Both studies showed that a portion of the females, which according to Dyce’s (1969) method, were categorized as ‘‘parous’’ were actually pigmented old nulliparous. The epidemiological implication of this finding is that the calculations of parous rate for C. imicola are over estimated by 23% and it reflects on the age structure grade and life expectancy estimations that in turn distort the calculations on the vectorial capacity. Accordingly, a correction factor for calculation of parous rate in C. imicola should be implemented. Despite these findings, as there are no convenient reliable alternative methods for age-grading, and there is no information on pigmentation of nulliparous females on most of the vector species (except C. imicola) the method of Dyce is still a valuable tool for separating parous from nulliparous females without dissecting and should in the meantime be used for selecting females for pathogen isolation and/or identification, as well as for age-grading. References
Fig. 1. Artificial breeding site for Culicoides imicola with two emergence traps.
Braverman, Y., 1970. An improved emergence trap for Culicoides. J. Econ. Entomol. 63, 1674–1675. Braveman, Y., Linley, J.R., Marcus, R., Frish, K., 1985. Seasonal survival and expectation of infective life of Culicoides spp. (Diptera Ceratopogoni-
358
Y. Braverman, K. Mumcuoglu / Veterinary Parasitology 160 (2009) 356–358
dae) in Israel with implications for bluetongue virus transmission, and a comparison of the parous rate in C. imicola from Israel and Zimbabwe. J. Med. Entomol. 22, 476–484. Dyce, A.L., 1969. The recognition of nulliparous and parous Culicoides (Diptera: Ceratopogonidae) without dissection. J. Aust. Entomol. Soc. 8, 11–15. Linely, J.R., Braverman, Y., 1984. The tergal pigmentation patterns of Culicoides variipennis and Culicoides furens (Diptera: Ceratopogonidae). J. Med. Entomol. 21, 636–647. Linely, J.R., Braverman, Y., 1986. The lateral abdominal pigmentation in Culicoides variipennis and Culicoides furens (Diptera: Ceratopogonidae): quantitative measurement of its relationship to age and oogenesis. J. Med. Entomol. 23, 51–63.
Lysk, T.J., 2007. Seasonal abundance, parity, and survival of adult Culicoides sonorensis (Diptera: Ceratopogonidae) in southern Alberta, Canada. J. Med. Entomol. 44, 959–969. Mullens, B.A., Cardona, C.J., McClellan, L., Szijj, C.E., Owen, J.P., 2006. Culicoides bottimeri as a vector of Haemoproteus lophortyx to quail in California, USA. Vet. Parasitol. 140, 35–43. Nelson, R.L., Scrivani, R.P., 1972. Isolations of arboviruses from parous midges of the Culicoides variipennis complex, and parous rates in biting populations. J. Med. Entomol. 9, 277–281. Orni, E., Efrat, E., 1973. Geography of Israel, 3rd ed. Israel Universities Press. Venter, G.J., Hermanides, K.G., 2006. Comparison of black and white light for collecting Culicoides imicola and other livestock associated Culicoides species in South Africa. Vet. Parasitol. 142, 383–385.
Contents lists available at ScienceDirect
Veterinary Parasitology journal homepage: www.elsevier.com/locate/vetpar
Short communication
Newly emerged nulliparous Culicoides imicola Kieffer (Diptera: Ceratopogonidae) with pigmented abdomen Yehuda Braverman a, Kosta Mumcuoglu b,* a b
Koret School of Veterinary Medicine, Hebrew University, Rehovot, Israel Department of Parasitology, Hebrew University–Hadassah Medical School, POB 12272, Jerusalem 91120, Israel
A R T I C L E I N F O
A B S T R A C T
Article history: Received 24 September 2008 Received in revised form 17 November 2008 Accepted 18 November 2008
The method of segregating nulliparous and parous females of Culicoides spp. based on the presence of burgundy-red pigment inside the abdominal wall of parous Culicoides midges, is used worldwide. Out of 320 females of Culicoides imicola trapped by emergence traps, set over an artificial breeding site for 10 and 24 days, 73 (22.8%) showed a red-pigmentation despite the fact that they were nulliparous. This finding indicated that 23% of the ‘‘parous’’ females that are examined for the presence of arboviruses and other pathogens or for agegrading purposes, are actually old nulliparous females, which had no chance of acquiring pathogens. This bias in parous rate distorts upward the calculation of vectorial capacity. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Pigmentation Nulliparous Parous Culicoides imicola Breeding
1. Introduction Dyce’s (1969) method of segregating nulliparous (females, which do not have follicular relics and did not develop egg) and parous (females, which have follicular relics and did lay at least one batch of eggs) of Culicoides spp. based on the presence of burgundy-red pigment inside the abdomen wall of parous midges is used worldwide, especially in selecting female specimens for arbovirus or any other pathogen isolation and/or identification (Nelson and Scrivani, 1972; Mullens et al., 2006; Lysk, 2007). This method is also used for the analysis of population age structure (Braveman et al., 1985; Venter and Hermanides, 2006). Linely and Braverman (1984, 1986) assumed that the pigments are ommochromes synthesized inside the epithelial tissue during egg development as local waste products. The pigment accumulates with age and completion of gonotrophic cycles. There is however, a wide range of pigment intensity in the various species and within individuals of different ages of the same species. In some
* Corresponding author. Tel.: +972 2 675 8093; fax: +972 2 675 7425. E-mail address: [email protected] (K. Mumcuoglu). 0304-4017/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2008.11.016
species with dark abdomens, e.g., Culicoides circumscriptus Kieffer, Culicoides newsteadi Austen and Culicoides univitattus Vimmer the pigment is weakly visible. According to Dyce (1969) his method of age grading Culicoides is not applicable to blood-engorged females when the gut contents darken the abdomen or when females show advanced follicular development. When Dyce (1969) tested his method on females of Culicoides variipennis occidentalis Wirth and Jones in California, found only one empty unpigmented and nulliparous female, while the remainder were strongly pigmented and prior to dissection were classified as empty and parous. On dissection, however, all 26 were found to be nulliparous. The aim of this study was to determine the rate of pigmented females of Culicoides imicola that hatched inside an emergence trap, situated over an artificial breeding site, despite the fact that these nulliparous females had no chance to take a blood meal and lay eggs. 2. Materials and methods An artificial breeding site for C. imicola exposed entirely to the summer sun (Fig. 1) was formed at the yard edge of a cowshed at the Kimron Veterinary Institute, Bet Dagan
Y. Braverman, K. Mumcuoglu / Veterinary Parasitology 160 (2009) 356–358
357
Table 1 Culicoides imicola trapped in emergence traps situated over an artificial breeding site. Date of trapping
No. (%) of C. imicola in the total catch
No. of C. imicola males
No. of C. imicola females
No. (%) of pigmented nulliparous females of C. imicola
24.06–04.07 04.07–29.07
266 (33) 336 (77)
93 189
173 147
62 (35.8%) 11 (7.5%)
Total
602 (38)
282
320
73 (22.8%)
(328000 N 348 500 E) at the coastal plain near Tel Aviv. Israel’s climate is Mediterranean in the north and arid in the south. In summer the entire area is dominated by a subtropical high that brings cloudless skies and no precipitation. Average summer temperature at the coastal plain in August is 24–26 8C with 70% relative humidity (Orni and Efrat, 1973). The water source was a water faucet installed on the fence that was adjusted to drip slightly. During the 4 months of experiment (June–September) the crumbled dusty dry cow manure became covered with algae and initially became a fertile breeding site for C. imicola. Later (August, September) it turned to a puddle and was too wet for C. imicola to breed and species such as C. circumscriptus became dominant. Two emergence traps, previously described by Braverman (1970) were used in June and July for collecting the adult C. imicola, while a third one was added during August and September. The design of the emergence trap and its submerged position inside the breeding site, does not enable escape of the emerged insects or infiltration of insects from the outside. The hatched and emerging midges were placed in 70% ethanol and glycerin (1:1, v/v) inside the jars of the emergence traps. A dissecting microscope was used to identify and segregate the pigmented and non-pigmented specimens. 3. Results and discussion Table 1 shows that out of 320 trapped C. imicola females 73 (22.8%) were pigmented nulliparous. No pigmented females of other Culicoides spp. were collected in the
emergence traps. The most suitable conditions for breeding C. imicola prevailed between 4 July and 29 July, i.e., rotting organic matter, saturated with water. Other Culicoides spp. that bred in sites, which turned to be too wet for C. imicola were C. circumscriptus, Culicoides puncticollis Becker, Culicoides cataneii Clastrier and Culicoides schultzei gp. These species seem to not compete on the breeding site with C. imicola, as they breed in the parts covered with water layers. As the emergence traps were not emptied daily, it could be assumed that some of the females that were not attracted by the light of the collecting jar, were held for 10 and 24 days, and survived for a few days inside the emergence traps due to the high humidity, continued to develop their eggs to the stage when the ommochromes were deposited in the epithelium and the red pigment seen in their abdomens was the result of aging inside the emergence trap. Hundreds of samples of C. imicola breeding site material that were taken during many years for breeding in the laboratory, where the emerged adults were collected within 24–48 h, pigmented specimens could never be observed (unpublished results). This fact supports the argument that pigmentation in nulliparous C. imicola occurs only in old females. These finding are in agreement with the results of Dyce (1969) about pigmented nulliparous Culicoides victoriae Macfie and Culicoides marmoratus Skuse in Australia and C. variipennis occidentalis in California. Both studies showed that a portion of the females, which according to Dyce’s (1969) method, were categorized as ‘‘parous’’ were actually pigmented old nulliparous. The epidemiological implication of this finding is that the calculations of parous rate for C. imicola are over estimated by 23% and it reflects on the age structure grade and life expectancy estimations that in turn distort the calculations on the vectorial capacity. Accordingly, a correction factor for calculation of parous rate in C. imicola should be implemented. Despite these findings, as there are no convenient reliable alternative methods for age-grading, and there is no information on pigmentation of nulliparous females on most of the vector species (except C. imicola) the method of Dyce is still a valuable tool for separating parous from nulliparous females without dissecting and should in the meantime be used for selecting females for pathogen isolation and/or identification, as well as for age-grading. References
Fig. 1. Artificial breeding site for Culicoides imicola with two emergence traps.
Braverman, Y., 1970. An improved emergence trap for Culicoides. J. Econ. Entomol. 63, 1674–1675. Braveman, Y., Linley, J.R., Marcus, R., Frish, K., 1985. Seasonal survival and expectation of infective life of Culicoides spp. (Diptera Ceratopogoni-
358
Y. Braverman, K. Mumcuoglu / Veterinary Parasitology 160 (2009) 356–358
dae) in Israel with implications for bluetongue virus transmission, and a comparison of the parous rate in C. imicola from Israel and Zimbabwe. J. Med. Entomol. 22, 476–484. Dyce, A.L., 1969. The recognition of nulliparous and parous Culicoides (Diptera: Ceratopogonidae) without dissection. J. Aust. Entomol. Soc. 8, 11–15. Linely, J.R., Braverman, Y., 1984. The tergal pigmentation patterns of Culicoides variipennis and Culicoides furens (Diptera: Ceratopogonidae). J. Med. Entomol. 21, 636–647. Linely, J.R., Braverman, Y., 1986. The lateral abdominal pigmentation in Culicoides variipennis and Culicoides furens (Diptera: Ceratopogonidae): quantitative measurement of its relationship to age and oogenesis. J. Med. Entomol. 23, 51–63.
Lysk, T.J., 2007. Seasonal abundance, parity, and survival of adult Culicoides sonorensis (Diptera: Ceratopogonidae) in southern Alberta, Canada. J. Med. Entomol. 44, 959–969. Mullens, B.A., Cardona, C.J., McClellan, L., Szijj, C.E., Owen, J.P., 2006. Culicoides bottimeri as a vector of Haemoproteus lophortyx to quail in California, USA. Vet. Parasitol. 140, 35–43. Nelson, R.L., Scrivani, R.P., 1972. Isolations of arboviruses from parous midges of the Culicoides variipennis complex, and parous rates in biting populations. J. Med. Entomol. 9, 277–281. Orni, E., Efrat, E., 1973. Geography of Israel, 3rd ed. Israel Universities Press. Venter, G.J., Hermanides, K.G., 2006. Comparison of black and white light for collecting Culicoides imicola and other livestock associated Culicoides species in South Africa. Vet. Parasitol. 142, 383–385.