Ke Zhang1, Heqing Huang2, Ran Zhou1, Boru Zhang3, Chen Wang4, Make Ente5, Boling Li6, Dong Zhang1, Kai Li7. 1. Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China. 2. Chongqing Academy of Environmental Science, Chongqing, 401147, China. 3. Qinhuangdao Forestry Bureau, Qinhuangdao, 066004, Hebei, China. 4. Mt. Kalamaili Ungulate Nature Reserve, Changji, 381100, Xinjiang, China. 5. Xinjiang Research Centre for Breeding Przewalski's Horse, Urumqi, 831700, Xinjiang, China. 6. China National Environment Monitoring Centre, Beijing, 100012, China. 7. Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China. likai_sino@sina.com.
Abstract
BACKGROUND: The departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period. Gasterophilus pecorum is the dominant bot fly species in the desert steppe of the Kalamaili Nature Reserve (KNR) of northwest China as a result of its particular biological characteristics. The population dynamics of G. pecorum were studied to elucidate the population development of this species in the arid desert steppe. METHODS: Larvae in the freshly excreted feces of tracked Przewalski's horses (Equus przewalskii) were collected and recorded. The larval pupation experiments were carried out under natural conditions. RESULTS: There was a positive correlation between the survival rate and the number of larvae expelled (r = 0.630, p < 0.01); the correlation indicated that the species had characteristic peaks of occurrence. The main periods during which mature larvae were expelled in the feces were from early April to early May (peak I) and from mid-August to early September (peak II); the larval population curve showed a sudden increase and gradual decrease at both peaks. Under the higher temperatures of peak II, the adults developing from the larvae had a higher survival rate, higher pupation rate, higher emergence rate and shorter eclosion period than those developing from peak I larvae. Although G. pecorum has only one generation per year, its occurrence peaked twice annually, i.e. the studied population has a bimodal distribution, which doubles parasitic pressure on the local host. This phenomenon is very rarely recorded in studies on insect life history, and especially in those on parasite epidemiology. CONCLUSION: The period during which G. pecorum larvae are naturally expelled from the host exceeds 7 months in KNR, which indicates that there is potentially a long period during which hosts can become infected with this parasite. The phenomenon of two annual peaks of larvae expelled in feces is important as it provides one explanation for the high rate of equine myiasis in KNR.
BACKGROUND: The departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period. Gasterophilus pecorum is the dominant bot fly species in the desert steppe of the Kalamaili Nature Reserve (KNR) of northwest China as a result of its particular biological characteristics. The population dynamics of G. pecorum were studied to elucidate the population development of this species in the arid desert steppe. METHODS: Larvae in the freshly excreted feces of tracked Przewalski's horses (Equus przewalskii) were collected and recorded. The larval pupation experiments were carried out under natural conditions. RESULTS: There was a positive correlation between the survival rate and the number of larvae expelled (r = 0.630, p < 0.01); the correlation indicated that the species had characteristic peaks of occurrence. The main periods during which mature larvae were expelled in the feces were from early April to early May (peak I) and from mid-August to early September (peak II); the larval population curve showed a sudden increase and gradual decrease at both peaks. Under the higher temperatures of peak II, the adults developing from the larvae had a higher survival rate, higher pupation rate, higher emergence rate and shorter eclosion period than those developing from peak I larvae. Although G. pecorum has only one generation per year, its occurrence peaked twice annually, i.e. the studied population has a bimodal distribution, which doubles parasitic pressure on the local host. This phenomenon is very rarely recorded in studies on insect life history, and especially in those on parasite epidemiology. CONCLUSION: The period during which G. pecorum larvae are naturally expelled from the host exceeds 7 months in KNR, which indicates that there is potentially a long period during which hosts can become infected with this parasite. The phenomenon of two annual peaks of larvae expelled in feces is important as it provides one explanation for the high rate of equinemyiasis in KNR.