Abstract
BackgroundThe 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.MethodsLarvae 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.ResultsThere 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.ConclusionThe 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.Graphical
Highlights
The departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period
The average number of larvae per pile of feces (NL) was 0.35 during the entire investigation period; the highest number was in early April with an average of 1.40, followed by mid-to-late April and mid-to-late August, with averages of 0.79 and 0.84, respectively
There was a positive correlation between the survival rate and the number of larvae (r = 0.630, p < 0.01), i.e. the survival rate of G. pecorum larvae was higher during the two peak periods
Summary
The departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period. Horse stomach bot flies undergo complete metamorphosis; they have four developmental stages, i.e. egg, larva, pupa and adult, one generation per year, and the larvae take 9–10 months to develop in the digestive tract of the host [8]. The larvae develop in the digestive tract of equids until they are mature, leave the host and develop into flies and start a new life cycle. Based on the differences between some recent findings and existing life history records of G. pecorum, a systematic study of the population dynamics and growth of local G. pecorum was carried out in vitro to understand the development of this species in the desert steppe
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