Spatial distribution of Gasterophilus pecorum (Diptera) eggs in the desert steppe of the Kalamaili Nature Reserve (Xinjiang, China)

Background The dominant Gasterophilus species in the desert steppe (Xinjiang, China) Gasterophilus pecorum poses a serious threat to the reintroduced Przewalski’s horses. We investigated the distribution pattern of G. pecorum eggs in June 2017. Methods Two sampling methods, transect and grid, were used, and the results were analyzed via geostatistics by semivariance. The nest quadrat was used to determine the optimal quadrat size. Results Eggs were found in 99 quadrats (63.1%) and 187 clusters (1.5%) of Stipa caucasica on the steppe. The mean oviposition count of a cluster was 3.8 ± 1.6. Three-eggs is the mode of which females oviposit on each ovigerous S. caucasica (22.0%). Semivariogram analysis revealed that the distance of spatial dependence for eggs was 921 m, 1233 m and 1097 m for transect 1, transect 2 and grid methods, respectively, while spatial continuity was 62%, 77% and 57.0% for transect 1, transect 2 and grid, respectively. The eggs showed a patchy, aggregated distribution pattern. This suggested the spherical model is most applicable. The proportion of ovigerous S. caucasica was significantly correlated with the distance from water resources (r = − 0.382, p = 0). Conclusion Our findings indicated that diversification of G. pecorum oviposition was a new adaptative strategy for its survival in the desert steppe ecological niche. This made it more efficient at infecting hosts in the local environment. Areas surrounding water resources, especially around the drinking paths of equids (500 m radius surrounding the water), were concentrated epidemic areas. It is suggested that more attention to be paid to the ecological characteristics of G. pecorum in order to develop control measures that would reduce the infection risk for Przewalski’s horses.

Analysis of volatiles from feces of released Przewalski’s horse (Equus przewalskii) in Gasterophilus pecorum (Diptera: Gasterophilidae) spawning habitat

The absolute dominant species that infests wild population of Przewalski’s horse (Equus przewalskii) is Gasterophilus pecorum, and feces of released Przewalski’s horse, a habitat odor, plays an important role in mating and ovipositing locations of G. pecorum. To screen out unique volatiles for attracting G. pecorum, volatiles from fresh feces of released horses at stages of pre-oviposition (PREO), oviposition (OVIP), and post-oviposition (POSO) of G. pecorum, and feces with three different freshness states (i.e., Fresh, Semi-fresh, and Dry) at OVIP were collected by dynamic headspace adsorption and determined by automatic thermal desorption GC–MS. Results show that there were significant differences in fecal volatiles within both test conditions. Of the five most abundant volatiles from the five individual samples, the most important volatile was ammonium acetate at OVIP/Fresh, followed by acetophenone (Semi-fresh), toluene (PREO, OVIP and POSO), butanoic acid (OVIP and Semi-fresh), acetic acid (PREO, POSO and Semi-fresh), 1,6-octadiene,3,7-dimethyl-,(S)- (PREO, OVIP and POSO), 1,5,9-undecatriene,2,6,10-trimethyl-,(Z)- (PREO and Semi-fresh) and caprolactam (all conditions), which seem to be critical substances in oviposition process of G. pecorum. The findings may be beneficial to development of G. pecorum attractants, facilitating prevention and control of infection by G. pecorum to released Przewalski’s horse.

Effects of Gasterophilus pecorum infestation on the intestinal microbiota of the rewilded Przewalski’s horses in China

Horse botflies have been a threat to the Przewalski’s horses in the Kalamaili Nature Reserve in Xinjiang of China since their reintroduction to the original range. As larvae of these parasites could infest the intestine of a horse for months, they could interact with and alter the structure and composition of its intestinal microbiota, affecting adversely its health. Nonetheless, there are no such studies on the rewilded Przewalski’s horses yet. For the first time, this study characterizes the composition of the intestinal microbiota of 7 rewilded Przewalski’s horses infected severely by Gasterophilus pecorum following and prior to their anthelmintic treatment. Bioinformatics analyses of the sequence data obtained by amplicon high throughput sequencing of bacterial 16S rRNA genes showed that G. pecorum infestation significantly increased the richness of the intestinal microbial community but not its diversity. Firmicutes and Bacteroidetes were found the dominant phyla as in other animals, and the parasitic infestation decreased the F/B ratio largely by over 50%. Large reduction in relative abundances of the two genera Streptococcus and Lactobacillus observed with G. pecorum infestation suggested possible changes in colic and digestion related conditions of the infected horses. Variations on the relative abundance of the genus groups known to be pathogenic or symbiotic showed that adverse impact of the G. pecorum infestation could be associated with reduction of the symbiotic genera Lactobacillus and Bifidobacterium that are probiotics and able to promote immunity against parasitic infection.

The impact of temperature on the life cycle of Gasterophilus pecorum in northwest China

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.

The seasonal abundance and its impact of temperatures on the development of life cycle of G. pecorum in Northwest China

Background: The departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period, and the Gasterophilus pecorum becomes the dominant species in the desert steppe, showing its special biological characteristics. The population dynamics of G. pecorum were studied to reveal the population development rule of G. pecorum in the arid desert steppe. Method: The larvae were collected and recorded in the newly excreted feces by tracking the Przewalski’s horses (Equus przewalskii), meanwhile, the larval pupation experiments were carried out under natural conditions. Results: (a) There was a positive correlation between the survival rate and the number of larvae (r = 0.630, p < 0.01), indicating that the species development had the characteristics of centralized occurrence; (b) The main periods of mature larvae discharge were from early April to early May (peak Ⅰ) and from mid-August to early September (peak II), and the larval population curve showed a sudden spike in increase and gradual decrease at both peaks; under higher temperature, the number of adults from peak II had higher survival rate, higher pupation rate, higher emergence rate and less eclosion time than that of peak I; (c) Although it has one generation a year, the occurrence peak twice annually displaying a bimodal population distribution phenomenon, which forms double parasitic pressure on the local host. This phenomenon is very rare in the study of insect life history, especially in the parasite epidemiology.Conclusion: The natural discharge period of the G. pecorum larvae in Kalamaili Nature Reserve (KNR) is longer than 7 months and have the potentially long term infection effect on the host. The above phenomenon is one important reason for the local equine animals to be severely infected with equine myiasis.

The Double Rhythm Development and Characteristics of the Gasterophilus Pecorum (Diptera: Gasterophilidae) Population in Desert Steppe

Background: The departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period, and the Gasterophilus pecorum becomes the dominant species in the desert steppe, showing its special biological characteristics. The population dynamics of G. pecorum were studied to reveal the population development rule of G. pecorum in the arid desert steppe. Method: The larvae were collected and recorded in the newly excreted feces by tracking the Przewalski’s horses (Equus przewalskii), meanwhile, the larval pupation experiments were carried out under natural conditions. Results: (a) There was a positive correlation between the survival rate and the number of larvae (r = 0.630, p < 0.01), indicating that the species development had the characteristics of centralized occurrence; (b) The main periods of mature larvae discharge were from early April to early May (peak Ⅰ) and from mid-August to early September (peak II), and the larval population curve showed a sudden spike in increase and gradual decrease at both peaks; under higher temperature, the number of adults from peak II had higher survival rate, higher pupation rate, higher emergence rate and less eclosion time than that of peak I; (c) Although it has one generation a year, the occurrence peak twice annually displaying a unique “ double rhythm development ” phenomenon, which forms a “ dual rhythm parasitism ” pressure on the local host. This phenomenon is very rare in the study of insect life history, especially in the parasite epidemiology. Conclusion: The natural discharge period of the G. pecorum larvae in Kalamaili Nature Reserve (KNR) is longer than 7 months and have the potentially long term infection effect on the host. The above phenomenon is one important reason for the local equine animals to be severely infected with equine myiasis.

Identification of volatile components from oviposition and non-oviposition plants of Gasterophilus pecorum (Diptera: Gasterophilidae)

Oviposition by Gasterophilus pecorum on shoot tips of Stipa caucasica is a key determinant of its severe infection of the reintroduced Przewalski’s horse (Equus przewalskii). Volatiles in shoots of grasses on which Przewalski’s horse feeds, including S. caucasica at preoviposition, oviposition, and postoviposition stages of G. pecorum, S. caucasica, Stipa orientalis, and Ceratoides latens at the oviposition stage, and S. caucasica in various growth periods, were collected by dynamic headspace adsorption and analyzed by automatic thermal desorption gas chromatography-mass spectrometry. Among five volatiles with highest relative contents under three sets of conditions, caprolactam and 3-hexen-1-ol,(Z)- were common to all samples. Caprolactam was highest in C. latens at oviposition stage of G. pecorum and lowest in S. caucasica at postoviposition stage, and that of 3-hexen-1-ol,(Z)- was lowest in C. latens and highest in S. caucasica at its oviposition stage. Particularly, in S. caucasica during the three oviposition phenological stages of G. pecorum, 3-hexen-1-ol,acetate,(Z)-, 2(5H)-furanone,5-ethyl-, and 3-hexen-1-ol,acetate,(E)- were unique, respectively, to the preoviposition, oviposition, and postoviposition stages; in three plant species during the oviposition stage of G. pecorum, 3-hexen-1-ol,acetate,(Z)-, 3-hexenal, and 1-hexanol were unique to S. orientalis, acetic acid, hexanal, and 2(5H)-furanone,5-ethyl- to S. caucasica, and 1,3,6-octatriene,3,7-dimethyl-, cis-3-hexenyl isovalerate, and acetic acid hexyl ester to C. latens; in S. caucasica, 2-undecanone,6,10-dimethyl- was unique to the early growth period, acetic acid and 2(5H)-furanone,5-ethyl- to the flourishing growth period, and 3-hexen-1-ol,acetate,(Z)- and 1,3,6-octatriene,3,7-dimethyl- to the late growth period. Furthermore, substances specific to S. orientalis and C. latens were also present in S. caucasica, except at oviposition stage. Our findings will facilitate studies on G. pecorum’s adaptation to the arid desert steppe and its future control.