Many endangered and vulnerable species, are threatened by tick biting and tick-borne diseases [27]. Giant pandas are one of the most iconic and recognizable wild animal species in nature conservation, and understanding the impacts of ticks and tick-borne diseases on these animals is of the utmost importance. However, a limited number of studies have addressed the effects of ticks on giant pandas. Previous studies about ticks and giant pandas were limited as forms of case reports of dead or diseased individuals and lack of systematic investigation in a wild environment. In this study, we conducted a survey of tick abundance on one giant panda undergoing reintroduction training over seven tick-active months in 2021. We collected and identified ticks from the ears of the giant panda which was living in its natural environment during the entire research period. We explored the changes of tick population and sex ratio over time. The correlation between tick abundance and climate factors during that period was also tested by a linear model.
In this research, we found all the ticks from the ears of the giant panda were from a single species, I. ovatus. Although multiple tick species were reported frequently on animals, a number of cases found that animals can be infested by a single tick species. For example, a survey about tick abundance on American black bear (Ursus americanus) found that all 1976 ticks collected from multiple areas of 278 black bears were identified as Ixodes scapularis [28]. An early case reported more than 2000 ticks as Haemaphysalis warburtoni from a two-year old giant panda in a natural reserve in Sichuan, China [29]. Although one meta-analysis study showed that a larger host body size may correlate to a higher diversity of ticks in the neotropical area [30], that study only included data from the neotropical area and did not consider the tick distribution on host body locations.
One previous study about tick species diversity on cattle revealed a significant difference across cattle body parts. Only 1.6% of the total tick species were found on the ears in that study [31]. Another research about tick distribution on horses found that tick species located specifically in different host body parts. In the ear area, only the Rhipicephalus spp. was reported in that study [32]. In our study, all the ticks were collected from the ear area of the giant panda in the result of the accessibility to the subject. Therefore, it seems that adult I. ovatus was the major species in the ear area of that giant panda in our research field, which agreed with parasitical pattern of ticks’ behavior on mammals in previous studies [28, 32].
Ixodes ovatus is the only tick species found in this study. This species was previously reported in North and North-east Asia, including China. Samples were collected within a wide altitudinal range from 1400 m to 4600 m in multiple studies [33]. In our study, the giant panda lived in the wild environment from 1998 m to 2500 m, which is the natural altitudinal range for I. ovatus as documented.
Ixodes ovatus were mostly reported parasitizing larger domestic and wild mammals including the Bovidae family (cattle, buffalo and goat), rodents, cats, dogs, bears and human [33]. Besides, the only other case that previously reported I. ovatus on giant pandas we could find was reported from one dead giant panda in 1987 in Ganxu province of China [34]. In that case, 103 various ticks were collected in total but only two of them were I. ovatus. However, in that study, the location was in the northwest of China, which was not in the same area to our current research site. So, environmental factors can affect the distribution of I. ovatus differently disregarding the possibility of the detachment of ticks from the dead animal in that study.
In our research, the average daily abundance of I. ovatus increased over time from March to June, then decreased until September. One previous investigation of the seasonal activity of I. ovatus in a natural environment [35], using mark-recapture methods on ticks, found adult I. ovatus showed high activity from April to mid-July, but decreased significantly in late August. This result showing tick activity peaked in June matches the abundance pattern of I. ovatus collected from the giant panda in our study.
Multiple factors may affect the activity of I. ovatus. Previous research that examined I. ovatus activity in an experimental environment found an increasing activity from April to June followed by a sharp decreasing after June [36]. In that study, ticks were put into plastic cylinders that were placed outdoors where adults were not exposed to sunlight and rain. Another study about the oviposition and development of I. ovatus showed that 17–25 ℃ was the optimal range for the egg hatching and development of I. ovatus [37]. However, they only tested five temperatures (15, 17, 20, 25, 27 and 30 ℃). In our study, the average daily temperature was 10.9 ℃ (95% CI: 10.28 ℃–11.53 ℃). Even in the months with highest temperature range (15.13 ℃; 95% CI: 14.78 ℃–15.49 ℃), the temperature was lower than the highest point of the optimal temperature tested in that previous study. Studies about other Ixodid species showed that the temperature positively corresponded to the activity of questing ticks [38, 39]. Therefore, our results showed that the chance for I. ovatus to actually get on giant pandas may be correlated to the temperature positively. Furthermore, the chance for the giant panda to get I. ovatus may be even higher in environments with higher temperatures.
Our study showed a negative correlation between average tick abundance and daily air pressure (R2 = 0.087, P < 0.001). One previous investigation found that the cases of severe fever with thrombocytopenia syndrome, one tick-borne disease, negatively correlated to the monthly average air pressure [40], which indicated the negative effect of air pressure to the tick activity.
In short, the results in the current study showed that I. ovatus abundance on the giant panda met the pattern of the activity of this species in previous laboratorial and field studies.