The survey of bumblebee species diversity in the Sichuan Gongga Mountain National Nature Reserve

Bumblebees (Hymenoptera: Apidae) are a group of pollinators in the genus Bombus, which play important roles in maintaining the balance of natural ecosystem and in promoting agricultural production. We conducted this survey to understand bumblebee species that are currently residing in the Sichuan Gongga Mountain National Nature Reserve and identify species that are under threaten. During the year of 2022-2023, we collected bumblebee samples from 23 plots of the Nature Reserve by sweeping nets for 3 times and recorded their food plants at the same time. Morphological characteristics and molecular barcoding techniques were combined used to identify the species of samples, calculated their abundance and evenness indices, and analyzed their altitudinal distribution patterns. The results indicated that a total of 919 bumblebee specimens were collected and DNA barcoding results indicated that they were from 21 species of 7 subgenus, the Shannon-Wiener index was 2.2093. Of these 21 bumblebee species, 3 of them were abundant species and 8 of them were rare species. In addition, 4 of the rare species (Bombus grahami, B. wolongensis, B. ladakhensis, B. waltoni) were not only rare in number but had a very narrow geographic distribution in the Reserve, indicating their endangered status. Therefore, they were species that urgently required high attention in the protective areas and protective measures should be taken as early as possible. Both the abundance and species richness of bumblebees exhibited a progressive rise with elevation. The largest numbers of bumblebee individuals and species were founded at elevations between 3 000-4 000 m. Bumblebees provided pollination services for at least 43 wild and economic plants in the Reserve. Compared with the 40-year-ago survey results of the same region, two bumblebee species in subgenus Psithyrus (B. bohemicus and B. expolitus), which had shown up in the last survey but were absent in this survey. Moreover, no species from subgenus Psithyrus was collected during this survey. The results suggested that they had probably already gone extinct locally because, as proposed, bumblebees in subgenus Psithyrus, which exhibited socially parasitic behavior, were more vulnerable to population decline or even extinction than other bumblebees. Taken together, we had identified the currently available resources and historical changes of bumblebee species in the Reserve and provided a list of endangered species, which could be invaluable for the protection of bumblebees in the Reserve.