Bombus digressus

Ecosur (El Colegio de la Frontera Sur) compiled a database of 26,211 bumblebee records to assess the status and extinction risk of the Mesoamerican Bombus species fauna. To our knowledge there are no recent studies of bumblebee decline in Mesoamerica, including Mexico and Central American countries. Our database consists of 12,210 records of what we consider historic data (1867-2004), obtained from insect collections in the Americas and Europe. The database also contains 14,001 recent bumble bee records (2005-2014), mainly obtained through collaborative sampling efforts conducted by the University San Carlos in Guatemala and El Colegio de la Frontera Sur in Mexico.

We evaluated spatial distribution of B. digressus over time across its Mesoamerican range using a measure of change in the EOO (see Figure 1 in the Supporting Information) and a measure of change in persistence (analytical methods described in Hatfield et al. 2014). We also assessed changes in the species’ relative abundance, which we consider to be an index of abundance relevant to the taxon, as specified by the IUCN Red List Categories and Criteria (IUCN 2012). For all calculations we divided the database into historical (1867-2004, N =59 ) and current (2005-2014, N=13) records. This time-frame was chosen to meet the IUCN criteria stipulation that species decline must have been observed over the longer of three generations or 10 years. Average decline for this species was calculated by averaging the change in abundance, persistence, and EOO. We used these measures of change between the recent and historic time periods to estimate the population trend that has occurred in the past 10 years, and applied that trend to IUCN Criteria. This analysis yielded the following results:

• Current range size relative to historic range: 72.23%   
• Persistence in current range relative to historic occupancy: 120.94%
• Current relative abundance relative to historic values: 16.68%
• Average decline: 30.05%