Results of a study that was released in January show that western bumble bee numbers are on a steep decline in Colorado.

According to the report, numbers of this bee species have dropped 72 percent in the Southern Rocky Mountain region between 1998 and 2020, with this region including the mountains that stretch through central Colorado, slightly extending into southern Wyoming and northern New Mexico.

The 72 percent drop in western bumble bee populations in the Southern Rocky Mountain region was the 5th-largest drop among 16 regions included in the study. The largest drop took place in the Madrean Archipelago – 83 percent – with this region spanning parts of Arizona, New Mexico, and northern Mexico. It’s also worth noting that bee populations dropped in all studied regions over the given time frame, dropping the least in the Greater Yellowstone Ecosystem – 15 percent.

Warmer temperatures and drought were determined to be two key factors in this widespread population drop. According to the research, lab studies indicate that warmer winter temperatures can drain energy reserves, thus increasing a risk of starvation. Warmer temperatures can also result in an earlier queen emergence, which can result in resource shortages if the queen emerges prior to spring flowering. Meanwhile, drought can also impact floral growth – another factor that limits resources for bees.

Researchers noted that continued impacts from a warming climate are likely, looking ahead to a grim future for the bee species.

While a ‘best case’ scenario showed that there could be an 8 percent increase in western bumble bee populations in the Southern Rocky Mountain region by the 2050s, middle and worst case scenarios predict a 69 percent and 91 percent drop, respectively. Across all 16 regions, ‘worst case’ scenarios showed drops in population ranging from 86 percent to 97 percent over the next three decades.

This drop in bee populations could be problematic for a number of reasons, including a potential decline in food supplies as many fruit and vegetable plants would lack essential pollinators.

Researchers involved in the bee population study also found that increased use of pesticides was a factor in their decline. One silver lining related to this finding is that Colorado lawmakers are already considering a bill that’s designed to protect the health of pollinators through a number of measures, including providing grants to producers that do not use seed-applied systemic insecticides.

Find the full study here.

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