A conservation conundrum: protecting bumble bees under the California Endangered Species Act

Abstract

Bumble bees (Bombus spp., Apidae) are important pollinators throughout North America, and across the world. Their long tongues, ability to fly in low temperatures and inclement weather, as well as their aptitude at buzz pollination (Heinrich 2004) make them second only to the honey bee as pollinators that contribute to the multi-trillion dollar agricultural industry (Delaplane and Mayer 2000;Kremen et al. 2002;Klein et al. 2007;Gallai et al. 2009). In wildlands and natural areas, they are essential as generalist pollinators of many plant families (Goulson 2010). However, there have been alarming reports of bumble bee population declines from multiple continents (Cameron and Sadd 2020).Notably, many species of bumble bees have been considered for listing as endangered species under the U.S. Endangered Species Act (ESA). The rusty patched bumble bee (B. affinis), native to much of eastern North America, was added in 2017 (USFWS 2017). Franklin's bumble bee (B. franklini), native to a small portion of southern Oregon and northern California, was Proposed Endangered in 2019 (USFWS 2019a). The western bumble bee (B. occidentalis) and Suckley's cuckoo bumble bee (B. suckleyi) are both currently under review for ESA listing by the U.S. Fish and Wildlife Service (USFWS 2016). The yellow banded bumble bee (B. terricola) was evaluated for inclusion on the endangered species list, but ultimately deemed not warranted for listing by the Service (USFWS 2019b).The specific causes of bumble bee declines are largely unknown, though several key threats have been identified. Pathogen infection (Cameron et al. 2016), insecticides (Wood and Goulson 2017), habitat loss (Williams and Osborne 2009), and climate change (Kerr et al. 2015) have all been individually identified as significant factors leading to observed declines. It is likely that each of these factors also interact, creating synergistic effects and accelerating declines (Cameron and Sadd 2020).California is home to more than half ( 27) of the ca. 50 bumble bee species in North America -more than any other state in the country. Two of California's species, Franklin's bumble bee and Crotch's bumble bee (B. crotchii), are largely endemic; when they occur outside of California, it is within a short distance from the state's boundary. According to an analysis by the International Union for the Conservation of Nature (IUCN) Bumblebee

Climate change winners and losers among North American bumblebees

“…However, there are discrepancies (e.g. B. franklini, which has not been observed since 2006 [36] and, yet, we estimate to be increasing). Our findings are also consistent with projections from Marshall et al [17] who predicted that some European bumblebee species' ranges would expand while others would contract with the advancement of climate and land-use change.…”