Abstract
Bumblebees are regularly exported to countries outside their native range for the purposes of commercial pollination. In contrast to the tight regulations imposed on biological control introductions, the movement of bumblebees has largely been without risk assessment. This study represents the first formal assessment of establishment risk for Bombus terrestris dalmatinus in the UK. The ability of workers to survive winter conditions is seen as the primary barrier to establishment, given the year-round colony activity of this sub-species. We use standardised cold tolerance indices as outlined by the EU policy support action ‘REBECA’ as well as assessing rapid cold hardening (RCH) ability. Cold tolerance was comparable to that of the UK-native Bombus terrestris audax, including a strong RCH response. Results suggest that B. t. dalmatinus could survive mild UK winters in southern areas and potentially displace B. t. audax. The implications of ongoing climate change on establishment risks are discussed.
Highlights
Given the economic importance of insect pollination (Gallai et al 2009) and the decline of the north American honeybee, Apis mellifera, (Tentcheva et al 2004), alternative pollinators have increasingly been used to enhance the yield and quality of commercially valuable crops
Most B. t. audax workers (96.6±3.3 %) survived 15 min at −5 °C, but this decreased to just 6.7±4.2 % survival following 15 min at −8 °C (Figure 1)
This led to concerns regarding establishment risk (Ings et al 2006), and since 2013, B. t. dalmatinus has only been licensed for pollination in glasshouses and polytunnels in the UK, as well as colony boxes being fitted with queen excluders (Natural England 2013)
Summary
Given the economic importance of insect pollination (Gallai et al 2009) and the decline of the north American honeybee, Apis mellifera , (Tentcheva et al 2004), alternative pollinators have increasingly been used to enhance the yield and quality of commercially valuable crops. Audax towards producing winter-active colonies in the southern UK (Stelzer et al 2010), and active workers could potentially survive mild UK winter conditions (Owen et al 2013) This has never been assessed for B. t dalmatinus but is key to determining whether this sub-species could become established and possibly displace the native B. t. There exists an extensive literature on insect cold tolerance and its application in assessing the establishment risk of introduced species (Hatherly et al 2005; Hughes and Bale 2009; Hughes et al 2010; Coombs and Bale 2014) These assessments form the basis of commercial licensing to release biocontrol agents in several EU countries (REBECA 2014). We directly compare the cold tolerance of B. t. dalmatinus with B. t. audax and determine the likelihood of establishment of B. t. dalmatinus in the UK
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