Trialling techniques for rearing long-tongued bumblebees under laboratory conditions

Abstract

Bumblebees are important pollinating insects, but many species have suffered declines over the last century. Long-tongued bumblebees have been identified as particularly at risk, partly due to their more selective diet. Attempts to study these species in captivity have been impeded by stress-induced behaviours which cause queens to kill or abandon their brood. Here, we attempt to further develop techniques, using queen pairing and Bombus terrestris cocoons, to successfully rear two common long-tongued bumblebee species (B. pascuorum and B. hortorum ) in captivity. Approximately half of queens laid eggs and 29% produced workers. Although challenges remain, there is a great deal to be gained from optimising the captive rearing of these species.pocket makers / pollination / Bombus pascuorum / Bombus hortorum / Bombus terrestris / rearing / cocoon / queen pairing

Effect of diet on incipient colony success for two long-tongued bumblebee species in the laboratory

“…Because both of these species are pocket makers and we are still in the early days of rearing optimisation, it is important not to discount the effects of queen behaviour on colony success. In personal observations of the queens here and in our previous work, we found B. hortorum queens to be much more sensitive to physical disturbances (Carnell et al 2020). Although this does not explain our findings here, decades of rearing work on a variety of species has clearly demonstrated that bumblebee species vary widely in their performance under captive conditions, across and within the pocket maker and pollen storer groups (Fandiño 2007;Ptáček et al 2015;Sheikh 2016;Velthuis and Van Doorn 2006).…”

“…We found that queens of B. pascuorum and B. hortorum can survive and successfully rear workers on both the less diverse hawthorn pollen and the more diverse wildflower mix and that a less diverse pollen mix can be as good as a more diverse one. A wax moth infestation developed towards the end of the experiment, but despite this, and the additional stress it may have imposed on queens, the proportion of queens that laid eggs was amongst the highest observed in these species when reared in captivity (Bučánková et al 2012;Ptáček et al 2015;Carnell et al 2020). Very few workers are required for queens to switch to male production (Carnell et al 2020), so it is quite likely that in the absence of wax moths this would have occurred.…”

“…To encourage egg laying and brood rearing, queens were given a B. terrestris cocoon (> 48 h old), from day 2. The callow B. terrestris worker was removed as soon as it eclosed to avoid negative effects on the queen that can otherwise occur (Bučánková et al 2012;Ptáček et al 2015;Carnell et al 2020). Cocoons were provided repeatedly until the queen had produced her own pupae.…”

“…Unlike short-tongued, 'pollen storer' bumblebee species that feed their larvae a regurgitated liquid mix of nectar, pollen and glandular secretions, long-tongued bumblebees lay their eggs directly onto a pollen mass, which the larvae consume in its solid form (Den Boer and Duchateau 2006;Pereboom 2000). Long-tongued bumblebees are understudied because they are very difficult to rear in the laboratory, but recent developments now make rearing long-tonged bumblebees in the laboratory possible (Bučánková and Ptáček 2012;Carnell et al 2020;Ptáček et al 2015). Long-tongued bumblebee species are often more selective in their diet than short-tongued species, and many rely heavily on pollen from the Fabaceae plant group (Goulson 2003).…”

“…Here, we investigate for the first time the nutritional requirements of long-tongued bumblebee incipient colonies, taking advantage of recent work enabling their laboratory rearing (Bučánková and Ptáček 2012;Carnell et al 2020;Ptáček et al 2015). We used B. pascuorum (Thoracobombus) and B. hortorum (Megabombus), both pocket maker species that are ecologically similar to many species of conservation concern, thus making them good models for investigating the biology of long-tongued bumblebees.…”