Decision making in honeybees: a time to live, a time to die?
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Insectes Sociaux
SHORT COMMUNICATION
Decision making in honeybees: a time to live, a time to die? J. O. Schmidt1 Received: 26 September 2019 / Revised: 24 February 2020 / Accepted: 10 March 2020 © International Union for the Study of Social Insects (IUSSI) 2020
Abstract Honeybees that sting vertebrate predators embed and leave their stingers in the flesh of the stung animal and die shortly thereafter. To determine whether bees make life-or-death decisions based upon risk–benefit evaluations, the vigor of defenses of colonies that had a small loss potential versus those that have large loss potential was compared. Colonies 3–4 days old have small reserves, and thus, risk fewer reserves to lose to a potential predator. In contrast, colonies 19–22 days old risk large quantities of vulnerable immature brood, constructed wax comb, nectar/honey, and pollen and have limited future reproductive potential if their nest is abandoned. As predicted by a risk–benefit hypothesis, older colonies with much at risk sent proportionately larger percentages of stinging defenders to confront threats than younger colonies with less to lose. The percentage of defenders that issue from the 19–22-day-old colonies correlated with the population of workers within the colonies. The percentage of workers that attack strongly increased as the weight of colony-fixed resources within the combs increased. In queenless colonies having no potential to reproduce by swarming and little, or no, reserves of nectar or pollen, only a small percentage of workers defended the colony. These results provide support for the ability of defending honeybee workers to make life-or-death decisions based on evaluating risks of colony loss versus the benefit derived from their personal loss of life. Keywords Sting autotomy · Stings · Risk–benefit · Africanized bees · Reproductive swarms
Introduction Honeybees, Apis mellifera L., are famous for their ability to autotomize their sting apparatus during the process of stinging a vertebrate potential predator (Rietschel 1937; Hermann 1971). The sting apparatus, thus embedded in the flesh of the victim, continues pumping venom into the wound for several minutes (Snodgrass 1984). During this process, most of the venom contained in the venom reservoir is delivered into the victim (Schumacher et al. 1994; Visscher et al. 1996). This system of venom delivery has benefits compared to systems in which the sting apparatus is not autotomized. When an individual of a nonautotomizing species departs, or is removed by the stung target, its venom delivery discontinues, often with only a small portion of the actual venom being delivered (Schumacher et al. 1994). When a species such as a honeybee autotomizes its sting, the venom delivery * J. O. Schmidt [email protected] 1
Southwestern Biological Institute, 1961 W. Brichta Drive, Tucson, AZ 85745, USA
continues without the presence of the stinging individual (Snodgrass 1984; Schmidt 2016). An additional advantage of this system is that the autotomizing insect now is freed
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