Hit-and-run trophallaxis of small hive beetles

Abstract

Some parasites of social insects are able to exploit the exchange of food between nestmates via trophallaxis, because they are chemically disguised as nestmates. However, a few parasites succeed in trophallactic solicitation although they are attacked by workers. The underlying mechanisms are not well understood. The small hive beetle (=SHB), Aethina tumida, is such a parasite of honey bee, Apis mellifera, colonies and is able to induce trophallaxis. Here, we investigate whether SHB trophallactic solicitation is innate and affected by sex and experience. We quantified characteristics of the trophallactic solicitation in SHBs from laboratory-reared individuals that were either bee-naïve or had 5 days experience. The data clearly show that SHB trophallactic solicitation is innate and further suggest that it can be influenced by both experience and sex. Inexperienced SHB males begged more often than any of the other groups had longer breaks than their experienced counterparts and a longer soliciting duration than both experienced SHB males and females, suggesting that they start rather slowly and gain more from experience. Successful experienced females and males were not significantly different from each other in relation to successful trophallactic interactions, but had a significantly shorter soliciting duration compared to all other groups, except successful inexperienced females. Trophallactic solicitation success, feeding duration and begging duration were not significantly affected by either SHB sex or experience, supporting the notion that these behaviors are important for survival in host colonies. Overall, success seems to be governed by quality rather than quantity of interactions, thereby probably limiting both SHB energy investment and chance of injury (<1%). Trophallactic solicitation by SHBs is a singular example for an alternative strategy to exploit insect societies without requiring chemical disguise. Hit-and-run trophallaxis is an attractive test system to get an insight into trophallaxis in the social insects.

Keywords: Aethina tumida; Apis mellifera; honey bee; host–parasite interaction; small hive beetle; solicitation; trophallaxis.

Figure 1

Perspex cages for the experiments. The lower 20 mm of which was restricted to a 2 mm gap by a piece of wood. This gap was wide enough for SHB to enter (Schmolke 1974), but too narrow for the honey bee workers.

Figure 2

Trophallactic contact between a honey bee worker and a small hive beetle. The screenshot of a movie showing a trophallactic contact between a honey bee worker and an SHB hiding in the gap between Perspex and wood. A second SHB to the right is about to interfere with feeding.

Figure 3

Comparisons of the behavioral interactions between the experimental small hive beetle groups. (A) Success (successful trophallactic events), (B) feeding duration, (C) begging duration, (D) begging events, (E) break duration, (F) soliciting duration. Means (A) or medians, quartiles, and ranges are shown (B–F). Significant differences between groups are indicated with different letters (Exp_female, experienced females; Exp_male, experienced males; In‐female, inexperienced females; In‐male, inexperienced males).

Figure 4

Soliciting duration in the experimental small hive beetle groups. Medians, quartiles, and ranges are shown. Successful experienced females and males were not significantly different from each other, but had a significantly shorter soliciting duration compared to all other groups, except successful inexperienced females. Significant differences are indicated with * = P < 0.05, *** = P < 0.001, ns = not significant.