Effect of juvenile hormone on caste determination and colony processes in the bumblebee Bombus terrestris

Abstract

To investigate the role of juvenile hormone (JH) in caste determination, first and second instar larvae of Bombus terrestris were topically treated with one of three doses (2, 10, or 20 μg/larva) of JH dissolved in acetone. Treated larvae belonged to very young colonies that had just been started by their queen. Therefore, all larvae were supposedly destined to develop into workers. Our study demonstrates that a single application of JH in the first or second instar can lead to the development of queens and that this effect is dose‐ and instar‐dependent. The brood (second, or third brood of the colony) to which the larvae belonged also had an effect. A clear size dimorphism of the female castes exists in B. terrestris. In this study, however, intermediates also developed from treated larvae. In fact, even untreated larvae in a treated colony developed into queens and intermediates, depending on the total dose of JH applied to the colony. There are no indications that a larva, once determined to become a queen, can be forced to become a worker by means of malnutrition. Treatment with JH also had an influence on colony processes. For instance, the appearance of queen larvae resulted in the advanced start of reproduction by workers and egg robbery, the so called competition point. This indicates again the close relationship between queen rearing and the queen‐worker conflict. However, the ultimate function of this casual connection is still unclear. Further, the queen reacted to the treatment by switching to the laying of haploid eggs at an earlier date in the colony development compared to untreated colonies.

Effect of the queen on worker reproduction and new queen production in the bumble beeBombus terrestris

“…II, III). This was consistent with the observed temporal link between the timing of queen production and the competition point in B. terrestris (Duchateau and Velthuis, 1988;Bloch, 1999;Bortolotti et al, 2001;Alaux et al, 2004) and, specifically, with the proposal that workers use the onset of queen development as a cue to commence egglaying (Crespi, 1992;Kukuk, 1992;Cnaani et al, 2000;Bourke and Ratnieks, 2001;Duchateau et al, 2004;Alaux et al, 2006). However, we also found that, in most colonies in Experiment 1, workers in the queenless compartments exhibited aggression and egglaying even though no new queens were developing (Tabs.…”

“…There is a tight temporal link between the onset of Corresponding author: A.F.G. Bourke, a.bourke@uea.ac.uk * Manuscript editor: Stan Schneider worker reproduction and queen production, with the competition point predictably occurring c. 10 days after the queen lays the first diploid eggs that will develop as new queens (Duchateau and Velthuis, 1988;Bloch, 1999;Bortolotti et al, 2001;Alaux et al, 2004). A variety of evidence supports pheromonal queen regulation of worker reproduction and queen development, but the exact mechanisms are not fully resolved (Crespi, 1992;Kukuk, 1992;Bloch and Hefetz, 1999a;Cnaani et al, 2000;Bourke and Ratnieks, 2001;Duchateau et al, 2004), partly because the experimental evidence is not always consistent across different studies.…”

Precocene-I inhibits juvenile hormone biosynthesis, ovarian activation, aggression and alters sterility signal production in bumble bee (Bombus terrestris) workers

“…This is, again, in line with the effects of precocene in other solitary insects (Lee and Tan, 1980;Samaranayaka-Ramasamy and Chaudhury, 1981;Deb and Chakravorty, 1982;Socha and Hodkova, 1983;Li et al, 1993;Kumar and Khan, 2004). This also confirms the gonadotropic function of JH in B. terrestris that was until now based on correlations (Roseler, 1977;Van Doorn, 1989;Bloch et al, 1996;Bloch et al, 2000b;Bortolotti et al, 2001;Shpigler et al, 2010), and provides direct evidence for the necessity of JH for oocyte development and egg laying in queenless B. terrestris workers. Similar conclusions were reached by a recent study performing allatectomy in B. terrestris workers (Shpigler et al, 2014), supporting the effect of precocene.…”

The organisation of larval feeding in bumblebees (Hymenoptera, Apidae) and its significance to caste differentiation

“…Queen production has been suggested to be related to high worker to larva ratios (Cumber, 1949; ment of larvae directly. Recent work on the physiological mechanisms underlying caste differentiation in B. terrestris suggests, however, that caste development is not under worker control (Cnaani et al, 1997Cnaani and Hefetz, 2001;Hartfelder et al, 2000, Bortolotti et al, 2001. These studies provide evidence for a direct influence of the queen's presence on caste-specific endocrine events during the larval development, and that size dimorphism is primarily a result of different development duration.…”