Glandular sources of pheromones used to control host workers (Apis mellifera scutellata) by socially parasitic workers of Apis mellifera capensis

Abstract

Pheromonal control by the honey bee queen is achieved through the use of secretions from diverse glandular sources, but the use of pheromones from a variety of glandular sources by reproductively dominant workers, has not previously been explored. Using the social parasite, Apis mellifera capensis clonal worker we studied the diversity of glandular sources used for pheromonal control of reproductively subordinate A. m. scutellata workers. To determine whether pheromones from different glandular sources are used by reproductively active workers to achieve dominance and evaluate the degree of pheromonal competition between workers of the two sub-species, we housed groups of workers of the two sub-species together in cages and analysed mandibular and tergal gland secretions as well as, ovarian activation status of each worker after 21days. The results showed that A. m. capensis invasive clones used both mandibular and tergal gland secretions to achieve reproductive dominance and suppress ovarian activation in their A. m. scutellata host workers. The reproductively dominant workers (false queens) produced more queen-like pheromones and inhibited ovarian activation in subordinate A. m. scutellata workers. These results show that tergal gland pheromones working in synergy with pheromones from other glands allow individual workers (false queens) to establish reproductive dominance within these social groups and to act in a manner similar to that of queens. Thus suggesting that, the evolution of reproductively dominant individuals (queens or false queens) and subordinate individuals (workers) in social insects like the honey bee is the result of a complex interplay of pheromonal signals from different exocrine glands.

Tergal gland components of reproductively dominant honey bee workers have both primer and releaser effects on subordinate workers

“…m . mellifera (Saiovici 1983), further supporting the role of a number of glands such as the tergal gland in reproductive division of labour (Okosun et al 2017).…”

“…capensis workers and allows host workers to tend to their needs because dominant honey bee workers do not participate in colony duties (Hillesheim et al 1989). They rather mimic and release glandular queen-like signals (Moritz et al 2000;Sole et al 2002;Okosun et al 2017) that elicit retinue behaviour and attract workers to feed them high-quality food such as royal jelly through trophallaxis (Korst and Velthuis 1982;Moritz and Crailsheim 1987;Schäfer et al 2006) and further establish dominance. Ethyl oleate in honey bee colonies delayed onset of foraging and transitioning of nurse bees to foragers (Leoncini et al 2004b;Castillo et al 2012).…”

“…Honey bee queens' pheromones serve several purposes in the colony such as regulating reproductive capacity of receivers that are normally their daughters, with a strong evidence that the degree of dominance is dependent on the queen's age, the quality and dose of her pheromones received or perceived by workers (De Hazan et al 1989;Smith et al 1993;Hoover et al 2005). Since reproductive dominance and control are achieved by pheromones, there exists strong evidence that pheromones from different glandular sources act in synergy depending on the context De Hazan et al 1989;Brockmann et al 2006;Maisonnasse et al 2010;Okosun et al 2015Okosun et al , 2017. The tergal glands, located on tergites II-IV in queens and workers (Billen et al 1986;Wossler et al 2000), are important exocrine glands that produce long-chain fatty acids, long-chain esters and a series of unsaturated and saturated hydrocarbons as components (Smith et al 1993;Wossler and Crewe 1999a;Okosun et al 2015).…”

“…In queenless situations, the production of queen glandular pheromones by workers allows them to take over the role of the queen and gain dominance (Sakagami 1958;Moritz et al 2000;Schäfer et al 2006;Zheng et al 2010). These reproductively dominant workers also known as false queens develop glandular pheromones that are qualitatively similar to those of a queen, and the release of these pheromones prevents their nestmates from making a similar switch in the production of pheromonal components (Crewe and Velthuis 1980;Katzav-Gozansky et al 2003;Härtel et al 2011;Okosun et al 2017). They escape the control systems in the colony by behaviourally avoiding the queen (Moritz et al 2002) and lay eggs that are not policed (Malka et al 2007).…”

“…False queen phenomena are well exhibited by workers of the Cape honey bee Apis mellifera capensis , displaying characteristics that include rapidly activating their ovaries, developing queen-like mandibular, Dufour's and tergal gland pheromone bouquet in the case of queen loss (Hemmling et al 1979;Ruttner and Hesse 1981;Moritz et al 2000;Sole et al 2002;Härtel et al 2011;Okosun et al 2017). They are successful social parasites in their own or in colonies of other honey bee races and can achieve pheromonal and reproductive dominance in other A .…”