Age at Which Larvae Are Orphaned Determines Their Development into Typical or Rebel Workers in the Honeybee (Apis mellifera L.)

Abstract

In the honeybee, diploid larvae fed with royal jelly develop into reproductive queens, whereas larvae fed with royal jelly for three days only and subsequently with honey and pollen develop into facultatively sterile workers. A recent study showed that worker larvae fed in a queenless colony develop into another female polyphenic form: rebel workers. These rebel workers are more queenlike and have greater reproductive potential than normal workers. However, it was unclear whether larvae orphaned at any time during their feeding period can develop into rebels. To answer this question, the anatomical features of newly emerged workers reared in queenless conditions at different ages during the larval period were evaluated. Our results showed that larvae orphaned during the final four or more days of their feeding life develop into rebel workers with more ovarioles in their ovaries, smaller hypopharyngeal glands, and larger mandibular and Dufour’s glands compared with typical workers with low reproductive potential that were reared with a queen or orphaned at the third to last or a later day of feeding life.

Honeybee worker larvae perceive queen pheromones in their food

“…This procedure caused some hatched bees to die before they were collected; therefore, only the surviving, freshly emerged workers were frozen and then dissected. We counted the number of ovarioles in both ovaries and measured the average sizes of the mandibular glands, Dufour's gland, and the acini in the hypopharyngeal glands of each worker with a stereomicroscope (Woyciechowski and Kuszewska 2012;Kuszewska and Woyciechowski 2015). The size of the mandibular gland was calculated as the average of the left and right glands (square root of longest × shortest diameters).…”

“…The latter possibility is of interest in view of the recent finding that worker larvae reared in a queenless colony develop into rebel workers, which are more queen-like than other workers (Woyciechowski and Kuszewska 2012). Compared with typical workers, the rebels have more ovarioles in the ovaries and less developed hypopharyngeal glands, which are used for brood food production, whereas their mandibular glands, which in queens produce QMPs, and Dufour's gland are larger (Kuszewska and Woyciechowski 2015). Rebel workers do not occur in honeybee colonies throughout the entire season but typically appear after swarming.…”

Reproduction of rebel workers in honeybee (Apis mellifera) colonies

“…Other anatomical parameters also differ, such as the sizes of the mandibular, Dufour's and hypopharyngeal glands; however, the sizes of those structures change with the age and social context of the workers. The number of ovarioles, ovary development (ovary activation) and the sizes of the hypopharyngeal, mandibular and Dufour's glands were determined to confirm that rebel and non-rebel workers were used in this study (Woyciechowski and Kuszewska 2012;Kuszewska and Woyciechowski 2015). The total number of ovarioles in both ovaries of each worker was recorded, and the ovarian development of all dissected bees was assessed.…”

“…A recent study showed that in the honeybee, the 'rebel worker' strategy is directly predicted by the assumptions of kin selection theory (Woyciechowski and Kuszewska 2012;Kuszewska and Woyciechowski 2015). Rebel workers develop immediately after swarming, which is the only natural means of colony multiplication.…”

“…Rebel workers develop immediately after swarming, which is the only natural means of colony multiplication. They have significantly more ovarioles in the ovary and larger mandibular and Dufour's glands than do typical sterile workers, along with underdeveloped hypopharyngeal glands (Woyciechowski and Kuszewska 2012;Kuszewska and Woyciechowski 2015), which synthesize and store brood food (Huang and Otis 1989). The proximate factor that influences rebel caste development is the absence of the queen during the final 4 or more days of the unsealed larva stage (Kuszewska and Woyciechowski 2013) or, more precisely, in the absence of the q u e e n 's m a n d i b u l a r g l a n d p h e r o m o n e (Woyciechowski et al 2017).…”