Egg laying and egg removal by workers are positively correlated in queenright Cape honeybee colonies (Apis mellifera capensis)

Apidologie, Jul 2018

Christian W.W. Pirk, Peter Neumann, H. Randall Hepburn

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Egg laying and egg removal by workers are positively correlated in queenright Cape honeybee colonies (Apis mellifera capensis)

Apidologie Egg laying and egg removal by workers are positively correlated in queenright Cape honeybee colonies (Apis mellifera capensis) ChristianW.W. PIRK 1 Peter NEUMANN 0 H. Randall HEPBURN 1 0 Martin-Luther-Universität Halle-Wittenberg, Institut für Zoologie / Molekulare Ökologie , Kröllwitzerstr. 44, 06099 Halle/Saale , Germany 1 Rhodes University, Department of Zoology and Entomology , 6140 Grahamstown , South Africa - Queenright Apis mellifera capensis colonies exhibit egg laying by workers in periods of both low and high egg removal. To reproduce workers should lay in times of low egg removal to increase survival of their eggs. Were this so, a negative correlation between egg laying and removal would be expected. Egg removal rates for queen (N=240) and worker-laid (N=240) eggs and egg laying by workers were tested in queenright colonies. Worker-laid eggs were removed significantly faster than queen-laid eggs; but significant differences in egg laying by workers occurred among colonies. Egg laying and removal are positively correlated and co-dependent. Egg removal appears triggered by the number of worker-laid eggs. Intercolonial variation for laying worker egg number and egg removal rates may explain the phenotypic variation in worker reproduction in queenright Cape honeybee colonies. Apis mellifera capensis / egg removal / laying workers / worker reproduction / worker policing - 1. INTRODUCTION With few exceptions (Oldroyd et al., 1994), worker-laid eggs are removed by other workers in queenright colonies of the European subspecies of Apis mellifera L. (Ratnieks and Visscher, 1989) . This seems to be based on relatedness grounds (Ratnieks, 2000) , because laying workers usually produce male offspring (Free, 1987). However, laying workers of the Cape honeybee (Apis mellifera capensis Eschscholtz) produce female offspring (Onions, 1912; Neumann et al., 2000; Hepburn and Radloff, 2002; Radloff et al., 2002) , leading to predictions that egg removal is either not expressed at all, or is less expressed in this subspecies (Greeff, 1996) . Nevertheless, queenright Cape honeybee colonies exhibit worker policing (Neumann, Pirk, Ratnieks, unpublished data), indicating that removal of workerlaid eggs can also be based on colony efficiency grounds. Brood above the queen excluder is more frequently observed in queenright colonies of Cape honeybees (Pettey, 1922; personal observations) than in other subspecies of A. mellifera (Visscher, 1996) . It has been shown that such brood is actually workerderived (Moritz et al., 1999) , indicating successful worker reproduction despite the presence of a queen and egg removal. Indeed, thousands of queenright colonies of the neighbouring subspecies Apis mellifera scutellata Lepeletier were taken over by laying A. m. capensis workers (Allsopp and Crewe, 1993; Martin et al., 2002) , showing that A. m. capensis workers are facultative social parasites (for details see Hepburn and Allsopp, 1994; Neumann et al., 2001; Calis et al., 2002; Moritz, 2002; Neumann and Hepburn, 2002; Reece, 2002; Wossler, 2002) . These observations strongly indicate that laying workers of A. m. capensis are able to evade worker policing, but what potential strategies, if any, could these laying workers use to increase the survival of their eggs? Earlier observations showed (Pirk, Neumann, Hepburn, Radloff, unpublished data) that worker policing is subject to environmental variation within colonies of A. m. capensis, thus leading to periods of low egg removal rates under unfavourable weather conditions within a colony. Because worker policing is only exercised against eggs (Ratnieks and Visscher, 1989) , worker-laid eggs need only survive three days after oviposition, which might fit well in a time window of low egg removal. So one potential strategy of laying A. m. capensis workers to evade worker policing, which we designate as hypothesis 1 could be that they are able to evaluate periods of low egg removal and lay their eggs during this time window. In this case one would expect a negative correlation between worker egg laying and the removal of worker-laid eggs by other workers, because workers should lay more eggs when there is less egg removal by other workers and vice versa. But, the same environmental factors which affect egg removal behaviour may also reduce egg-laying activity (hypothesis 2). This might be simply due to the generally reduced activity of workers during periods with unfavourable weather conditions (Riessberger et al., 1998) . Alternatively, periods with unfavourable weather conditions may also reduce the survival chances of worker-derived offspring because nurse bees change from the care of young larvae to the care of older larvae during such periods (Blaschon & Crailsheim, 2001) . This may easily outweigh the risk of being removed by other workers. Thus, unfavourable weather conditions may not only reduce the activity of egg removal beha (...truncated)


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Christian W.W. Pirk, Peter Neumann, H. Randall Hepburn. Egg laying and egg removal by workers are positively correlated in queenright Cape honeybee colonies (Apis mellifera capensis), Apidologie, pp. 203-211, Volume 33, Issue 2, DOI: doi:10.1051/apido:2002004