Genotype-environment interactions in honeybee guarding behaviour

Honeybees have an age-based division of labour that is influenced by genetic variability for the tendency to perform specific tasks. Individuals in a honeybee colony comprise diverse genotypes and their interactions can influence task allocation. Colonies from an African race (Africanized honeybees, AHB, Apis mellifera scutellata Ruttner) usually produce a much stronger defensive response than do European races of honeybees (EHB), and these races may differ in how individuals are allocated to the tasks of guarding and stinging. We observed guarding behaviour in colony environments that varied in proportions of genotypes (AHB, EHB) and population size. In large colonies, AHB showed much greater guarding persistence (number of days guarding) than EHB; hybrids were intermediate. In another series of experiments, three families each of AHB and EHB were cofostered in colonies with different AHB: EHB ratios, then tested in large and small colonies. In colonies of both sizes, colony environment interacted with both famly and type (AHB or EHB) for propensity to guard. Individuals of both types guarded more persistently in large colonies, but family and type both interacted with environment. EHB were more likely to initiate guarding bouts in low-AHB colonies, but persistence did not change with environment. AHB were insensitive to effects of environment for the tendency to initiate guarding behaviour, but were more persistent in high-AHB environments. EHB and AHB may differ in how they allocate individuals to guarding. The positive reinforcement of behaviour that occurs in high-defensive environments and in large populations could cause a stronger stinging response through alarm pheromone recruitment. (C) 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.