Rapid inter-generational changes in morphology and behaviour in colonies of Africanized and European honey bees (Apis mellifera) from tropical Yucatan, Mexico

Abstract

SUMMARYAn evaluation of honey bee (Apis mellifera) defensive behaviour, worker morphometrics and worker brood cell size was conducted in an apiary in an area undergoing Africanization with the aim of documenting the rate of change of these traits across generations, and their reliability to accurately identify colonies. Ten European and 10 Africanized parental colonies (generation P; groups 1and 2, respectively) were selected in accordance with their morphometrics and subjective evaluation of their behaviour in the field. These colonies were tested for three traits of defensiveness using a standard protocol. Colonies' worker morphometrics and worker cell dimensions were also measured. After the P generation colonies were tested, queens were removed and colonies were allowed to requeen themselves. The virgin queens of the following generation (F1) were allowed to mate freely and, six months later, colonies were again tested. This procedure of mother-daughter queen replacement and testing of colonies was performed two more times (F2 and F3 generations). Wilcoxon- Mann-Whitney tests and Pearson's correlation analysis were used to test for differences between groups in defensive and morphological traits and to determine the relationship between traits in each generation. The results of this study showed that individual colonies dramatically changed their worker morphometrics and defensive behaviour from one generation to the next. However, all colonies, whether originally Africanized or European, came to resemble more the Africanized type across subsequent generations. Correlations between morphometrics and defensive behaviour were not always consistent. Although morphometrics might still be a reliable method for quick identification of colonies it seems that defensive behaviour alone may provide an inadequate trait by which to discriminate among neotropical honey bee types, especially Africanized-European hybrid colonies.