Variance and Heritability of the Capped Developmental Stage in EuropeanApis MelliferaL. and Its Correlation with IncreasedVarroa JacobsoniOud. Infestation

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Abstract
A time-saving method for determining the duration of the capped stage (sealed brood) of large numbers of colonies is described. The results of 112 colonies covering 22 different origins and hybrids of European honeybee races are presented. Differences up to 9 h between strains and up to 19 h within individual colonies could be detected. Influenced by seasonal effects, the average capped period is about 7 h shorter in early than in late summer. For one group of test colonies (n= 21) the Varroa infestation after 18 months of undisturbed colony and mite population development has been determined. The correlation between the capped period and the susceptibility of the colonies to mites is calculated as r = 0·48. By linear regression, an 8·7% reduction of the final mite infestation is calculated for a 1-h reduction of the capped period. The heritability of the duration of the capped period is estimated with h2 = 0·232. This may be a realistic value for test populations of European honeybee under field conditions.