Ruttner did work on crosses between different bee races from the late 1960s.
He edited a chapter Called 'Races of Bees' in Dadant - the Hive and the Honeybee'
The is a table on page 36 of my 1975 edition which states that Ligustica * Carnica is 'aggressive' with a 70% increase in honey production whereas Carnica * Ligustica is gentle with a 10% increase in honey production.
The most aggressive cross he lists is Carnica * AMM.
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