Here's a difference apparent from the few quotes:

>. We examined nest usurpation by African swarms over a two-year period in a southern-Arizona apiary that contained 76 five-frame European colonies.

Usurpation found where colony size was tiny.

>During the 12 month study period, the European derived colonies were managed commercially

Usurpation not found where colony size was "commercial" (my assumption
is at least one deep brood box).


I am sure this is a simplistic and  probably wrong explanation, but it
just stood out to me as an obvious difference.

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