The most common and most likely answer to this crossword clue is the 7 letter word DULOSIS
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The straight part
We know that "practice in colony" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case practice in colony = dulosis.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DULOSIS mean?
DULOSIS noun- Process by which parasitic ants steal pupae from the nests of other ants and raise them in their own nest, so that they become part of the colony and perform tasks in it.