The most common and most likely answer to this crossword clue is the 10 letter word DROSOPHILA
I've seen this crossword clue in Financial Times
D
R
O
S
O
P
H
I
L
A
Buddy explains!

The straight part
We know that "insect" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case insect = drosophila.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 DROSOPHILA mean?
DROSOPHILA noun- Any fruit fly of the genus Drosophila