On turning red, there's some risk it'll kill insects (6)

'kill insects' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'on turning red there's some risk it'll' is the wordplay.
'on turning' says the letters should be written backwards.
'there's' means one lot of letters go next to another.
'some' indicates taking the first letters.
'it'll' becomes 'is' (I can't explain this - if you can you should believe this answer much more).
The initial letter of 'risk' is 'r'.
'red' reversed gives 'der'.
'der'+'r'+'is'='DERRIS'

Can you help me to learn more?