The key is to check the number of immature or wingless thrips that are being found (a good hand lens is useful here).
(The key; is; to check the number of immature or wingless thrips) (immature or wingless thrips; are being found; ) (a good hand lens; is; useful; L:here)
The key immature or wingless thrips a good hand lens
is are being found is
to check the number of immature or wingless thrips
useful L:here