#$%^&*AU2020201642A120200326.pdf#####Abstract The present invention relates to expression systems comprising a fluorescent marker protein under the control of a muscle actin promoter suitable for expression in insects, wherein expression of the fluorescent marker in an insect results in a phenotype that is visible to the naked eye when the insect is exposed to light. The muscle actin promoter is preferably that of Mexfly (Anastrepha ludens).