Highly refined oils applied to citrus crops can cause suffocation in insects by excluding what essential element?

Highly refined oils used on citrus crops primarily function as a form of pest control by creating a physical barrier that suffocates insects. This occurs because these oils coat the surfaces of the insects' bodies, effectively sealing them off from their environment. The essential element that is excluded in this process is oxygen. Insects, like many living organisms, require oxygen for respiration; thus, when they are covered in oil, their ability to absorb oxygen is hindered. As a result, they can suffocate due to lack of access to this vital gas.

Other options, such as light, heat, or water, do not have the same direct relationship with suffocation in insects. While these elements have their roles in the broader context of plant health and pest control, it is the exclusion of oxygen that specifically leads to suffocation when highly refined oils are applied.