The present invention provides compositions and methods of use and application of such compositions that not only ensure that necessary nutrients are supplied to plants but also harmlessly and reliably prevent damage to plants caused by harmful insects. The compositions include film forming agents for coating plants that include cellulose which contains at least one of a mineral ingredient and a saccharide ingredient, wherein the mineral ingredient preferably includes citric acid. This film forming agent for coating plants is sprayed over plants, and a cellulose film is thereby formed on the surfaces of the plant, supplying the nutrients to the plant and protecting the plant from insect damage.