[They can spray you with insecticide against your will or agreement.]
Aircraft Disinsection Requirements
Overview
Disinsection is permitted under international law in order to protect public health, agriculture and the environment. The World Health Organization and the International Civil Aviation Organization stipulate two approaches for aircraft disinsection– (1) spray the aircraft cabin with an aerosolized insecticide while passengers are on board or (2) or spray or treat the aircraft's interior surfaces with a residual insecticide (residual method) while passengers are not on board.
Although the Report of the Informal Consultation on Aircraft Disinsection sponsored by the World Health Organization (November 6-10, 1995) concluded that aircraft disinsection, if performed appropriately, would not present a risk to human health, the report also noted that some individuals may experience transient discomfort following aircraft disinsection by aerosol application.
Under the Chicago Convention, which governs international civil aviation, a country could impose a disinsection requirement should they perceive a threat to their public health, agriculture or environment. Accordingly, travelers are advised to check with their travel agent or airline reservations agent when booking flights or if they have questions about their final destination’s policy.
The following provides general information about disinsection requirements. Note: Policies may be changing. DOT continues to work to ensure that this list is accurate and up to date.
Countries requiring the disinsection of all in-bound flights with an aerosolized spray while passengers are on board:
Ecuador (only Galapagos and Interislands)
Grenada
Guyana
India
Kiribati
Madagascar
Panama
Seychelles
Tanzania
Timor-Leste
Trinidad and Tobago
Uruguay
Zimbabwe
(There are more. Check the lists on the DOT site.)
https://www.transportation.gov/airconsumer/spray