citrus – n. a juicy fruit such as an orange, grapefruit, or lemon that has a thick skin and that comes from a tree or shrub that grows in warm areas

detect – v. to discover or notice the presence of something that is hidden or hard to see, hear, taste, etc.

epidemic – n. an occurrence in which a disease spreads very quickly and affects a large number of people

stem – n. the main stalk of a plant that develops buds and shoots and usually grows above ground