Which of the following is classified as a "botanical" insecticide?

Pyrethrum is classified as a "botanical" insecticide because it is derived from the flowers of the chrysanthemum plant, specifically from the species Chrysanthemum cinerariifolium and Chrysanthemum coccineum. This natural origin is what defines it as a botanical insecticide, distinguishing it from synthetic insecticides. Pyrethrum works by targeting the nervous system of insects, causing paralysis and death, which makes it an effective method for pest control.

The other options listed are synthetic or semi-synthetic compounds. Pyriproxyfen is a synthetic insect growth regulator, Spinosad is derived from naturally occurring bacteria but is considered semi-synthetic, and Malathion is a synthetic organophosphate insecticide. The key distinction is that botanical insecticides come directly from plant materials, while synthetic insecticides are chemically engineered.