What does Bacillus thuringiensis (Bt) primarily target?

Bacillus thuringiensis, commonly known as Bt, is a naturally occurring bacterium that is widely used as a biological pesticide. Its primary mode of action targets specific insects, particularly caterpillars and certain insect larvae. When ingested by these pests, Bt produces toxins that lead to the destruction of their midgut cells, ultimately causing death. This makes it an effective control agent for various moth and butterfly larvae that can be detrimental to turf and ornamental plants.

This specificity is what makes Bt a preferred choice in pest management, especially in integrated pest management (IPM) programs, as it minimizes harm to non-target organisms, including beneficial insects and pollinators. The other options listed in the question do not align with the specific effectiveness of Bacillus thuringiensis, as it is not designed to control weeds, adult beetles, or fungi. Therefore, option B accurately reflects the primary target of Bacillus thuringiensis.