What is the most commonly used microbial insecticide and what insect larvae is it effective against?

• A. Spinosad, used to control beetle larvae
• B. Bacillus thuringiensis, or Bt, used to control caterpillars
• C. Beauveria bassiana used to control aphids
• D. Metarhizium anisopliae used to control nematodes

Answer: (B)

Bacillus thuringiensis (Bt) is the most commonly used microbial insecticide. It works by producing crystal (Cry) proteins during its spore stage. When caterpillar larvae ingest Bt formulations, these toxins are activated in the caterpillar’s alkaline gut, bind to gut cells, create pores, disrupt digestion, and ultimately kill the insect. This mode of action makes Bt particularly effective against caterpillars (Lepidoptera) that feed on leaves, which is why it’s widely used in agriculture and home gardening. While other microbial products exist, none are as universally applied for caterpillar control as Bt.