Identification
• Insects, especially caterpillars, infected with a virus often have a dark exterior and may be flaccid, resembling a limp bag of dark liquid. Caterpillars may often be seen hanging in a U shape from their prolegs.

Host range
• Insects are attacked by at least 450 kinds of viruses. The most common types are nuclear polyhedrosis viruses (NPV) which include 50% of all insect viruses. Most NPV’s (90%) attack caterpillars.

Life cycle
• Viruses are ingested, usually by immature insects, and invade the cells of the host. In a relatively short time the entire body of the host becomes a virus factory. At death, the host is usually a bag of liquid containing millions of viral particles.

Other information
• Immature insects are often attacked by naturally occurring viruses. Many are host-specific, e.g., they attack only a single genus or even species of insect.