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What Are Zombie Caterpillars?

Zombie caterpillars are caterpillars that are infected with a gene in a baculovirus that alters the normal behavior of the caterpillar. Zombie caterpillars are just one example of a virus controlling another organism.

What is a Baculovirus?

Baculoviruses are a group of bacterial pathogens that attack and infect a large range of insects and other arthropods. The most studied baculoviruses are those that infect the larval stage of moths and butterflies. These viruses are readily dispersed from place to place by rain and wind and have been shown to have no negative effect on humans, other mammals, birds, fish, and other non-target organisms. So, these viruses are excellent candidates for species-specific insecticidal applications. Caterpillars, wasps, and flies act as natural hosts for Baculovirus.

How does the virus turn caterpillars into zombies?

A gene in a baculovirus creates the zombie-like behavior in caterpillars. Zombie caterpillars are caterpillars that are infected with a gene in a baculovirus that alters the normal behavior of the caterpillar. Baculovirus infected caterpillars exhibit unnatural and potentially destructive actions, via zombie-like actions. These responses include:

  • The virus makes caterpillars move toward light. Baculovirus manipulates genes associated with the caterpillar’s vision and causes the caterpillar to be more attracted to sunlight than usual.

  • The virus causes inhibition of caterpillar larval development (molting). Normally, caterpillars periodically pause feeding to go through larval molts. However, baculovirus-infected larvae do not molt, due to the action of an enzyme in the virus.

  • Baculoviruses also can affect a caterpillar’s climbing behavior and ensure they die at elevated positions. This response enhances virus transmission and distribution, but also exposes the caterpillars to predators that find it easier to prey upon caterpillars if they are at higher levels of the host plant.

How do zombie caterpillars die?

A single gene in a caterpillar virus sends its victims running for the treetops, where they die and their bodies liquefy, sending an ooze of virus particles down on other caterpillars below them. The virus stops the caterpillars from molting and sends them up into the treetops during the day (a behavior they normally save for the cover of darkness), where they die as they wait to molt. Normally, spongy moth caterpillars feed on tree leaves at night when predators including birds and squirrels can't see them. Then during the day, the caterpillars climb down and hide in the tree bark or under leaves on the ground. However, caterpillars abandon that sensible strategy when they're infected with a baculovirus.

Are there other zombie insects?

Yes, there are instances of zombie ants and zombie cockroaches, however these zombies are made through parasitic insects and not a bacterial virus.

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