Nearly 50 insurance companies have swiftly answered a voter revolt against skyrocketing rates by announcing they will stop writing certain policies in California, an industry spokesman says.

At least six other insurance companies, including Aetna Life & Casualty and Fireman's Fund Insurance Cos., said they have withdrawn or intend to withdraw from the auto insurance business in California as a result of the passage of Proposition 103, which was backed by consumer advocate Ralph Nader.On Wall Street, stocks of several companies handling large amounts of insurance in California were down Wednesday.