Zenith National Insurance Corp. reported first-quarter net income of $57.5 million, or $1.55 per share on revenues of$280.8 million compared to net income of $39.3 million, or $1.10 per share, on revenues of $305.7 million last year. “Our net income improved in the first quarter of 2006 due to the continuation of favorable workers’ compensation deflation trends,” said Chairman and President Stanley Zax. “Also, higher short-term interest rates and investments resulted in increased investment income in the first quarter of 2006.”