Casey's General Stores Inc. earnings dropped to 58 cents per share during the third quarter of its fiscal year, down from 97 cents per share for the year-ago period. Year-to-date earnings were $3.72 per share, compared with $4.54 a year ago, according to a release. Casey's third quarter ended Jan. 31. The company said fuel margins per gallon were off slightly during the quarter because of rising wholesale costs for most of the period. Same-store sales of groceries and other merchandise for the first nine months increased 6.1 percent to $1.6 billion, while total gross profit increased 5.4 percent to $501.8 million. Casey's also said it would buy back $300 million in common stock over two years.