The employer contributions toward the cost of the fund shall be as actuarially determined and approved by the board and, in making such determination, the adjutant general of the state shall supply the board with such information at such times and in such manner as the board shall specify by rules and regulations. The amounts determined as the employer contributions shall be certified to the Office of the State Treasurer at such times as the board shall specify by rules and regulations. It shall be the duty of the state treasurer to pay to the board, from funds appropriated or otherwise available to the fund, the amounts certified by the board. All employer contributions shall be irrevocable and may be used only for the exclusive benefit of members.