It’s grain, not missile, silos these spies are tiptoeing around. U.S. authorities nabbed a Chinese agribusinessman — suspected of operating with his government’s blessing — carrying contraband on a flight from Chicago to Beijing. Hidden under the microwave popcorn, they found envelopes containing single kernels of specialized corn varieties. They’re seen as vital to China’s shaky food supply, especially with a nouveau middle class hungry for corn-fed beef. China holds huge U.S. debts — and relies heavily on Midwestern grain imports — so high-yield seed could alter the balance of power.