Adam Clarke on Amos 7:1

Behold, he formed grasshoppers - גבי gobai is generally understood here to signify locusts. See the notes on Joel 1 (note) and Joel 2 (note).

The shooting up of the latter growth - The early crop of grass had been already mowed and housed. The second crop or rowing, as it is called in some places, was not yet begun. By the king's mowings we may understand the first crop, a portion of which the king probably claimed as being the better hay; but the words may signify simply the prime crop, that which is the best of the whole. Houbigant thinks the shearing of the king's sheep is meant.