Or HaChaim on Exodus 10:12/אור החיים על שמות י׳:י״ב

1 בארבה, with locusts. The word may either refer to a single locust which stuck to Moses' staff, or he may have articulated the word ארבה as he inclined his staff as a sign that the reason he inclined his staff was in order to initiate the plague of locusts.