Why does he address the Zekenim?
Radak: They saw more, i.e. what passed in their days - "Zekenecha v'Yomeru Lach" (Devarim 32:7).
Malbim: They will remember if such a matter occurred in previous generations.
Why does it add "v'Ha'azinu Kol Yoshevei ha'Aretz"?
Malbim: They will tell this wonder to their children after them.
What does "ha'Haysah Zos" refer to?
Rashi: What is said below. Radak - the prefix Hei introduces a question. Malbim - was it in your days? You lived a long time!
Was this not in the days of their fathers? Also in Egypt, locusts ate everything!
Radak: The locusts in Egypt were only one species. Even though it says "va'Yiten l'Chasil Yevulam [vi'Ygi'am la'Arbeh]", "va'Yavo Arbeh v'Yelek v'Ein Mispar" (Tehilim 78:46, 105:34), Arbeh was primary; the other two merely came with it. Therefore, the Torah mentioned only Arbeh, and they were for [a short] time 1 . Here were four species - Gezem, Arbeh, Yelek and Chasil, and for four years, one after the other. Such an evil did not happen before Yo'el.
Malbim: Makas Arbeh was in the days of their ancestors; but not in the days of their fathers.
Malbim (4): Here there were four species, and each ate what the previous left over. This never occurred before.
The primary opinion in the Midrash holds that the first eight Makos were decreed for a week each; Pharaoh asked Moshe to pray to end Arbeh [and Tzfarde'a, Arov and Barad] earlier. (PF)
It says about the locusts in Egypt "v'Acharav Lo Yihyeh Ken" (Shemos 10:14). Below (2:2), it says "Kamohu Lo Nihyah Min ha'Olam" (the locusts in the days of Yo'el were worse)!
Refer to 2:2:5:1-3.
