What are Gezem, Arbeh, Yelek and Chasil?
Rashi: They are four species of locusts.
Radak: Some expound the names - Gezem is Gozez (cuts and detaches) the grain; Arbeh is the Rav (greatest) of the species; Yelek is Lokek and Lochech (licks and devours) the vegetation; Chasil cuts off (eradicates) everything, like "Yachselenu ha'Arbeh" (Devarim 28:38).
What is "Yeser ha'Gezem"?
Radak: What Gezem will leave over at the end of its (the first) year; Arbeh will eat it in the second year. The four species did not come at once, rather, one after the other, over four years - "v'Shilamti Lachem Es ha'Shanim Asher Achal ha'Arbeh..." (2:25).
Do locusts come for particular Aveiros?
Shabbos 33a: Robbery is punished via locusts, which causes hunger. People will eat the flesh of their children. It says "ha'Oshkos Dalim ha'Rotzetzos Evyonim...; "Hikeisi Eschem... Ganoseichem... Yochal ha'Gazam" (Amos 4:1, 9), and it says here "Yeser ha'Gazam Ochal ha'Arbeh v'Yeser ha'Arbeh Ochal ha'Yelek v'Yeser ha'Yelek Ochal he'Chasil", and it says "va'Yigzor Al Yamin v'Ra'ev... Besar Zero'o Yochelu" (Yeshayah 9:19) - we read this Besar Zar'o (flesh of his children).
