Are periodical cicadas a threat to field crops? The quick and dirty answer to this question is NO. Are they a threat to the health and welfare of anything? There is no quick and dirty answer to this question.
The best way to answer the second question is to start by looking at what the periodical cicada is, what it feeds on, where one would expect to find them, and its life cycle.
The periodical cicada or 17-year cicada is an insect with an extremely long life cycle that takes 17 years to get from the egg stage to the adult stage. Some people mistakenly refer to this insect as a locust. Unfortunately, locusts and cicadas are not one-in-the-same. Locusts are a type of grasshopper (Order Orthoptera). Cicadas (Order Hemiptera) are not grasshoppers. And the 2 look nothing like one another.