Gavriil Popov: An electronic music pioneer?

A few days ago, I purchased the above album from Presto Music (a site that has a good selection of classical music, suitable for filling in  some gaps in my collection) and I've listened to the recording several times. When I paid attention to the first piece in the suite, I thought, "Is that a theremin?"

Gavriil Popov's Symphonic Suite No. 1 dates from 1933 and was derived from film music. A theremin is an electronic instrument, dating from 1928. 

So I ran a search, and here's the answer to my question, from Laurel Fay: "Appropriately, the performance features a theremin, an electronic instrument invented in Russia in the 1920s by Lev Termen (1896-1993). In his score, Popov offset the futuristic sound of the 'electric' theremin with the 'human' voices of a soprano and tenor." And here is another article. 

The use of electronics alongside regular acoustic symphonic instruments is no longer startling; this Wikipedia piece on Finnish composer Kaija Saariaho notes, "Her work in the 1980s and 1990s was marked by an emphasis on timbre and the use of electronics alongside traditional instruments."

But Popov's piece dates to the early 1930s. Wouldn't the use of an electronic instrument in a "serious" composition back then be unusual and pioneering? Is there an earlier example?