One way to quickly find out what underlying provider a metasearch engine uses is to search for "my user agent". You will then normally see the user agent of the crawler in the result snippet.
Doing this on DuckDuckGo: https://duckduckgo.com/?q=my+user+agent&t=hk&ia=answer , reviles http://www.bing.com/bingbot.htm in the snippet for whatsmyuseragent.org .
> In July 2016, DuckDuckGo officially announced the extension of its partnership with Yahoo! that brought new features to all users of the search engine, including date filtering of results and additional site links. It also partners with Bing, Yandex, and Wikipedia to produce results or make use of features offered. The company also confirmed that it does not share user information with partner companies, as has always been its policy.
[0] https://en.wikipedia.org/wiki/DuckDuckGo