Which beetle cannot fly and resembles the merchant grain beetle?

The sawtooth grain beetle is the correct choice because it is a common pest in stored products and closely resembles the merchant grain beetle, particularly in terms of size and overall shape. What distinguishes the sawtooth grain beetle is its distinctive serrated edges along its thorax, which gives it a sawtooth appearance.

This beetle is notable for its lack of wings or inability to fly, which is a key characteristic that matches the criteria of the question.

In contrast, while other beetles listed may share some physical traits with the merchant grain beetle, they either do not exhibit the same physical resemblance or they are capable of flight, which is not the main characteristic being sought in this query.