The smell of the shield bug (aka stink bug)
Shield bugs (also known as stink bugs) are a group of insects in the superfamily Pentatomoidea. As summarized by this article from Rice University, the components of the chemical odor of these insects consist primarily of long chain alkanes, aldehydes, and esters. Esters are to be expected as they're the primary components of many odors. This article also includes other ecological info about the shield bugs' stink, as well as links to some references (including this peer reviewed journal article by Krall et all (1999)). 

Another article mentions a 2006 study from Clemson University that identified 2 of the aldehydes in stink bug odor as trans-2-decenal and trans-2-octenal.