Italics in chapter-titles etc.

[jezZiFeR]

Hello,

I have a LuaTeX-problem for a while now, or at least my problem might have to 
do with it. In the moment words in the titles (of chapters etc.) are not 
italicized, even though in my preamble I still use the command:
\DeclareFieldFormat{citetitle}{\mkbibemph{#1}}

I use LyX 2.2.3 on OS 10.13 and use LuaTeX (and KOMA-script article). Why do 
the emphasized word not appear italicized?

Thanks
Jess