Mr. Lusmar was the first husband of Eva Bechtold Rudolf. They had at least one child, a daughter named Katarina Lusmar. Mr. Lusmar probably died by 1768 or 1769. His wife Eva Bechtold remarried to Baltasar Rudolph and the couple had their first child in 1770.
There are no Lusmars in any of the early immigration records, so that surname was probably misspelled in the 1775 Grimm census.
Although Mr. Lusmar is not named in the 1775 census, his daughter Katharina is. I've included a copy of that census entry below to connect him to his daughter in Grimm.
Head of the Household Baltasar Rudolf [sic], age 36
Wife Eva [Bechtold] Rudolf [sic], age 40
Child #1 Johann Konrad Rudolf [sic], age 14
Child #2 Georg Karl Rudolf [sic], age 18 (out of order, maybe 8?), see notes above
Child #3 Georg Heinrich Rudolf [sic], age 5
Child #4 Carolina Rudolf, age 3
Stepdaughter Katarina [sic] Lusmar [?], age 16
Eichhorn, Alexander, Dr., and Dr. Jacob and Mary Eichhorn. The Immigration of German Colonists to Denmark and Their Subsequent Emigration to Russia in the Years 1759-1766, Druck and Bindung: Druckerei and Verlap Steinmeier GmbH & Co. KG, 86738, Deiningen, Germany; Published 2012.
Stumpp, Karl, The Emigration from Germany to Russia in the Years 1763 to 1862, published by the American Historical Society of Germans from Russia, Lincoln, Nebraska, 1978-1993.
Pleve, Igor. List of Colonists to Russia in 1766, "Reports by Ivan Kulberg," Ministry of Education and Science of Russian Federation, Saratov State Technical University; Published in Saratov, Russia 2010.
Rauschenbach, Georg. Deutsche Kolonisten auf dem Weg von St. Petersburg nach Saratow, Transportlisten von 1766-1767, Published in Moscow, Russia, 2017.
↑The 1775 and 1798 Census of the German Colony on the Volga, Lesnoy Karamysh, also known as Grimm; Published by the American Historical Society of Germans from Russia, Lincoln, Nebraska, USA; Published date: 1995; family #74 in the 1775 Grimm census, Baltasar Rudolf family.