there are disclosed macrolides isolated from the fermentation broth , with avermectin bla , avermectin blb or 22 , 23 - dihydro avermectin bla as a substrate , of a known microorganism identified as ma - 6181 . the structure of the novel compounds isolated from the microorganism are presented based upon analytical studies . the compounds are highly potent antiparasitic , insecticidal , and anthelmintic agents . compositions for such uses are also disclosed .