of compounds named as 4 34 deoxy 4 34 epi methylamino avermectin bla blb which is best described by the following structural formula str1 wherein r is hydrogen or methyl and b benzoic acid substituted with one two or three substituents selected from the group consisting of when r is a methyl group the compound is 4 34 deoxy 4 34 epi methylamino avermectin bla and where r is hydrogen the compound is 4 34 deoxy 4 34 epi methylamino avermectin blb the preferred acid addition salts are formed with benzoic acid salicyclic acid gallic acid benzenesulfonic acid and citric acid the most preferred acid addition salt is that formed with benzoic acid the stability studies indicate the benzoic acid salt is more stable than the corresponding hydrochloride salt the benzoic acid salt as shown in table 2 of example 12 shows virtually no change after 32 weeks at room temperature and at 47 u00b0 c in the first and a slight drop at 47 u00b0 c in the second sample the data for the benzoic acid salt table 2 of example 12 when compared with the hydrochloride salt table 1 of example 12 indicates the benzoic acid salt is markedly more resistant to degradation the data also indicates in table 3 of example 13 the benzoic acid salt after 32 weeks at room temperature and 47 u00b0 c is more resistant to degradation.