Catalyzes the first and rate-limiting reaction of the four reactions that constitute the long-chain fatty acids elongation cycle. Uses malonyl-CoA to add 2 carbons per cycle to the chain of long-chain fatty acids. Condensing enzyme required for the formation of isopentadecanoate (C15iso) and isoheptadecanoate (C17iso), both play critical roles in animal development and growth. 11-methyldodecanoyl-CoA + H(+) + malonyl-CoA = 3-oxoisopentadecanoyl-CoA + CO2 + CoA H(+) + isopentadecanoyl-CoA + malonyl-CoA = 3-oxoisoheptadecanoyl-CoA + CO2 + CoA Lipid metabolism; fatty acid biosynthesis. Expressed in the gut and unidentified head cells. Loss of function induces an egg-laying defect from the second day of adulthood with progeny arrested at the larval stage L1. The small larvae maintain morphological integrity and survive for up to 3 to 4 days. Animals had reduced levels of isoheptadecanoate (C17iso) and isopentadecanoate (C15iso). The phenotype could be fully suppressed by feeding with C17iso and partially suppressed by feeding with C15iso. Belongs to the ELO family.