Lenders continued to introduce price differentials between their mortgage rates for owner-occupiers and for investors during September.Comparison site Mozo reported that 12 lenders made changes to their rate structures last month, increasing rates for investors by as much as 40 basis points. Changes to investor rates have dominated activity in the mortgage market since May.In the latest round of changes, Adelaide Bank increased variable rates for investors by 40 bps on loans with loan-to-valuation ratios up to 90 per cent and by 20 bps for loans with LVRs over 90 per cent (these already attracted a 35 bps premium).ME added 40 bps to the investor option on its Basic Home Loan and 36 bps to its Flexible Home Loan with a member package.CUA had previously introduced a 30 bps premium for investors borrowing its Fresh Start Basic and Fresh Start Access loans but has now extended the pricing difference to all its variable rate loans.Citibank added 27 bps to variable and fixed rates for investors.HSBC has stopped accepting new mortgage applications from investors altogether and has added 27 bps to the variable rate for all existing investor borrowers.Other lenders that increased rates for investors last month include Auswide Bank, Bendigo Bank, Credit Union SA, firstmac, loans.com.au, People's Choice Credit Union and Suncorp.