Pattaya is in tropical zone. All China is laying more to North. There are some mosquitos in Shenzhen, but they are living in parks around ponds. Whole city is free of mosquitos - at least as per my impressions at time of few visits in different seasons: wind from ocean blows them.
By the way: in Pattaya I never met mosquitos at time when I had stay in hotels at first line near sea like Bondy, Rooms Club, Tui's, B&B - also wind blows them.