Hi, I'm not too sure about the mossies, never had any problems myself, but as for things to do of an evening, there is tones! The city never goes to bed really! , but heres a few,

1. Victoria Peak- you can go up the peak, its better in the day time, but great a t night too, the views are amazing (if its not too foggy!)
You can reach the peak via the Peak Tram, the 120-year-old funicular railway that departs from its terminus on Garden Road (nearest MTR: Central). Plan to arrive a half-hour before sundown and watch as the city lights come on in their varicolored brilliance.

2. Temple Street Night Market- even if just to soak up the atmosphere! in central Kowloon starts at Temple Street's junction with Jordan Road, terminates five blocks north on Kansu Street.

3.Hong Kong Skyline light show, A Symphony of Lights; You can listen to the show's music and English narration nightly live along the Tsim Sha Tsui waterfront between the Avenue of Stars and the Hong Kong Cultural Centre, the promenade outside the Golden Bauhinia Square in Wan Chai every Monday, Wednesday and Friday night, and on radio every night on 103.4FM along the harbour front

to name but a few! Hope you have a great time, I love it there!
Lisa