I just returned from Sri Lanka, and yes, mosquitos are a problem just about everywhere on the island. I forgot to investigate before I left (or I may have read that they are not prevalent there), so my driver took me to a pharmacy, and I bought some citronella oil spray. I think it may have helped, but you are better off taking DEET from home.

I did not visit Galle, so I cannot help with your itinerary, unfortunately. I thoroughly enjoyed the Sinharaja National Forest, but I'm not sure if it can be done as a day trip from Galle. Driving times on the island are very long.

I have visited Galle, although I did it as a day trip from one of the beaches. I do not think it is a good location for day trips other than to the beaches. You should allow (much) more time than you would expect for travel on most of the roads in SL.

Surfing is possible in various spots around Galle, try Mirissa, Narigama, and Ahangama areas. October is inter monsoonal so weather may be unpredictable. National parks may be too far for a day trip. You may try Kanneliya which is rainforest very good for small amphibians, frogs, serpents and birds if that is of interest to you. Sinharaja rainforest, Yala NP will take about 3 hours each way. There are some low country tea plantations close to Galle but need to make some inquiries about visitation. Mosquito repellant by the brand name Odomos is available in many pharmacies in Sri Lanka. I use this all the time when visiting the jungles etc and find it quite effective.

I was recently talking to a good friend of mine, who is a wind and wave surfer frequenting Srilanka's beaches.October through April is said to be ideal surfing conditions for south Srilanka.The warm tropical currents ensure consistent clean swells of not more than 5 ft, with an occasional big ones.Said to be quite ideal for beginners too.Some of the known surf points are,starting from the
southernmost,Mirissa,Welligama Beach,Midigama,Plantation point,
Ahangama,Kabalana,Unawatuna and Hikkaduwa reef.

The more adventurous and advanced surfing is in the east coast area of Arugam Bay.

Galle is not the best of places to stay.Look for beautiful seaside cabanas,cottages,boutique bungalows between Matara-Mirrisa and Unawatuna.

Yala national park,known for its healthy population Leopards and Eles, is worth a visit.

So is the Sinharaja Reserve forest and many tea plantations nearby.There are many.One such recommended place The Handunugoda Tea Estate

http://hermanteas.com/tea-appreciation/

Riding a scooter in Srilanka has its element of risk,single track,often getting pushed off the road by the buses and other larger vehicles.Cops on the prowl and at every bend.Out to make a quick buck.Keep all documents ready at all times.Speed limit being 70kms/hr on national highways.

I had a car and driver when I was there last month.There were some anxious moments,but having driven and driven around in India it was rather 'bland and zestless'

Mosquitos as CL mentioned above are everywhere.Be prepared to get mauled relentlessly.I particularly found the sting very sharp and painful than anywhere else in the world.The repellent I had take with me was a citronella based Mozaway. Didtn't seem to be very effective.
I'd sometimes wished I had taken a full-body bee suit.

..and of course Mohammed above will have great and up to date advise.

Interested to read about others' experiences with mosquitoes. I am a mosquito magnet, unless I am taking Malarone, which I don't remember doing for S.L. But I also don't remember having a problem with them despite not wearing repellent. Maybe it was because I was there in January.

Thursdays, here's my mosquito story, in detail:

1. Like you, I thought there were no mosquitoes in SL, so I didn't take Malarone, nor did I bring DEET.

2. On my first morning in Negombo, the British expat hotel owner told me that mosquitoes were prevalent all over SL, and I should buy some citronella spray. I ignored his advice for the first three days.

3. I stayed in Dambulla for the next four nights, and did indeed notice some red bites around my ankles--nothing seriouus, just a few red spots. I was not certain that they were mosquito bites, so I bought some citronella spray as a precaution.

4. After that, I did not get any more bites, but it may have been due to the fact that I moved to a new location, and not due to the citronella.

So in summary, I am still not convinced that there are many mosquitoes in SL, but there are some sort of critters that bite humans, especially when one has to walk around the sites barefoot.

CaliforniaLady - it wasn't so much that I thought there were no mosquitoes, but that the CDC didn't show any malaria, or, for that matter, dengue and chikungunya. I don't recall any bites round my ankles either, but I usually get mosquito bites further up. There was a lot of water around when I was there, as there had been much more rain than usual and there were floods in part of the island. The barefoot requirement was a real pain as a lot of places were wet and muddy.

Not sure whether I just got lucky or it's the difference between October and January.

Or perhaps, thursdays, the bugs liked chewing on my skin better than yours. It's difficult to make a scientific conclusion based on the facts at hand.

I'm still not sure what type of bugs they were--they never identified themselves.

Mosquitoes didn't really get us anywhere either (Galle, Udewalawe, Kandy, Nawalapitiya, Dambulla, Polonuwarra) We went in April though. Hot and sticky in many of those places, but just lucked out on mozzies, I guess.