Dear Sanne,
Thank you for your message. Mosquito nets are only recommended to avoid yellow fever and malaria when visiting the Amazon Forest and not for the trek which is in the Andes area. It is true that there are some mosquitos, mainly in Machu Picchu, but they are not dangerous, only annoying. So, don't worry, you won't need a net, a lotion is enough.
Should you need anything else, feel free to contact us again.
Best wishes,