Wool should be washed by hand unless you have a washing machine that uses lukewarm water (below 28°  Celsius) and has a very gentle wool cycle.
To avoid felting, please observe the following:
Use very little soap and use a wool mark approved detergent. Be careful to keep the same temperature during the entire washing and rinsing process (not above 28° Celsius). After washing and rinsing place the garment in a washing bag and spin it lightly in a washing machine. Then place the garment flat on towel and leave to dry.
Woolen garments do not necessarily need washing very often. Airing outside in damp weather will often be sufficient. Yarns from cotton and yarns made from mixed fibres containing flax and bamboo could be washed in warm water, but still we recommend the same washing instructions as for wool. 

Always store yarn and knitwear in a plastic bag or densely woven cotton bag.  
The insecticides available can have side effects and might cause allergic reactions and are therefore not advisable to use. Furthermore, a treatment with insecticides will last for approximately 3 months and will be washed out in the first washing.