Aphids/mealybugs are common in the winter months when the air in the house is very dry and the roots are wet. Drafts can also be a cause. Besides the pest control products available at garden centres, there is a home remedy: mix equal parts of liquid (potassium hydroxide-based) soap with methylated spirits (denatured alcohol) and spray the plant. You usually have to repeat this a couple of times as aphids and mealybugs are persistent. Try to avoid spraying the flowers, though, as the mixture can cause spotting on the petals.