Are they somewhat oval in shape? You could have mealybugs. The nymph forms are smaller than grains of sand and are a pale buff yellow. They hatch under the dead mother's body. If you find this soft gramular material under the white ovals, you have them.

Sucking insects like aphids and mealys will cause a leaf to curl, because they drain the plane of the leaf that they grow on of nutrients, causing it to grow more slowly than the opposite (usually upper) surface. This has the added benefit to them of creating a refugia from predators.

I think maybe it is. Now my leafs will fall themselves although they are still green. How can I get rid of it? Does these bugs will infect the other leafs or my other plants? Thank you very much!

Control options galore!

You could take a hose and apply a water jet on the plant. This washes off the bugs, you have to repeat the action once a week for several weeks. However, you risk damaging the plant.

You could prune off the parts of the plant that are infested. You might get a bushier plant that way.

You can take rubbing alcohol and a q-tip, and dab the alcohol on each insect if there are not too many of them, chanting expletives at each one in the process. (Of course this is one of my favorites, but then again, I am an entomologist bwahahahahaha.)

You can take the chemical route and use a standard insecticide you can buy from a garden center, provided the product is labeled for the bug and plant (legal matters here).

You can use a product like Safer's Soap, which works well on many soft-bodied pests like aphids and mealybugs. It has been my experience the plant sometimes is shocked into cessation of growth for a while after 1 application. The plant eventually revives but I have also lost plants this way.

You can buy lacewing and/or ladybird beetle larvae and release them onto your plant, or collect the immature predators from other plants and put them on your infested salvia. You can't be squeamish of handling critters like these, however.

Last resort: You can toss the plant and buy a new one from Richard!

Joseph