See addition to answer below my original answer in italics.

Dieback in camellias can be related to root problems, fungal canker, or possible winter damage. Black spots on dead leaves could be fungal fruiting bodies. The white spots and insect you saw could be aphids or scale.  In order to manage the problem, you first must identify which one it may be.

Here are a few links with information on diseases and insects with photos:

Clemson Cooperative Extension – Camellia Diseases & Insects http://www.clemson.edu/extension/hgic/pests/plant_pests/shrubs/hgic2053.html

The U. S. National Arboretum – Camellias: Expanding Their Territory http://www.usna.usda.gov/Gardens/faqs/Camellia.html

American Camellia Society https://www.americancamellias.com/care-culture-resources/insects-and-diseases 

You can contact your local Virginia Cooperative Extension Office for help with identifying the problem and for management recommendations. Just ask for the Master Gardener Help Desk. Find your local office at: http://www.ext.vt.edu/offices/index.html.  

For some reason the photos you had attached did not appear until after I submitted my answer to your question.  It appears that you have cottony camellia scale. 

Here is link to the Virginia Cooperative Extension publication Scale Insects:  http://pubs.ext.vt.edu/2808/2808-1012/2808-1012_pdf.pdf.  For control recommendations go to:  https://pubs.ext.vt.edu/456/456-018/Section04-Home-Ornamentals.pdf.  Page 4-58. 

You could still have something else going on with the plant, so you may still want to contact the local Master Gardener Help Desk.