Lecanium scales spend the winter on twigs and branches in an immature or nymphal stage. Development resumes in the spring and mature females produce large numbers of eggs which are protected by their soft waxy covering. The white grains you discover under the waxy shell are the eggs.
Crawlers that hatch from these eggs move to leaves, settle, and feed on sap during the rest of the summer. They move back to twigs and branches prior to leaf drop and settle for the winter.
Lecanium scale is rarely a problem in well managed pecan groves. Insecticides applied to control major pecan pests often control scale insects in the nymphal stage. In addition, lecanium scale is often kept in check by beneficial insects. You might notice small holes in the waxy shell indicating that the scale has been visited by tiny wasps, whose larvae devour scale eggs.