The psyllids or plant suckers are a group of sap sucking true bugs (Hemiptera). There are more than 40 species found in Britain. A gallery and more information on these species can be found at British Bugs. 

Box

Suckers are growths that appear from the root systems of many trees and shrubs such as lilac, cherries, Robinia. On grafted plants such as roses, suckers can grow from below the graft union, on the rootstock material. Suckers are usually removed by gently pulling off when young.

Box is host to several invertebrate species suffer from a number of other problems.

• In spring a white waxy substance covering a droplet of liquid, excreted by box sucker nymphs often spills from the cupped leaves, leaving white waxy smears on foliage
• In April to May flattened, pale green, wingless nymphs live among the leaves at the shoot tips
• New shoot extension in spring can be stunted and the cupped leaves at the shoot tips produce a cabbage-like appearance
• Any damage is usually superficial and this insect is part of the biodiversity this plant supports

Damage from this insect is superficial and is not necessary to manage this insect especially on established box hedges or topiary plants that are going to be clipped. It is part of the biodiversity box plants support

• Often suckers do not affect the growth or vigour of plants and so should be tolerated
• Regular clipping removes affected parts of the plant
• Encourage predators and other natural enemies of suckers, in the garden, such as birds, ladybirds, wasps and ground beetles

• Box sucker overwinters as eggs on its host plant. These hatch in spring when new growth begins 
• The nymphs suck the plant's sap and secrete chemicals that stunt new growth and distort the leaf shape, although this damage is not usually serious 
• The nymphs excrete a sugary liquid called honeydew that is coated with a white waxy secretion from their bodies
• Yellowish brown winged adults, 2-3mm long (1/8in), develop in May to June
• No further damage occurs after June