are they pests?
Yes,  crop pests.
Scale insect
Many scale species are serious crop pests. I
what is the scale insect? They are small insects of the order Hemiptera, suborder Sternorrhyncha.
wiki:20189615
Scale insect [SEP] As pests
Many scale species are serious crop pests. In 1990, they caused around $5 billion of damage to crops in the United States. The waxy covering of many species of scale protects their adults effectively from contact insecticides, which are only effective against the first-instar nymph stage known as the "crawler". However, scales can often be controlled using horticultural oils that suffocate them, systemic pesticides that poison the sap of the host plants, or by biological control agents such as tiny parasitoid wasps and ladybirds. Insecticidal soap may also be used against scales. One species, the cottony cushion scale, is a serious commercial pest on 65 families of woody plants, including "Citrus" fruits.