can you name such a  plant source?
The most important plant wax is carnauba wax, a hard wax obtained from the Brazilian palm "Copernicia prunifera".
Wax
From the commercial perspective, the most important plant wax is carnauba wax, a hard wax obtained from the Brazilian palm "Copernicia prunifera". Containing the ester myricyl cerotate, it has many applications, such as confectionery and other food coatings, car and furniture polish, floss coating, and surfboard wax. Other more specialized vegetable waxes include jojoba oil, candelilla wax and ouricury wax.
what is the scale insect? They are small insects of the order Hemiptera, suborder Sternorrhyncha. are they pests? Yes,  crop pests. what are the various stages of their life? They develop from the egg through a first instar (crawler) stage and a second instar stage before becoming adult. what do they look like? They  vary dramatically in appearance, from very small organisms (1–2 mm) that grow beneath wax covers (some shaped like oysters, others like mussel shells), to shiny pearl-like objects (about 5 mm), to animals covered with mealy wax. what is that substance of which the covers are made? They secrete a waxy coating for defence, making them resemble reptilian or fish scales, and giving them their common name. are insects the only source of this substance, or are there other sources as well? No, they can be obtained from plants and animals as well. The best known animal wax is beeswax. Lanolin is a wax obtained from wool
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Wax [SEP] Plant waxes
Plants secrete waxes into and on the surface of their cuticles as a way to control evaporation, wettability and hydration. The epicuticular waxes of plants are mixtures of substituted long-chain aliphatic hydrocarbons, containing alkanes, alkyl esters, fatty acids, primary and secondary alcohols, diols, ketones and aldehydes. From the commercial perspective, the most important plant wax is carnauba wax, a hard wax obtained from the Brazilian palm "Copernicia prunifera". Containing the ester myricyl cerotate, it has many applications, such as confectionery and other food coatings, car and furniture polish, floss coating, and surfboard wax. Other more specialized vegetable waxes include jojoba oil, candelilla wax and ouricury wax.