What's in a name? Although arbor sounds as if it should have something to do with trees, it doesn't. It comes from the first two letters of arthropod + the first three letters of borne. Arborviruses are transmitted (borne) to humans by mosquitoes and ticks (arthropods).
Since the name Arborvirus proved too clever by far; the spelling had to be replaced by Arbovirus, dropping the second "r" because of the potential of misidentification with trees. The first two letters of each word, arthropod' and borne, became the arbo that now associates this category of viruses with arthropods.