This is based on gene sequence comparisons. The gene in question is closely related to its plant counterpart and phylogenetically distant to any other known insect genes.

So the most parsimonious explanation is that the gene is horizontally transferred from plants to insects. The chance that it has evolved independently from another insect gene is very, very low.

They assumed HGT because they couldn’t find any ortholog phenolic glucoside malonyltransferase genes in related whitefly species, eliminating convergent evolution as a possible explanation. In addition, the phylogenetic analysis showed that the BtPMaT1 gene clustered with other similar plant genes.