Jumping plant lice or
psyllids form the
family Psyllidae of small plant-feeding insects that tend to be very host-specific, i.e. each plant-louse species only feeds on one plant species (monophagous) or feeds on a few closely related plants (oligophagous). Together with
aphids,
phylloxerans,
scale insects and
whiteflies, they form the group called
Sternorrhyncha, which is considered to be the most "primitive" group within the true bugs (
Hemiptera). They have traditionally been considered a single family, Psyllidae, but recent classifications divide the group into a total of
seven families; the present restricted definition still includes more than 70 genera in the Psyllidae. Psyllid fossils have been found from the early
Permian before the
flowering plants evolved. The explosive diversification of the flowering plants in the
Cretaceous was paralleled by a massive diversification of associated insects, and many of the morphological and metabolic characters that the flowering plants exhibit may have evolved as
defenses against herbivorous insects.
