Jumping plant louse
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| Psyllidae | ||||||||||||||
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 Psylla alni
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71 genera |
Psyllids or jumping plant lice are small plant-feeding insects that tend to be very "host specific", i.e. they only feed on one plant species (monophagous) or feed on a few 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 six families; the present restricted definition still includes 71 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.
Several genera of psyllids, especially among the Australian fauna, secrete coverings called "lerps" over their bodies, presumably to conceal them from predators and parasites.
[edit] Coevolution
Insect-plant interactions have been important in defining models of coevolution and cospeciation, referring to whether plant speciation drives insect speciation and vice versa, though most herbivorous insects probably evolved long after the plants they feed on.
Citrus greening, caused by a bacterium Liberibacter asiaticum is an example of a plant pathogen that has coevolved with its insect vector, the Asian Citrus Psyllid, AsCP, Diaphorina citri, such that the pathogen causes little or no harm to the insect, but causes a major disease which can reduce citrus quality, flavor, and production as well as causing citrus trees to die. The AsCP was found in Florida in 1998, and has since spread across the southern U.S. into Texas. This disease, also known as Huanglongbing, was found in Florida citrus groves in 2005. Management methods to reduce the spread of this disease and psyllid populations depend on an Integrated Pest Management approach using insecticides, parasitoids, predators, and pathogens specific to the AsCP.
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