Psyllid Insect Vectors & Transmitters Of Citrus Greening Disease

In 1998 the Asian citrus psyllid, scientifically known as Diaphorinacitri, was detected for the first time in the U.S. in Florida. Initially, there were no alarms. Then, in 2005, citrus greening disease appeared on diseased plants with mottled, discolored, distorted leaves and damaged fruits that bore witness to the illness. Citrus greening disease was directly linked to citrus psyllids or plant lice. Psyllids are the vectors that carry and inject bacteria into citrus and the bacteria then cause greening disease.

Asian Citrus Psyllid – DiaphorinacitriFeatures and Life Cycle

These are small, brown, gnat-like, true insects termed “psyllids”. They are about 3 to 4 mm in size and feed on citrus leaves and shoots. Psyllids have a typical life cycle which includes eggs, nymphs, and adult females and males. Adults and nymphs are pictured in photos below (click to enlarge).

The psyllid transmit the disease-causing bacterium into the citrus plants. Other evidence of psyllid activity includes common psyllid nymph forms with their distinctive white wax-like exudates (see photo below).

These are the basic features of Diaphorinacitri:

  • Are of two sexes with female and male insects
  • Both adult males and females feed upon leaves by means of a sharp piercing and sucking mouth part that Permits penetration and feeding from the phloem of the citrus plant
  • Fertilized females deposit yellow, ovoid eggs, which resemble tiny seeds, on new citrus leaf shoot folds and surfaces
  • Eggs develop and generate nymphs or immature larvae that go through five progressive stages (instars) with intervening molts of exoskeleton to develop into mature insects within about 30 to 45 days
  • Have a life span of about 30 to 90 days
  • Feed preferentially on cultivated citrus and citrus-related members of the family Rutaceae and include popular ornamental plant species such as orange jasmine, Murrayapaniculata, and orange boxwood,Severinia Buxifolia. Thus, certain landscape ornamentals may permit psyllid populations to build up and this increases the risk of spreading the disease to other ornamental and citrus plants.

Citrus Leaf and Plants Effects of Psyllid, Diaphorinacitri, Feeding and Growth

The psyllids feed voraciously on the leaves of citrus plants. Citrus greening disease occurs in most citrus species, types, varieties, cultivars, and related plants such as: sweet oranges, mandarins, grapefruits, lemons, tangelos and some citrus relatives such as Atalantia(wild lime, wild lemon) Balsamic Citrus(Uganda powder flask fruit), Calodendrum (cape chestnut), Clausena(wampee), Fortunella(kumquat), Microcitrus(finger lime), Murraya (orange jasmine), Poncirus(trifoliata orange), Severinia (orange boxwood), Swinglea(tabog), Toddalia(orange climber, a liana), and Triphasia(limeberry).

The psyllids prefer fresh citrus shoots and leaves which are valuable for laying eggs within and nurturing nymphs. Phloem plant vessels, which transport sugars and other nutrients throughout the plant, are pierced by the insects. Then plant fluids and dissolved nutrients are sucked up and into the insect.

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Since many psyllids are frequently infected with the pathogenic bacterium of citrus greening disease, these feeding psyllids are disease vectors which often inject greening-disease bacteria into the phloem.

The citrus greening disease bacteria cause leaf curling and mottling and distorted, bitter fruits. These disease effects are possibly related to partial and full blockage of the phloem by the bacteria and some plant byproducts produced in response to the bacterial infection.

Can Citrus Greening Disease Be Cured

Perhaps, or maybe, is probably the best answer – but not right now. Currently, citrus greening disease cannot be cured. There are ladybug and wasp predators of the nymph forms of the citrus psyllids, but these are only partially effective for control of psyllids since even a few surviving nymphs, upon becoming mature adults, can produce more psyllids. Much additional research and study is needed to find the appropriate means to kill and destroy the predator insects and the infective bacteria of citrus greening disease. Until that time comes many citrus plants remain vulnerable to devastating greening disease.

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