Photographer: Pest and Diseases Image Library
Copyright: CC BY-NC 3.0
Diaphorina citri are small brownish insects, growing to only about 1/8 inch in length, and usually feed on the underside of leaves. They feed with their heads down almost touching the surface of the leaf and, because of the shape of their head; their bodies are lifted at about a 45° angle. Adults can live for 1-2 months at temperature below 68oF. The adult female abdomen turns bright yellow-orange when she becomes gravid and lay bright yellow-orange, almond-shaped eggs on the tips of growing shoots.
Larva Description: Diaphorina citri nymphs are generally yellowish-orange in color and feed exclusively on new growth. The feeding nymphs produce waxy tubules that direct the honeydew away from their bodies. Also, they move in a slow, steady manner and have five nymph stages (instars) that look similar, but the nymphs increase in size after each molt. The later instars have large wing pads.
Host Plant: The host range of Diaphorina citri includes 25 genera in the family Rutaceae, although not all of those species are good hosts. The most common or preferred hosts are in the genera Citropsis (cherry oranges), Citrus (lemon, lime, orange, grapefruit, kumquats etc.) and Murraya (curry, orange jasmine and jessamine).
The most serious damage caused by Diaphorina citri is due to its ability to efficiently vector the phloem-inhabiting bacteria, Candidatus liberibacter asiaticus that causes citrus greening disease (Huanglongbing). This disease has already forced the Florida citrus market to grow indoors and went from over 80 citrus companies in Florida alone to only 35 firms; leaving trees, people and their livelihoods devastated by this bacterium.
For more information on Citrus Greening Disease (Huanglongbing) click here
Development from egg to adult requires 16-17 days, and, the psyllid could complete up to 30 generations per year. Asian citrus psyllid populations decrease in density when citrus is not flushing because the immature stages require flushing plant material. Diaphorina citri was present year-round in southern Florida on orange jasmine, a common ornamental shrub. Densities peaked in May, August, and October through December in southern Florida. This coincided with new flush growth in the orange jasmine. This plant is thought to serve as an alternate host for Diaphorina citri when citrus is not in flush because of its more continuous flushing pattern.
In June 1998, the insect was detected on the east coast of Florida, and seemed limited to dooryard host plantings at the time of its discovery. By September 2000, this pest had spread to 31 Florida counties. The psyllid was first detected in California in 2008 and is now confirmed to be in San Diego, Imperial, Riverside, San Bernardino, Orange, Los Angeles, Ventura and Tulare Counties, resulting in quarantines and restricted areas. In 2009, Diaphorina citri was found in Georgia, South Carolina, Louisiana and Texas. Certain areas in South Texas have been quarantined due to the presence of this insect. In 2012, Citrus Greening Disease was found in a commercial orchard in San Juan, Texas. Now the Texas Department of Agriculture has quarantined Cameron, Hidalgo and Willacy counties in South Texas. Also, Fort Bend, Harris and Montgomery counties have been quarantined.
U.S. Habitat: Where citrus trees grow, in states that are warm year round and maintain humidity’s above 50%. This is why Florida and California have become so susceptible to Diaphorina citri; and why South Texas is in danger also.
U.S. Present: CA, FL, GA, LA, SC and TX
Yellow "sticky card traps" are placed in citrus trees in residential or commercial properties, both the color and the pheromones on the trap attract the psyllids to it. If the Asian citrus psyllid is found on a tree the next step is to analyze the populations for Huanglongbing. Nursery trees and propagation source trees exposed to psyllids in an HLB-infected area must be considered as compromised, particularly since there is no reliable diagnostic method available to certify with certainty that they are disease-free. Success in citrus production will depend on internal grove management.
Asian citrus psyllid populations in Florida have many generalist predators such as spiders, lacewings, hover flies and minute pirate bugs. Two lady beetles, Olla v-nigrum and Harmonia axyridis, are the most important predators of Asian citrus psyllid nymphal populations in Florida. They consume the nymph stage of the psyllid and interrupt the insect’s lifecycle altogether. Also there are two, tiny, wasp parasites of the nymphs that have been imported, investigated for safety to the environment, and released in Florida. Tamarixia radiata and Diaphorencyrtus aligarhensis both imported from Taiwan; with only T. radiata establishing. The wasp lays its eggs underneath the psyllid nymph where the larva feeds on and kills its host. The parasite then emerges as an adult. The 2 ladybird beetles and wasp parasitoids are natural means of maintaining the Asian citrus psyllid populations and preventing the insect vector from continuing the Citrus Greening Disease lifecycle. Thankfully, both adults and nymphs are also susceptible to insecticides.
da Graça, J. V.; Kunta, M.; Sétamou, M.; Rascoe, J.; Li, W.; Nakhla, M. K.; et al.(2015). Huanglongbing in Texas: Report on the first detections in commercial citrus. Journal of Citrus Pathology, 2(1).
Halbert, S. E., & Manjunath, K. L. 2004. Asian citrus psyllids (Sternorrhyncha: Psyllidae) and greening disease of citrus: a literature review and assessment of risk in Florida. Florida Entomologist, 87(3):330-353.
McFarland, C. D. and M. A. Hoy. 2001. Survival of Diaphorina citri (Homoptera: Psyllidae), and its two parasitoids, Tamarixia radiata (Hymenoptera: Eulophidae) and Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae) under different relative humidities and temperature regimes. Florida Entomol. 84:227-233.