Why is it a problem? The green citrus psyllid causes direct damage to new growth of both young and adult citrus trees. This is expected to reduce growth rates and yield. It is not known to vector the HLB pathogen although adults can acquire the bacterium.
Where and when is it a problem? Green citrus psyllids are mostly a problem above about 1200 m asl. Most damage is seen during the spring flush, although flush can be attacked at any time. The green citrus psyllid was first recorded in 2013. It has been reported from Mendrelgang in Tsirang, near Mongar, and around Punakha and Wangdue.
Adults are small (about 2 mm long) with a green body and transparent wings. Eggs are pale yellow and turn bright yellow-orange as they mature. Eggs are laid on young leaves that rapidly fold inwards longitudinally at 90° along midribs, forming a ‘pouch gall’ that protect the nymphs as they develop. Nymphs are generally pale yellow when young with red eyes and black-tipped antennae. Late instar (older) nymphs have a green body and large yellowish wing pads. They move fast when the pouch galls are opened. The five nymphal stages look similar, but increase in size after each moult. Like the Asiatic citrus psyllid, nymphs of the green citrus psyllid also produce lots of honeydew and often have honey dew tubules.
Direct feeding damages are seen as ‘pouch galls’ on the shoots. Heavy infestations result in every shoot having ‘pouch galls’ with hardly any normal, expanded leaves. Damage occurs on both young and matured trees.
Confusion with other pests: There are currently three psyllids recorded on citrus in Bhutan. Adults are easily identified by colour and pattern. As the common names suggest, the bodies of the adult green citrus psyllids are green, black psyllids (Diaphorina communis) are black, and the Asiatic citrus psyllid, also known as the brown psyllid, is brown. Additionally, there are two other green psyllid species that have been observed on Zanthoxylum sp. Although these other green psyllid species may land and even feed on citrus it is not known whether they can develop on citrus.
In most cases, the presence of pouch galls has proved to be quite diagnostic. However, an unidentified midge also causes leaf rolls that may be confused with the pouch galls. The midge rolls the adaxial leaf surfaces inward along the midribs resulting in wart-like, tubular leaf galls. New leaf rolls usually contains the larvae inside. Pouch gall have also been mistaken for leaf mine damage, although leaf mining alone does not cause such folding of leaves.
Lifecycle: Adults and the five nymphal stages are all sap-sucking, and eggs are inserted into leaves. Little is known of their biology, but they can be expected to be able to pass through several generations a year.
Dispersal: Adults are probably weak fliers, but can easily move between hosts within an orchard.
When can damage be expected? This pest feeds on new growth. Damage is typically greatest during the spring flush, but can be expected on any new growth that appears through the year.
Hosts: The green citrus psyllid has been observed on mandarin, lemon, lime, orange and wild citrus.
Management is only required if damage is so extensive that it will significantly reduce plant growth rates. Please contact NPPC for advice if this occurs.
Monitoring should be conducted as part of regular orchard inspections, especially around the commencement of the spring flush. Look for symptoms such as the pouch galls. Look for eggs and nymphs inside the pouch galls or even honey dew and sooty mould inside aged pouch galls as nymphs may have left the pouch galls. Adults can be collected by tapping branches onto a tray (preferably blue coloured but white has worked well too).
- There are currently no non-chemical control methods developed for this pest.
- Mineral Oil may be effective but has not yet been tested.
Chemical control has not been assessed for the control of green citrus psyllids in Bhutan.
Image acknowledgements: GAC Beattie/Namgay Om