Rhynchocoris poseidon

Crop: Citrus

Why is it a problem? Feeding on the sap of young mandarins can cause a considerable early (“summer”) fruit drop, although compensatory development of the remaining fruit can lessen its economic importance. Damage can be severe, but management is generally not needed in most years and orchards.

Where and when is it a problem? It is a problem below 1000 m asl, causing fruit drop from April to September. It can cause near complete loss in some areas. 

IDENTIFICATION

Adults are large (2–2.5 cm long) and have bodies that are more or less pentagonal. They have prominent spines on each shoulder of the pronotum. The abdomen carries, laterally, six pairs of short spines. The color is rather uniformly green (sometimes more brownish), with lateral rows of dark spots on the abdomen. Farmers recognize it as it smells if you catch it. Eggs are about 1 mm in diameter and initially white but become marked with black and red as they develop. There are five nymphal stages. Early-stage nymphs are marked with black, green, yellow, white, and orange and can have a rather black-and-white spotted appearance. Later stages look more like adults and are mainly green with black markings.

 

SYMPTOMS

The bug sucks fluid from developing fruit and leaves poison, which makes the tree abort the attacked fruit. Otherwise, the bug leaves no traces on dropped fruits. The bug causes a “Summer Fruit Drop” in mandarins when the fruits are about marble size and slightly bigger (from April to September). Dropped fruits can have brown secondary spots around feeding punctures, caused by the entry of secondary infections by microorganisms. Usually, the fruits have a brownish discoloration in the fruit center. The seed coat can also be discolored. Bug attacks can also cause shrinkage of the seed cotyledon.

Young nymphs are gregarious. Early in the morning, groups can be seen sitting on the trunks of citrus trees in a neat circle. Adults and nymphs are often observed crowded on tree trunks.

 

 

 

 

 

 

 

Confusion with other pests: Adults and nymphs are characteristic.

BIOLOGY

Lifecycle: In early summer, the females lay their eggs in batches of about 15 eggs, usually on the upper surface of citrus leaves, between May and September. The nymphs take 4-6 weeks to develop into adults. During the early stages, nymphs will crowd together on the bark. At altitudes ranging from 500 to 1000 m, there is probably only one generation per year. Two generations are possible at lower altitudes. Young nymphs are gregarious.

Dispersal: Adults fly.

When can damage be expected? The citrus shield bug can cause a very large fruit drop in some orchards. However, the causes of such outbreaks are not yet understood.

Hosts: Hosts include citrus and native Rutaceae.

MANAGEMENT PRACTICES

This is an important citrus pest, but losses can normally be minimized by frequent inspection and physical control.

Monitoring

Inspect trees weekly from April to June for young bugs in orchards where the citrus shield bug is known to be a problem. Search the trunks of trees in the early morning. Pest numbers can vary considerably between years, so vigilance is important. The action level is 10% or more trees infested with one or more bugs.

Effect of variety

Not known.

Non-chemical management

• From April to June, young bugs (nymphs) gather early in the morning on the trunks of citrus trees and can be easily killed by hand or a flat piece of wood.
• The most important predator in Bhutan is the red tree ant. They can be encouraged, even increased, by placing ant nests from forest trees in mandarin trees. However, farmers are not keen, as they can cause other problems. Nonetheless, ants are an important friend of citrus farmers and should be protected and enhanced.

Chemical management

• Pesticides are not recommended as they interfere with important natural control mechanisms (including egg parasitoids and red tree ants).
• Spot or selective spraying with any contact insecticide can be done when the young bugs group together, particularly early in the morning.

 

Version: NPPC 2017. Citrus shield bug V1.0. Bhutan Pest Factsheet. www.PestsofBhutan.nppc.gov.bt. Date produced: 14 April 2017. Contact: nppcsemtokha@gmail.com

Image acknowledgements: NPPC.