Observation Series
Giant Shield Bug and Its Host Plant

Dillenia suffruticosa, commonly known as Simpoh Air, is a common mid-size shrub found at wasteland or along the fringe of forest. It can be easily identified by its large bright-yellow flowers, pink seed pods, red-to-orange seeds and large simple leaves. The large yellow flowers blooms throughout the years and attract a variety of small to mid-size creatures.

A large stink bug or shield bug (Pycanum rubens) belonging to the Tessaratomidae family, is a common resident of this shrub. Shield bug, as its name implies, looks like a shield when view from the top of the insect. It is also called stink bug due to its ability to release a disgusting scent when disturbed. This particular Pentatomid bug is likely to be the largest of its kind in Singapore. I had not seen anything larger than this one yet. The adult bugs do not seem to gather in large number but in pairs or alone. Mating pairs are commonly seen but its eggs seem to be a mystery.

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Its colourful nymphs can be found on the same host plant. They are rather unusual with an almost rectangular-shape body plus an attractive light green, orange or red colour shade, which probably represent the different stages of development. Based on my observation, the newly born nymph starts red with a while lining at the top edge of its body. It is quite tiny in size. As it grows larger in size, it molts to an orange colour nymph. The final stage should be light green in colour. However, I cannot be 100% sure this is the right sequence of body colour changed. This colour-changed phenomenon can be seen in other Pentatomid bugs too.

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The left picture shows the molting of a nymph to the orange colour stage. In the background is a new born nymph. A group of newly born nymphs (picture left below) was seen nearby on the same leaf where the molting took place. The relative size of a new born nymph to that of a nymph at the light green stage and adult is shown in the pictures below. photo photo photo

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This was a newly molted adult bug found underneath the leaf of its host plant in June 2011. The whitish cast can be seen in front of the bug. It is probably correct that the final stage of the nymph is the light green stage. The adult bug picture on the right is there for contrast purpose.

The bug does contribute to the food chain. The one below was trapped in a spider web and was well prepared for the feast. The tiny orange spider (probably Argyrodes miniaceus) seen on the bug was not the host of the feast. It was likely to be an uninvited guest. The host, the Common Garden Spider (probably Parawixia dehaani), was seen resting on a leaf nearby.

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This bug was referred by most people as Pycanum rubens. However, I received a note from Philippe Magnien in April 2011 that the bug is likely to be Pycanum alternatum (or maybe P. pretiosum). In the Pentatomoidea website hosted by North Dakota State University, 3 host plants were listed for P. rubens but they did not include Dillenia suffruticosa.

On 4 December 2011, I found 2 set of eggs in the park where this bug is abundance. The first set of 10 eggs was found under the leaf the bug's host plant. Judging from the appearance of the eggs, they might be hatching soon. Could they be the eggs that I have been searching for? I cannot be sure. The other batch, seen on the top surface of the leaf of Bay Leaf Tree (Syzygium polyanthum), had 12 eggs. Based on the appearance, they should belong to a type of bug.

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For additional information on this shield bug, you can read my article which is based on my field observation of the bug. More pictures of the adult bugs and the nymphs.

Last updated: 10 June 2012

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