Damning Evidence

Last October I presented a blog illustrating some foes of folks attempting to grow and flower orchids in a rainforest habitat Here is further evidence of the damage that some local, native cockroaches can o to orchid flowers.

As an entomologist with a fondness for cockroaches (I have identified some 70+ species on my rainforest block!) I was reluctant to accept that they could do significant damage to exotic orchids. How wrong was I! To reduce the damage to my plants from Red-legged Pademelons and Cassowaries, I suspend my orchids on the balcony of the verandah using barbed wire. This is some 7-10 m from the ground. [Why barbed wire? Well it spaces the plants nicely and prevents the hangers from moving towards other plants. But be careful; barbed wire hangers in the wrong place can be a hazard to humans and wildlife.]

But I digress. I have a number of Stanhopea orchids. These are large plants that flower from beneath. That is they are potted in baskets and the flower spike emerge either laterally or from beneath the basket. So it is not practical to bring the plants into the house when they are flowering. So they are at the mercy of the ambient fauna. Examination of the flowers at night provided some distressing observations.

A portion of the balcony where the orchids are kept.
The evidence! This is a blattellid cockroach in the genus Beybienkoa. It is an undescribed species and not uncommon around our forest. It can be seen eating the petals of the Stanhopea wardii.

At the same time, an equally destructive character, a katydid named Austrosalomona sp. 10, was doing its share to reduce the orchid display to shreds. The katydid is much larger than the cockroach so it would consume much more. But there is the numbers game to consider. I collected more than 60 specimens of the cockroach but only found 3 of the katydid.

I might be partially responsible for the orchid carnage because just a few metres away from the flowering plants is the bird-feeding tray. It had the remnants of the day's offerings which consisted of mango seeds, orange halves and banana. This is absolutely irresistible to any self-respecting cockroach passing by. So I was not too surprised to find a number of species feeding on the fruit. What was a surprise was to find them eating orchid flowers.

Here we find two species of closely related cockroaches feeding on the fruit at the bird feeder. Beybienkoa sp. 1 is much larger than its close relative Carbrunneria paramaxi (Roth) seen here feeding with it.

As an aside, I might say that cockroaches are fairly easy to identify. They have many characters that can be used in identification. The most useful and often definitive are features of the male and female genitalia. But the colour patterns of the pronotum, banding of the legs, pattern and spotting of the face and size are all very useful in separating species.
The pronotum of many cockroach species is species-distinctive relative to pattern, spotting etc.

This is another blattellid species, Neotemnopteryx sp. It is one of four species in the genus that we have here on the property. This one is a female and I cannot associate it with a species name. Females in this genus are almost identical to one another. Hopefully, the males can recognise them better than I can!

It should be noted that of the 60+ individuals of the Beybienkoa species found on the fruit and orchid, only 3 were males. The reason for this may be that females are constantly producing eggs and require more food than the males to nurture this process. All of the individuals of the other species were females as well. However, there was one male of the Austrosalomona katydid feeding on the orchid.
The Australasian Cockroach, Periplaneta australasiae, is an unwanted visitor. This species is a cosmopolitan pest and I have not found it far from the house. It should be controlled wherever it occurs. Unlike the native species, this one gets into the house and can live there if conditions are right. It can transmit a variety of diseases and maladies because it runs over garbage and sewage as well as food and in so doing moves disease organisms with it. Fortunately, the majority of native cockroaches cannot survive for long in the house. They are much more attuned to outside conditions and the general dry atmosphere of the home combined with foods they do not eat, contributes to their demise in domestic situations. But the Australasian Cockroach it is different. These cockroaches should be eliminated from homes, hospitals restaurants and the like.

If you would like to learn more about cockroach ecology, behavior and natural history, there is a recent book that will answer most questions. See below.

Reference

Bell, W. J., Roth, L. M., Nalepa, C. 2007. Cockroaches, Ecology, Behavior, and Natural History. Pp. 1-230. Johns Hopkins University Press, Baltimore, Maryland.