Wednesday, 25 June 2008

BYO Beetles

BYO - Not "bring your own" but "breed your own" beetles. For anyone interested in learning more about invertebrates you may want to try rearing beetles and observing their life cycle. Oh and I know this is not specifically related to Tasmania but it is a convenient test for my first use of this blogging software.

Tenebrio molitor - (Mealworm beetle or Darkling Beetles)
  • Order: Coleoptera
  • Sub-order: Polyphaga
  • Superfamily: Cucujoidea
  • Family: Tenebrionidae
This Mealworm Beetle (Tenebrio molitor) is one of the largest Tenebrionids with adults at 12 and 20 mm. It is considered a commercial pest of stored grain and grain products. However, the larvae, or mealworms as they are known, are often bred and sold for feeding fish and wild birds. As they are readily available in many countries they are a great species to observe the beetle life cycle.

We ordered ours over the Net and they arrived safely packaged overnight. We kept them in a small plastic fish tank with a layer of oatmeal and bran for food. An apple cut in half an placed face down as seen in the photo, should provide enough moisture.

Obviously the apple will need replacing and the food topped up as needed. A fine mist spray could be used but be careful. Mealworms are built to tolerate very dry conditions. Too much moisture could lead to fungal infection.



All Coleoptera (Beetles) experience a complete metamorohisis, also called holometabolism, which includes four stages; the egg, larva, pupa, and imago(adult). When our mealworms arrived they were already well along in there larval development. As any arthropod grows it needs to moult or shed it's skin. The periods between each moult are known as instars and in the case of mealworms they go through about 15 instars.

Here is a photo of a mealworm:

..... and another which is in the process of moulting. When they first moult they appear white but within a day or so they take on the golden brown colouring.



A week after receiving the mealworms some were already passing through their final moult into the pupal stage. This next image shows the final larval moult.



....and here is a ventral view of the new pupa.


I removed the first four and kept them in a seperate container so that I could time their progression into adults. The next photo was take six days after pupation.

On day ten, the beetles emerged which was sooner than I had expected. The emergence process took about 20 minutes.


Notice the beetle has not yet attained its mature colouring. It is also still quite soft. This stage is described as the teneral imago.



Over the next couple of days they gradually darken and harden until reaching a dark brown, almost black, colouration.


Four days after emergence I've noticed the first interest in mating.

....and so the cycle continues.


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