Tribolium confusum

Although most frogkeepers use Drosophila as their basic frog food, flour beetle larvae are a very useful backup for when your fly cultures fail, and also a good way of diversifying the diet. Flour beetles are probably the easiest of the ten different types of livefood I culture, and among the most productive. However, at the outset I came close to disposing of my cultures in frustration. What changed? I worked out a simple way of harvesting the larvae (and only the larvae), described below.

What's a flour beetle?

Tribolium beetles are a common pest in stored grain products, including materials such as flour stored in your home. The adult beetles are about 4 mm in length, are closely related to and look like a tiny version of a mealworm (Tenebrio sp.). They are cultured in a similar way to mealworms using a dry, flour-based medium. There are two common species of flour beetle found worldwide, Tribolium castaneum, the red flour beetle and Tribolium confusum, the confused flour beetle. I should point out that the beetles are not confused, it's taxonomists who cause all the problems. When they were first named, Tribolium confusum was called Tribolium castaneum until it was realized that there had been a mistake so the name was changed. Confused? The beetles aren't. What's the difference between them? It's hard to tell with the naked eye, but adult confused flour beetles have the antennae which gradually enlarge toward the tip while the antennae of the red flour beetle have the last three segments of the antenna abruptly enlarged. The important difference is that Tribolium confusum cannot fly, but Tribolium castaneum may fly on occasions, so if you don't want your house filled with flour beetles (ooh, nasty), culture T. confusum.

Adult female beetles may live for as long as two years, depositing 300 to 400 eggs during that time, although most egg laying is done by young adults. The mature larva is brownish-white, has six almost invisible legs, and is up to 12mm long. The complete life cycle requires one to four months, depending on the temperature.

How do you grow flour beetles?

The standard growth medium consists of sifted flour plus dried yeast. I use strong brown bread flour and sift it to remove the larger flakes of bran which will get in the way later. However, dried yeast granules do not pass though a fine sieve, so instead I use powdered baby milk (packed with nutritional goodies) in a ratio of about 4:1 flour:milk, although I don't bother to measure the quantities accurately.

The cultures need to be kept dry or you will have problems with mites and mold. I do add vegetable peelings sparingly to supply a little moisture and reduce cannibalism by the adult beetles, but this is not essential. Open plastic boxes are often used for flour beetle cultures, but the beetles can sometimes climb out, so I cover my cultures with lids containing a large, fine-mesh ventilation panel, which also keeps intruders out. I also place a few pieces of screwed up kitchen paper towel on top of the culture which the beetles like to climb on. This makes it easy to harvest the adults when you need to start a new culture. Adult beetles sometimes build up to high densities in cultures. Since old beetles lay fewer eggs than young beetles, and because the adults may cannibalize eggs and larvae, it is best to remove excess adults by removing the paper towel with its passengers and replacing it with fresh paper.

The adult beetles have glands on the abdomen and thorax which release a pungent gas containing bitter-tasting quinones when the insects are agitated. This is one reason (in addition to preventing mold and mites) why cultures need good ventilation. It also means that most frogs find the adult beetles distasteful, although some frogkeepers use do use the pale-coloured newly emerged beetles. Frogs that have been exposed to the nasty-tasting adult beetles will often refuse to take them again, and may also refuse the larvae, presumably on the basis of smell. For this reason, it is necessary to separate the larvae from the beetles.