Red flour beetle

The red flour beetle (Tribolium castaneum) is a species of beetle in the family Tenebrionidae, the darkling beetles. The red flour beetle, and other closely related beetles like Gnatocerus cornutus, are a worldwide pest of stored products, particularly food grains, and a model organism for ethological and food safety research.

Adult beetles are small, around 3–4 mm long (1/8 inches), and have a uniform rust, brown or black color. The head and pronotum are sometimes darker than rest of body.

The red flour beetle attacks stored grain and other food products including flour, cereals, pasta, biscuits, beans, and nuts, causing loss and damage. The United Nations, in a recent post-harvest compendium, estimated that T. castaneum and T. confusum, the confused flour beetle, are "the two most common secondary pests of all plant commodities in store throughout the world." A research on hermetic storage of wheat and maize flour protects against red flour beetle (2017) was conducted that found 12 days under hermetic storage results in 100% RFB mortality and confirms that hermetic environments are sufficient for controlling insect pests.

The beetle is of Indo-Australian origin and less able to survive outdoors than the closely related species T. confusum. It has, as a consequence, a more southern distribution, though both species are worldwide in heated environments. The adult is long-lived, sometimes living more than three years. Although previously regarded as a relatively sedentary insect, it has been shown in molecular and ecological research to disperse considerable distances by flight.

Female red flour beetles exhibit polyandrous mating behavior. Within a single copulation period, a female will mate with multiple males. Any one male may have a low sperm count, having depleted its supply through prior matings, so mating with several increases the female's likelihood of obtaining an adequate amount of sperm.

Although multiple mating events may also increase the likelihood of finding genetically compatible sperm, genetic compatibility is not always a major factor driving polyandrous behavior. Increased embryo viability due to increased genetic compatibility did not significantly increase the number of adult beetles over time, which indicates that it did not play a significant role in the fitness of the overall population. However, increased genetic compatibility could increase the genetic diversity of a population, which can be advantageous in situations of rapid environmental change.

The availability of resources and population size can greatly affect how many matings each individual participates in. Increased population size within a given area with fixed resources can limit how many offspring can survive. This can result in heavy competition between males to be a female's last mate, which carries an advantage as ejaculate from one mating can be removed during subsequent matings. When resources are limited, increased cannibalism among competing males can ultimately decrease fitness for the population as a whole, as it decreases both offspring production and survival.

In red flour beetles, a male's ability to attract females (via pheromones) is genetically based. Higher attractiveness does not, however, correlate with higher fitness of offspring. Genes for more attractive pheromones are not a reliable indicator that the male also has genes which will improve offspring survival.