Red flour beetle

Red flour beetle
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Family:	Tenebrionidae
Genus:	Tribolium
Species:	T. castaneum
Binomial name
Tribolium castaneum (Herbst, 1797)

Wikispecies has information related to: Tribolium castaneum

The red flour beetle (Tribolium castaneum) is a species of beetle in the family Tenebrionidae, the darkling beetles. It is a worldwide pest of stored products, particularly food grains, and a model organism for ethological and food safety^[1] research.

The red flour beetle attacks stored grain and other food products including flour, cereals, pasta, biscuits, beans, and nuts, causing loss and damage. It may cause an allergic response, but is not known to spread disease or cause damage to structures or furniture. The United Nations, in a recent post-harvest compendium, estimated that Tribolium castaneum & Tribolium confusum, the confused flour beetle, are "the two most common secondary pests of all plant commodities in store throughout the world."^[2]

The red flour beetle is of Indo-Australian origin and less able to survive outdoors than the closely related species Tribolium 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.^[3]

Adult

This species closely resembles the confused flour beetle, except with three clubs at the end of each of its antennae.

Female red flour beetles are polyandrous in mating behavior. Within a single copulation period, a single female will mate with multiple different males. Female red flour beetles engage in polyandrous mating behavior in order to increase their fertility assurance. By mating with an increased number of males, female beetles obtain a greater amount of sperm. Obtaining a greater amount of sperm is especially important since many sexually active male red flour beetles are non-virgins and may be sperm-depleted. It is important to note that red flour beetles engage in polyandry to obtain a greater amount of sperm from males, not to increase the likelihood of finding genetically compatible sperm.^[4]

Patterns of reproductive fitness and variation in the red flour beetle

Polyandry and multiple mating in the red flour beetle

Red Flour beetles engage in polyandrous mating behavior. Polyandry specifically refers to when a female mates with multiple males. For females, polyandry can serve as a fertility assurance, thereby increasing the number of progeny.^[4]

Potential fitness benefits of polyandrous mating behavior

Successful insemination

Multiple mating events can ensure that females obtain a greater net amount of sperm, resulting in an increased likelihood of successful fertilization.^[4] In nature, repeated matings could result in males that have a low sperm count.^[4] Due to the males' low sperm count, a female may need to mate with several males before being successfully inseminated.^[4]

Although multiple mating events may result in an increased likelihood for finding genetically compatible sperm, genetic compatibility cannot always be considered a major fitness advantage for polyandrous behavior.^[4] The increased viability of embryos—due to increased genetic compatibility—did not significantly increase the number of adult beetles over time, and therefore, did not play a significant role in the fitness of the overall population.^[4] However, it must be noted that increased genetic compatibility could increase the genetic diversity of the population, which maybe useful in various different environments.^[5] High genetic diversity within a population can lead to high phenotypic variation, which can subsequently enable some variants to better survive and reproduce given a sudden environmental change.^[5]

Potential fitness detriments for polyandrous behavior

Male competition for access to females

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.^[5] Therefore, males must often compete with other males to be the last male that mates with the female, to increase his fertilization rate.^[6] By being the last male to mate with a female, it is likely that his ejaculate removed previous ejaculate from previous males, increasing the chances that his sperm fertilizes the female.^[6] In fact, in areas with limited resources, higher rates of cannibalism among competitor males can result in an overall decrease in fitness of the population since there is a net decrease in offspring production and survival.^[5]

Reduced offspring fitness

Polyandrous behavior may not always result in the propagation of adaptive genes. In the red flour beetles, the ability of a male to attract females—through pheromones—is genetically based.Males vary in the ability to attract females.^[7] However, offspring fitness is not related to the ability of the males to attract females.^[7] In other words, just because a male reproduced more often due to increased ability to attract females, does not necessarily mean the offspring have inherited the traits that result in increased fitness.^[7]

Variation in polyandrous behavior and mate choice

Variation in mating behavior between different populations

Females of different geographic regions—and subsequently, different genetic backgrounds—often show great variation in mating behavior.^[5] Certain strains of females avoid multiple mating events while other strains of female engage in higher degrees of polyandry.^[5] This variation suggests that polyandry can be advantageous in some populations but not in others.^[5]

Mate choice in female beetles

Female beetles vary in which males they choose to copulate with. Moreover, female beetles can specifically choose which male's sperm is utilized for fertilization through cryptic choice.^[8] Females that have multiple sperm receptacles can store sperm from different males and can later choose which sperm is used for fertilization.^[8]

Mate choice in male beetles

Male beetles can also vary in the females they choose to mate with. Males are extremely selective in their mate choice. They prefer to mate with mature, virgin females.^[6] If a male mates with a virgin female, his sperm has an extremely high chance to fertilize the female if another male does not mate with her.^[6] Males are able to differentiate between virgin females and non-virgin females through scent; the wax-like secretions of competitor males could be found on the reproductive glands of non-virgin females, but not on virgin females.^[6] Males that possess an increase in the number of odor receptors are better able to choose which females to reproduce with and subsequently, increase their fitness.^[6] Some males possess better suited characteristics to detect the maturity and reproductive status of the female, and as such, will preferentially breed with only those females that will have the highest production of offspring.^[6] Likewise, males that deposit stronger scents will have an indirect fitness advantage due to their^[5] odor deterring other potential mates from an already inseminated female.^[6]

Polygamy in red flour beetles

Polygamy in red flour beetles is a behavior common to both males and females of this species. Polyandry is thus polygamy in the female members of a population as discussed in the section above. On the other hand, polygyny refers to polygamy practiced by males in a population.

Polygamy in populations that lack genetic diversity

In red flour beetles, females that engage in polygamous behavior produce more offspring than those that are less polygamous. Polygamy is mostly seen in populations that lack genetic diversity. Polygamy in less genetically diverse populations is a means of avoiding fertilization between beetles that are closely related since they may be genetically incompatible.^[9] The more partners that a male or female has, the higher the chances that at least one of the matings is with an unrelated partner and the greater the genetic diversity in the offspring. In this way, genetic incompatibility is reduced and diversity is increased in a population. For this reason, females copulate with more males when genetic diversity is low in order to attain fertilization success and also increase fitness in their subsequent offspring.

Absence of fertilization failures in related beetles

In some studies, however, it has been noted that fertilization can still occur when related beetles mate. Nonetheless, it is worth noting that there is a significantly lower number of offspring produced when inbred beetles mate than when the matings are between out-bred partners. Successful fertilization observed in a small portion of research in related beetles has led some biologists to claim that there may be no inbreeding depression in red flour beetles.^[10] Even though there is successful fertilization, it is observed that a lower number of total offspring is produced, which can be argued to be a type of inbreeding depression since it lowers reproduction fitness.

Male and female recognition of relatives

During mating, red flour beetles are known to engage in polygamous behavior. Male flour beetles have been known to recognize their relatives while the females do not have this capability. Lack of the ability to recognize their relatives has led females to mate with any male within the population.^[10] Female red flour beetles are also known to store sperm after mating. More sperm is stored by the first mating, which leads to less sperm stored in subsequent matings. However, amount of stored sperm does not stop the last male mate from fertilizing the egg.^[11] This is due to the fact that with each mating, males can remove previously stored sperm thus giving their own sperm an advantage to fertilize the egg.

Polygyny and fertilization success

In red flour beetles, males are known to engage in polygamous behavior. Research largely shows that Male red flour beetles engage in polygamous behavior to avoid inbreeding depression, especially when there is competition from other males. There is a higher fertilization success in out-bred males when they compete with inbred males to fertilize the same female.^[12]

In polygamous beetles, the male that last fertilizes the female ends up having a higher fertilization success. Polygamy can thus be seen as an evolutionary result as males compete to be the last to fertilize the female's egg and contribute more to the next generation. Sperm precedence is thus a means of evolutionary competition through which the males try to achieve greater reproductive success.^[13]

See also

• Home stored product entomology
• Flour beetle

References

External links

• Tribolium castaneum genome. Beetlebase.
• Tribolium species comparison.
• Confused and red flour beetles. University of Florida IFAS.

Further reading

• Granousky, T. A. 1997. "Stored Product Pests". In: Handbook of Pest Control, 8th Ed. Hedges, S.A. and D. Moreland (editors). Mallis Handbook and Technical Training Company.