''Callosobruchus maculatus'' is a species of

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s known commonly as the cowpea weevil or cowpea seed beetle.Tran, B. M. D. and P. F. Credland. (1995)
Consequences of inbreeding for the cowpea seed beetle, ''Callosobruchus maculatus'' (F.) (Coleoptera: Bruchidae).
''Biological Journal of the Linnean Society'' 56 483-503. It is a member of the leaf beetle family,

Chrysomelidae The insects of the beetle family Chrysomelidae are commonly known as leaf beetles, and include over 37,000 (and probably at least 50,000) species in more than 2,500 genera, making up one of the largest and most commonly encountered of all beetle ...

, and not a true

weevil Weevils are beetles belonging to the Taxonomic rank, superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and Herbivore, herbivorous. Approximately 97,000 species of weevils are known. They b ...

. This common pest of stored

legume A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock f ...

s has a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

, occurring on every

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

except

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

.Cowpea weevil (''Callosobruchus maculatus'' (Fabricius, 1775)).
PaDIL. The beetle most likely originated in

West Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, Maurit ...

and moved around the globe with the trade of legumes and other crops. As only a small number of individuals were likely present in legumes carried by people to distant places, the populations that have invaded various parts of the globe have likely gone through multiple bottlenecks. Despite these bottlenecks and the subsequent rounds of

inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and o ...

, these populations persist. This ability to withstand a high degree of inbreeding has likely contributed to this species’ prevalence as a pest. It is used as a

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

for both research and education due to its quick

generation time In population biology and demography, generation time is the average time between two consecutive generations in the lineages of a population. In human populations, generation time typically ranges from 22 to 33 years. Historians sometimes use this ...

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

, and ease of maintenance.

Description

The cowpea weevil lacks the "snout" of a true weevil. It is more elongated in shape than other members of the leaf beetle family. It is reddish-brown overall, with black and gray

elytra An elytron (; ; , ) is a modified, hardened forewing of beetles (Coleoptera), though a few of the true bugs (Hemiptera) such as the family Schizopteridae are extremely similar; in true bugs, the forewings are called hemelytra (sometimes alterna ...

marked with two central black spots. The last segment of the abdomen extends out from under the short elytra, and also has two black spots.Cowpea weevil.
Texas A&M AgriLife Extension. The beetle is sexually dimorphic and males are easily distinguished from females. The females are sometimes larger than males, but this is not true of all strains. Females are darker overall, while males are brown. The plate covering the end of the abdomen is large and dark in color along the sides in females, and smaller without the dark areas in males.A Handbook on Bean Beetles, ''Callosobruchus maculatus''.
beanbeetles.org, Emory University and Morehouse College. There are two morphs of ''C. maculatus'', a flightless form and a flying form. The flying form is more common in beetles that developed in conditions of high larval density and high temperatures. The flying form has a longer lifespan and lower

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...

, and the sexes are less dimorphic and can be more difficult to tell apart. The egg is clear, shiny, oval to spindle-shaped, and about 0.75 millimeters long. The

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

is whitish in color.

Life cycle

Eggs of Callosobruchus maculatus on cowpea and azuki

A female adult can lay over a hundred eggs, and most of them will hatch. She lays an egg on the surface of a bean, and when the larva emerges about 4 to 8 days later, it burrows into the bean.Raina, A. K. (1970)
''Callosobruchus'' spp. infesting stored pulses (grain legumes) in India and comparative study of their biology.
''Indian Journal of Entomology'' 32(4), 303-10. During development, the larva feeds on the interior of the bean, eating the tissue just under the surface, leaving a very thin layer through which it will exit when it matures. It emerges after a larval period of 3 to 7 weeks, depending on conditions. In colder climates the gestation period is typically longer taking anywhere from 4–13 weeks to emerge. Larval crowding can occur when up to 8 or 10 larvae feed and grow within one bean. Crowding limits resources for each individual, leading to longer development time, higher mortality, smaller adult size, and lower fecundity. Once the beetle emerges as an adult, it may take 24 to 36 hours to mature completely. The lifespan is 10 to 14 days. However, in colder climates lifespans typically range from three to four weeks. The adult requires neither food nor water, but if offered water, sugared water, or yeast, it may consume it. A female given nutrients may lay more eggs. The beetle tolerates a range of

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...

and temperature, making it adaptable in climates worldwide. Its developmental time varies with factors such as humidity, temperature, legume type, crowding, and inbreeding levels in the population.Fox, C. W. and D. H. Reed. (2011)
Inbreeding depression increases with environmental stress: an experimental study and meta-analysis.
''Evolution'' 65(1), 246-58. A bean that is too dry will be impossible for the larva to bore into, and wet beans may have fungal growth. In experiments, a humidity range of 25% to 80% was acceptable, with different optimal levels at each life stage. The most eggs hatched between 44% and 63% humidity, and 44% produced the highest survival. The adult lives longer at 81% to 90%.Schoof, H. F. (1941)
The effects of various relative humidities on the life processes of the southern cowpea weevil, ''Callosobruchus maculatus'' (Fabr.) at 30 C., +/-0.8 degrees.
''Ecology'' 22(3), 297-305. In another experiment, temperatures of 17 °C (63 °F) and 37 °C (99 °F) with a constant humidity stressed the beetle, and the ideal temperature range was 24 °C (75 °F) to 28 °C (82 °F). The age of the female at oviposition affects the development and survival of the offspring. The eggs of older females are less likely to hatch, the larvae take longer to develop, and fewer larvae survive to adulthood.Fox, C. W. and D. H. Reed. (2010)
Inbreeding depression increases with maternal age in a seed-feeding beetle.
''Evolutionary Ecology Research'' 12(8), 961-72.

Reproduction

Copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...

is injurious for the female beetle. The male possesses

penile spines Many mammalian species have developed keratinized penile spines along the glans and/or shaft, which may be involved in sexual selection. These spines have been described as being simple, single-pointed structures (macaques) or complex with two o ...

which damage the female reproductive tract. The female may forcefully kick the male during copulation, ending the mating. It is possible that male may benefit from harming the female because the injury could reduce matings or mating success with other males, or increase her egg production. When the female is experimentally prevented from kicking the male (by removal of the hind legs), matings continued for longer than usual, and injury increased. However, the amount of time before she became receptive again and the rate of oviposition were not affected. This suggests that penile spines do not increase the reproductive success of males, and it is suspected that the spines do not increase reproductive success for either sex, and may have no adaptive value.Edvardsson, M. and T. Tregenza. (2005)
Why do male ''Callosobruchus maculatus'' harm their mates?
''Behavioral Ecology'' 16(4), 788-93. After mating, the female glues single eggs to a bean. The female generally lays fewer eggs when there are fewer hosts. In an experiment, females presented with three large beans laid more eggs than females presented with three small beans. Occasionally, females deposit many eggs onto nonviable surfaces, especially if there are few or no hosts available. This leads to a higher mortality rate in eggs and potential larvae, but it may also lead to host expansion in the long term.Cope, J. M. and C. W. Fox. (2003)
Oviposition decisions in the seed beetle, ''Callosobruchus maculatus'' (Coleoptera: Bruchidae): effects of seed size on superparasitism.
''Journal of Stored Products Research'' 39(4), 355-65.

Habitat

Temperature and

in legume storage areas are relatively constant and the food density is high. The female lays eggs on legumes in the field or in storage. Inbreeding is more common in laboratory situations where the beetle is allowed to breed continuously; breeding in the field is more limited. The beetle is known for attacking the

cowpea The cowpea (''Vigna unguiculata'') is an annual herbaceous legume from the genus ''Vigna''. Its tolerance for sandy soil and low rainfall have made it an important crop in the semiarid regions across Africa and Asia. It requires very few input ...

(''Vigna unguiculata''), but it readily attacks other beans and peas such as the

mung bean The mung bean (''Vigna radiata''), alternatively known as the green gram, maash ( fa, ماش٫ )٫ mūng (), monggo, or munggo (Philippines), is a plant species in the legume family.Brief Introduction of Mung Bean. Vigna Radiata Extract G ...

(''Vigna radiata'') and

adzuki bean ''Vigna angularis'', also known as the adzuki bean , azuki bean, aduki bean, red bean, or red mung bean, is an Annual plant, annual vine widely cultivated throughout East Asia for its small (approximately long) bean. The cultivars most familiar ...

(''Vigna angularis'').Beck, C.W., Blumer, L.S. (2013)
Life Cycle of Bean Beetles, Callosobruchus maculatus (Coleoptera: Chrysomelidae)
/ref> The adult is more likely to seek the legume in which it developed as a larva, but if it is not available or less common, the beetle will utilize another type.Messina, F. J. (2004)
How labile are the egg-laying preferences of seed beetles?
''Ecological Entomology'' 29(3), 318-26.

Behavior

Females are more likely than males to take advantage of sugar water or other resources. In an experiment to test the hypothesis that access to nutritional resources would affect the frequency of second matings, females with access to sugar were less likely to mate more than once. Available food makes the female less receptive to advances from males, which present a

nuptial gift A nuptial gift is a nutritional gift given by one partner in some animals' sexual reproduction practices. Formally, a nuptial gift is a material presentation to a recipient by a donor during or in relation to sexual intercourse that is not simpl ...

as part of courtship.Fox, C. W. and J. Moya-Laraño. (2009)
Diet affects female mating behaviour in a seed-feeding beetle.
''Physiological Entomology'' 34(4), 370-78. The gift is a

spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...

, nutritional content mixed into his

ejaculate Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential component ...

, a package which can be up to 20% of his body weight. Females with other nutritional resources can afford to refuse a mating. A female without an additional nutrient source is less choosy in the mating process. She does not even refuse matings with close relatives, such as brothers.Edvardsson, M., et al. (2008)
No evidence that female bruchid beetles ''Callosobruchus maculatus'' use remating to reduce costs of inbreeding.
''Animal Behaviour'' 75(4), 1519-24. The species does suffer from

inbreeding depression Inbreeding depression is the reduced biological fitness which has the potential to result from inbreeding (the breeding of related individuals). Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. In ...

, but it does not seem to take behavioral action to avoid it. In addition, bean beetles are known to exhibit homosexual behavior. Males will mount both females and other males. This could potentially have fitness benefits for the male, as the male does not waste time determining whether his partner is male or female. Sometimes it is faster to test physically than to attempt to determine via other methods. The female usually oviposits on the smooth side of a bean rather than the rough top, and it avoids legumes without smooth surfaces.Nwanze, K. F., et al. (1975)
Evidence for ovipositional preference of ''Callosobruchus maculatus'' for cowpea varieties.
''Environmental Entomology'' 4(3), 409-12. It also has a way of distributing the eggs among small and large legumes so that each larva has access to roughly the same amount of nutrients; its assessment of legumes is based on mass rather than surface area, and on the number of eggs already present. When preparing to

pupa A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...

te, the larva digs a cell in the bean and lines it with feces. If it encounters another larva in the bean, both retreat and create walls of feces. If the wall is removed, the two larvae fight to the death. This behavior is not well understood.Mano, H. and Y. Toquenaga. (2008)
Wall-making behavior in ''Callosobruchus maculatus'' (Coleoptera: Bruchidae).
''Annals of the Entomological Society of America'' 101(2), 449-55.

Host Preference

The bean beetle, ''Callosobruchus maculatus'', oviposit their eggs on the

bean. The species that are most common for the beetle to lay their eggs on are

black eyed peas Black Eyed Peas (also known as The Black Eyed Peas) is an American musical group consisting of rappers will.i.am, apl.de.ap, Taboo (rapper), Taboo. The group's line-up during the height of their popularity in the 2000s featured Fergie (singer ...

mung beans The mung bean (''Vigna radiata''), alternatively known as the green gram, maash ( fa, ماش٫ )٫ mūng (), monggo, or munggo (Philippines), is a plant species in the legume family.Brief Introduction of Mung Bean. Vigna Radiata Extract G ...

, and

s. If more than one host is available, the beetle will choose its host depending on the variety and size of the bean as well as the texture of the seed coat.Boeke, S.J., Dicke, M., van Huis, A., and van Loon, J.J.A. (2004
Host preference of ''Callosobruchus maculatus'': a comparison of life history characteristic for three strains of beetle on two varieties of cowpea.
''JEN'', 28, 390-396 One study showed that the beetles will choose their host depending on the geographic region in which they live.Kawecki, T.J and Mery, F. (2003)
Evolutionary conservatism of geographic variation in host preference in ''Callosobruchus maculatus''.
''Evolutionary Entomology'', 28, 449-456. It has also been found that the beetle will often switch hosts if a new host becomes available to them.Rova, E. and Björklund M. (2011
Can preference for oviposition sites initiate reproductive isolation in ''Callosobruchus maculatus''?
''PLoS ONE'' 6, 1-6. Over time the beetles will start specializing on the new host and will lose preference for the ancestral host. The beetle larvae grow inside the bean until they emerge as an adult. The time it takes the larvae to develop varies across hosts, with longer development times on less suitable hosts. It has been found that beetles that choose to

oviposit The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...

their eggs on the black eyed pea have a shorter development time, suggesting that the black eyed pea is a more suitable host. The

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

and

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...

have an effect on the developmental time as well; higher temperatures and a relative humidity range of 40%-60% shorten developmental time. The emerged adult beetles mate assortatively, meaning they mate with others that developed on the same host bean. If the hybrids of the population are less fit,

assortative mating Assortative mating (also referred to as positive assortative mating or homogamy) is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be exp ...

can lead to

speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

. One study looked at this and found

beginning to occur in early generations but because there was no selection against hybrids, recombination destroyed any

linkage Linkage may refer to: * ''Linkage'' (album), by J-pop singer Mami Kawada, released in 2010 *Linkage (graph theory), the maximum min-degree of any of its subgraphs *Linkage (horse), an American Thoroughbred racehorse * Linkage (hierarchical cluster ...

that was formed between host and mating preference which did not allow

to be completed.

Predation

The predators of ''C. maculatus'' include several

parasitoid wasp Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causin ...

s. '' Anisopteromalus calandrae'', '' Uscana mukerjii'', and '' Dinarmus'' wasps specifically target ''Callosobruchus'' species.Soundarajan, R. P., et al. 2012
Biological control of bruchid ''Callosobruchus maculatus'' (F.) in blackgram.
''Journal of Biopesticides''. 5(Supplementary): 192-95.Bull, J. C., et al. (2006)
Habitat shape, metapopulation processes and the dynamics of multispecies predator–prey interactions.
''Journal of Animal Ecology'' 75(4), 899-907.Kapila, R. and H. C. Agarwal. (1995)
Biology of an egg parasite of ''Callosobruchus maculatus'' (Fab.) (Coleoptera: Bruchidae).
''Journal of Stored Products Research'' 31(4), 335-41. '' Dinarmus basalis'' parasitizes small larvae and halts their development. This limits the damage they can do to beans, but their presence still makes the beans unfit for human consumption and usually makes them unfit for sowing, as well. ''Uscana mukerjii'' is an egg parasite which prevents the egg from hatching, thereby preventing damage to the legume.

Control

Callosobruchus maculatus on blackeyed peas

The beetle is considered "medically harmless" to humans. It is a damaging agricultural pest. In developing countries, small-scale farmers mix the crushed leaves of ''

Cassia occidentalis Cassia typically refers to cassia bark, the spice made from the bark of East Asian evergreen trees. Cassia may also refer to: Plants ;Cinnamon trees * ''Cinnamomum cassia'' (, ''ròuguì''), the cassia or Chinese cinnamon, found in southern Chin ...

'' into bean stores to deter the beetle.Lienard, V., et al. (1993)
Biological activity of ''Cassia occidentalis'' L. against ''Callosobruchus maculatus'' (F.) (Coleoptera: Bruchidae).
''Journal of Stored Products Research'' 29(4), 311-18. Other '' Cassia'' are useful, as well. The powdered leaves are effective, and a warm-water extract and the

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the o ...

from the seeds are better.Kestenholz, C., et al. (2007)
Comparative study of field and laboratory evaluations of the ethnobotanical ''Cassia sophera'' L. (Leguminosae) for bioactivity against the storage pests ''Callosobruchus maculatus'' (F.) (Coleoptera: Bruchidae) and ''Sitophilus oryzae'' (L.) (Coleoptera: Curculionidae).
''Journal of Stored Products Research'' 43(1), 79-86. The seed oil does not stop oviposition, but it increases the mortality of the eggs and the first-

instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...

larvae. The warm-water extract deters the adult female from ovipositing. Other botanical

biological pest control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

agents tested include nishinda (''Vitex negundo''),

Tasmanian blue gum ''Eucalyptus globulus'' subsp. ''globulus'', commonly known as the Tasmanian blue gum, southern blue gum, or blue gum, is a subspecies of tree that is endemic to southeastern Australia. It has mostly smooth bark with some persistent slabs of old ...

(''Eucalyptus globulus''), bankalmi (''Ipomoea sepiaria''),

neem ''Azadirachta indica'', commonly known as neem, nimtree or Indian lilac, is a tree in the mahogany family Meliaceae. It is one of two species in the genus ''Azadirachta'', and is native to the Indian subcontinent and most of the countries in Afr ...

(''Azadirachta indica''),

safflower Safflower (''Carthamus tinctorius'') is a highly branched, herbaceous, thistle-like annual plant in the family Asteraceae. It is commercially cultivated for vegetable oil extracted from the seeds and was used by the early Spanish colonies along ...

(''Carthamus tinctorius''),

sesame Sesame ( or ; ''Sesamum indicum'') is a flowering plant in the genus ''Sesamum'', also called benne. Numerous wild relatives occur in Africa and a smaller number in India. It is widely naturalized in tropical regions around the world and is cu ...

(''Sesamum indicum''), and

gum arabic Gum arabic, also known as gum sudani, acacia gum, Arabic gum, gum acacia, acacia, Senegal gum, Indian gum, and by other names, is a natural gum originally consisting of the hardened sap of two species of the '' Acacia'' tree, ''Senegalia sen ...

(''Acacia nilotica'' syn. ''Acacia arabica''). Hermetic storage technologies like the Purdue Improved Cowpea Storage bags have also proven successful in controlling ''C. maculatus''. These technologies work by separating the container environment from the surrounding air and forcing the insects inside to deplete the available oxygen inside the container Not only does this ultimately kill the insects, but it also reduces the level of damage they inflict as active feeding ceases below a certain threshold of oxygen Murdock, L.L. Margam, V., Baoua, I., Balfe, S., Shade, R.E. 2012. Death by desiccation: Effects of hermetic storage on cowpea bruchids. Journal of Stored Products Research, 49: 166-170. Animal agents of biological control include the parasitoid wasps that target the beetle. In laboratory trials ''D. basalis'' has eliminated the beetle. ''A. calandrae'' and ''U. mukerjii'' may also prove useful. Freezing the whole storage area will also control ''C. maculatus''. A period of six to 24 hours at -18 °C kills all the adults and larvae. If the cooling is slow, the beetle can acclimatize, so longer freezing is required.Johnson, J. A. and K. A. Valero
Control of cowpea weevil, ''Callosobruchus maculatus'', using freezing temperatures.
In: ''Proceedings of the Annual International Research Conference on Methyl Bromide Alternatives and Emission Reductions''. Orlando, Florida. November 6–9, 2000. pp. 90-91.

References

{{DEFAULTSORT:Callosobruchus Maculatus Bruchinae Agricultural pest insects Animal models Beetles described in 1775 Taxa named by Johan Christian Fabricius Cosmopolitan arthropods Storage pests