The spermalege (also known as the organ of BerleseSiva-Jothy, M. T. (2006) "Trauma, disease and collateral damage: conflict in cimicids," ''Philosophical Transactions of the Royal Society B,'' 361, 269–275.) is a special-purpose organ found in female

bed bug Bed bugs are insects from the genus ''Cimex'' that feed on blood, usually at night. Their bites can result in a number of health impacts including skin rashes, psychological effects, and allergic symptoms. Bed bug bites may lead to skin changes ...

s that appears to have evolved to mitigate the effects of

traumatic insemination Traumatic insemination, also known as hypodermic insemination, is the mating practice in some species of invertebrates in which the male pierces the female's abdomen with his aedeagus and injects his sperm through the wound into her abdominal ca ...

. The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege.Reinhardt, K., Naylor, R. & Siva-Jothy, M. T. (2003) "Reducing a cost of traumatic insemination: female bedbugs evolve a unique organ," ''Proceedings of the Royal Society B,'' 270, 2371–2375. The evolution of the spermalege as a female counter-adaptation for traumatic insemination was first proposed by the French entomologist Jacques Carayon in 1966.Carayon, J. (1966) Traumatic insemination and the paragenital system. In ''Monograph of Cimicidae (Hemiptera—Heteroptera)'' (ed. R. L. Usinger), pp. 81–166. College Park, MD: Entomological Society of America.

Structure

The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege. The ectospermalege is derived from the

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the o ...

. It consists of a groove in the right-handed posterior margin of the fifth

sclerite A sclerite ( Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonl ...

, overlying a pleural membrane. In order to access the female's

haemocoel The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

during traumatic insemination, male bed bugs insert their needle-like

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...

Ryne, C. (2009) "Homosexual interactions in bed bugs: alarm pheromones as male recognition signals," ''Animal Behaviour'', 78, 1471–1475. into the groove, and pierce the pleural membrane. This piercing produces wounds that leave melanised scars. The mesospermalege is derived from the

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Emb ...

. It is a membrane-bound sac attached to the wall of the haemocoel, directly beneath the groove of the ectospermalege. In all bed bug species except ''Primicimex cavernis,'' sperm are injected into the mesospermalege.Reinhardt, K. & Siva-Jothy, M. T. (2007) "Biology of the bed bugs (Cimicidae)," ''Annual Review of Entomology,'' 52, 351–374. The structure contains two main types of

hemocyte A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...

, though their function is not yet fully understood. The first of these is

phagocytic Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is c ...

and may absorb

seminal fluid Semen, also known as seminal fluid, is an organic bodily fluid Body fluids, bodily fluids, or biofluids, sometimes body liquids, are liquids within the human body. In lean healthy adult men, the total body water is about 60% (60–67%) of t ...

, whereas the other may digest

spermatozoa A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell (biology), cell, or moving form of the ploidy, haploid cell (biology), cell that is the male gamete. A spermatozoon Fertilization, joins an ovum to form a zygote. (A zygote ...

Function

The ectospermalege is visible externally in most bed bug species, giving the male a target through which to impale the female. In species without an externally visible ectospermalege, traumatic insemination takes place over a wide range of the body surface.

Exactly why males 'comply' with this aspect of female control over the site of mating is unclear, especially as male ''P. cavernis'' appear to be able to penetrate the abdomen at a number of points independent of the presence of an ectospermalege. One possibility is that mating outside the ectospermalege reduces female
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 ...
to such an extent that the mating male's paternity is significantly reduced ... The ectospermalege appears to act as a mating guide, directing the male's copulatory interest, and therefore damage, to a restricted area of the female's abdomen.

The spermalege structure serves to reduce the wounding and immunological costs of traumatic insemination. The piercing wound typically occurs in the

exocuticle The cuticle forms the major part of the integument of the Arthropoda. It includes most of the material of the exoskeleton of the insects, Crustacea, Arachnida, and Myriapoda. Morphology In arthropods, the integument, the external "skin", or "s ...

of the mesospermalege, and is repaired by "scarring substance" developed in the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the ...

. At least nine species of bacteria and fungi have been identified from the male

intromittent organ An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs ...

, and the mesospermalege reduces the likelihood of infection from such pathogenic organisms.

References

{{Reflist Animal reproductive system Cimicomorpha