Microstigmus
Encyclopedia
The thin-waisted social wasps (genus Microstigmus), which typically resides in neotropic regions from Central
to South America
, are a small genus
of wasps that build nests and live in colonies ranging in size from 1 to 18 members. Microstigmus is widely considered to be the only true eusocial
species within the Crabronidae
family. Like all Hymenoptera, Microstigmus has an interesting sex determination pattern. Females are 2n (diploid), spawning from eggs that have been fertilized, while males are 1n (haploid) and spawn from unfertilized eggs. Female wasps contain the eggs within their egg sac and have the option of fertilizing them or not, thus having complete control on the gender of the offspring. This wasp genus, part of the suborder Apocrita
, is distinguished physically by the narrow waist (petiole) between the end segment of the thorax (mesosoma
) and the beginning of the abdomen (metasoma
). Specifically, it is in the subgroup of "apoid
wasps", those that exhibit social behavior in nesting and foraging. Evidence does exist that in some species social altruism
is visible; however, studies on these topics have been limited. The small size and enclosed nest structure makes it difficult to obtain significant data. Although it was originally classified under the Sphecidae
family due to its elongated petiole
, Microstigmus has been reclassified into the new Crabronidae
family.
covering the internal organs in each of them. The species of Microstigmus ranges in length from 2.5 to 5.5 mm (0.0984251968503937 to 0.216535433070866 ). Being within the family Crabronidae, Microstigmus has a thread like waist connected between the thorax
and abdomen. Unlike other Hymenoptera
, the head and thorax (mesosoma) lack branched or plumose hairs. The wasps also have their posterior metatarsus modified into a cleaning mechanism. Many of the different species in this family have varying color schemes that serve to warn predators (some have venomous stings) or to provide camouflage
.
Sphecid wasps also have a silk gland that is important in many functions, such as nest building. The glands are formed initially with one multinuclear terminal cell from which a canal (pathway from gland to environment) is exposed to the outside environment via spinnerets. This epidermal gland evolves independently for most species under the Pemphredoninae
subfamily.
s. Most of the time, the kill is performed with the powerful mandibles literally biting through the head of the prey causing either death or immobilization. Social wasps will kill the prey and then return to the nest to provide for the young. This can be done in several ways. One is for the wasp to suck out the inner bodily fluids of the prey and carry the hemolymph
back to the nest where the adults will regurgitate
some of the fluids to the larva wherein the adult retains some of the hemolymph. This trophallaxis
between adults and larva may have played a role in social wasp evolution in three primary ways. Adults who provide nourishment for larva and get food in return may reduce the need to forage for food for themselves. Therefore flights from the nests may be more efficient where flights are only performed for larval food foraging and nest construction materials over species that do not practice trophallaxis. The larval-adult saliva exchange may also increase reproductive fitness in females. An example would be a period of inclement weather where food is hard to come by. The reproducing females would still have a source of nutrition and be able to continue reproductive cycles which are crucial in eusocial
colonies. There might also be a situation where the trophallaxis benefits the adults but also hinders the larva in form of nutritional castration where the lack of food results in underdeveloped reproductive organs thus leading to the creation of a worker class.
coating. In most instances the beginnings of the nest are created all by a single queen wasp that decides to spawn more workers once the nest has reached a certain size (generally the size of a walnut). While most social insects build their nests over time gradually increasing in size, the Microstigmus construct the entire confines of the nest in one effort and thus the workers and queen are confined to the nest until it is fully completed. As such all of the construction materials are gathered prior to the building of the nest as seen with Microstigmus comes.
The biology/anatomy of the larva has unique characteristics (associated only with Microstigmus) that reveal evolutionary features. One is the concial supranal process which is potentially an adaptation for obtaining the prey provisions stuck on the walls of a nursery cell. During the larval stage, there also is a complete lack of spinnerets which indicate that a pupal stage with a cocoon is not present in some species of Microstigmus (M. xylicola nests have been found with pupa present). The spinulose lobe of the mandible is not like most and is a possible modification for ingestion of collembolans. Other aspects of Microstigmus biology are shared with other genera in the Crabronidae family such as antennal papillae, lack of galeae, and tridenatate mandibles which indicate close relation to Spilomena and distant from Ammonplanus. While these characteristics differentiate the genera, they may change in future as more specimens are being collected for study. As such, new patterns may arise in differences in characteristics and thus result in new genera that are define by different guidelines.
.
Adults also inspect the nest, clean by ejecting excess material, and silk which is reinforcement of the nest structure through adding silk to the petiole. More rarely, individuals would partake in nest defense, usually from small arthropods, and mate where a female and a male would exit the nest joined at the genitalia.
Before leaving the nest, the adults generally make an inspection walk around the nest and will also perform the same task upon returning, generally to make sure the nest is in good order and not damaged in any way. Another potential reason for the inspection routine could be to check for parasites around the nest. Along with the inspections, adults also perform the maintenance routes where the wasps remove particles and waste and check the integrity of the nest. Females occasionally will apply silk to reinforce the nest surface, pedicel and attachment point between the leaf and pedical.
Continuing the idea of eusociality, it is important for social insects to be able to discriminate against non-nest members. However, in the Thripoctenus species, tolerance of non-related individuals was observed, and may have some social benefit. One hypothesis and is that in a solitary nest where more members can provide more work, the additional help is kept around in order to benefit the overall fitness of the colony. A second hypothesis is that additional members would increase the longevity of the nest as it is theorized that each wasp is only capable of so much silk production which is the key building block in nest construction.
Kin selection
based on Hamiliton’s Rule provides an explanation to the population genetics framework and specifies the patterns of local and family genetic makeup that results in the most favorable outcome. The key to this is that the genetic structure spawns nonrandom genotypes which coupled with differential reproduction makes kin selection possible. Inter-nest relatedness was high resulting in few independent haploid genomes which makes possible the development of a social hierarchy.
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
to South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, are a small genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of wasps that build nests and live in colonies ranging in size from 1 to 18 members. Microstigmus is widely considered to be the only true eusocial
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
species within the Crabronidae
Crabronidae
Crabronidae is a large family of wasps, that includes nearly all of the species formerly comprising the now-defunct superfamily Sphecoidea. It collectively includes well over 200 genera, containing well over 9000 species. Crabronids were originally a part of Sphecidae, but the latter name is now...
family. Like all Hymenoptera, Microstigmus has an interesting sex determination pattern. Females are 2n (diploid), spawning from eggs that have been fertilized, while males are 1n (haploid) and spawn from unfertilized eggs. Female wasps contain the eggs within their egg sac and have the option of fertilizing them or not, thus having complete control on the gender of the offspring. This wasp genus, part of the suborder Apocrita
Apocrita
Apocrita is a suborder of insects in the order Hymenoptera.Apocrita includes wasps, bees and ants, and consists of many families. It includes the most advanced hymenopterans and is distinguished from Symphyta by the narrow "waist" formed between the first two segments of the actual abdomen; the...
, is distinguished physically by the narrow waist (petiole) between the end segment of the thorax (mesosoma
Mesosoma
The mesosoma is the middle part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma. It bears the legs, and, in the case of winged insects, the wings....
) and the beginning of the abdomen (metasoma
Metasoma
The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circulatory system, and the apical segments are typically...
). Specifically, it is in the subgroup of "apoid
Apoidea
The superfamily Apoidea is a major group within the Hymenoptera, which includes two traditionally-recognized lineages, the "sphecoid" wasps, and the bees, who appear to be their descendants.- Nomenclature :...
wasps", those that exhibit social behavior in nesting and foraging. Evidence does exist that in some species social altruism
Altruism in animals
Altruism is a well-documented animal behaviour, which appears most obviously in kin relationships but may also be evident amongst wider social groups, in which an animal sacrifices its own well-being for the benefit of another animal.- Overview :...
is visible; however, studies on these topics have been limited. The small size and enclosed nest structure makes it difficult to obtain significant data. Although it was originally classified under the Sphecidae
Sphecidae
Sphecidae is a cosmopolitan family of wasps that include digger wasps, mud daubers and other familiar types that all fall under the category of thread-waisted wasps.The are predominently solitary wasp,distributed world wide.At present this family consist of eight subfamilies and three tribes...
family due to its elongated petiole
Petiole (insect)
In entomology, the term petiole is most commonly used to refer to the constricted first metasomal segment of members of the Hymenopteran suborder Apocrita; it may be used to refer to other insects with similar body shapes, where the metasomal base is constricted...
, Microstigmus has been reclassified into the new Crabronidae
Crabronidae
Crabronidae is a large family of wasps, that includes nearly all of the species formerly comprising the now-defunct superfamily Sphecoidea. It collectively includes well over 200 genera, containing well over 9000 species. Crabronids were originally a part of Sphecidae, but the latter name is now...
family.
Biology
Like all insects, the wasps of this genus have three body segments, with an exoskeletonExoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
covering the internal organs in each of them. The species of Microstigmus ranges in length from 2.5 to 5.5 mm (0.0984251968503937 to 0.216535433070866 ). Being within the family Crabronidae, Microstigmus has a thread like waist connected between the thorax
Thorax (insect anatomy)
The thorax is the mid section of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods....
and abdomen. Unlike other Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, the head and thorax (mesosoma) lack branched or plumose hairs. The wasps also have their posterior metatarsus modified into a cleaning mechanism. Many of the different species in this family have varying color schemes that serve to warn predators (some have venomous stings) or to provide camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
.
Sphecid wasps also have a silk gland that is important in many functions, such as nest building. The glands are formed initially with one multinuclear terminal cell from which a canal (pathway from gland to environment) is exposed to the outside environment via spinnerets. This epidermal gland evolves independently for most species under the Pemphredoninae
Pemphredoninae
The subfamilly Pemphredoninae also known as the aphid wasps, is a large group in the wasp family Crabronidae. Historically, this subfamily has frequently been accorded family status. The subfamily consists of solitary, predatory wasps, each genus having its own distinct and consistent prey...
subfamily.
Diet
Like with most wasp species, those in the Microstigmus genus are predators. Prey for the wasps can vary from flies to aphidAphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
s. Most of the time, the kill is performed with the powerful mandibles literally biting through the head of the prey causing either death or immobilization. Social wasps will kill the prey and then return to the nest to provide for the young. This can be done in several ways. One is for the wasp to suck out the inner bodily fluids of the prey and carry the hemolymph
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
back to the nest where the adults will regurgitate
Regurgitation (digestion)
Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...
some of the fluids to the larva wherein the adult retains some of the hemolymph. This trophallaxis
Trophallaxis
Trophallaxis is the transfer of food or other fluids among members of a community through mouth-to-mouth or anus-to-mouth feeding. It is most highly developed in social insects such as ants, termites, wasps and bees. The word was introduced by the entomologist William Morton Wheeler in 1918...
between adults and larva may have played a role in social wasp evolution in three primary ways. Adults who provide nourishment for larva and get food in return may reduce the need to forage for food for themselves. Therefore flights from the nests may be more efficient where flights are only performed for larval food foraging and nest construction materials over species that do not practice trophallaxis. The larval-adult saliva exchange may also increase reproductive fitness in females. An example would be a period of inclement weather where food is hard to come by. The reproducing females would still have a source of nutrition and be able to continue reproductive cycles which are crucial in eusocial
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
colonies. There might also be a situation where the trophallaxis benefits the adults but also hinders the larva in form of nutritional castration where the lack of food results in underdeveloped reproductive organs thus leading to the creation of a worker class.
Nesting
Nests generally have a rough external appearance with a brownish-gray hue although some species have a whitish appearance with smooth texture. Species usually form communal nests that hang from a strong support such as a tree branch, vine, or overhanging rock formation via a petiole which is produced from a root tip rather than silk. The nests are typically built with substrate surface material such as bark, lichens, and sand grains interlaced with silky secretion produced by the female wasps. The nests are developed into conical structures approximately 12 mm in length. Most of the infant holding cells are the near the bottom and the adults reside in the upper hollow section of the next close to the entrance. The interior of the entrance is covered by a translucentTransparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...
coating. In most instances the beginnings of the nest are created all by a single queen wasp that decides to spawn more workers once the nest has reached a certain size (generally the size of a walnut). While most social insects build their nests over time gradually increasing in size, the Microstigmus construct the entire confines of the nest in one effort and thus the workers and queen are confined to the nest until it is fully completed. As such all of the construction materials are gathered prior to the building of the nest as seen with Microstigmus comes.
Larva interaction
As Microstigmus is a social genus that lives together in a colony, larval care is provided by adults. In the Microstigmus thysanoptera, the adults form a compact mass of prey provisions and silk fibers which, upon hatching, the larva consumes. The fecal matter produced by the larva that have molted is removed from the nest along with other trash by the adults performing housekeeping duties. Larval incubation habits indicate the sociality among wasps, as females will routinely bring food to the same incubation cell in a cooperative effort. Social divisions also reveal the specialization of roles and thus how each individual contributes to the overall colony. No two eggs are at the same stage of development and only one egg is available for care at any given time. This is supported by the fact that there is only one female with significantly larger ovaries over the other females at any given time and this select female is considered the primary egg layer.The biology/anatomy of the larva has unique characteristics (associated only with Microstigmus) that reveal evolutionary features. One is the concial supranal process which is potentially an adaptation for obtaining the prey provisions stuck on the walls of a nursery cell. During the larval stage, there also is a complete lack of spinnerets which indicate that a pupal stage with a cocoon is not present in some species of Microstigmus (M. xylicola nests have been found with pupa present). The spinulose lobe of the mandible is not like most and is a possible modification for ingestion of collembolans. Other aspects of Microstigmus biology are shared with other genera in the Crabronidae family such as antennal papillae, lack of galeae, and tridenatate mandibles which indicate close relation to Spilomena and distant from Ammonplanus. While these characteristics differentiate the genera, they may change in future as more specimens are being collected for study. As such, new patterns may arise in differences in characteristics and thus result in new genera that are define by different guidelines.
Adult/nest interaction
A typical worker female exhibits repetition of select behaviors, mainly with a purpose of sustaining the colony. They would forage for food for the young which can range from decaying dead insects and bodily fluids of paralyzed insects to decaying fruit. Adults usually feed off nectar as their primary source of nourishment but in some colonies such as M. nigrophthalmus the adults feed off the secretion of the larva (a form of defecation). Adults deliver the food to the young through a process called trophallaxisTrophallaxis
Trophallaxis is the transfer of food or other fluids among members of a community through mouth-to-mouth or anus-to-mouth feeding. It is most highly developed in social insects such as ants, termites, wasps and bees. The word was introduced by the entomologist William Morton Wheeler in 1918...
.
Adults also inspect the nest, clean by ejecting excess material, and silk which is reinforcement of the nest structure through adding silk to the petiole. More rarely, individuals would partake in nest defense, usually from small arthropods, and mate where a female and a male would exit the nest joined at the genitalia.
Before leaving the nest, the adults generally make an inspection walk around the nest and will also perform the same task upon returning, generally to make sure the nest is in good order and not damaged in any way. Another potential reason for the inspection routine could be to check for parasites around the nest. Along with the inspections, adults also perform the maintenance routes where the wasps remove particles and waste and check the integrity of the nest. Females occasionally will apply silk to reinforce the nest surface, pedicel and attachment point between the leaf and pedical.
Eusociality
In a social context, in colonies of wasps with more than one adult, one adult would almost always remain at the nest site while the others would go out and forage for food or construction materials. Nest defense are also done together with most of the females congregating around the nest during an attack.Continuing the idea of eusociality, it is important for social insects to be able to discriminate against non-nest members. However, in the Thripoctenus species, tolerance of non-related individuals was observed, and may have some social benefit. One hypothesis and is that in a solitary nest where more members can provide more work, the additional help is kept around in order to benefit the overall fitness of the colony. A second hypothesis is that additional members would increase the longevity of the nest as it is theorized that each wasp is only capable of so much silk production which is the key building block in nest construction.
Kin selection
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...
based on Hamiliton’s Rule provides an explanation to the population genetics framework and specifies the patterns of local and family genetic makeup that results in the most favorable outcome. The key to this is that the genetic structure spawns nonrandom genotypes which coupled with differential reproduction makes kin selection possible. Inter-nest relatedness was high resulting in few independent haploid genomes which makes possible the development of a social hierarchy.