Hymenoptera

Definition

The Hymenoptera is a large order of organisms within the phylum Arthropoda, which contains insects like, bees, wasps, sawflies, and ants. The name is derived from the greek words "Hymen" or "membrane" and "Ptera" or "wings", which is perfectly describing the fact that their wings are connected into one point called the "Hamuli", and the membraneous tissue it is formed. Like most insects, these appeared at an early stage of earth's history, which according to a study done by D.A. Grimaldi, M.S. Engel et al [11], have been around since 281 million years ago (Triassic Period). The Hymenopteran who have evolved into a societal way of living(Cretaceous Period), similar to pre-historical humans, created a very well adapted form of resilience for the succession of its offspring. However, many different species still live solitarily, requiring others only for mating. The organisms, who have a social life, live in a nest (ants) or a hive (bees, wasps), which are all descendants of one queen. When the hive or nest is established by a queen in early spring, it begins producing its offspring that will work in their pre-assigned roles, depending on their gender.

Classification

Domain: Eukarya

Kingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Superorder: Hymenopterida

Order: Hymenoptera

Suborder: Apocrita - Ants, Bees, Wasps

Suborder: Symphyta - Sawflies, some wasps

Anatomy

Bee's anatomy

Wasp's anatomy

The anatomy of hymenopterans are very similar to other insects. The ones who fly, usually have two pairs of wings. Their mouths can have two forms, just mandibles used for chewing, or with the addition of the proboscis used for drinking liquids, such as nectar. They have two larger compound eyes, used to differentiate brightness and color, and also three smaller eyes called "ocelli" that are much simpler. Flying insects have their hind wings with hooked bristles called "hamuli" that holds both the fore wings and hind wings together. The number of hamuli vary between species and their sizes, with wasps having more than the usual two to three hamuli present in smaller species. Like most insects, their bodies are divided into three sections, head, thorax and abdomen.

The hymenoptera have an ovipositor, that in older species evolved into a blade-like structure used for slicing plant tissues. However, many today use them for piercing. In some species, we see today an ovipositor that evolved into a stinger in which the tip is used to inject venom and their eggs are laid from the base of the structure. The stinger is usually used to immobilize prey, that could be used to insert their eggs inside, but we see many bees and wasps using for self defense.

The larvae of the hymenoptera have a head region, three thoracic segments, and nine or ten abdominal segments. The hymenoptera, is further divided into the Symphyta and Apocrita. The former includes sawflies, whose larvae feed on leaves, have large mandibles for chewing; six thoracic limbs, and six to eight abdominal prolegs. However, their prolegs do not have spines, and their antennae are reduced to just stubs. Furthermore, the larvae that lives on wood or stem borers have no abdominal prolegs and the thoracic legs are smaller than the non-borers.

The Apocrita, whose species are wasps and bees, however, cannot live freely. The lack of legs, and their shape resembling a maggot, requires them to be taken care either by the solitary wasp who laid them, or by the workers and queen in a beehive. If the larvae was laid by a wasp, it will most likely be living inside of the immobilized insect it captured, where the offspring can feed off of the prey. The larvae laid in the insect have some morphological differences, the head is reduced into the prothorax, the compound eyes are poorly developed, with no ocelli; very small or absent antennae and toothlike mandibles. It also lacks the ability to defecate, since their digestive system is not completed, to avoid contamination in the environment they live. The larvae that has a stinger, generally has ten spiracles, for breathing, while the parasitic form usually has nine.

Reproduction

Haplodiploid sex-determination system

In the order Hymenoptera, reproduction uses the Haplodiploid sex-determination system, in which the number of chromosomes determines their gender. If the eggs are fertilized by both parent's gametes, the individual is diploid and develops into a female.

Haplodiploid system diagram

However, if the egg is not fertilized by two sets of gametes, the zygote is haploid, and develops into a male. The important factor in this system is that the female is under total control of which gender her offspring will be, depending on what the nest or hive needs in the moment.

Although this system seems very simple to understand, it actually is much more complex than only the number of chromosomes present. In many hymenopterans, the gender is determined in a single gene locus with many alleles. In these organisms, males are haploid and females are diploid heterozygous at the sex locus. However, a diploid organism could be homozygous which develops into a male. This is more likely to happen when we have parents who were siblings reproducing. Diploid males are known for being produced by inbreeding, in many ant, bee, and wasp species. These males organisms, usually are infertile but you can find some species with fertile diploid males.

A problem that appears due to this reproduction system is that females on average have more genes in common with their sisters than with their daughters. Therefore, cooperation among kindred females may be unusually advantageous, which contributed to the multiple origins of eusociality within this order. In many colonies, we see the removal of eggs laid by other workers due to the increase in relatedness to direct siblings, a behavior called worker policing.

Thelytoky

Thelitoky Diagram

Some hymenopterans also use a type of parthenogenesis, which is the production of an embryo without fertilization, to produce other females. Through the process of thelytoky, a female is produced from the fusion of two haploid proto-eggs in the same meiosis, producing a diploid zygote. This method of reproduction tends to maintain heterozygosity of the genome of the mother to the daughter. Many ant species use this method, some of them are: desert ant Cataglyphis cursor, the clonal raider ant Cerapachys biroi, the predaceous ant Platythyrea punctata, and the electric ant (little fire ant) Wasmannia auropunctata. It also occurs in the Cape honey bee Apis mellifera capensis.

Major Families

According to the NCSU Department of Entomology [4]

Sawflies: Larvae feed on leaves, or burrow into plant tissues

1)Diprionidae: Conifer sawflies

2)Tenthredinidae: Common sawflies

3)Cephidae: Stem sawflies

Horntails: Larvae are wood borers

1)Siricidae: Wood or Horntail wasp

Parasitic Wasps: Larvae are parasitoid of other insects

1)Ichneumonidae: Largest family, parasitoids of spiders

2)Braconidae: mostly parasitoid of lepidopterous larvae

3)Encyrtidae: mostly parasitoid of aphids and scale insects

4)Eulophidae: parasitoid of beetles, moths, and other insects

5)Trichogrammatidae: egg parasites

Gall Wasps: Larvae are herbivores which induce the formation of plant galls and live in or on these tissues

1)Cynipidae: most species live on oak trees

Predatory Wasps: Adults provision nest sites with prey that they catch and paralyze by stinging

1)Sphecidae: prey on caterpillars and spiders

2)Pompilidae: prey on spiders

3)Tiphiidae: prey on beetle larvae

4)Scoliidae: prey on beetle larvae

5)Vespidae: prey on caterpillars

Social Wasps: The nests are tended by sterile female workers

1)Vespidae: yellowjackets, hornets, paper wasps

Ants: True social insects. Wingless workers forage for resources

1)Formicidae: Ants

Solitary Bees: Adults build their individual nests and provision them with plant material (nectar or pollen)

1)Halictidae: Sweat bees

2)Megachilidae: Leafcutting bees

3)Anthophoridae: Carpenter bees

Social Bees: True social insects. Communities are found in nests in the soil (Bumble Bees) or in cavities (Honey Bees). Sterile female workers forage for resources such as nectar or pollen

1)Apidae: Bumble bees and Honey bees

Ecology

Eusociality:

Melissodes desponsa bee body covered in pollen

According to C.J.A. Bradshaw, C.R. McMahon [1], is an advanced social system where colonies of organisms are created for the succession of its offspring. This system exists when the adults belong to two or more overlapping generations, they take care cooperatively for the offspring, and are divided into reproductive and non-reproductive castes. This division of labor means that some females give up the ability to have offspring to facilitate reproduction by other individuals in the same colony.

According to Norman F. Johnson [9], the beginning of such society is after a virgin queen from a colony mates with one or several males. Then, the queen builds her nest, which could be in the soil, a natural cavity, or out in the open. The colony founding can be sometimes cooperative, and determining which individual will become the primary reproducer is established through behavioral interactions among the founders. Males are only needed for insemination of the new queens, which soon after will die. The eggs produced by the new queen, will develop into the first female worker generation, which usually cannot reproduce. These workers have many functions, they take care of the offspring, forage for resources, defend the nest and the queen. These functions are sometimes divided by workers, and sometimes by morphological differences in their bodies. Once well established, more males and females are produced to continue the growth of the colony.

Pollination:

Pollen Particles

European honey bee drinking nectar of a flower

Pollination is the transfer of pollen, which can be via wind, water, insects, from the male structure (Anthers) of a flower to the female structure (Stigma) of either the same flower (Monoecious) or another (Dioecious) of the same species. This phenomena is what makes hymenopterans so important for the ecosystem they are present, since most plants rely on them for fertilization. Therefore, plants have evolved a symbiotic relationship with them, in which the plants produce the sweet nectar these insects require in their diet, and the hymenopterans while in search of the nectar carry particles of pollen in their bodies and pollinate other flowers. One of the reasons to why this is very important, is because without the help of pollinators, plants would have an even smaller chance for fertilization, since wind and water are not the best option.

References

[1]Bradshaw, C. J. A., and C. R. McMahon. 2008. Fecundity. Encyclopedia of Ecology:1535–1543.

[2]Contributors, W. 2021, April 22. Wasp. Wikipedia, The Free Encyclopedia. https://en.wikipedia.org/wiki/Wasp.

[3]Contributors, W. 2021, March 12. Hymenoptera. Wikipedia, The Free Encyclopedia. https://en.wikipedia.org/wiki/Hymenoptera.

[4]Department of Entomology. 2015. Hymenoptera. NC State Agriculture and Life Sciences. https://genent.cals.ncsu.edu/insect-identification/hymenoptera/.

[5]The Editors of Encyclopaedia Britannica. 1999. Wasp. Encyclopædia Britannica, inc. https://www.britannica.com/animal/wasp.

[6]Greenwood, D. 2019, May 30. Bee Larvae. https://beehivehero.com/bee-larvae/.

[7]Institution Archives, S. (n.d.). Wasps, Ants, and Bees (Hymenoptera). Department of Systematic Biology, Entomology Section, National Museum of Natural History, in cooperation with Public Inquiry Services, Smithsonian Institution. https://www.si.edu/spotlight/buginfo/hymenoptera.

[8]Jernigan, C. M. 2017, June 13. Bee Anatomy. Arizona State University School of Life Sciences Ask A Biologist. https://askabiologist.asu.edu/honey-bee-anatomy.

[9]Johnson, N. F. 2001. Hymenoptera. Encyclopedia of Biodiversity:417–426.

[10]Lindauer, M. 1999. Hymenopteran. Encyclopædia Britannica, inc. https://www.britannica.com/animal/hymenopteran/Natural-history#ref39798.

[11]Peters, R. S., L. Krogmann, C. Mayer, A. Donath, S. Gunkel, K. Meusemann, A. Kozlov, L. Podsiadlowski, M. Petersen, R. Lanfear, P. A. Diez, J. Heraty, K. M. Kjer, S. Klopfstein, R. Meier, C. Polidori, T. Schmitt, S. Liu, X. Zhou, T. Wappler, J. Rust, B. Misof, and O. Niehuis. 2017. Evolutionary History of the Hymenoptera. Current Biology 27:1013–1018.