Hymenoptera. Vespina. Vespida. Bees, ants, sawflies, horntails and other wasps. Male reproductive system. Male genitalia of Hymenoptera. Symphyta. Phylogenetic systematics of Hymenoptera. Phylogenetic systematics of Symphyta. Xyeloidea, Tenthredinoidea, Pamphilioidea, Cephoidea, Siricoidea, Xiphydrioidea, Orussoidea. Xyelidae, Blasticotomidae, Tenthredinidae, Diprionidae, Cimbicidae, Argidae, Pergidae, Pamphiliidae, Megalodontesidae, Megalodontidae, Cephidae, Siricidae, Anaxyelidae, Xiphydriidae, Orussidae.

Rhogogaster punctulata (Tenthredinoidea) ovipositing

Tenthredo silensis (Tenthredinoidea)

Tenthredo maculata (Tenthredinoidea)

Tenthredo trabeata (Tenthredinoidea)

Cephus pygmeus (Cephoidea) in copula

Xiphydria prolongata (Xiphydrioidea)

Research about 'Symphyta'

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Phylogeny of Hymenoptera

What you see in the figure below is a graph representing the evolutionary history of Hymenoptera or phylogenetic relationships within Hymenoptera. Such a graph is called a phylogenetic tree or cladogram. Monophyletic groups, i.e. exclusive groups with a single evolutionary origin, are called clades or lineages or branches. The ancestor of all Hymenoptera, represented by the branch at the bottom of the tree (the root or stem of the tree), split into two or more species. One of the descendant species gave rise to the present-day Xyeloidea and another evolved into an unnamed group comprising all the other hymenopterans. Xyeloidea and non-xyeloid Hymenoptera are sister groups. On the evolutionary way to Apocrita (so to speak), Tenthredinoidea butted off first, then Pamphilioidea, followed by Cephoidea, Siricoidea, Xiphydrioidea, and Orussoidea.

What are 'Symphyta' and Hymenoptera?

'Symphyta' are part of the insect order Hymenoptera, which originated about 250 million years ago. In the members of the basal lineages of Hymenoptera, thorax and abdomen are connected broadly, there is no waist between the two. At some point in the evolution of Hymenoptera, about 200 million years ago, a constriction evolved between the first and second abdominal segment. All those hymenopterans that have this so-called wasp waist are called Apocrita. All the basal groups of Hymenoptera that do not have a waspwaist are called 'Symphyta'. In the phylogenetic tree (cladogram) shown below, all symphytan groups are shown in red. The lack of a waspwaist is demonstrated most clearly in the photo of Tenthredo trabeata shown above.

The group Apocrita has evolved from a single ancestral species and this ancestral species is not an ancestor of any insect that is not a member of the group Apocrita. In other words, Apocrita is a coherent group, a monophylum. It is a natural group. The waspwaist evolved in this ancestor of Apocrita and is a derived feature which is only found in Apocrita and is an indicator for their monophyly. Such a unique derived feature is called a synapomorphy. 'Symphyta' are all the groups of Hymenoptera that are not Apocrita. The most recent ancestor of all 'Symphyta' is also the most recent common ancestor of all Hymenoptera and therefore an ancestor of Apocrita, in other words it is not unique to 'Symphyta'. 'Symphyta' are not a coherent group, they are a paraphylum. The lack of a waspwaist is an old feature which is found in other insect groups as well, such as beetles and flies. Such a primitive feature is called a symplesiomorphy. Quotation marks are used to indicate that 'Symphyta' are not a natural group or monophylum.

What about common names?

There is no English name for Hymenoptera, so the name is usually translated as "wasps, ants, and bees", or "ants, bees, and other wasps" or something similar. The English name sawflies is sometimes used for 'Symphyta', sometimes just for the basal superfamilies of 'Symphyta', namely Xyeloidea, Tenthredinoidea, Pamphilioidea, and Cephoidea, whereas the remaining symphytan superfamilies Siricoidea, Xiphydrioidea, and Orussoidea are called horntails and woodwasps. Obviously, common names can be confusing because they are often not clearly defined and used in different ways. Another example for this is the name butterflies. This is sometimes used for the entire order Lepidoptera, but sometimes only for Macrolepidoptera, to distinguish them from moths (= Microlepidoptera. Another problem with common names is that they can be misleading. For example, when people hear the word sawflies, they naturally think that sawflies are flies. However, they are not flies (= Diptera) at all. Since common names are often poorly defined, potentially ambiguous, and sometimes misleading, it is better to avoid them. Instead, you can use anglocized versions of the latin names, i.e. you can speak of symphtyans, apocritans, and hymenopterans.

In the basal groups of symphytans, the ovipositor (which is used for cutting into plants and laying eggs) is shaped like a saw, hence the name sawfly.

Biology of 'Symphyta'

Except for their most derived superfamily Orussoidea, 'Symphyta' are phytophagous, that is they eat plants. More precisely, it is the larvae that eat. The adults are mainly concerned with procreation. The larvea of most species of the three basalmost symphytan lineages – Xyeloidea, Tenthredinoidea, and Pamphilioidea – are external feeders, i.e. they live on the surface of the plants on which they feed. The ancestor of Unicalcarida (Cephoidea, Siricoidea, Xiphydrioidea, and Euhymenoptera), however, evolved a feeding strategy in which the larvae are internal feeders – they live inside the plants that they consume. Consequently, the larvae lost eyes and legs. Today, this feeding habit is still found in Cephoidea, Siricoidea, and Xiphydrioidea.

The ancestor of Euhymenoptera (Orussoidea and Apocrita) evolved a parasitic mode of life. The larvae of Orussoidea and some apocritan taxa live inside the larvae of other insects, which, in turn, live inside the stems of trees. In order to oviposit (lay their eggs), the females of these parasitoid species have to detect a larva of their host species inside the stem of a tree, drill their ovipositor through the wood and insert the tip into the larva. The parasitic larva develops inside the host larva, which remains alive for a while, but eventually is killed.

Parasitic Hymenoptera have very long ovipositors, which consist of an ovipositor blade and an ovipositor sheath, both of which are normally on the outside of the body. In Orussoidea, however, the ovipositor blade is inside the body cavity and due to its enormous length loops through the abdomen and thorax, as shown in the figure below (ovipositor blade in red, body cavity in grey), after Vilhelmsen et al. (2001), who also report on the unusual morphology of the antennae and foretibiae which are used to locate the host larva inside the tree (Zoomorphology 121: 63-84).

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