Hymenoptera

Hymenoptera (from Ancient Greek ὑμήν: membrane and πτερόν: wing) is a large order (over 150,000 species recognized) of highly specialized insects with the complete metamorphosis that include the bees, wasps, ants, ichneumon flies, sawflies, gall wasps, and related forms, often associate in large colonies with complex social organization.

Anatomy

Head

The head is generally hypognathous, but in some systematic groups, it can also be prognathous. It is very mobile, connected to the thorax by a thin neck. It has large compound eyes, and typically three simple eyes, ocelli.

Antennae

The antennae are varied in shape, sometimes different in both sexes. The scape is elongated and the pedicel is short and conical in shape.

On the pedicel, there is the flagellum composed of a more or less high number of segments of various shapes, which can reach a number even in several tens. In general, in advanced forms, the number of distal segments is reduced and the shape is almost discoid.

The morphology and position of the antennae is an important element of systematic identification.

Mouthparts

The mouthparts are chewing, chewing-brushing or chewing-sucking. In all forms there are jaws that often perform functions not associated with feeding: in many Hymenoptera, for example, they are used during flickering to open the pupal cell or, in endoparasitic species, to open a passage in the host’s integument; in others, they are used for the construction of the nest and for transporting material used for the purpose.

The element that significantly differentiates the mouthparts of the Hymenoptera is the maxillo-labial complex, consisting of the two jaws and the lower lip.

Although the shape of the jaw varies in shape, it is typical: composed of a proximal element, called a hinge, articulated to the hypostome and a distal, sometimes particularly elongated, called the jamb. On the jamb articulate the maxillary palpus composed of 1-6 elements and, more internally, the two lobes called respectively galea and lacinia (in order from outside to inside).

As happens in the masticatory mouth-type apparatus of insects, the lower lip is composed of two parts: a fixed one, called postlabial, and a mobile distal one, called prelabium. The postlabial is divided into two morphological elements, the submentum and, more distally, the mentum. The prelabium includes a basal element called prementum on which the labial palps articulate on the outside, and the lobes on the inside. These are distinguished in two lateral paraglossae, and in the central glossa. Overall, the paraglossae and the glossa form the ligula.

Thorax

The thorax is characterized by a large development of the mesothorax compared to the prothorax and metathorax, the latter rather reduced in development. A peculiarity of Hymenoptera Apocrita is the connection of uritis with the actual thorax, forming a fourth segment called propodeum.

The legs are generally well developed and robust. Sometimes they present morphological adaptations that make them suitable for digging or grabbing prey and transporting supplies.

Wings

The wings, when present, are four in number and membranous; the front ones are more developed than the rear ones. In the rest position, they are folded back horizontally along the back of the abdomen.

The most significant morphofunctional element of the wings of the Hymenoptera is the connection apparatus of the posterior wing to the anterior wing. The posterior margin of the front wings is folded and hooks are attached to it, called hamuli arranged along the costal margin of the posterior wings.

This apparatus ensures that the front and rear wings form a single rowing surface. The strength of the connection apparatus can be such that the wings remain definitively connected even in the resting phase.

Abdomen

The abdomen is sessile or pedunculated, consisting of 10 uritis, the latter of which are more or less modified and reduced. In Apocrita there is marked differentiation of the morphology of the abdomen in the front.

Ovipositor

In the more ancestral hymenopterans, the ovipositor is blade-like, and has evolved for slicing plant tissues. In the majority, however, it is modified for piercing, and, in some cases, is several times the length of the body.

In some species, the ovipositor has become modified as a stinger, and the eggs are laid from the base of the structure, rather than from the tip, which is used only to inject venom. The sting is typically used to immobilise prey, but in some wasps and bees may be used in defense.

References

  1. Hoell, H.V.; Doyen, J.T.; Purcell, A.H. (1998). Introduction to Insect Biology and Diversity (2nd ed.). Oxford University Press. pp. 570–579. ISBN 978-0-19-510033-4.