Agricultural entomology: The order of Hymenoptera

Agricultural entomology: The order of Hymenoptera

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Bibliographic reference:
Phytopathology, agricultural entomology and applied biology” – M.Ferrari, E.Marcon, A.Menta; School edagricole - RCS Libri spa

The order of Hymenoptera includes about 100,000 species of very variable dimensions: from very small to large. The forms and behaviors are very diverse; however, they have the common characteristic of having two pairs of membranous and transparent wings, hence the name of the order (Hymen = membrane). The order includes various species that have a social behavior, considered the most advanced among insects. The head is distinct from the thorax, has two compound eyes, usually large, and three ocelli; the antennae, of variable shape and length, are shorter in females. The buccal apparatus is, in the most primitive species, typically chewing, but is transformed, in the more evolved species, into chewing-lapping-sucking or chewing-lapping; the jaws, characteristics of the chewing apparatus, are sometimes reduced and mainly perform functions of manipulation of materials and construction of the nests. The thorax has a particular development in the mesothoracic part which becomes the predominant. The wings are membranous; the front ones are larger than the rear ones; in some species they are reduced or lacking, also depending on the social role of individuals. The legs are of the ambulatory type, but can be modified for the taking of food (e.g. pollen collection, capture and prey capture). The abdomen is made up of 10 segments and can be sessile (suborder Sinfiti) or pedunculate (suborder Apòcriti) when the first or the first two segments are narrower than the thorax. Females generally have a well-developed ovipositor (terebra) which can be modified into a sting (spike); in this case the lovositter, who has lost the primary function, assumes the function of defense / offense. Reproduction occurs by amphigonia, but in different groups it also occurs by parthenogenesis and in some (eg Cinipids) there is an alternation between amphigonic and parthenogenetic generations. Hymenoptera are oviparous; the development is of the holometabol and, sometimes, hypermetabol type.
In the Symphites the larvae are similar to the caterpillars of the Lepidoptera; they have well developed heads and are polypods. The pseudo-legs start from the second abdominal segment unlike those of the Lepidoptera that start from the third or subsequent uritis.
In the Apocrites the larvae are apode and have a generally reduced body. The pupae are exarate and often protected by a loose cocoon.
The diet is very varied and depends not only on the species but also on the stage of development. Most of the species have solitary habits, however many live in societies that can have annual (wasps) or multi-year (bees and ants) duration.
The Order is divided into two suborders:
- Symphites;
- Apocrites: these are further divided into: Terebrant and Aculeate.

Suborder Sìnfiti

Adults have a sessile abdomen. The larvae are generally polypod, only rarely apod. Although similar to those of Lepidoptera, the polypod larvae of the Symphites are distinguished from these by the pseudo-legs that start from the second abdominal segment and by having 6-8 pairs of pseudo-legs and not 5 pairs like most of the caterpillars of butterflies. The females have serrated ovipositor which they use to pierce the tissues of the leaves and stems, where they lay their eggs. The adults are mainly pollinifagi; some are insect predators (Diptera larvae and other Hymenoptera). The larvae are generally phytophagous; some dig tunnels inside the affected organs (threatening forms), in this case they are free of pseudo-legs.

Argidi family
The adults of the Argids are insects from 5 to 10 mm long; the larvae live, sometimes gregarious, on various plants whose leaves are gnawing. Females generally lay in young branches. Among the species we remember:
- Arge rosae L. and Arge pagana Panz., Argidi della rosa.

Diprionid family
Diprionids group species that attack only conifers. The females lay their eggs in the needles and the larvae that emerge, frequently gregarious, gnaw the leaves, causing serious damage to the plants; include:
- Neodiprion sertifer Geoffr. and Diprion pini L., which attack the pine.

Tentrèdinidi family
The Tentredìnidi are the largest family of the Sinfiti; they include small and medium-sized shapes (from 2 to 15 mm in length) that frequently reproduce by parthenogenesis. Often the females lay at the level of the floral organs, inside the tissues of leaf peduncles or of stems and young branches; the larvae generally gnaw the leaves from the outside, while others remain inside the galls. Among the species we remember:
- genus Hoplocampa Hartig, the species of this genus attack the fruit trees by digging tunnels in the fruit trees.

Suborder Apòcriti

In adult insects, the abdomen is often pedunculated; in some cases it is sessile. The larvae are apode. Adults feed on nectar and pollen, on other materials of plant origin, on prey and rarely on animal liquids. The larvae parasitize other insects or are phytophagous or are nourished by adults with various substances (nectar, pollen, etc.) and sometimes with materials they themselves elaborate (honey, royal jelly). The suborder of the Apocrites is further divided into two sections:
- Terebrant: females have a long ovipositor (terebra) which, at times, can even exceed the body of the insect in length.
- Aculeate: the females are endowed with a short and pointed sting or sting that derives from the transformation of the ovipositor.

Terebranti section
Females use the terebra to puncture the plant or animal tissues in which they lay. The larvae that develop can be phytophagous or parasites of other insects or Arthropods in general. Often the substances introduced into the plant tissues, by means of a lovopositor, induce the formation of characteristic galls, inside which the larvae develop. The Terebranti section includes some superfamilies including those of the Icneumonoidei, of the Calcidoidei and of the Cinipoidei.

- Icneumonoidei superfamily
Icneumonoids are for the most part insect pests; females can lay eggs both on and near or within their victims' bodies. Normally lovideposition occurs in the juvenile stages of the victims (larvae or pupae). The parasitoid larva develops by feeding on the host, until it reaches maturity.

Icneumonidae family
To the family of Icneumonids belongs:
- Rhyssa persuasoria L., parasitoid of xylophagous insect larvae;
- genus Pimpla Fabr., which attacks especially the chrysalis of Lepidoptera.

Braconid family
To the Braconid family belongs:
- Ascogaster quadridentatus Wesm., Endophagous parasitoid of larvae of Tortricide Lepidoptera;
- Opius concolor Szepl., Parasitoid of larvae of the Tripetid Diptera.

Aphidid family
Parasitoids of Aphids belong to the family of Aphidids including:
- Aphidius matricariae Hal .; parasitoid of Aphids in the adult stage; this species is bred in biofactories for the biological control of Aphid populations.
- Aphididius colemani Viereck: Parasitoid hymenoptera of several species of aphids, mainly Aphis gossypii is Myzus persicae.

- Chalcidoidal superfamily
Predominantly parasitoid species of insects belong to this superfamily; certain species are bred and used in biological control. Some species are phytophagous. The superfamily of the Calcidoidei includes several families among which we remember:

Aphelinidae family
Aphelinidae are small Hymenoptera many of which are parasites of Aphids and Cochineals; among these we remember:
- Aphelinus mali Hald., Parasitoid of the Laniger apple aphid;
- Prospaltella (= Encarsia) pernicious Tow., Parasitoid of the Cochineal of San Josè.

Trichogrammatidi family
Trichogrammatids are parasitoids or oophages of various Lepidoptera; among these we remember:
- Trichogramma maidis Pint. et Voeg., parasitoid of the corn borer.

Eulophides family
Parasitoid insects of larvae of fruit miners of fruit and vegetable and flower crops belong to the Eulophids; among these we remember:
- Diglyphus isaea Walk: it is used in biological control, in greenhouses, against Agromizida Diptera, leaf miners.

Encirtidi family
Various parasitoid species of Cochineals belong to the Encirtidi family; among these we remember:
- Metaphycus helvolus (Comp.), Introduced in Italy to combat Cochineal Saissetia oleae.

- Cinipoidei superfamily
To the superfamily of the Cinipoidei belong small insects, mainly phytophages (Cinipids); some are parasitoids of other insects, others are phytophages.

Cinipidi family
Cynipids are all phytophages; most of them are responsible for the formation of gall characteristics which, however, do not cause serious damage to crops. Generally they reproduce by amphigonia and by parthenogenesis; often the amphigonic and parthenogenetic generations alternate. The different generations (amphigonic and parthenogenetic) cause the formation of galls, on the same plant, very different from each other and, sometimes, even on different plant organs. The Cinipids particularly attack the oaks on which they determine, in Europe, about 200 different types of galls; various species of the genus Cynips are responsible for these.

Aculeati Section
The Aculeati are Hymenoptera with a sting or sting; this is in connection with poison glands. This section includes the most advanced forms of insects of the order of Hymenoptera; Aculeate are able to live in very complex societies. Some species are predators, others parasitoids and still others glyciphages and pollinifagas; finally some species feed on various substances of both animal and vegetable nature. The Aculeati are divided into various superfamilies, among which we remember: Formicoidei, Vespoidei, Apoidei.

- Formicoid superfamily
Formicoids are all social insects. Among these Hymenoptera there are winged and atterous forms; some species are equipped with a stinger, as a defense / offense organ. In species where the sting is absent, defense from predators is often carried out with the release of formic acid. Societies include, for the most part, sterile and sterile females, called workers, and fertile (usually winged) males and females that appear at certain times of the year. Fertilization takes place in flight (nuptial flight) and immediately afterwards the males die; fertilized females (queens) lose their wings and form a new colony. The larvae hatched from the first eggs are fed by the same queen, the others by the newly born workers, who feed them with regurgitated materials and small insect larvae. The pupae can be protected by a cocoon, in some cases the cocoon is missing. The workers can be, in certain species, destined to more tasks for which there can be more castes (e.g. workers and soldiers). In some species of ants the phenomenon of slavery is known; the workers of these species catch the pupae of different species and raise them to exploit them as workers. In other cases, it is the same fertilized queen who introduces herself into the nest of related species, laying her eggs there; the larvae are bred by the host species. Ants, which are equipped with strong jaws, can feed on various materials such as seeds, foodstuffs, animal and vegetable residues and some grow mushrooms; they also feed on honeydew produced by Aphids, protecting them from natural enemies and spreading them in the environment. For these reasons, ants can be harmful, both directly and indirectly. Some species are predators of various phytophagous insects so they become very useful in controlling these; among these we mention the species belonging to the Formica rufa group (F. rufa, F. polyctena, F. lugubris and F. aquilonia) which capture the larvae of various defoliating Lepidoptera, in particular the Processionaries.

- Vespoid superfamily
Vespoids are identifiable by the crescent shape of the eyes and the position of the wings which, at rest, fold longitudinally to the body. Females, even workers, are always equipped with a stinger. Vespoids live solitary or in societies, mono or polygenic, generally annual. They are mainly carnivorous species and feed on carrion, insects and other arthropods; the larvae are fed on meat. Some species feed on sugary substances, such as nectar or fruit juices, despite having, unlike bees, a short ligula. Among the social species we mention the common wasps:
- Vespula vulgaris L., Vespula germanica F., who build nests almost always underground.

- Apoid superfamily
This superfamily includes various species of Hymenoptera; these are distinguished from wasps by their body covered with thick hair and by the presence of fringed hair for the collection of pollen. The buccal apparatus is mainly chewing-lapping-sucking or lapping-sucking; it is endowed with a ligula developed, more or less long, suitable to suck the nectar. Apoidea feed on nectar and pollen. The pollen, collected from the body by visiting the flowers, is generally transported in a sort of basket made up of feathery brush hairs, located in the hind legs (more rarely in the lower part of the abdomen).
The larvae are fed with nectar, honey, pollen and in certain cases (eg Bees) with the so-called royal jelly, secreted by the supracerebral glands. Some species have solitary behavior, others form organized societies; these, of varying duration, are made up of fertile females (queens), fertile males and sterile workers; the sterile caste is not always differentiated (eg Bumblebees) and in certain species it is absent. The societies live in nests, placed in the ground or in the hollows of the trees, built with the aid of the jaws, always present; often the bees produce wax for the construction of the cells, where they lay and accumulate honey. Among the various species we remember:
- genus Bombus Latr .: they are social insects that live in mainly annual societies; they winter like young fertilized females. They build their nests in the ground, among moss or in bedding. Some species of bumblebees are now bred and used as pollinators.
- Apis mellifera L., domestic bee; important not only as a pollinator, but also for the production of honey and wax. Forms a multi-year company.

Apis mellifera

Video: Diptera (May 2022).