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Information on the basics of Entomology

 

Introduction                                                                                                                                                                                                                                                                                         Contents

 

An Introduction To The Study of Invertebrate Zoology 1

Kingdom:  Animalia, Phylum: Arthropoda

Subphylum: Hexapoda: Class: Insecta: Order: Strepsiptera

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Order:  Strepsiptera (14 Families)

  General Summary

  Morphology & Habits

  Sample Examinations

  References      Citations

 

 

General Summary of Strepsiptera

 

          The Strepsiptera -- <Adults> & <Juveniles> -- are characterized by some remarkable biological phenomena. Their parasitic activity is limited to the growth stages and the adult female.  The adult males are free living. There is marked sexual dimorphism where the females are prothetelous, ie., their larva has a body form while they are sexually mature.

  

          The eggs may also be polyembryonic. As many as 40 embryos developing from a single egg, e.g. Halictoxenus parasitic on Halictus simplex (Hymenoptera). They are usually described as having a type of hypermetamorphic life cycle in which two larval types exist according as the development is to be towards a male or female adult. The hosts to which their parasitic attentions are directed appear to be restricted to the Hymenoptera (Vespoidea and Apoidea), the Rhynchota (Homoptera), and, in one rare instance the Orthoptera (Borradaile & Potts, 1958).

 

          Among the hymenopterous hosts the solitary bee Andrena is parasitized by Stylops. The female is entirely endoparasitic in the host bee, and appears as a hernia-like extrusion from between the tergites of adjacent segments as in Polistes.  The body of that female is legless and wingless and composed of a subtriangular unsegmented cephalothorax and a clearly 10-segmented abdomen. It lies in the host so that the cephalothorax is visible. Behind the mouth ventrally is a transverse slit which leads into a brood chamber found under the cuticle of the first five or six abdominal segments. Genital pores communicate between the internal genital system and the brood chamber.  It is through the transverse slit on the cephalothorax that copulation with the male occurs. By way of it, too, are born the first-formed triungulin larvae, the female being viviparous (Borradaile & Potts, 1958)..


            The first-formed larvae are 6-segmented legs that are very small. They leave the parent parasite and the host bee to wait, on flowers visited by the latter, a new host to which they attach themselves. From there they are moved to the nest of the bee. There  they seek out the larvae of Andrena into which they burrow to live as endoparasites. A maggot that absorbs nutrients through the skin follows a molt.  However, further instars occur during this growth stage.


           If the ensuing individual is a female a modification of the molting process, during what is regarded as the pupal period, occurs. In this process the last larval and pupal exuviae are not thrown off completely but become separated from the body ventrally to form a space-the brood- chamber-which by a transverse cleft in the anterior region makes contact with the exterior. The development of parasite and host proceeds together so that the adult phase of the two occurs simultaneously with the parasite's cephalothorax projecting in the manner described (
Borradaile & Potts, 1958)..

 

          If the resultant individual is a male, pupation occurs in the host after the head region has projected from between two abdominal segments of the bee. The casting of the pupal skin releases the male that flies away to seek a young endoparasitic female on another bee.


           The male is characterized by fore wings that are modified as small membranous balancers, the hind wings being expansive and fan-folded, with simple longitudinal veins but without cross-veins. Prothorax and mesothorax have undergone substantial reduction. The legs vary in structure throughout the order and are more suited for attachment to the female at copulation than for locomotion.


          The Strepsiptera are noted for the effects produced on their hosts by their presence. Such effects may lead to parasitic castration and concomitant effects on organization.  For example, parasitized bees may be deficient in their pollen-collecting apparatus and in many cases there are changes in color and the adoption of secondary sexual characters belonging to the opposite sex (
Borradaile & Potts, 1958).

 

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Further Morphology and Habits

 

          All Strepsiptera, which were first known as Stylopids, are parasitic on certain adult insects.  Members of this order were frequently incorporated into the Coleoptera as a superfamily:  Stylopoidea.

 

          The males have twisted wings, and the front wing is reduced to a halter while the hind wing is very elongated and pleated.  Females are apterous.  Mouthparts are vestigial and nutrients enter by diffusion from the host.  The male is the free-living active form, while the female spends her entire life in the abdomen of a host insect.  Eggs hatch and triangulin larvae emerge.  As the parasite larvae mature the female form remains indistinct with little more than a head, which protrudes from the host segments.  The male does leave the host, however. 

 

          Insemination of the female occurs on the host.  Genitalia of the female are on the cervix region.  After impregnation the female simply turns into a bundle of eggs.  These egg hatch, releasing triungulin larvae en masse, which then escape through the body wall of the host.  They seek out a new host by perching on flowers, etc., or wherever another insect (e.g., bee) might alight.

 

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Details of Insect Taxonomic Groups

 

          Examples of beneficial species occur in almost every insect order, and considerable information on morphology and habits has been assembled.  Therefore, the principal groups of insect parasitoids and predators provide details that refer to the entire class Insecta.  These details are available at <taxnames.htm>.

 

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References

 

Introduction                                                                                                                                                                                                                                                                                         Contents