**4. Conclusion**

*Life Cycle and Development of Diptera*

along a dorso-ventral axis.

**3.4 The pupa**

puparium.

By comparison, an atlas of immature morphology based on the third instar of 34 economically important species has been developed. The segments of the maggot typically bear spines in regular patterns (**Figure 7**) and the larvae of some species may possess structures that vary from simple setae to large protuberances. Several other structures including the median oral lobe, the lateral spiracles accompanied by a variable number of sensilla associated with the sensory organs of the gnatho-

Tephritids have distinct anterior and posterior spiracles. Modern scanning electro-microscopy have aided in the location of the lateral spiracles along the thoracic and abdominal segments, as well as along the caudal segment that bears the posterior spiracles [49]. The lateral spiracles, which are always present along the lateral and anterior portion of a segment, have been known to have a varying number of campaniform sensilla associated with it around the posterior end of the spiracle. The number of sensilla may range from one (as in some *Aciurina* and *Trupanea* species) to as many as four (as in *Stenopa affinis* Quisenberry). When more than one spiracular sensilla is present, they are typically arranged adjacent to the spiracle,

Dipteran pupa becomes more impervious to the surrounding environmental conditions and the larva becomes morphologically reduced and evolved to feed on nutrient-rich substrates; flies as a whole may occupy a broad range of trophic niches. The puparium is the hardened, penultimate larval integument of the developing fly (**Figure 8**). It is remarkable in its external morphology in tephritid fruit flies. When the third instar larva is ready to pupate, it leaves the medium, and its anterior spiracles evert, body shortens and ceases to move and it attaches to a firm substrate. The cuticle then transforms into a puparium, which is initially soft and white, but soon hardens, turning tan and eventually becomes brown and with bristle. Shortly after the puparium forms, then metamorphosis then takes place. The prepupal integument is shed and adheres to the inner wall of the puparium. The pupa forms within the puparium after the prepupal molt. The pupa develops independently of the puparium and has bilobed thoracic spiracles for respiration. The larval tracheae adjacent to the anterior and posterior spiracular openings remain open, thus allowing for gas exchange for the developing pupa within the

According to Ref. [50], there exists a pre-puparial stage in which the mouthparts contain series of invaginations. During this stage, the integument typically assumes a waxy appearance, but the processes of tagmentation (hardening and darkening of the integument) are delayed. The darkening of the integument may be triggered

cephalon have been newly identified for various frugivorous species.

**154**

**Figure 8.**

*Pupal forms of Diptera.*

These phylogenetic and morphological reviews of Diptera provide an evolutionary framework for future comparative work on species that are critically important to both society and science. The order Diptera has been divided into two or three suborders: the monophyletic Nematocera and the paraphyletic Brachycera, with the latter being divided further into the Orthorrhapha and Cyclorrhapha. The living dipteran species have been classified into about 10,000 genera, 150 families, 22–32 superfamilies and 8–10 infraorders. The typical dipteran body morphology is reflected in its life cycle which includes a series of distinct stages or instars; consisting of a brief egg stage, three or four instars, a pupal stage of varying length, and an adult stage that lasts from less than 2 hours to several weeks or even months. The species-richness, morphological variability and ecological diversity of this order of insects dictate the economic importance of the group to man and reflects the range of organisms in the order. Future work will focus on contributions and progress in understanding of the bioecological processes and economic impacts of dipteran flies in human life especially in relation to health, agricultural productivity and food security.

## **Conflict of interest**

Author has no conflict of interest.
