A pupa (from Latin pupa 'doll'; pl.: pupae) is the life stage of insects from the Holometabola clade undergoing metamorphosis between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages thereof being egg, larva, pupa and imago (adult). The processes of entering and completing the pupal stage are controlled by the insect's hormones, especially juvenile hormone, prothoracicotropic hormone, and ecdysone. The act of becoming a pupa is called pupation, and the act of emerging from the pupal case is called eclosion or emergence. The pupae of different groups of insects have different names such as chrysalis for the pupae of butterflies and tumbler for those of the mosquito family. Unlike the fully motile larval and imago stages, the pupal stage of an insect is typically sessile, where the pupa remains anchored to a location until the metamorphosis is completed, and may be enclosed in protective structures such as cocoons, nests or shells.
Position in life cycle The pupal stage follows the larval stage, or in some cases a prepupal stage, and precedes adulthood (imago) in insects with complete metamorphosis. The pupa is a non-feeding, usually sessile stage, or highly active as in mosquitoes. It is during the pupal stage that the adult structures of the insect are formed while the larval structures are broken down. The adult structures grow from imaginal discs. Contrary to popular belief, larvae do not completely liquify inside the cocoon.
Duration The pupal stage may last weeks, months, or even years, depending on temperature and the species of insect. For example, the pupal stage lasts eight to fifteen days in monarch butterflies. The pupa may enter dormancy or diapause until the appropriate season to emerge as an adult insect. In temperate climates pupae usually stay dormant during winter, while in the tropics pupae usually do so during the dry season.
Emergence Insects emerge (eclose) from pupae by splitting the pupal case. Most butterflies emerge in the morning. In mosquitoes, the emergence is in the evening or night. In fleas, the process is triggered by vibrations that indicate the possible presence of a suitable host. Prior to emergence, the adult inside the pupal exoskeleton is termed pharate. Once the pharate adult has eclosed from the pupa, the empty pupal exoskeleton is called an exuvia; in most hymenopterans (ants, bees and wasps) the exuvia is so thin and membranous that it becomes "crumpled" as it is shed. Measuring the timing of this emergence is of interest to chronobiologists because the process is regulated by circadian clocks in many species, necessitating different assays to measure eclosion timing.
Pupal mating In a few taxa of the Lepidoptera, especially Heliconius, pupal mating is an extreme form of reproductive strategy in which the adult male mates with a female pupa about to emerge, or with the newly moulted female; this is accompanied by other actions such as capping of the reproductive system of the female with the sphragis, denying access to other males, or by exuding an anti-aphrodisiac pheromone.
Defense Pupae are usually immobile and are largely defenseless. To overcome this, pupating species often avoid predators by covering the pupa with a cocoon, camouflaging it, or placing it underground. Some species of lycaenid butterflies are protected in their pupal stage by ants. Pupae of other species make sounds or vibrations to scare potential predators. A few species use chemical defenses including toxic secretions. The pupae of social hymenopterans are protected by adult members of the hive.
Types Based on the presence or absence of articulated mandibles that are employed in emerging from a cocoon or pupal case, pupae can be classified into two types:
Decticous – a pupa with articulated mandibles. Examples are pupae of the orders Neuroptera, Mecoptera, Trichoptera and few Lepidoptera families. Adecticous – a pupa without articulated mandibles. Examples include the orders Strepsiptera, Coleoptera, Hymenoptera, Diptera and Siphonaptera. Based on whether the pupal appendages are free or attached to the body, pupae can be classified into three types:
Exarate – appendages are free and are not usually encapsulated within a cocoon. Decticous pupae are always exarate; some adecticous pupae are as well. (Neuroptera, Trichoptera, Cyclorrhapha of Dipterans, Siphonaptera, most Coleoptera, Hymenoptera, and a few Lepidoptera) Obtect – appendages are attached closely to the body and are commonly encapsulated within a cocoon. Some adecticous pupae are obtect forms. (Most Lepidoptera, Nematocera and Brachycera of Dipterans, Staphylinidae and Chrysomelidae Coleopterans, many Chalcidoidea Hymenopterans) Coarctate – enclosed in a hardened cuticle of the penultimate larval instar called a puparium. However, the pupa itself is of the exarate adecticous pupal form. (Cyclorrhapha of Dipterans)
Chrysalis of butterflies
… excerpt ends here. Continue reading the full article.
