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Pupa of the rose chafer beetle, Cetonia aurata
Tumbler (pupa) of a mosquito. Unlike most pupae, tumblers can swim around actively.

A pupa (from Latin pupa 'doll'; pl.: pupae) is the life stage of insects from the Holometabola clade undergoing transformation 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. 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. Pupae may further be enclosed in other structures such as cocoons, nests, or shells.[1]

Position in life cycle

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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.[2]

Duration

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The pupal stage may last weeks, months, or even years, depending on temperature and the species of insect.[3][4] For example, the pupal stage lasts eight to fifteen days in monarch butterflies.[5] 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.

Adult Hercus fontinalis, a species of parasitoid wasp, emerging from cocoon
Eclosion of an African swallowtail butterfly (Papilio dardanus)

Emergence

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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.[citation needed] 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

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Male mottled emigrant butterfly (Catopsilia pyranthe) mating with newly emerged female

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.[6][7]

Defense

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Pupae are usually immobile and are largely defenseless. To overcome this, pupae often are covered with a cocoon, conceal themselves in the environment, or form underground.[8] Some species of Lycaenid butterflies are protected in their pupal stage by ants. Another means of defense by pupae of other species is the capability of making 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

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Based on the presence or absence of articulated mandibles that are employed in emerging from a cocoon or pupal case, the pupae can be classified in to two types:[9]

Based on whether the pupal appendages are free or attached to the body, the pupae can be classified as one of three types:

  • Exarate pupa – 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 few Lepidoptera).
  • Obtect pupa – appendages are attached closely to the body and are commonly encapsulated within a cocoon. Some adecticous pupa are obtect forms. (Most Lepidoptera, Nematocera and Brachycera of Dipterans, Staphylinidae and Chrysomelidae Coleopterans, many Chalcidoidea Hymenopterans)
  • Coarctate pupa – 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

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"Chrysalis" redirects here. For other uses, see Chrysalis (disambiguation).
Common crow butterfly (Euploea core) chrysalis illustrating the Ancient Greek origin of the term: χρυσός (chrysós) for gold

A chrysalis (Latin: chrysallis, from Ancient Greek: χρυσαλλίς, chrysallís, plural: chrysalides, also known as an aurelia) or nympha is the pupal stage of butterflies. The term is derived from the metallic–gold coloration found in the pupae of many butterflies, referred to by the Ancient Greek term χρυσός (chrysós) for gold.

When the caterpillar is fully grown, it makes a button of silk which it uses to fasten its body to a leaf or a twig. Then the caterpillar's skin comes off for the final time. Under this old skin is a hard skin called a chrysalis.[10]

Because chrysalises are often showy and are formed in the open, they are the most familiar examples of pupae. Most chrysalides are attached to a surface by a touch fastener-like arrangement of a silken pad spun by the caterpillar, usually cemented to the underside of a perch, and the cremastral hook or hooks protruding from the rear of the chrysalis or cremaster at the tip of the pupal abdomen by which the caterpillar fixes itself to the pad of silk. (Gr. kremastos 'suspended')[11]

Like other types of pupae, the chrysalis stage in most butterflies is one in which there is little movement. However, some butterfly pupae are capable of moving the abdominal segments to produce sounds or to scare away potential predators. Within the chrysalis, growth and differentiation occur.[12] The adult butterfly emerges (ecloses) from this and expands its wings by pumping haemolymph into the wing veins.[13] Although this sudden and rapid change from pupa to imago is often called metamorphosis, metamorphosis is really the whole series of changes that an insect undergoes from egg to adult.

When emerging, the butterfly uses a liquid, sometimes called cocoonase, which softens the shell of the chrysalis. Additionally, it uses two sharp claws located on the thick joints at the base of the forewings to help make its way out.[14] Having emerged from the chrysalis, the butterfly will usually sit on the empty shell in order to expand and harden its wings. However, if the chrysalis was near the ground (such as if it fell off from its silk pad), the butterfly would find another vertical surface to rest upon and harden its wings (such as a wall or fence).

Moth pupae are usually dark in color and either formed in underground cells, loose in the soil, or their pupa is contained in a protective silk case called a cocoon. The pupa of some species such as the hornet moth develops sharp ridges around the outside called adminicula that allow the pupa to move from its place of concealment inside a tree trunk when it is time for the adult to emerge.[15]

Pupa, chrysalis, and cocoon are frequently confused, but are quite distinct from each other. The pupa is the stage between the larva and adult stages. The chrysalis generally refers to a butterfly pupa although the term may be misleading as there are some moths whose pupae resembles a chrysalis, e.g.: the plume winged moths of the family Pterophoridae and some geometrid moths. A cocoon is a silk case that the larvae of moths, and sometimes other insects, spin around the pupa.

Cocoon

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For other uses, see Cocoon (disambiguation).
Dwarf birch spinner moth (Eriogaster arbusculae) cocoon

A cocoon is a casing spun of silk by many moths and caterpillars,[16] and numerous other holometabolous insect larvae as a protective covering for the pupa.

Cocoons may be tough or soft, opaque or translucent, solid or meshlike, of various colors, or composed of multiple layers, depending on the type of insect larva producing it. Many moth caterpillars shed the larval hairs (setae) and incorporate them into the cocoon; if these are urticating hairs then the cocoon is also irritating to the touch. Some larvae attach small twigs, fecal pellets or pieces of vegetation to the outside of their cocoon in an attempt to disguise it from predators. Others spin their cocoon in a concealed location—on the underside of a leaf, in a crevice, down near the base of a tree trunk, suspended from a twig or concealed in the leaf litter.[17] Contrary to popular belief, larvae do not completely liquify inside the cocoon.[18]

The tough brown cocoon of an emperor gum moth

The silk in the cocoon of the silk moth can be unraveled to harvest silk fibre which makes this moth the most economically important of all lepidopterans. The silk moth is the only completely domesticated lepidopteran; it does not exist in the wild.

Insects that pupate in a cocoon must escape from it, and they do this either by the pupa cutting its way out, or by secreting enzymes, sometimes called cocoonase, that soften the cocoon. Some cocoons are constructed with built-in lines of weakness along which they will tear easily from inside, or with exit holes that only allow a one-way passage out; such features facilitate the escape of the adult insect after it emerges from the pupal skin.

Puparium

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Puparium of Eupeodes americanus
Parasitoid wasp Xenomorphia resurrecta inside a fossilized fly puparium, as revealed by X-ray microtomography

Some pupae remain inside the exoskeleton of the final larval instar and this last larval "shell" is called a puparium (plural, puparia). Flies of the group Muscomorpha have puparia, as do members of the order Strepsiptera, and the Hemipteran family Aleyrodidae.[19]

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See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Pupa

View on Grokipedia
from Grokipedia
A pupa (plural: ) is and immobile stage in the life cycle of holometabolous , which undergo complete metamorphosis, positioned between the active larval and reproductive phases; during this non-feeding period, the insect's internal tissues undergo histolysis and histogenesis to reorganize the body into its form, often encased in a protective structure. This stage is characteristic of the superorder Endopterygota, encompassing over 80% of insect species, including orders such as (butterflies and moths), Coleoptera (beetles), (bees, ants, wasps), and Diptera (flies). The pupal stage typically lasts from a few days to several months, depending on the , environmental conditions like and humidity, and whether the pupa is in —a dormant state to overwinter or aestivate. Externally, the pupa appears quiescent and often forms a hardened or silk cocoon for protection against predators and , while internally, larval structures like mouthparts and musculature break down, and adult features such as wings, legs, and genitalia develop from imaginal discs. Upon completion, the adult ecloses by splitting the pupal case and expanding its wings, a process that can take hours as the hardens. Insect pupae are classified into three main morphological types based on the positioning of appendages and protective coverings: obtect pupae, where legs, wings, and antennae are appressed and glued to the body, forming a compact structure often called a chrysalis in butterflies; exarate pupae, with appendages free and extended from the body, typical in exposed or cocoon-protected forms like those of beetles and bees; and coarctate pupae, which resemble exarate but are enclosed within the hardened last larval skin (puparium), as seen in flies. These variations reflect adaptations to different habitats and lifestyles, with obtect forms common in Lepidoptera for aerial protection, and coarctate in soil-dwelling Diptera for durability. Notable examples include the chrysalis of monarch butterflies (Danaus plexippus), which hangs exposed and transforms over 8–15 days in temperate conditions, and the puparium of house flies (Musca domestica), buried in moist soil for 3–6 days before emergence. In social like honeybees (Apis mellifera), pupae develop within wax cells, contributing to colony reproduction and taking about 12 days from to worker . The pupal stage's vulnerability underscores its ecological role, as it bridges larval herbivory and or predation, influencing in terrestrial ecosystems.

Overview and Role in Development

Definition and Characteristics

The pupa is the third developmental stage in the holometabolous metamorphosis of insects, succeeding the larval stage and preceding the emergence of the adult imago. This stage is characteristic of the Endopterygota superorder, encompassing orders such as Coleoptera (beetles), Lepidoptera (butterflies and moths), Hymenoptera (bees, ants, and wasps), and Diptera (flies). During pupation, the insect transitions from a feeding, motile larva to a non-feeding, largely immobile form focused on internal restructuring. Key features of the pupa include its quiescent nature, with minimal or no locomotion in most species, as larval muscles dissolve prior to the formation of adult musculature. The body is compact, with segments closely apposed and imaginal appendages—such as legs, wings, and antennae—folded tightly against the body or within protective pockets. Pupae typically cease feeding entirely, possessing reduced or non-functional mouthparts, and are often enclosed in a hardened or external case, such as a cocoon in some , for protection during vulnerability. In contrast to hemimetabolous , which lack a pupal stage and exhibit gradual external changes from to , the pupa represents a distinct resting phase enabling complete tissue reorganization in holometabolous forms. Basic anatomy includes the development of structures from imaginal discs—clusters of undifferentiated cells that form wings, limbs, and other features—and, in certain species, a fusion of the head and into a .

Position in the Life Cycle

The pupa occupies a central position in the life cycle of that undergo complete metamorphosis, or holometaboly, serving as the quiescent stage that bridges the larval phase of feeding and growth with the phase of reproduction and dispersal. In this developmental sequence, the hatches into a specialized for nutrient acquisition and body mass increase, after which the larva enters the pupal stage for internal reorganization before eclosing as the , or , which prioritizes , oviposition, and environmental exploration. This four-stage progression—, , pupa, and —characterizes over 80% of species, underscoring the pupa's role as an obligatory intermediary in holometabolous development. The evolutionary advent of the pupal stage enabled radical shifts in , allowing worm-like, feeding-focused larvae to transform into structurally diverse adults, such as those with wings or specialized sensory organs, thereby promoting ecological specialization and . Fossil evidence indicates that holometaboly, including the pupa, first appeared approximately 310 million years ago during the Pennsylvanian subperiod (late ). By comparison, with incomplete metamorphosis, termed hemimetaboly, bypass the pupal stage entirely, progressing through eggs that hatch into nymphs resembling miniature adults and undergoing gradual, incremental changes across multiple instars without a dedicated restructuring phase. This hemimetabolous pattern, seen in groups like orthopterans and hemipterans, contrasts sharply with holometaboly by limiting morphological discontinuity and emphasizing progressive development toward adulthood.

Physiological Processes

Formation and Hormonal Regulation

The formation of the pupa in holometabolous is initiated during the final larval through a precisely timed molting process known as pupation, which transforms the larval body into a non-feeding, immobile preparatory for adult emergence. This transition is triggered by a decline in (JH) titers from the corpora allata glands, which normally maintain the larval state by preventing metamorphic . Concurrently, the brain secretes prothoracicotropic hormone (PTTH), stimulating the prothoracic glands to release , which is rapidly converted to the active form (20E). The rise in 20E levels, in the absence of JH, commits epidermal and cells to pupal development, marking the onset of . Apolysis, the initial step in pupal formation, involves the separation of the old larval from the underlying , facilitated by 20E-induced of molting enzymes such as chitinases and proteases. Following apolysis, the secretes a new, unsclerotized pupal beneath the detached larval one, which is later shed during . This hormonal cascade is tightly regulated: low JH permits 20E to bind nuclear ecdysone receptors (EcR), activating early genes like Broad-Complex (BR-C), a essential for pupal-specific and tissue remodeling. BR-C isoforms, such as Z1, are expressed in response to the first 20E pulse, suppressing larval traits while promoting pupal commitment without inducing differentiation. Recent studies using have elucidated the role of receptors in timing pupation, revealing that disruptions to EcR or downstream factors like E93 delay or arrest the process, leading to retention of larval tissues and incomplete . For instance, in the yellow fever mosquito (), CRISPR knockout of E93 results in pupae that eclose but retain larval tissues and die during the pupal stage, underscoring EcR's control over developmental timing via gene cascades. Additionally, environmental factors such as climate warming can disrupt this regulation; elevated temperatures in urban heat islands alter 20E titers during the prepupal stage, potentially advancing or desynchronizing pupation and affecting synchrony with host plants or predators in species like the . These insights highlight the sensitivity of hormonal pathways to abiotic stressors, with implications for insect under .

Internal Metamorphosis

During the pupal stage, internal metamorphosis in holometabolous involves extensive histolysis, the programmed breakdown of larval tissues to recycle nutrients for adult development. Larval muscles, such as the dorsal external oblique muscles (DEOMs) in , undergo triggered by signaling through the ecdysone receptor isoform B1, which activates cell-autonomous death pathways involving . Similarly, the larval histolyzes via a combination of and , initiated by an early pulse that upregulates genes like those encoding and autophagic proteins. The also experiences selective histolysis, with many larval neurons pruned through caspase-mediated to clear space for adult circuitry. Complementing histolysis, histogenesis drives the formation of adult structures from clusters of undifferentiated cells known as imaginal discs, which proliferate and differentiate during pupation. In , wing imaginal discs evaginate and expand dramatically, transforming from folded sacs into flat epithelial sheets through oriented and migration, regulated by signaling pathways such as Wingless (Wg, a Wnt homolog) for proliferation along disc margins and Decapentaplegic (Dpp, a BMP homolog) for patterning and growth control across the disc. These pathways interact dynamically; for instance, Dpp signaling represses Wg expression in central regions via transcription factors like Dorsocross, ensuring balanced disc expansion. Leg and eye discs follow analogous processes, with Wg and Dpp coordinating histoblast proliferation to form segmented appendages and ommatidia, respectively. Organ remodeling extends to vital systems, adapting them for adult function without external feeding, relying instead on larval reserves mobilized during histolysis. The brain undergoes profound rewiring, where larval circuits are partially dismantled via of and Kenyon cells, while surviving neurons extend new processes to form adult-specific connections, such as in olfactory and circuits. This remodeling repurposes larval neurons for adult behaviors, with aiding local neurite to refine connectivity. Concurrently, Malpighian tubules—the renal organs—are remodeled by renal stem cells (RSCs) that partially activate during pupation to replace larval principal cells near the gut junction, with further remodeling in adults enhancing stone resistance and ion transport efficiency. The tubules shut down physiologically during early pupation, losing microvilli, before RSC-driven regeneration restores functionality. Recent research highlights additional layers of in pupal . Post-2020 studies show that the pupal influences efficiency, with gut like species delaying pupation rates by influencing host immune responses and dynamics, while their reduction can accelerate the transition. In and other , turnover during pupation reshapes community composition, supporting resource reallocation for histogenesis. Advances in live imaging have revealed the dynamic unfolding of imaginal discs; for example, time-lapse of pupae captures wing disc evagination as a coordinated epithelial unfolding driven by actomyosin contractility, occurring over hours post-pupariation. Such techniques also document real-time cell rearrangements in notum regions, where crowding triggers to limit proliferation.

Duration and Emergence

The duration of the pupal stage in varies widely across species and is heavily influenced by environmental conditions such as temperature, , and photoperiod. In many dipterans like the (Musca domestica), the pupal period typically lasts 3-6 days under optimal warm conditions, allowing rapid development to adulthood. In contrast, certain beetles, such as the warehouse beetle (Trogoderma variabile), can experience delayed pupation due to larval extending up to 2 years. Higher temperatures generally accelerate pupal development and shorten the overall duration, while lower or shorter photoperiods can extend it by inducing metabolic slowdowns. Diapause represents a key mechanism extending pupal duration, occurring as either obligatory (mandatory for the species, often one generation per year) or facultative (environmentally induced) dormancy to overwinter or avoid harsh conditions. It is commonly triggered by short day lengths (photoperiods) signaling seasonal change, leading to suppressed metabolic activity and halted histolysis or . For instance, in the (Ostrinia nubilalis), facultative pupal can last several months under short-day conditions at moderate temperatures, enabling survival until spring. Warmer climates may shorten non-diapausing pupal stages but paradoxically increase risks by altering photoperiod cues or inducing estival (summer) in some species, as observed in the oriental tobacco budworm (Helicoverpa assulta), where high temperatures prolong the pupal phase. Emergence, or eclosion, marks the end of the pupal stage, involving enzymatic degradation of the pupal cuticle followed by adult expansion. Chitinases, such as those in the insect chitinase family (e.g., CHT5 in beetles), are secreted to soften and break down the chitinous pupal exoskeleton, facilitating the adult's exit. Once free, the adult insect pumps hemolymph into its wings and body under increased pressure generated by abdominal contractions, expanding and hardening the new cuticle within minutes to hours. Eclosion timing is often synchronized to minimize predation, with many butterflies emerging at dawn when visibility is low and predators are less active.

Behaviors and Defenses

Defensive Adaptations

Pupae, being immobile and vulnerable during metamorphosis, employ a range of physical defenses to evade detection by predators. Cryptic coloration is prevalent, allowing pupae to blend seamlessly with their environment; for instance, swallowtail butterfly (Papilio spp.) pupae exhibit green or brown hues that mimic twigs or leaves, enhancing survival against visually hunting birds. Immobility further reinforces this camouflage, as pupae remain stationary to resemble inert plant parts. Chemical defenses in pupae often build on larval strategies, involving both sequestration of hostplant toxins and endogenous synthesis. Monarch butterfly (Danaus plexippus) pupae sequester cardenolides acquired during the larval stage from milkweed (Asclepias spp.), rendering them toxic to avian predators and thereby deterring attacks. In contrast, some beetle pupae synthesize alkaloids de novo. These compounds are stored in hemolymph and exuded as a reflexive defense, highlighting the pupal stage's reliance on pre-formed chemical armaments. Behavioral and social adaptations compensate for pupal immobility, particularly in species with symbiotic interactions. Myrmecophilous lycaenid butterfly pupae benefit from ant tending, where attendant ants (Crematogaster spp.) aggressively defend the pupae against predators and parasitoids, improving survival rates in ant-colonized habitats. Acoustic signaling serves as another mechanism; pupae of some Hymenoptera and lycaenids produce substrate-borne vibrations via stridulation to alert tending ants or startle potential predators, modulating ant attendance and deterring attacks. Recent research post-2020 has illuminated how environmental stressors impact these defenses. In tobacco hornworm (Manduca sexta) pupae, mechanical disturbance via vibrations triggers sex-specific behavioral responses such as twitching and pulsating, with males exhibiting more frequent and prolonged reactions. These findings emphasize the need for integrated approaches to understand pupal resilience amid global environmental shifts.

Reproductive Behaviors

In certain species of , such as butterflies in the Heliconius, pupal mating occurs where males copulate with females immediately upon or during their emergence from the pupal case, a first documented in the late . This facultative strategy is observed sporadically; for instance, in , field studies recorded only two instances among 11 emerging females, with males patrolling host plants like species to locate pupae using chemical cues from the plants and potentially from the pupae themselves. Females in these species store received during pupal in a , allowing them to fertilize eggs post-emergence without further copulation, as evidenced by high mating success rates (19 out of 20 recaptured virgin females were found mated). Pupal is facilitated by sex pheromones emitted from female pupae in some moths, which arrest and attract patrolling males prior to adult eclosion. In the Cydia pomonella, female pupae release pheromones that draw males to the site, enabling pre-emergence copulation and reducing post-eclosion mate-searching risks. Calling behaviors during the pupal stage are less common but include vibrational signals in select species; for example, some lepidopteran pupae produce substrate-borne vibrations to signal readiness or deter rivals, though these are primarily documented in adult contexts and extended to pre-emergence interactions in low-mobility pupae. Silk pheromones, deposited on pupal cocoons by some moths, may also aid in mate location by providing persistent chemical trails that males detect near emergence sites. Parthenogenesis in the pupal stage, known as pupal pedogenesis, is a rare asexual reproductive mode observed in certain , particularly gall midges of the family (Diptera), where unfertilized eggs develop within the pupa into larvae that emerge viviparously. This process allows reproduction without fertilization, often in isolated or low-density conditions, and involves endosomatic development of reproductive structures inside the pupal body, leading to the mother's death upon offspring emergence. The evolutionary advantages of pupal mating include securing mates in sparse populations by enabling males to monopolize emerging females on predictable host plants, thereby increasing reproductive success amid high larval mortality and asynchronous eclosion.

Classification and Variations

General Morphological Types

Pupae are primarily classified into three morphological types based on the configuration of appendages and protective structures: exarate, obtect, and coarctate. In exarate pupae, the appendages—such as legs, wings, and antennae—are free and not fused to the body wall, allowing for a more adult-like appearance and limited voluntary movement. This type is prevalent in orders like Coleoptera (beetles) and Hymenoptera (such as bees and wasps). In obtect pupae, the appendages are appressed and glued to the body, forming a compact structure often seen in exposed forms. This type is common in Lepidoptera (butterflies and moths) and some Diptera (flies). In contrast, coarctate pupae are enclosed within the hardened larval exoskeleton (puparium), which conceals the typically exarate appendages of the internal pupa and provides enhanced protection during vulnerable stages. A secondary classification distinguishes pupae by mouthpart structure: decticous and adecticous. Decticous pupae possess functional, articulated mandibles that enable the pupa to bite or chew its way out of enclosures, facilitating escape and reflecting a more active phase. These are always exarate and occur in basal , such as sawflies (e.g., Arge pagana in Argidae). Adecticous pupae, conversely, have reduced or non-functional mandibles, relying instead on other mechanisms like silk-dissolving enzymes or external aids for emergence, and are typically immobile. This type is widespread in advanced , including moths. These morphological types carry functional implications tied to their and development. Exarate pupae's free appendages permit slight repositioning or defensive responses, aiding in exposed environments, while obtect forms prioritize compactness for aerial or silk-protected contexts, and coarctate forms emphasize for in concealed or soil-dwelling habitats. Distributionally, exarate pupae dominate in Coleoptera and most , coarctate pupae are characteristic of Diptera (higher flies), and obtect forms prevail in . Evolutionarily, decticous pupae represent the primitive condition, with adecticous forms derived secondarily, though direct evidence for transitional hybrids remains limited. Variations in pupal development include the prepupa, an interpolated stage in insects exhibiting hypermetamorphosis, such as certain beetles in the family Meloidae (oil beetles), where it precedes the true pupa between the active larva and pupation. In contrast, some insects with incomplete metamorphosis, such as thrips and whiteflies, feature a pseudopupa or false pupa, which is not a true pupal stage but a quiescent pre-adult phase lacking the full metamorphic remodeling seen in holometabolous insects.

Specific Enclosing Structures

In the pupal stage of many , particularly , the chrysalis serves as a distinctive enclosing structure, consisting of a naked, obtect pupa that is externally hardened without . This form arises from the sclerotization process of the larval , where the outermost layers tan and rigidify following apolysis, providing a protective shell for . The chrysalis is secured to a substrate, often a or , via the cremaster—a specialized, hook-like at the posterior abdominal end that anchors it firmly. Many butterflies also produce a silk girdle, a simple thread spun around the body just prior to pupation, which provides additional support by holding the pupa in place against the substrate..pdf) Emergence of the adult occurs when the splits the chrysalis along a weakened dorsal seam, allowing the to extricate itself and expand its wings. Cocoons represent another specialized pupal enclosure, primarily constructed by larvae of various moths in the and certain beetles in the Coleoptera, through the and weaving of silk glands into a multilayered protective case. These structures incorporate crystals embedded within the matrix, which significantly bolster tensile strength and puncture resistance, adapting the cocoon to withstand predation and environmental pressures. Adult moths typically escape the cocoon by exploiting pre-formed exit valves in the or by secreting proteolytic enzymes, such as cocoonase, that selectively degrade the sericin protein binding the fibers. In Diptera, such as houseflies (Musca domestica), the puparium forms a robust, barrel-shaped case from the tanned and contracted final larval , encasing the coarctate pupa and the for protection. Prominent respiratory horns project from the anterior end through specialized slits in the puparium wall, enabling tracheal while minimizing exposure. Post-2020 biomechanical analyses have highlighted the puparium's capacity to endure compressive forces, with its layered, sclerotized distributing stress to safeguard internal tissues during or handling. These enclosing structures exhibit notable variations in construction and function: chrysalides depend on direct sclerotization of the pupal for rigidity without extrinsic materials, contrasting with the externally fabricated of cocoons; puparia, meanwhile, repurpose the larval into a seamless, hardened barrel. Not all pupae require such enclosures, as seen in exarate pupae of many beetles (Coleoptera), which are often placed in earthen cells or remain exposed in soil habitats without additional casings.

References

  1. https://askabiologist.asu.edu/complete-metamorphosis
  2. https://entomology.mgcafe.uky.edu/content/insect-basics
  3. https://www.floridamuseum.ufl.edu/educators/resource/butterfly-life-cycle/
  4. https://genent.cals.ncsu.edu/bug-bytes/morphogenesis/
  5. https://agsci.oregonstate.edu/sites/agscid7/files/ippc/entomology-insects-britannica.pdf
  6. https://aptivepestcontrol.com/pests/flies/house-flies/the-four-stages-of-the-house-fly-life-cycle/
  7. https://www.perfectbee.com/beekeeping-articles/honey-bee-life-cycle
  8. https://www.britannica.com/animal/insect/Natural-history
  9. https://faculty.ucr.edu/~legneref/entomol/metamorphosis.htm
  10. https://repository.si.edu/bitstream/handle/10088/22894/SMC_122_Snodgrass_1954_9_1-124.pdf
  11. https://entomology.unl.edu/insects-complete-metamorphosis/
  12. https://biology.byu.edu/phylogeny-of-holometabolous-insect-orders
  13. https://pmc.ncbi.nlm.nih.gov/articles/PMC6711285/
  14. https://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-015-0428-8
  15. https://pmc.ncbi.nlm.nih.gov/articles/PMC10735215/
  16. https://doi.org/10.1146/annurev-ento-011019-025103
  17. https://doi.org/10.22271/j.ento.2021.v9.i4e.8804
  18. https://www.liebertpub.com/doi/10.1089/crispr.2022.0066
  19. https://pubmed.ncbi.nlm.nih.gov/36374965/
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