Life Cycle Terms for Lepidoptera
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Adult: The fourth and final stage in the lepidopteran life cycle. Formed in the pupa, the adult body emerges nearly ready for its two important functions: dispersal
and reproduction. The adult form is most easily distinguished by the presence
of functional wings (with very few exceptions). The adult stage is sometimes called
an imago.
Caterpillar: The common name for the second stage in the lepidopteran life cycle. See the
official name, larva, below.
Chrysalis: A butterfly pupa; the abdominal end is typically held tightly in place to the surface where the
chrysalis is formed by a cremaster.
Cocoon: The silken enclosure in which a moth spends its pupal period. Not all moths
utilize a cocoon, nor do any butterflies. Some moth species (such as the bagworms,
in FamilyPsychidae) spin cocoons as larvae and go through both larval and pupal
stages within the cocoons. Some moths add leaves, other plant material, or debris
to the cocoon.
Cremaster: Extension off the abdominal end of the pupa, typically used to attach the pupa to some structure (though not necessarily).
The cremaster may consist of small to quite pronounced hooks, and can attach to
the inside of a cocoon (if the species spins a cocoon), or it can be used to attach to the substrate
(branch, leaf, etc.) in the case of a butterfly chrysalis.
Diapause: An extended period in which an insect has very little metabolic activity and
is thus relatively inactive. The trigger for diapause is typically some environmental
condition such as day length or temperature. The immediate response of the insect
is initiated by both nerves and hormones and the result is the suspension of many
activities. The function of diapause is to help the insect survive through an
upcoming difficult period (e.g., lack of food due to a season of cold weather).
The stage of life when diapause can occur is genetically determined; depending
on the species it can be as an embryo, larva, pupa, or adult. Among Lepidoptera,
pupal diapause is probably the most common.
Ecdysis: The process of removing the cuticle of the previous stage and emerging as the body of the next stage. Essentially
identical with molt.
Eclosion: The act of the adult’s breaking out from within the pupal cuticle; the last molt in the insect’s life cycle.
Egg: The structure composing the first part of the butterfly or moth life cycle.
Technically, an egg is only the female contribution to the next generation, being
a single cell with the appropriate amount of genetic material (chromosomes) and
an abundance of nutritional material (largely yolk) to sustain life just after
fertilization. But in common usage, “egg” also means the stage of life of a new
butterfly or moth that begins with fertilization and continues until a caterpillar
emerges. The confusion is a result of the fact that the external appearance of
an egg changes little from the time of fertilization until just before a tiny
caterpillar breaks through the surface. Of course, internal changes are many,
including all of the embryonic development such as cell reproduction, blastulation,
gastrulation, and organogenesis.
Holometabolous: Having a complete set of metamorphic changes during the life cycle. That is,
progressing from egg/embryo to larva to pupa to adult, skipping none of these
forms. Butterflies and moths are holometabolous.
Imago: The adult butterfly or moth. See adult.
Instar: An period during an insect's life, typically within the larval phase of life,
between two molts. For example, one could refer to a second instar caterpillar. See also stadium
Larva: The second stage in the lepidopteran life cycle. The larva is a worm-shaped
organism specialized for spectacular growth by means of nearly constant eating.
The larva lacks two abilities that the adult will eventually have: flight and
reproduction.
Metamorphosis: The series of changes that lead to the forming of an adult lepidopteran organism.
All Lepidoptera undergo three distinct metamorphic transformations: from egg (embryo) to larva, from larva to pupa, and from pupa to adult. This form of metamorphosis, since it skips no stage, is called complete metamorphosis. See the FAQ on this amazing transformation.
Molt, Molting: The process of breaking out of a cuticle, either periodically during larval growth or when going to the next metamorphic stage (from larva to pupa or from pupa to adult). Molting is signaled by hormonal
changes (see FAQ #10 on this).
Pupa: The third stage in the lepidopteran life cycle. Although seemingly quiet as
seen externally, the pupa is busily destroying most of its larval cells and replacing
them by reproduction of relatively few cells that had no function in the larva.
Thus, a nearly complete reconfiguration of the animal occurs beneath the pupal
cuticle, to make the adult body.
Pheromone: A chemical released by one organism and sensed by another individual of the
same species. Among Lepidoptera pheromones are often used to direct one sex to
the other, to facilitate reproduction. Typically, the male follows a pheromone
to the female. This communication method is especially important for night-flying
moths. Each species is likely to utilize a unique (or nearly unique) chemical
or mix of chemicals, thus avoiding inter-species reproductive errors.
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