The Monotrysia is a group of insects in the Lepidoptera

Lepidoptera

Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

n order which is not currently considered to be a natural group or clade

Cladistics

Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...

. The group contains only moth

Moth

A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s and most of these (apart from the recently discovered family Andesianidae) are small and are relatively understudied (compared to Ditrysia) in many regions of the world. The group is so named because the female has a single genital opening for mating

Mating

In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...

 and laying eggs

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

, in contrast to the bulk of the Lepidoptera (Ditrysia

Ditrysia

The Ditrysia are a natural group or clade of insects in the Lepidopteran order containing both butterflies and moths. They are so named because the female has two distinct sexual openings: one for mating, and the other for laying eggs .About 98% of described species of Lepidoptera belong to Ditrysia...

), which have two female reproductive openings. They comprise all of the group Heteroneura

Heteroneura

Heteroneura is a natural group in the insect order Lepidoptera that comprises over 99% of all butterflies and moths. This is the sister group of the infraorder Exoporia , and is characterised by wing venation which is not similar or homoneurous in both pairs of wings....

but the Ditrysia.

Sources

• Davis, D. R. (1986). A new family of monotrysian moths from austral South America (Lepidoptera: Palaephatidae), with a phylogenetic review of the Monotrysia. Smithsonian Contributions to Zoology, 434: 1-202.
• Davis D. R. (1999). The Monotrysian Heteroneura. Pages 65-90 in: Lepidoptera: Moths and Butterflies. 1. Evolution, Systematics, and Biogeography. Handbook of Zoology Vol. IV, Part 35. N. P. Kristensen, ed. De Gruyter, Berlin and New York.
• Davis, D. R. and Gentili, P. (2003). Andesianidae, a new family of monotrysian moths (Lepidoptera: Andesianoidea) from South America. Invertebrate Systematics, 17: 15-26.Abstract
• Dugdale, J.S. (1974). Female genital classification in the classification of Lepidoptera. New Zealand Journal of Entomology, 1(2): 127-146. pdf