INTERESTING INSECTS

By R J B Hoare and N A Martin (2018)

Maidenhair fern moth

Diathrausta aduncalis Felder & Rogenhofer, 1875

This is the type species of the genus Musotima.

Every genus has a tye species, which helps determine which other species should also be included in the genus.

This endemic moth is found throughout New Zealand. It is found in native ecosystems on or near its host plants, some species of native maidenhair ferns, Adiantum species (Pteridaceae).

Conservation status: It is found in small numbers where its host plants grow in native habits, and is not threatened.

There are several generations per year in warmer areas such as Auckland, but there may be only one generation a year in colder areas.

At rest the adult moths are triangular, about 8-10 mm long and with 15-20 mm wingspan. The upper sides of the wings in the male are dark brown with areas of paler brown, white and black; in the female the white areas are mainly replaced by orange brown. The underside is similar to the upper side in both male and female but with the patterning less distinct. The body is mainly dark brown above, with some white areas at the base of the abdomen, and white on the underside. The three pairs of legs are banded dark brown and white for most of their length, but pure white at the tips. The head bears a pair of long antennae that are folded back when the moth is at rest. It is presumed that, as in other moths, the females attract males using chemicals released from the abdomen; male and female then mate. The female moth then lays eggs on young fern fronds.

Eggs and Caterpillars

Several eggs may be laid on the underside of a young fern frond. The pale eggs are oval and several may be laid together, overlapping each other. The surface of the egg is sculptured. Just before it hatches the caterpillar can be seen inside the egg.

The newly hatched caterpillar has a black head and a pale body that becomes green after it starts eating. It initially feeds on the underside of the fern frond and may feed on the sporangia. At first the caterpillar just eats the frond tissue leaving the upper epidermis (top layer of frond) intact, creating a ‘window’ in the fern frond. On young expanding fronds, it chews the edge of the frond and makes holes. Caterpillars grow by moulting, changing their skin. Older caterpillars have a pale head capsule with pale brown markings and a dark stripe along the side. The body is green with a translucent glassy appearance, and covered with short setae (bristles). When fully grown the caterpillar is about 10 mm long. The caterpillar has the usual number of legs: three pairs on the thorax and, and 4 pairs of prolegs (false legs) on the abdominal segments.

Pupae

When the caterpillar is full grown it finds a sheltered area of the fern frond and attaches itself by the tip of its abdomen and by a thin silk thread. It then moults into a pupa that is at first green, but then turns brown with a few darker markings. Shortly before moth emergence, the colour of the wings and legs can be seen through the cuticle (skin) of the pupa. When the moth is ready to emerge the cuticle of the pupa at the front splits and the moth pushes its way out. It hangs itself from the plant to harden and dry its wings.

Adult female Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T71]

Adult male Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae), museum specimen. Creator: Birgit E Rhode. © Landcare Research. [Image: 2T7W]

Underside of adult male Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6N]

Underside of adult female Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T72]

Egg of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). The egg is to the left of the picture (fern sorus to the right). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6R]

Three overlapping eggs of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6S]

Small black-headed caterpillar of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6U]

Neonate (newly hatched) caterpillar and egg shell of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae); note the feeding damage to the sporangia. Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6Z]

Young, black-headed caterpillar of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) feeding on frond of Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T6H]

Older, brown-headed caterpillar of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) feeding on frond of Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6I]

Caterpillar of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6J]

Pupa of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Darren Snaith. © Plant & Food Research. [Image: 2T6M]

Empty pupal case of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T70]

Adults of the Maidenhair fern moth, Musotima aduncalis, are similar in appearance to other species of Musotima in New Zealand. This species can be recognised by the shape of the hindwing, which is irregularly scalloped, with several dark patches in the fringe (narrow scales around the margin of the wing). Musotima nitidalis and M. ochropteralis, the other two species present on the mainland of New Zealand, have a more smoothly rounded hindwing, without dark patches in the fringe. The white spot about 2/3 of the way along the forewing in male M. aduncalis is roughly rectangular, whereas in M. nitidalis, the spot is comma-shaped. The female of M. aduncalis lacks a white spot in this position. The Australian maidenhair fern moth, Musotima ochropteralis, is a bright yellowish moth, much paler than M. aduncalis, and has a distinct white S-shaped line crossing the middle of the forewing.

The caterpillars of the Maidenhair fern moth are found on various species of native maidenhair ferns, Adiantum species (Pteridaceae). This is the only species of Musotima on native maidenhair ferns. Another species, Australian maidenhair fern moth, Musotima ochropteralis, lives on two naturalised species, European maidenhair fern, Adiantum capillus-veneris and Delta maidenhair, Adiantum raddianum. Musotima caterpillars of both species can be recognised by their appearance and the distinctive feeding damage done to their host plants. The young caterpillars are pale green with a black head capsule. The older caterpillars are green and have a pale head capsule with pale brown markings and a dark stripe along the side. The caterpillars have a translucent glassy appearance. The caterpillars eat the frond tissue leaving the upper epidermis (top layer of frond) intact. Caterpillars also chew right through the expanding fronds. The pupae of both species are similar, green with a few darker spots.

Adult male Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T73]

Underside of adult female Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T72]

Adult female Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T71]

Dead adult male Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6P]

Adult Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T75]

Underside of adult Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) reared from caterpillar on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T74]

Eggs of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T76]

Egg of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6W]

Small black-headed caterpillar of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6Y]

Small black-headed caterpillars of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T77]

Large brown-headed caterpillar of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6K]

Pupa of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Darren Snaith. © Plant & Food Research. [Image: 2T6M]

No pathogens or predators of the Maidenhair fern moth have been reported. It is likely that birds, spiders and predatory insects catch and eat the moths.

Parasitoids

Three species of wasps have been found that are parasitoids of Maidenhair fern moth, Musotima aduncalis, One, a tiny parasitoid wasp, lays an egg in the egg of the moth. When the wasp larva hatches from the egg it feeds on the moth egg. When the wasp larva is fully grown it it pupates in the moth egg which turns black. When the adult wasp is ready to emerge, it chews a hole in the egg.

A second, larger parasitoid wasp, Diadegma sp.(Ichneumonidae), kills the caterpillar when it is fully grown and about to pupate. The wasp larva emerges from the caterpillar and spins an oval, dark grey cocoon in which it pupates. When the adult wasp is ready to emerge it chews a round hole in its cocoon.

The third parasitoid, the basket-cocoon wasp, Meteorus pulchricornis (Braconidae), is a recent arrival in New Zealand. It parasitizes small to medium sized caterpillars. Its distinctive cocoon dangles by a thread.

Black parasitised egg of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6T]

Black parasitised egg of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae), note the exit hole made by the adult parasitic wasp (Hymenoptera). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6V]

Cocoon of Diadegma species (Hymenoptera: Ichneumonidae) a parasitoid of Maidenhair fern moth, Musotima aduncalis (Lepidoptera: Crambidae), note the caterpillar head capsule on the cocoon. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T60]

Cocoon of Diadegma species (Hymenoptera: Ichneumonidae) a parasitoid of Maidenhair fern moth, Musotima aduncalis (Lepidoptera: Crambidae), note the dark round exit hole of the adult wasp. Creator: Tim Holmes. © Plant & Food Research. [Image: 2T5Y]

Adult female of Diadegma species (Hymenoptera: Ichneumonidae), a parasitoid of Maidenhair fern moth, Musotima aduncalis (Lepidoptera: Crambidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T62]

Underside of an adult female of Diadegma species (Hymenoptera: Ichneumonidae), a parasitoid of Maidenhair fern moth, Musotima aduncalis (Lepidoptera: Crambidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T61]

Side view of a dead adult female of Diadegma species (Hymenoptera: Ichneumonidae), a parasitoid of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T63]

Side view of a dead adult male of Diadegma species (Hymenoptera: Ichneumonidae), a parasitoid of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T5X]

Cocoon of female Basket-cocoon parasitoid, Meteorus pulchricornis (Hymenoptera: Braconidae) suspended from a lacebark leaf (Hoheria populnea) after emerging from a caterpillar of the lacebark looper, Epiphryne undosata (Lepidoptera: Geometridae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G0T]

Cocoons of female Basket-cocoon parasitoid, Meteorus pulchricornis (Hymenoptera: Braconidae) after the adults have emerged: note the cut open ‘lid’. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G0U]

Adult female Basket-cocoon parasitoid, Meteorus pulchricornis (Hymenoptera: Braconidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2G0Z]

Underside of an adult female Basket-cocoon parasitoid, Meteorus pulchricornis (Hymenoptera: Braconidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2G0Y]

Caterpillars of the maidenhair fern moth, Musotima aduncalis, only feed on native species of maidenhair ferns, Adiantum (Pteridaceae). The moth lays eggs on the adventive species, Adiantum raddianum, but the caterpillars fail to develop.

Caterpillars eat right through very young expanding fronds, but on older fronds they eat the frond tissue leaving the upper epidermis (top layer of frond) intact. Neonate (just hatched) caterpillars may feed on sporangia.

Neonate (newly hatched) caterpillar and egg shell of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) on Common maidenhair fern, Adiantum cunninghamii (Pteridaceae); note the feeding damage to the sporangia. Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6Z]

Small black-headed caterpillar of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae) feeding on young frond of Common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2T6L]

Frond of Adiantum fulvum (Pteridaceae) with feeding damage from caterpillars of Maidenhair fern moth, Musotima aduncalis, (Lepidoptera: Crambidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2T6Q]

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.