INTERESTING INSECTS

By N A Martin (2017 revised 2018)

Green fern aphid

Aulacorthum filicis van der Goot, 1917

This adventive aphid is from the Island of Java, Indonesia. It lives on young fronds of ferns. In New Zealand it is widespread on some species of native ferns in native forests around Auckland. Its presence in other areas is uncertain.

Conservation status: Lives on native ferns in native ecosystems; could be a minor pest in gardens.

In New Zealand, the green fern aphid appears to breed all year. Only female aphids are known. Winged females locate new host plants. There may be several generations producing wingless adults followed by a generation of winged females. The older nymphs of the winged females have wing buds.

Adult green fern aphids may be wingless or have wings. The adult wingless females are grass-green with brown to black legs, antennae, siphuncles and cauda. The body is about 1.7 mm long. At rest the antennae are held over their back. Aphids have sucking mouthparts. The two pairs of long stylets, special shaped rods, are held in the rostrum, which is held on the underside of their body when the aphid is not feeding.

Winged females are grass-green with a darker area on the dorsal (top) side of the thorax (middle part of the body). The wings have dark veins and are held above the body. The fore wings are larger than the hind wings.

Adult females give live birth to nymphs that look like small wingless adults. The first instar (stage) nymph has pale legs and siphuncles, and the end of the abdomen is rounded. There are four nymphal stages. Nymphs go from one stage to the next by moulting, changing their skin. Older nymphs have brown legs and siphuncles, and develop a pointed end to the abdomen that remains pale. The mature nymph moults into the adult.

Nymphs that are going to develop into winged adults have wing buds. Winged aphids usually develop when the quality of food from the host plant deteriorates.

Feeding and honeydew

Like other Hemiptera, the green fern aphid has sucking mouthparts. The two pairs of long stylets (specially shaped rods) are held in the rostrum. When it wishes to feed, the aphid moves the tip of the rostrum to the surface of a leaf. The stylets are then gradually pushed into the plant. One pair of stylets, the maxillae, form two tubes; one through which saliva is injected into the plant and a second through which plants juices are sucked up into the insect.

The green fern aphid inserts the stylets into the phloem (the plant vessels for transmitting sap from the leaves to other parts of the plant). The sap has a high volume of water and sugars, more than the insect needs. The green fern aphid excretes the excess water and sugar, which is called honeydew. The green fern aphid excretes the excess sugars from the siphuncles. Fern fronds can become covered with honeydew.

Wingless female green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae); the arrows point to one of the two siphuncles and the cauda. Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKC]

Winged green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 29GV]

Dorsal side of a winged green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKV]

Underside of a winged green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKW]

Young nymph of the green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FL0]

Recently moulted nymph of the green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKE]

Late instar nymph of the green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKF]

Nymph of green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), with wing buds. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKX]

Colony of wingless Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), on underside of frond of shining spleenwort, Asplenium oblongifolium (Aspleniaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2FKY]

Small colony of wingless Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), on underside of frond of shining spleenwort, Asplenium oblongifolium (Aspleniaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKG]

Colony of wingless Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), on underside of frond of shining spleenwort, Asplenium oblongifolium (Aspleniaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2FKZ]

In New Zealand five species of aphids have been found breeding on ferns. Two species are only found on ferns, while three species are polyphagous.

Normally aphids require specialist skills for their identification, but adult female Green fern aphids are sufficiently distinctive to enable colonies to be recognised on fern host plants. The wingless females are grass-green with dark-brown to black legs, antennae, siphuncles and cauda. Winged aphids are uncommon and have darker upper surface of the thorax, area of the body between the wings. The fore wings are much larger than the hind wings.

The colour of the black fern aphid easily distinguishes it, but the polyphagous species may look a little like the Green fern aphid. For example, the wingless females of the lily aphid, Neomyzus circumflexus (Buckton, 1876), are pale green with dark joints on their legs. The dorsal (upper) side of the body of winged lily aphids is black.

Green wingless aphids may be confused with the fern mirid, Felisacus elegantulus (Hemiptera: Miridae), which also lives on some of the same species of fern. The adult mirids look quite different from the fern aphid, being long and thin with wings held horizontally over the body. The fern mirid nymphs are also quite different in appearance to fern aphids.

Wingless female green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae); the arrows point to one of the two siphuncles and the cauda. Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKC]

Winged green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 29GV]

Dead winged green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), showing wing venation. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKT]

Dorsal side of a winged green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKV]

Nymphs and wingless female of the lily aphid, Neomyzus circumflexus (Hemiptera: Aphididae) on young frond of Single crepe fern, Leptopteris hymenophylloides (Osmundaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 1HYU]

Winged female of the lily aphid, Neomyzus circumflexus (Hemiptera: Aphididae) on young frond of Single crepe fern, Leptopteris hymenophylloides (Osmundaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 1HYV]

Nymph of the fern mirid, Felisacus elegantulus (Hemiptera: Miridae) on the underside of Shaking brake, Pteris tremula (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15K2]

Adult fern mirid, Felisacus elegantulus (Hemiptera: Miridae) on the underside of Shaking brake, Pteris tremula (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15K7]

Parasitoids

At least one parasitoid wasp (Hymenoptera) of the green fern aphid is known. The adult female wasp lays an egg in an aphid. The wasp larva hatches and lives and grows within the aphid. When the wasp larva is fully grown it kills the aphid whose body swells and turns into a grey-brown ‘mummy’ in which the wasp pupates. When the adult wasp has formed and emerged from its pupa in the mummified aphid, it chews a round hole in the skin of the mummy through which it emerges.

Pathogens

One fungal pathogen an Entomophora species (Fungi: Entomophthoraceae), has been found.

Predators

A larva of the Yellow haired ladybird, Adoxellus flavihirtus and two larvae of the Tasmanian lacewing, Micromus tasmaniae have been found feeding on green fern aphids. They are also likely to be prey of hoverflies, predatory midges and birds.

Several brown mummified green fern aphids, Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), each containing a pupa of a parasitoid wasp (Hymenoptera). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKL]

Mummified Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), killed by a parasitoid wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKS]

Mummified Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), killed by a parasitoid wasp (Hymenoptera), note the exit hole for the adult wasp. Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKM]

Underside of a female wasp parasitoid (Hymenoptera) of Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKN]

Upper side of a female wasp parasitoid (Hymenoptera) of Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKP]

Dead male wasp (Hymenoptera), parasitoid of Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKJ]

White fungal pathogen, Entomophora species, infesting a green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKK]

Larva of yellow haired ladybird, Adoxellus flavihirtus (Coleoptera: Coccinellidae) feeding on a Green fern aphid, Micromyzella filicis (Hemiptera: Aphididae) on a young frond of Sickle spleenwort, Asplenium polyodon (Aspleniaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2CBG]

Larva of Tasmanian lacewing, Micromus tasmaniae (Neuroptera: Hemerobiidae) in a colony of green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FK9]

Larva of Tasmanian lacewing, Micromus tasmaniae (Neuroptera: Hemerobiidae) in a colony of green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKA]

Two cocoons of Tasmanian lacewing, Micromus tasmaniae (Neuroptera: Hemerobiidae) in a colony of green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FKB]

In New Zealand, the green fern aphid has been found on ferns in three families. It lives on the underside of young fronds.

Fern aphids feed by inserting its stylets into the phloem (vessels transferring nutrients) in the fern fronds and suck the plant sap. Feeding by many aphids on young, expanding fern fronds can cause them to become distorted. This distortion can be seen after the aphids have gone. Feeding on older fronds causes no physical damage. Plant sap is high in sugars and low in other nutrients. The aphids excrete the excess sap, which is known as honey dew. Heavy deposits of honey dew can make surfaces sticky.

Colony of wingless Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), on underside of frond of shining spleenwort, Asplenium oblongifolium (Aspleniaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2FKZ]

Small colony of wingless Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), on underside of frond of shining spleenwort, Asplenium oblongifolium (Aspleniaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKG]

Wingless female and nymph of Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), on frond of common maidenhair fern, Adiantum cunninghamii (Pteridaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FKH]

Wingless female and nymph of Green fern aphid Micromyzella filicis (van der Goot, 1917) (Hemiptera: Aphididae), on frond of Hanging spleenwort, Asplenium flaccidum (Aspleniaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2S4Y]

The green fern aphid appears to cause only occasional damage to native ferns in the native ecosystems. In gardens it may occasionally be of concern. If an insecticide is felt necessary chose one that will cause least harm to predators and parasitoids.

Aphids on New Zealand ferns

In New Zealand five species of aphids have been found breeding on ferns. Two species are only found on ferns, while three species are polyphagous. The two specialist fern feeders are the black fern aphid, Idiopterus nephrelepidis Davis, 1909 and the green fern aphid, Micromyzella filicis (van der Goot, 1917). The latter is common in Auckland. The three polyphagous species are, Brachycaudus helichrysi (Kaltenbach, 1843), Myzus ornatus Laing, 1932, and Neomyzus circumflexus (Buckton, 1876).

Aphids on worlds plants; Micromyzella filicis. www.aphidsonworldsplants.info/d_APHIDS_M.htm#Micromyzella.

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.

Dr Robert Foottit, Canadian National Collection of Insects, Ottawa, Canada, for identification of aphids.

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

1 August 2018, NA Martin. Host plant list updated, photos added.