INTERESTING INSECTS

By N A Martin (2010, revised 2018)

Black fern aphid, Maidenhair fern aphid

The country of origin of this adventive aphid is not certain, but it is probably from tropical areas of the Americas. In New Zealand it is present in the North and South Islands. It is one of five species of aphid found on native ferns in New Zealand.

Conservation status: Widespread, possibly a minor pest in gardens.

In New Zealand the black 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 fern aphids may be wingless or have wings. The adult wingless females are black with transverse rows of white flat topped setae (hairs) on the tubercles of the top (dorsal) of the abdomen and thorax (middle part of the body). There is a black point (cauda) at the tip of the abdomen. The long legs, siphuncles and antennae are pale, translucent. The basal segments of the antennae are black. At rest the antennae are held over their back. Aphids have sucking mouthparts, called stylets, which are long, specially shaped rods contained in the rostrum (a sheath-like structure), which is held on the underside of their body.

Winged females have a dark upper surface of the thorax (the area of the body between the wings), but pale tubercles are not obvious. The forewings are much larger than the hind wings. The veins of the forewings have dark borders and their arrangement is diagnostic (see recognition).

Adult females give live birth to nymphs that look like small wingless adults. The first instar (stage) nymph is grey and 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. The older nymphs are black like the adults and have transverse white topped tubercles. 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 black fern aphid has sucking mouthparts. The 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. The stylets 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 black 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 black fern aphid excretes the excess water and sugar, which is called honeydew. The black fern aphid excretes the excess sugars from the siphuncles. Leaves may become covered with honeydew.

Nymphs and a wingless female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae); the arrows point to one of the two cornicles and the cauda. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JL]

Winged female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae). The large forewings have black veins and the smaller hind wings are pale. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JT]

Wingless female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae), giving birth to first instar (stage) nymph (arrow) and small black nymphs. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JJ]

Nymphs and moulted skins of black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15JN]

Nymphs and moulted skins of black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15JP]

Wingless female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae), showing the black basal segments of the antennae. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JQ]

Winged female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15JU]

A damaged winged female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae), showing the small hind wing and forewing. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JW]

Winged female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae), showing the curved radial vein touching the medial vein. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JS]

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 the black fern aphid is sufficiently distinctive to enable it to be recognised. The wings of winged females have black along the veins and the curved radial vein touches the medial vein (see figure). The wingless females and nymphs are also black, but they have rows of white topped setae on tubercles on the upper side of their abdomen and thorax (middle part of the body).

Winged female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae). The large forewings have black veins and the smaller hind wings are pale. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JT]

Winged female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae), showing the curved radial vein touching the medial vein. Creator: Tim Holmes. © Plant & Food Research. [Image: 15JS]

Nymphs and a wingless female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15JL]

Nymphs and a wingless female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15JR]

One possible natural enemy of the black fern aphid was found in a colony of aphids in New Zealand. The fly larva was initially thought to be a predatory Syrphidae (Diptera). The aphids are also likely to be eaten by various other predators such as ladybirds, lacewings, hoverflies, predatory midges and birds, and to be parasitised by wasp parasitoids.

Fly (Diptera) larva, a possible predator of black fern aphid, Idiopterus nephrelepidis (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15JI]

Fly (Diptera) larva, a possible predator of black fern aphid, Idiopterus nephrelepidis (Hemiptera: Aphididae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15JH]

In New Zealand, the black fern aphid has been found on ferns from five families and has been found on similar ferns in other countries. Two host associations (scored 6 out of ten) are based on an adult with a small number of nymphs. It is not certain that the aphids can grow to maturity on these two host plants.

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 honeydew. Heavy deposits of honeydew can make surfaces sticky.

Nymphs and wingless female black fern aphid Idiopterus nephrelepidis Davis, 1909 (Hemiptera: Aphididae) on a young frond of Hound's tongue fern, Microsorum pustulatum (Polypodiaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2S4X]

The black 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).

Heie OE 1993. The Aphidoidea (Hemiptera) of Fennoscandia and Denmark. V: Family Aphididae: Part 2 of Tribe Macrosiphini of Subfamily Aphidinae, Brill. 242 p.

Meijias DZ, Hidalgo NP, Mier MP 2010. First report of Idiopterus nephrelipidis (Hemiptera: Aphididae) in Central America. Florida Entomologist 93(3): 460-463.

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

David Teulon for host plant records.

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, photo on Microsorum added.

3 November 2017. NA Martin. Host plant list updated.

20 May 2016. NA Martin. New information about aphids on New Zealand ferns. Host list updated.

22 February 2014. NA Martin. Completely revised with photographs of correct the species