INTERESTING INSECTS

By N A Martin (2019)

Silver fern mealybug

This unnamed mealybug was examined by Rosa Henderson, Landcare Research, who concluded that it a previously unknown species of Crisiococcus that was similar in appearance to a named species, Crisiococcus tokaanuensis Cox, 1987. She gave me this name Crisiococcus sp. nr. tokaanuensis to use. For this factsheet, I am using the following name, Crisiococcus sp. (Cyathea).

This endemic mealybug is the only one found on New Zealand tree ferns. The Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) has not yet been described and named. It has been found on two species of tree fern, Cyathea species (Cyatheaceae) in the Auckland Region, but is probably in most parts of the country where these ferns grow.

Conservation status: Unknown; this native mealybug is in native ecosystems in Auckland and is probably widespread.

Diagramme of the life cycle of a typical mealybug (Hemiptera: Pseudococcidae). Creator: JM Cox. © Drawing published in Fauna of New Zealand 11:1-228, Fig. 1. [Image: 2F19]

The Silver fern mealybug appears to breed mainly in spring and early summer when young fern fronds are present, though females with protective white wax egg sacs may be seen throughout the year. It is not known how long it takes from egg to adult. All life stages are found on the underside of fern fronds.

The adult female is oval, about 2-3 mm long and about 1.0-1.5 mm wide. The body is pale orange with a covering of powdery white wax. The mature female has a short pair segmented antennae and three pairs of legs. There is no distinct division between the head or thorax (middle section of the body) and abdomen. On the underside of the head there is a short rostrum that guides the feeding stylets. The mature female forms a dense white wax egg sac. On young fronds the egg sac is a longer and made of fluffy white wax with orange-yellow eggs often exposed.

The nymphs look like small adult females. There are three female nymphal instars (stages) and two male nymphal instars. These feeding stages grow by moulting (changing skin). The actively feeding nymphs appear to surround themselves with white wax. The second instar male makes a fluffy white cocoon in which develop two pre-adult non-feeding stages, a prepupa and a pupa. The prepupa and pupa have wing buds. The adult male emerges from the pupa. The moulted prepupal and pupal skins are pushed out the end of the cocoon. The adult male does not have a rostrum or stylets and does not feed. When it is ready to emerge from the cocoon, the back end of the cocoon is pushed open and the male backs out. After it has opened the back of the cocoon, its wings (1 pair) expand and harden. It also grows a pair of long wax tails. It is presumed that the wax tails help balance the insect in flight. The male may mate with females of the same colony or fly to another colony to mate.

Feeding and honeydew

Mealybug adult females and nymphs have sucking mouthparts. Specially shaped rods called stylets are held in the short sheath-like rostrum. When it wishes to feed, the mealybug moves the tip of the rostrum onto the surface of the plant leaf or stem. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (nutrient transport vessels) of the plant. The mealybugs suck the plant’s sap, which is high in sugars and low in other nutrients. Mealybugs have a short white wax anal tube through which they excrete the excess sugary liquid, which is called honeydew.

Walking, flying and dispersal,br/>The adult male has legs and wings. It can walk around the leaves where its cocoon was and it can fly to other fronds or to different tree ferns. Adult females and nymphs also have legs and can walk. They may move about the frond on which they were born and onto other fronds of the fern. In other insects with a none flying adult female, the first stage larvae or nymphs are able to disperse to new trees. They usually do this using the wind. It is likely that some first instar nymphs climb to a prominent place on a frond and await a gust of wind.

An adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the white wax fluffy wax from an old extensive egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P1]

An adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30PH]

Two adult female Silver fern mealybugs, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the white egg sacs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NL]

Egg sac with an adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Smith's tree fern, Cyathea smithii (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NK]

An adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the white egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NN]

An extensive fluffy white wax egg sac and the adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P3]

A fluffy white wax egg sac of Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the exposed eggs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NS]

First instar (stage) nymphs of Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) around their egg sac on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P2]

First instar (stage) nymphs of Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). This is the stage that spreads to other parts of the plant and to new plants. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NR]

Young adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NT]

Second instar (stage) nymph of Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). This may be a male before it makes its cocoon. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P6]

Cocoon made by a male Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P5]

A cocoon opened to expose the pupa of a male Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30PE]

Side view of an adult male Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the two long white wax tails. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30PB]

An adult male Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the two long white wax tails. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30PC]

An adult male Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the two long white wax tails. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30PD]

Mealybugs (Pseudococcidae) require specialist skills for their identification. However, when some species are on their host plants, they have distinct features that enables them to be named with confidence. The Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) is the only species of mealybug that has been found on two species of tree fern, Cyathea species (Cyatheaceae). The mealybugs are found on the underside of young and older fronds. The bright white wax egg sacs can make them easy to recognize.

Two adult female Silver fern mealybugs, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the white egg sacs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NL]

An adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the white egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NM]

An adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the white egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NN]

First instar (stage) nymphs and an adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the fluffy white egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NQ]

No pathogens of the Silver fern mealybug are known.

Parasitoids

One unnamed wasp (Hymenoptera) parasitoid has been reared from a colony of Silver fern mealybug. The wasp larva lives in the mealybug. When the wasp larva is fully grown it kills the mealybug. And the wasp forms a hard skin in the mealybug in which it pupates. When the adult is fully developed, it emerges from it pupa and pushes open one end of the mealybug shell and leaves.

Predators

Larvae of a gall fly, (Diptera: Cecidomyiidae), was found associated with a colony of the mealybug. The larvae of gall flies have been found feeding on mealybugs.

Other potential predators include hoverflies (Diptera: Syrphidae) and ladybirds (Coleoptera: Coccinellidae).

The underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae) with an adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) that has been parasitised by a wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NW]

The underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae) with two adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) that have been parasitised by a wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NX]

The underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae) with two adult female Silver fern mealybugs, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) one of which (darker) has been parasitised by a wasp (Hymenoptera). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NY]

The empty shell of adult female Silver fern mealybugs, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) that has been parasitised by a wasp (Hymenoptera): note the open end through which the adult wasp emerged. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NU]

The empty shell of adult female Silver fern mealybugs, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) that has been parasitised by a wasp (Hymenoptera): note the open end through which the adult wasp emerged. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NV]

Two images of the underside of an adult wasp (Hymenoptera) that had parasitised a female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P7]

A side view of an adult wasp (Hymenoptera) that had parasitised a female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P8]

Two images of an adult wasp (Hymenoptera) that had parasitised a female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P9]

A top view of an adult wasp (Hymenoptera) that had parasitised a female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30PA]

A larva (arrow) of a predatory fly (Diptera) Cecidomyiidae) feeding on a Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NZ]

A larva of a predatory fly (Diptera) Cecidomyiidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P0]

Silver fern mealybug has only been found on two species of tree ferns, in the genus Cyathea (Cyatheaceae). The mealybug lives of the underside of young fronds expanding and mature fronds. A mature frond may only have a female with an egg sac, while a young green frond may have several dense colonies.

Feeding and honeydew

Mealybug adult females and nymphs have sucking mouthparts. Specially shaped rods called stylets are held in the short sheath-like rostrum. When it wishes to feed, the mealybug moves the tip of the rostrum onto the surface of the plant leaf or stem. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (nutrient transport vessels) of the plant. The mealybugs suck the plant’s sap, which is high in sugars and low in other nutrients. Mealybugs have a short white wax anal tube through which they excrete the excess sugary liquid, which is called honeydew.

Egg sac with an adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30PF]

Adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30PG]

An adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae): note the white wax fluffy wax from an extensive egg sac Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NI]

Young nymphs of Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) and fluffy wax egg sac on the underside of a frond of Silver fern, Cyathea dealbata (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30P4]

Egg sac with an adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Smith's tree fern, Cyathea smithii (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NJ]

Egg sac with an adult female Silver fern mealybug, Crisiococcus sp. (Cyathea) (Hemiptera: Pseudococcidae) on the underside of a frond of Smith's tree fern, Cyathea smithii (Cyatheaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30NK]

Why is there so much white wax?

Most mealybugs produce much white flocculent wax with which they are covered and which also covers the areas of plants they inhabit. To the human eye this makes it much easier to find the colonies of mealybugs. However, does it make it easier for predators and parasitoids to find them, or is the white wax some kind of deterrent and warning colouration? Other insects with a scale stage also cover themselves with white wax. This suggests to me that it may be some kind of deterrent and warning.

Cox JM. 1987. Pseudococcidae (Insecta: Hemiptera). Fauna of New Zealand. 11: 1-230.

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

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