INTERESTING INSECTS

By N A Martin (2017)

Myrsine mealybug

This distinctive endemic mealybug was discovered in the Hunua Ranges, Auckland in 1 January 2005. A specimen from the Waikato was collected in 1933 and later misidentified as Rastrococcus asteliae.

The mealybug lives on the underside of leaves of its endemic host plants, Myrsine australis and Myrsine divaricata (Primulaceae), in native ecosystems. It is found in both the North Island and South Island. In the South Island it only known from Bank Peninsula and in the North Island it has been found in the Auckland Region and Waikato. In Auckalnd City it is found in native forest remnants in urban areas.

Conservation status: Currently known from Auckland, Waikato and Banks Peninsula on its host plants in native ecosystems.

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]

This mealybug breeds all year. There do not appear to be discrete generations. It is not known how long it takes from egg to adult. All stages live on the underside of host plant leaves.

The adult female is oval, about 2 mm long and 1 mm wide. It is yellow-brown and covered with white flocculent wax which extends into 10 pairs of wax filaments. The wax is produced by numerous glands with pores in the skin (epidermis). The lateral filaments have a core of thin, stiff wax rods that are covered with flocculent wax. The insect has three pairs of legs and two antennae. There is no distinct division between the head or thorax (middle section of the body) and abdomen. On the underside of the body there is a short rostrum that guides the feeding stylets.

Adult females give birth to live nymphs. The nymphs are like small adults in appearance. There are three female nymphal instars (stages) and two male nymphal instars. These feeding stages grow by moulting (changing skin). 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 adult male does not have a rostrum or stylets and does not feed. It has one pair of simple wings. 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, it 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. 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 excrete the excess sugary liquid, which is called honeydew, through a short white wax anal tube.

Walking, flying and dispersal

The adult male has legs and wings. It can walk around its colony and it can fly to other colonies on the same or different plants. Adult females and nymphs also have legs and can walk. They may move about the leaf where they were born, or they can move to a new leaf on the same branch. In other insects with a none flying adult female, the first stage larvae or nymphs are able to disperse to new host plants. They usually do this the using wind. It is likely that some first instar nymphs climb to a prominent place on a leaf or branch and await a gust of wind.

Drawing of the underside of female Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). The small drawings are of pores, some of which secrete wax. Creator: DJ Williams. © modified from drawing by DJ Williams published in Zootaxa. 1085: 47-60, Fig 1. [Image: 2FAW]

Drawing of the upper side of female Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). The small drawings are of spines and pores. The dense clusters of pores secrete the wax fringes. Creator: DJ Williams. © modified from drawing by DJ Williams published in Zootaxa. 1085: 47-60, Fig 1. [Image: 2FAX]

Colony of Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae) on underside of Myrsine australis (Primulaceae) leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FA2]

Recently moulted nymphs of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae), note the lack of wax on the lowest nymph. Creator: Martin Heffer. © Plant & Food Research. [Image: 2FA9]

Nymph of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae), moulting, note the old skin at its rear end. Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAQ]

Wings of adult males of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae), extending from their cocoons, note the absence of the wax tails that still have to grow. Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAN]

Wings of adult male Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae), extending from its cocoon. Creator: Martin Heffer. © Plant & Food Research. [Image: 2FAA]

Winged adult male Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae), note the two white wax tails. Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAC]

Yellow areas on upper side of Myrsine australis (Primulaceae) leaf on which Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae) are feeding on the underside. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FAV]

Adult female Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae) on underside of Myrsine australis (Primulaceae) leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2KTA]

The Myrsine mealybug, Rastrococcus namartini, lives on the underside of leaves of its endemic host plans Myrsine australis and Myrsine divaricata (Primulaceae). It may also be present on other Myrsine species. The Myrsine mealybug can be distinguished from any other mealybugs living on leaves or stems by its long lateral fringes. Where the mealybug is feeding on the underside of a leaf, the upperside has a yellow (chlorotic) area which aids detection of the insect. However, it is not the only insect causing chlorotic areas on leaves of these plants.

Adult female Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Rosa C. Henderson. © Landcare Research. [Image: 2FAY]

Colony of Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae) on underside of Myrsine australis (Primulaceae) leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FA2]

No pathogens of the Myrsine mealybug, Rastrococcus namartini, are known.

Parasitoids. A tiny wasp (Hymenoptera) is a parasitoid of the Myrsine mealybug. The female wasp lays an egg in a mealybug. When the wasp larva is fully grown it kills mealybug nymphs at the second instar (stage). The body swells and becomes dark coloured forming a ‘mummy’. When the adult parasitoid has emerged from its pupa it chews a hole in the skin of the mummy through which it leaves the mummy.

Predators. Syrphid (hoverfly) eggs are sometimes found laid in a Myrsine mealybug colony. Larva eat the mealybugs, but none has fully grown and formed a pupa and no pupae have been found on host plants. The mealybugs are also likely to be preyed upon by ladybirds, lacewings and gall fly larvae.

Nymph of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae) parasitised by a tiny wasp (Hymenoptera). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAE]

Nymph of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae) parasitised by a tiny wasp (Hymenoptera). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAF]

Two parasitised nymphs of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae) with exit holes made by adult wasp (Hymenoptera). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAD]

Adult wasp (Hymenoptera) of parasitoid of nymphs of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAK]

Upper side of adult wasp (Hymenoptera) of parasitoid of nymphs of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAS]

Underside of adult wasp (Hymenoptera) of parasitoid of nymphs of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FAT]

Syrphid (Diptera) egg in a colony of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2F9W]

Syrphid (Diptera) egg in a colony of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2F9X]

Syrphid (Diptera) egg in a colony of Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2F9Y]

Syrphid (Diptera) larva (arrow) feeding on a Myrsine mealybug Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2F9Z]

Syrphid (Diptera) larva that has been feeding on Myrsine mealybugs Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2FA0]

The Myrsine mealybug, Rastrococcus namartini, lives on the underside of leaves of its endemic host plants Myrsine australis and Myrsine divaricata (Primulaceae). It may also be present on other Myrsine species.

Mealybug adult females and nymphs feed by inserting their stylets into the phloem, the nutrient transport vessels of the plant. The mealybugs suck the plant sap. Plant sap is high in sugars and low in other nutrients. Mealybugs excrete the excess sugary liquid, which is called honey-dew, through a short white wax anal tube. Where the mealybug is feeding on the underside of a leaf, the upperside has a yellow (chlorotic) area. However, it is not the only insect causing chlorotic areas on leaves of these plants.

Upper side of leaves of Myrsine divaricata (Primulaceae) with yellow (chlorotic) spots caused by feeding of Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FA5]

Underside of leaves of Myrsine divaricata (Primulaceae) with colony of Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FA6]

Underside of leaves of Myrsine australis (Primulaceae) with colony of Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae), note the yellow colour of the leaf where the colony is living. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FA1]

Yellow areas on upper side of Myrsine australis (Primulaceae) leaf on which Myrsine mealybug, Rastrococcus namartini (Hemiptera: Pseudococcidae) are feeding on the underside. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2FAV]

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. However, recent observations indicate that the wax may impede movement of some ladybird larvae.

Williams DJ, Henderson RC. 2005. A new species of the mealybug genus Rastrococcus Ferris (Hemiptera: Sternorrhyncha: Pseudococcidae) from New Zealand. Zootaxa. 1085: 47-60.

DJ Williams for permission to use the drawing of the adult female.

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

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

1 August 2017, NA Martin. New Photos of adult female added.