INTERESTING INSECTS

By N A Martin (2018)

Melicytus whitefly

This endemic whitefly has only been found in Canterbury in the South Island of New Zealand. It lives on large and small leaved species of Mahoe, Melicytus species (Violaceae).

Conservation status: Endemic species, not endangered, found in the South Island mainly in native ecosystems.

Diagramme of the life cycle of the greenhouse whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae). (based on figure 20 from Crop & Food Research Broadsheet 91. Creator: Based on figure 20 from Crop & Food Research Broadsheet 91. © Plant & Food Research. [Image: 3BG]

There have been no studies of the annual cycle of the Melicytus whitefly. There are probably overlapping generations. Adults have been seen from late spring to early summer. Melicytus whitefly has the same life stages and life cycle as the greenhouse whitefly, Trialeurodes vaporariorum.

The adult whitefly is covered with white wax. When the adults emerge, the pale cream body colour can be seen and the wings are transparent, but soon the body, wings and legs become covered with white wax. There are males and females in this species. Males of other whitefly may be seen sitting alongside females before mating. Like most adult insects, they have three pairs of legs and two pairs of wings. The head has a pair of black compound eyes and pale antennae. Like other Hemiptera, the underside of the head has a rostrum that holds the long stylets used for feeding. Feeding is mainly on the underside of leaves. When feeding the adult appears to rotate around the place where the stylets are inserted. This create a circular patch of white wax on the underside of the leaf.

Adult females lay eggs on the underside of the leaf, often in circles around where they are feeding. The pale, oval eggs are laid on their sides but may have a peg at one end that is inserted into the leaf. The hatched egg shells are brown. The first larva hatches from the egg. It has three pairs of legs and is usually called a crawler. It walks away from the egg and settles at a suitable feeding site, usually above or close to a leaf vein with phloem ducts (tubes that transmit nutrients from the leaf to other parts of the plant). The crawler is oval and flat. There are four larval instars (stages). The larvae grow by moulting, (i.e. changing skin). The old skin splits on the upper dorsal side and is pushed off the rear end of the new larva which stays and feeds in the same place.

The bodies of larvae are pale brown. The fourth instar larva is surrounded by a short fringe of white wax rods and develops areas of white wax on its upper side. When it is reaches full size, it pupates inside the larval skin, which is now called a puparium. The Puparium is about 0.93 mm long and 0.71 mm wide. When the adult is almost ready to emerge, a T-shaped split occurs in the skin of the puparium and the adult pulls itself out. Its wings expand and harden, and the body and wings become covered in white wax.

Feeding and honeydew

Whitefly adults and larvae have sucking mouthparts. Long specially shaped rods called stylets are held in the sheath-like rostrum. When it wishes to feed, the whitefly 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 (or nutrient transport vessels) of the plant. The whiteflies suck the plant’s sap, which is high in sugars and low in other nutrients. Whiteflies excrete the excess sugary liquid, which is called honey-dew. In the larvae, the excess liquid is excreted into a structure called the vasiform orifice where it accumulates. When a droplet has formed, a tongue-like structure called the lingula flicks the droplet away from the larva. It can be flicked up to 2 cm away.

Honeydew makes the plant leaves sticky. Sometimes black sooty mould fungi grow on the sticky surfaces.

Adult and eggs of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Cook Strait mahoe, Melicytus obovatus (Violaceae): note the white wax on the leaf around the feeding site of the adult. © MPI. [Image: 2R6D]

Adults and eggs of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Cook Strait mahoe, Melicytus obovatus (Violaceae). © MPI. [Image: 2R6C]

Puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Swamp mahoe, Melicytus micranthus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6P]

Puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Swamp mahoe, Melicytus micranthus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6N]

Microscope slide of puparium of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) from a leaf of Swamp mahoe, Melicytus micranthus (Violaceae): note that the pink colour is from a stin used when making the slide. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2RKJ]

Larvae and puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Cook Strait mahoe, Melicytus obovatus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6E]

Larvae and puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Cook Strait mahoe, Melicytus obovatus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6F]

A dried puparium of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on a dried leaf of Swamp mahoe, Melicytus micranthus (Violaceae). Creator: Nicholas A. Martin. © Landcare Research. [Image: 2RKK]

Dried larvae and puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a dried leaf of Cook Strait mahoe, Melicytus obovatus (Violaceae). Creator: Nicholas A. Martin. © Landcare Research. [Image: 2RKL]

In New Zealand, Melicytus whitefly is one of two species of whitefly found on shrubs and trees of Melicytus species (Violaceae). The other species is Mahoe whitefly, Asterochiton aureus, Maskell, 1879, that has been found on two large leaved Melicytus species throughout New Zealand. While specialist knowledge is required to distinguish the adults, the larvae and puparia of each species are easy to recognise.

The larvae Melicytus whitefly are pale or tan coloured, and while the puparia are tan coloured and they are often partly coated with white wax. They also have a short fringe of wax rods.

The larvae of Mahoe whitefly are transparent and the puparia have a dark pigment running the length of the body. There is no white wax coating or any wax rods.

Adults and eggs of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Cook Strait mahoe, Melicytus obovatus (Violaceae). © MPI. [Image: 2R6C]

Puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Cook Strait mahoe, Melicytus obovatus (Violaceae). © MPI. [Image: 2R6S]

Puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Swamp mahoe, Melicytus micranthus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6N]

Puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae) on the underside of a leaf of Swamp mahoe, Melicytus micranthus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6P]

Underside of leaves of Swamp mahoe, Melicytus micranthus (Violaceae) nymphs of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae): note the white wax made by the larvae and puparia. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6M]

Colony of Mahoe whitefly, Asterochiton aureus (Hemiptera: Aleyrodidae) on a leaf of Māhoe, Melicytus ramiflorus (Violaceae): note the many dark puparia and two recently emerged white adults. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R41]

Puparia and a recently emerged adult Mahoe whitefly, Asterochiton aureus (Hemiptera: Aleyrodidae) on a leaf of Māhoe, Melicytus ramiflorus (Violaceae): note the puparium below the adult from which it emerged. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R3Z]

Eggs and first instar (stage) larvae of Mahoe whitefly, Asterochiton aureus (Hemiptera: Aleyrodidae) on the underside of a leaf of Māhoe, Melicytus ramiflorus (Violaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2R4E]

Egg shells and second, third and fourth instar (stage) larvae of Mahoe whitefly, Asterochiton aureus (Hemiptera: Aleyrodidae) on the underside of a leaf of Māhoe, Melicytus ramiflorus (Violaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2R45]

Puparium of Mahoe whitefly, Asterochiton aureus (Hemiptera: Aleyrodidae) on a leaf of Māhoe, Melicytus ramiflorus (Violaceae). Creator: Nicholas A. Martin. © Landcare Research. [Image: 2R4I]

Dark puparia of Mahoe whitefly, Asterochiton aureus (Hemiptera: Aleyrodidae) and white Serene scale, Serenaspis minima (Hemiptera: Diaspididae) on a leaf of Large-leaved mahoe, Melicytus macrophyllus (Violaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R3W]

One collection of Melicytus whitefly from a Christchurch native forest reserve included specimens infested with fungi.

No parasitoids and predators of the Melicytus whitefly have been recorded. However, it is likely that parasitic wasps that attack other whitefly are also likely to be found parasitizing Melicytus whitefly. It is also likely that spiders and other generalist insect predators feed on whiteflies.

Melicytus whitefly have been found on shrubs and trees of large and small leaved Melicytus species in the South Island, particularly in Canterbury and on Banks Peninsula. Some heavily infested leaves may be smaller than normal leaves.

Feeding and honeydew

Whitefly adults and larvae have sucking mouthparts. Long specially shaped rods called stylets are held in the sheath-like rostrum. When it wishes to feed, the whitefly 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 (or nutrient transport vessels) of the plant. The whiteflies suck the plant’s sap, which is high in sugars and low in other nutrients. Whiteflies excrete the excess sugary liquid, which is called honeydew. Honeydew makes the plant leaves sticky. Sometimes black sooty mould fungi grow on the sticky surfaces.

Underside of leaves of Cook Strait mahoe, Melicytus obovatus (Violaceae) with larvae and puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6G]

Underside of leaves of Cook Strait mahoe, Melicytus obovatus (Violaceae) with larvae and puparia of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6H]

Sooty mould on leaves of Cook Strait mahoe, Melicytus obovatus (Violaceae) growing on honeydew excreted by by Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6I]

Sooty mould on leaves of Swamp mahoe, Melicytus micranthus (Violaceae) growing on honeydew excreted by Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6L]

Underside of leaves of Swamp mahoe, Melicytus micranthus (Violaceae) nymphs of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae): note the white wax made by the larvae and puparia. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R6M]

Underside of leaves of Narrow-leaved mahoe, Melicytus lanceolatus (Violaceae) nymphs of Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae): note the white wax on the leaf. © MPI. [Image: 2R6R]

Sooty mould on leaves of Melicytus sp. (Violaceae) growing on honeydew excreted by Melicytus whitefly, Bemisia flocculosa (Hemiptera: Aleyrodidae). © MPI. [Image: 2R6T]

Dumbleton LJ. 1957. The New Zealand Aleyrodidae (Hemiptera: Homoptera). Pacific Science. 11: 141-160.

Gill R, Holder P. 2011. A new species of Bemisia (Hemiptera, Aleyrodidae) from New Zealand. Zootaxa. 2794: 63-68.

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.

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

Ministry for Primary Industries (MPI) for photographs.