Trialeurodes species 1
Hounds tongue fern whitefly
Trialeurodes sp. 'pustulatum' of NA Martin 2010
The Hounds tongue fern whitefly is in the genus Trialeurodes and is awaiting formal description and naming. It one of several species of Trialeurodes found on New Zealand ferns that are waiting to be described and named.
Biostatus and distribution
This undescribed endemic whitefly has been found in Auckland, Taupo and Dunedin on its native fern host plant, Hounds tongue fern, Microsorum pustulatum (G. Forst.) Copel. (Polypodiaceae). It is rare In Auckland, but common in Dunedin city.
Conservation status: Probably widespread; uncommon in Auckland, but probably commoner south of the city in the North Island and in the South Island.
Life stages and annual cycle
There is one generation per year. Adults are seen from spring to early summer. Larvae are present from summer to autumn and puparia are present from winter to spring.
Hounds tongue fern whitefly has the same life stages as the greenhouse whitefly, Trialeurodes vaporariorum. The adult whitefly is covered with white wax some of which may come off onto plants on which it is feeding. The adults are about 1.5 mm long with a wing span of about 3 mm. When the adults emerge from the puparium the white body colour can be seen and wings are transparent, but soon the body and wings are covered with white wax. Adult males may be seen sitting alongside females prior to mating. Adults have two pairs of wings and three pairs of legs. A rostrum holding the feeding rods, stylets, is on the underside of the head.
Eggs and Larvae
Adult females lay eggs on the underside of fronds, both on new season and last season fronds. Eggs are mostly laid in dense rings around a feeding site. The elongate, oval eggs are laid on their side with a peg at one end that is inserted into the leaf. They are tiny, a pale tan colour and shiny. They can become covered with white wax from the adult’s wings. The first larva to hatch from the egg and is usually called a crawler. It has 3 pairs of legs and walks away from the egg and settles in 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 stages. The larvae grow by moulting, changing skin. The old skin splits on the upper, dorsal, side and the next larval stage pulls itself out and settles nearby to feed. Larvae after the first stage (instar) are pigmented with a short wax fringe. Most older larvae have dark pigment in the central part of the body that may extend to the rest of the body.
When the fourth stage, instar, larva reaches full size it has vertical sides similar to that of greenhouse whitefly (see life cycle drawing). The mature whitefly larva forms a pupa inside the larval skin, which is now called a puparium. When the adult is almost ready to emerge, red eyespots can be seen through the walls of the puparium. A T-shaped split occurs in the skin of the puparium and the adult pulls itself out. Its body and wings harden, and become covered in white wax.
Feeding and honeydew
Whitefly adults and larvae have piercing and sucking mouth parts. The long stylets, special shaped rods, are held in the 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, nutrient transport vessels of the plant. They suck the plant sap. Plant sap is high in sugars and low in other nutrients. Whitefly excrete the excess sugary liquid that is called honeydew. In the larvae the excess liquid is excreted into the vasiform orifice where it forms a droplet. 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 centimetres away.
Honeydew makes plant leaves sticky. Sometimes black ‘sooty mould’ fungi grow on the sticky surfaces.
Identification of adult and juvenile whiteflies requires specialist knowledge. However, some species of whitefly on ferns in New Zealand appear to be found only on one host plant. Two species of whitefly live on the Hounds tongue fern, Microsorum pustulatum (Polypodiaceae): Trialeurodes species 1 and Trialeurodes asplenii (Maskell 1890). They can be distinguish by sharp eyes and with a 10xs hand lense.
Trialeurodes species 1
Adults: White, but little white loose wax. Present in spring and early summer
Eggs: Most eggs laid in rings
Larvae: Dark pigment present
Puparium: dark pigment, no long wax filaments
Adults: White and mealy, with lots of loose wax. Present most of the year
Eggs: Scattered, some in rings
Puparium: white, with long wax filaments
Whitefly associated with a mass of white wax on the underside of fronds may be seen on other species of ferns. These are currently regarded as distinct species, because of differences in adult behaviour and the appearance of live juveniles. Most New Zealand fern whiteflies do not have scientific names and need to be formally described.
Parasitized puparia were seen in Dunedin. A possible predatory fly larva was also seen in a whitefly colony in the city. No pathogens have been recorded from Hounds tongue fern whitefly in New Zealand.
The Hounds tongue fern whitefly, Trialeurodes species 1 only breeds on the native fern host plant, Microsorum pustulatum (G. Forst.) Copel. (Polypodiaceae).
Adult and juvenile whitefly feed by inserting their stylets into the phloem, nutrient transport vessels of the plant. They suck the plant sap. Feeding by very large numbers of whitefly could weaken a young frond. Plant sap is high in sugars and low in other nutrients. Whiteflies excrete the excess sugary liquid which is called honeydew. This makes the plant leaves sticky. Sometimes black ’sooty mould’ fungi grow on the sticky surfaces.
Whitefly on New Zealand Ferns
At present only one species of whitefly living on ferns in New Zealand has been properly described and given a scientific name. This is Trialeurodes asplenii (Maskell 1890), which is found on shining spleenwort Asplenium oblongifolium Colenso (Aspleniaceae), its primary host and Hounds tongue fern, of Microsorum pustulatum (G. Forst.) Copel. (Polypodiaceae), a less favoured host plant. Whiteflies have been found on more than eight other species of fern. Those that have been examined carefully all show distinct differences in appearance and biology from Trialeurodes asplenii indicating that there are several previously unknown species of fern whitefly in New Zealand. Important differences between these species include the presence of absence of pigmentation on the fourth instar (stage) larva and puparium, and the arrangement and appearance of wax filaments around the edge of the fourth instar (stage) larva and puparium and the presence or absence of wax filaments on the dorsal surface of the puparium. Most of these fern whitefly each appear to be found only on one species of fern. All the whitefly on New Zealand fern species appear to be in the genus Trialeurodes. At present these whitefly species have been given provisional, tag, names until they are formally described.
Why is there so much white wax?
The shining spleenwort whitefly, Trialeurodes asplenii (Maskell 1890), and other species of fern whitefly produces much white flocculent wax with which the colony of juveniles becomes coated. To the human eye this makes it much easier to find the colonies of juvenile whitefly. However, does it make it easier for predators and parasitoids to find, 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.
Martin NA 1999. Whitefly: Biology, identification and life cycle. Crop & Food Research, Broadsheet No. 91: 1-8.
Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.