HortFACT
Identification
Adults are about 1.5mm long. They have four large wings; at rest the front pair are folded over the hind pair. Two forward-pointing antennae arise from the top of the head. On the underside of the head is a central, backward-pointing rostrum holding the sharp mouthparts which are used to stab plant tissues and then suck up the juices.
The yellow body and the rest of the insect, except the black eyes, is covered in a white, waxy powder. Males and females are similar in appearance. Males can often be seen sitting next to females and fluttering their wings.
Greenhouse whitefly adults are easily distinguished from another common species, the cabbage whitefly (Aleyrodes proletella [L.]),which has dark flecks on its wings and is found mainly on cruiciferous plants, i.e. those related to cabbages.
The elliptical eggs are laid on the underside of leaves. They are pale yellow for about two days, after which they turn black.
The first instar larva, or crawler, is about 0.3mm long, flat, oval and almost transparent. The legs are very small. The second, third and fourth instars, which are often called the scale stage, are also oval and almost transparent, though some yellow internal organs are visible. The body is surrounded by a short, transparent fringe which in the early instars lies against the host plant. Longer hairs are found on top of the body. Before the change from one larval instar to the next, the body swells and becomes rounded. In the fourth instar the fringe of hairs is raised up from the surface of the plant.
The larva pupates within the skin of the fourth instar, which is now termed a puparium. Shortly before it emerges, the adult can be seen in the puparium.
Sometimes black scales, or puparia are seen on plants. These are whitefly larvae that have been parasitised by a tiny wasp of the genus Encarsia.
Host plants
Greenhouse whitefly is a pest of glasshouse crops and outdoor plants. It has been recorded from a wide range of plants. It is a pest on solanaceous plants such as tomatoes, cucurbits, such as cucumbers and pumpkins; legumes, such as beans and Compositae, such as the milky thistle.
Damage
Whitefly feed on plant juices and heavy infestations may seriously weaken the host plant. The more usual form of damage is the disfiguration of leaves and fruit caused by the honeydew that is secreted by the larval whitefly. Often black sooty moulds grow on this honeydew, further disfiguring the host plant.
Distribution
Greenhouse whitefly occurs throughout the world as a major pest of glasshouse plants. It is a pest on outdoor plants in temperate and subtropical regions. In New Zealand it occurs throughout the country in glasshouses and outdoors.
Life cycle
| Egg |  |
| Larvae | |
| Puparia | |
| Adult | |
| Days |
In glasshouses the life cycle is continuous and the rate of development depends on the temperature. The chart shows the time taken for an individual from Auckland to develop at 20oC. The egg stage lasts 9 days. After hatching from its egg the first instar larva moves a short distance away from the eggshell before settling down and feeding. This stage lasts 7 days.
The second and third larval instars are sedentary and take 7 and 5 days respectively The fourth instar and pupa last 11 days after which the adult emerges from a split in the upper side of the puparium. Adults live 10-40 days. The female starts to lay eggs within a few hours of emergence. She can lay five eggs a day and about 100 in her lifetime. Whitefly m Auckland and throughout New Zealand take longer to develop than overseas races. Another difference is that eggs from unfertilised females produce female off-spring in New Zealand whereas in North America and Europe unfertilised eggs give rise to males.
N.A. MARTIN