HortFACT
Identification
One definition of the word 'scale' is 'a thin plate or flake protecting the skin (body)'. This kind of protection is found in the scale insects, which have a single plate or flake covering the body of their sedentary life stages. Such insects are further classified according to whether the body and plate are joined together (unarmoured scales) or separate (armoured scales).
The greedy scale is an armoured scale insect. Males are unknown; reproduction is by parthenogenesis, i.e., unfertilised eggs are laid.
The wax armour of the adult scale is fawn with an off-centre black, then white, circular peak. This armour covers the shiny yellow body of the scale, which is teardrop-shaped, about 1.6 mm long by 1.6 mm wide, and lies flat on the surface of the host plant. Small, sausage-shaped, yellow eggs are laid at intervals over a 3-4-week period in batches of 3 to 8; each adult produces a total of between 26 and 120. The eggs remain protected under the armour until they hatch into crawlers.
Crawlers, about 0.2 mm long and pip-shaped, are active, six-legged, first-stage nymphs, and are the only scale stage without protective wax armour. They disperse from the parent by crawling, and two silk threads produced by anal glands enable the crawler to drop - or be carried (by animals or the wind) - to other plants. On finding a favourable site the crawler inserts its piercing mouthparts into the plant tissue, spins a circular protective cover of white silk, and is then a settled crawler or whitecap. This stage moults and pushes the cast-off skin into the underside of the protective cover, shedding its now superfluous legs. The resulting second instar, or primary settled stage, has a circular armour of white wax with a central, fawn-yellow cap.
The scale insect increases in size again after a final moult. This very young mature stage is fully protected by the cast skin, which is pushed into the wax cover, giving it a brown/black appearance. Extracted plant fluids surplus to the scale's nutritional requirements are converted to wax and deposited at the anal end of the scale cover, giving the next stage an 'off centre' appearance. This middle (or intermediate) mature stage has fawn-yellow wax armour, and dwarfs the younger stages in a scale colony. Eggs for the next generation begin to form in the body. and when these are ready for laying the final, mature adult, stage has been reached.
Host plants
A wide range of host plants are infested. These are characteristically woody perennials, and
include ornamentals, native trees, shrubs, and most fruit trees. Greedy scale is a continual pest on kiwifruit and feijoas, and an infrequent pest on apples, figs, quinces, pears, and peaches. Other hosts include gorse, citrus, rose, privet, karaka, willows, oak, mistloe, rangiora, hakea, carnation Himalayan balsam, boronia, and Ceanothus.
Damage
Feeding by the scale has a gradual debilitating effect on plants, resulting eventually in the death of growing shoots. This may cause undesirable side-branching after 3-4 years or the death of small or young host plants.
In spring, when a crawler settles and feeds on a developing kiwifruit, a dimple is formed by inhibition of growth at that point. Feijoa fruits show similar depressions, which become blackened and are therefore readily visible on the green skin. Scales settling later in the season and on harder fruits such as apples do not cause such a depression; but fruit quality is impaired, and the produce cannot be exported.
Distribution
Greedy scale is cosmopolitan. In New Zealand it is present in most North Island regions, and so far has been found as far south as Canterbury.
Life cycle
| Egg |  |
| Crawler | |
| White-Cap | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
All life stages occur to some extent throughout the year. However, there are usually two major generations each year, a summer one spanning 4-5 months and an autumn-winter-spring one of 7-8 months, although in some seasons there may be a partial third generation. During winter, with its relatively cooler temperatures, the majority of scales slowly develop through the middle mature stage, and by October/November the fully mature adults are producing eggs. The hatched crawlers settle in sheltered places on stems, fruits, and leaves and spin their whitecap (October to December). Higher summer temperatures accelerate development, and crawlers are again produced over the period February-April. Differences in summer temperatures due to latitude, altitude, site aspect, etc., lead to variation in development rate. This results in considerable overlap of life stages in autumn until the colder winter temperatures partially synchronise the distribution of stages in the scale population.
The approximate duration in weeks of each life stage is as follows (winter generation figures in parentheses): crawler/white-cap 2-3 (2-3); second instar 4-5 (6-8); young mature 2-3 (3-4); middle mature 4-5 (14-15); fully mature 3-4 (2-3)
A. M. FERGUSON