A typical sign of an infestation of scale insects is punctures in the leaves, followed by the secretion of a toxic saliva that causes yellow, red or brown discolouration at the puncture site. Over time, the insects secrete honeydew, which is usually colonised by sooty moulds. If the infestation is not treated, the plant will eventually die.

Scales (Coccoidea)

There are over 2,600 known species of scale insects, making them the largest and most specialised family of scale insects. Many of them are economically significant pests. There are 213 species native to Europe.
Scale of this genus have three larval stages:
They are only mobile in the first stage, when they search for a suitable place above ground on the plant to suck plant sap. Unlike other scale insects, Cape scale insects do not produce honeydew, which means that they do not cause sooty mould infestation. In the first stage, aphids often climb up plants and then let the wind carry them to new food plants. Successful resettlement is mainly dependent on medium to high humidity, while dry conditions or heavy rain usually kill the insects.
From the second larval stage onwards, female scale insects are sedentary and no longer have legs. The second stage is the most important feeding stage.
Reproduction takes place in the third stage. The hermaphroditic mating occurs soon after the last moult. While the females continue to feed in the third stage, the males can no longer take in food due to their atrophied mouthparts.

Scales (Diaspididae)

There are over 1,100 known species of scale insects, around 150 of which are native to Europe.
The females go through only two larval stages, while the males go through four. From the second stage onwards, the males develop under a boat-shaped shield that is more or less transparent. Depending on the species, reproduction can be parthenogenetic and/or involve the males.
The dispersal stage of the animals is the nymph stage. They cannot fly, but they also use the wind as a means of transport. Once they have found a suitable place on a plant, they settle down and remain there. They suck plant sap and excrete honeydew. In nature, honeydew is usually collected by ants, but in cultivation it forms the basis for sooty moulds.

There are two types of scale insects, which differ in terms of reproduction and lifestyle. The damage they cause and how to combat them are identical.

Diaspididae

Scale insects of the genus Diaspididae are usually hermaphroditic, with both male and female sexes. However, parthenogenesis is also not uncommon. The males are significantly smaller and more delicate. Depending on the species, they can be winged, wingless or have a larva-like appearance. The genitals are relatively long, located on the outside and easily recognisable; they must reach from the female's genital opening to below the shield.
The females attract the males by secreting sexual pheromones. Depending on the species, females can lay 50-400 eggs in their lifetime. The newly hatched young, which are barely recognisable, migrate for 2-3 days and look for a new place to settle. The females then lose their legs and attach themselves firmly.

Coccoidea

Scale insects lf the genus Coccoidea usually reproduce sexually, with winged males fertilising females, who then lay eggs under their shields or in waxy sacs. The larvae are mobile for 2-3 days, search for a place to feed and develop into immobile females, which excrete their shields as excrement through an additional intestinal opening. However, many species can also reproduce asexually (parthenogenetically), which enables rapid spread without males, especially in weakened plants and dry, warm air.

• Egg laying: Females lay hundreds to thousands of eggs, either under their shield or in special waxy sacs.
• Hatching: Tiny, six-legged larvae (crawlers) hatch from the eggs and actively search for a suitable place, usually on young shoots.
• Settlement: After finding a place to feed, they insert their proboscis and become sedentary (nymph), causing their shield to grow.
• Development: Females remain immobile, while males (if present) develop, often becoming winged, but only live briefly to mate.
• Hibernation: They can hibernate outdoors as larvae or eggs. This depends on the species and the temperature.

Chemical plant protection must be carried out consistently and repeatedly. In the event of infestation, at least 2-3 treatments at intervals of 2 weeks are necessary. It is advisable to spray wet plants in the evening so that the spray remains on the plant for a long time and can penetrate under the shields. When using chemical plant protection measures, it is important to constantly change the groups of active ingredients. Mineral oil is quite reliable, but frequent use can cause problems with the compatibility of different orchids.
Searching for the insects, which is often recommended on the internet, has proven to be counterproductive. In the case of sexual reproduction, the eggs are distributed on the plant or fall onto the substrate. Even in parthenogenesis, the young animals, which are barely visible to the human eye, are distributed over the plant.

Scale insects can be controlled biologically, but there are significant differences between cup scale insects and flat scale insects.
Flat scale insects are accepted by both ladybirds and the parasitic wasp Aphytis melinus.
In the case of cup scale insects, the species must be identified. Coccus hesperidum can be controlled quite successfully with the parasitic wasps Microterys flavus, Metaphycus helvolus and Encyrtus lecaniorum.
Saissetia species of cup scale insects must be controlled with the following parasitic wasps: Metaphycus and Encyrtus, as well as Coccophagus lycimnia.

These treatment methods from 1848 are provided for informational and entertainment purposes only. Please note that the use of some of the chemicals mentioned here is no longer permitted today, as they can be harmful to health (including that of the user) and very harmful to the environment. Reading, reflecting and smiling are permitted, but do not attempt to replicate these methods.