Identification and Control of Scale Insect Pests and Diseases in Chinese Orchids

The body surface of scale insects hardens and is covered with a layer of hard shell, or has powdery waxy secretions. The insect body attaches to the plant surface, and the mouthparts pierce into the plant to absorb sap. Whether they are oviparous or viviparous depends on the species of scale insect. Some species can only be viviparous, so the population consists entirely of females. Some species are oviparous and require a mating process, with both males and females present. Regardless of whether they are oviparous or viviparous, females have no wings after growing up, and their appearance is similar to that of nymphs, only larger in size. Females lay eggs directly beneath their bodies, relying on their own bodies to protect the eggs. They can lay dozens to hundreds of eggs at a time. Males become winged adults after going through the pupal stage, and fly to mate with females. Scale insects can occur on the leaves, leaf sheaths, stems, or even roots of plants. Some scale insects prefer concealed locations, multiplying in large numbers under leaf sheaths or in leaf folds, and only when their numbers become too great do they spread to the leaf surface or stems, such as the citrus mealybug (Planococcus citri). Some do not have a concealed habit, such as the brown soft scale (Chrysomphalus ficus), the hemispherical scale (Saissetia coffeae), etc., which are scattered on the underside or upper surface of leaves. The damage caused by scale insects results from their feeding on plant sap. At the feeding sites, plants show yellow-white or yellow-brown spots or halos. Feeding by individual scale insects on leaves may cause small speckled marks, while large numbers of scale insects clustered together, due to their large feeding volume, cause entire sections of leaves or stems to appear dark brown and show shrinkage. The wounds created by scale insects piercing and sucking plant tissues with their mouthparts can also lead to infection by pathogens, making the affected plants more susceptible to disease. Chen Mingzhao