Aphids

• Aphids feed on young growth segments of the orchid, such as the flower spikes that grow from buds before flowers bloom. Aphids are small insects with soft bodies that tend to cluster in groups, according to the Orchid Plant Care website. Aphids can mottle orchid flowers and stunt the growth of stems.
  
  

Mealybugs

• Mealybugs are the most common orchid pest, according to Paul J. Johnson, a botanist at South Dakota State University. Nearly 300 species of mealybugs exist in North America and Canada, though only a few affect orchids. Mealybugs feed on roots, flowers, leaves and stems and can cause serious damage to the plant, even death.
  
  

Scales

• Scales come in hard and soft varieties. Soft scales produce honeydew, while hard scales do not. Both hard and soft scales are round, though hard scales have dome-shaped shells. Scales feed on the underside of leaves. Scales will feed on every known variety of orchid, according to botanists at the University of Hawaii.
  
  

Twospotted Spider Mites

• The twospotted spider mite feeds on the chlorophyll in orchid leaves. These are true arachnids with eight legs and are greenish-yellow in appearance with a dark spot on either side of their bodies (hence the name). Twospotted spider mites leave pin-prick holes in the leaves as they feed. Sometimes the leaves will turn yellow because of lack of chlorophyll, and sometimes they will fall off completely, according to Orchid Plant Care.
  
  

Management

• There are several strategies for avoiding insect infestations, and for treating them once they occur. Orchid Plant Care recommends carefully controlling temperature, water, light, humidity and fertility to keep orchids strong. They also recommend keeping stems, leaves and flowers clean by removing all dead plant debris, favorite hiding places for mealybugs and aphids. A hard spray of water can be used when pests are discovered to dislodge them from the orchid. Use pesticides in extreme cases, but orchids are very sensitive to harsh chemicals and often do not survive pesticide treatment.