Mealybugs

Nearly 300 species of mealybugs are known from Canada and the United States. Fortunately, only a few species are common or serious pests of orchids. Mealybugs are classified in the family Pseudococcidae, and are closely related to the scale insects. In fact, mealybugs are best thought of as a kind of soft scale that does not form the protective cover that most scales produce for protection. The pest species are in the genera Pseudococcus, Planococcus, Phenacoccus, and Dysmicoccus.

Immature to adult mealybugs may measure 0.5-8.0 mm in body length. All of the orchid feeding species are coated with a waxy secretion that hides the body of these insects. The more common species of these odd insects that infest orchids are immediately recognized in the adult stage by the white, yellowish-white, whitish-grey, or pale pink to pale blue in color coating. The body is oval and the sides of the body have short waxy filaments and there may be 2-4 short to long filaments on the posterior end of the body. These filaments sometimes give the impression of numerous legs.

Fungus Gnats

Fungus gnats are small, dark, short-lived flies, of the families Sciaridae and Mycetophilidae (order Diptera), whose larvae feed on plant roots or fungi and aid in the decomposition of organic matter. The adults are 2-5 mm long, and are important pollinators, and can also help spread mushroom spores. One control for fungus gnats is the product Gnatrol, which kills the gnats.

Nonchemical Control
Reduce the proportion of organic matter in your media, eliminate wet areas around germination chambers and floors under benches, reduce algal growth, practice good sanitation and inspect incoming plant material. Monitor adults with yellow sticky cards. Use Guardian Gnat Patrol

Aphids

Aphids, also known as greenfly, blackfly or plant lice, are minute plant-feeding insects in the superfamily Aphidoidea in the homopterous division of the order Hemiptera. Recent classification within the Hemiptera has changed the old term 'Homoptera' to two suborders: Sternorryncha (aphids, whiteflies, scales, psyllids...) and Auchenorryncha (cicadas, leafhoppers, treehoppers, planthoppers...) with the suborder: Heteroptera containing a large group of insects known as the 'true-bugs'; gnat bugs, pond skaters, shore bugs, toad bugs, water boatmen, backswimmers, etc.

About 4,000 species of aphids are known, classified in 10 families; of these, around 250 species are serious pests for agriculture and forestry as well as an annoyance for gardeners. They vary in size from 1-10 mm long.

As insects, aphids have only six legs and a pair of antennae, the mouthparts are formed into a set of thin piercing stylets, the body is a pear-shaped ovoid, and pest aphids are immediately recognizable by the presence of a pair of short tubes (siphunculi or cornicles) protruding from the posterior upper portion of their abdomen