There are several species of insects; some are beneficial to plants by acting as predators to parasites while only a handful can cause damages and injuries to plants. Detecting plant pests before they have an opportunity to grow in numbers and cause extensive damage is an important part of pest control and management. One of the signs to look for is the presence of white milky deposits on plants left by some insects.
Mealybugs, belonging to family Pseudococcidae (order Homoptera ), are tiny insects measuring 0.06 to 0.12 inch long. They have soft, white dusty bodies with waxy coatings, short spines on the body margin and fully formed legs. Mealybugs have sucking mouth parts that feed on leaves, twigs and roots. After feeding, they often leave behind large amounts of honeydew (whitish, waxy deposits). Feeding can cause distortion, yellowing and loss of leaves, which can lead to the weakening and, sometimes, death of plants.
Mealybugs attract other insects, most especially ants that feast on honeydew. In addition, black sooty fungus grows on mealybugs' honeydew. Dealing with mealybugs can be a bit tricky because they cluster themselves into vast colonies, hide in obscure places and cover themselves with their own honeydew. Applying horticultural oil and pesticide soaps or detergents by using a sprayer can help remove mealybugs. Mealybugs' preferred hosts are Aphelandra, Ardisia, asparagus ferns, Cryptanthus, Dieffenbachia, Dracaena, false aralia, ficus, Gynura, Hoya, Maranta, Nephrolepis and Pothos. Mealybug infestations on the roots are difficult to detect, and it may take several months after the initial attack before you can find them. Close inspection of the roots can help detect the presence of mealybugs prior to purchase of potted plants.
Also known as plant lice, aphids (order Homoptera) are as small as mealybugs, measuring 0.06 to 0.12 inch. These soft-bodied insects come in various colors, from pale white or green to black. Characterized by pear-shaped bodies, aphids have six long legs and two antennae that protrude from the sides of the head. Some aphids have wings while others are wingless, which are more common. Their waxy covering gives them their powdery or woolly appearance.
Aphids appear in clusters on the undersides of young leaves and stems. They also feed on flower buds and roots, causing the plant to weaken. Aphids can also cause curling and distortion of leaves, hardening of flower buds and deformation of flowers that cause plants to look unappealing. Just like mealybugs, aphids also attract ants that feed on their excrement made of honeydew, a white, sticky material that leaves a shiny appearance to the foliage. Sooty mold or black fungus grows on honeydew, further aggravating the plant's situation.
Lady bugs and lady beetles can feed on aphids and are effective in controlling these pests. Other methods of controlling aphids include spraying with insecticide soap, handpicking, and wiping the leaves using swabs with alcohol. Spraying insecticides can help control larger numbers of aphids.
Closely related to mealybugs and aphids, whiteflies (order Homoptera) measure approximately 0.1 inch long. They have four broad, delicate wings with a white, powdery, waxy appearance. An adult female whitefly can lay hundreds of eggs at a given time. These eggs hatch within a week and turn into crawlers (flattened nymphs) that move around the plant. They soon feed on plants and attach themselves in clusters to the undersides of leaves and stems. Whiteflies love vegetables and ornamental plants, where they feed on leaves by using their mouth parts to suck out the plant sap, causing plants to weaken and die. They excrete the excess food in a form of honeydew, which becomes a base for sooty black fungus. Leaves covered with sticky white honeydew have a glazed appearance, become pale, turn yellow and drop off.
Treating infested plants by spraying insecticide and insecticidal soap early on will prevent the whitefly population from growing. Dipping in insecticides can help treat heavily infested plants. Introducing predators such spiders, lady beetles and lacewings that feed on whiteflies are effective biological pest controls. Another form of biological pest control is Encarsia formosa, a tiny parasitoid, which can manage the spread of whiteflies in greenhouses. E. formosa invades and develops inside the bodies of whiteflies, causing them to weaken and die.