Mealybugs and scales are difficult to control with conventional insecticides. This situation is primarily due to physical factors, not biochemical resistance. Mealybugs and scales are protected by their sedentary habits (making them less likely to contact pesticides), sheltered feeding locations (under leaves, at plant nodes, or on roots within the soil) and the water-repellent waxes which cover their bodies.

Mineral oils and insecticidal soaps (potassium salts of fatty acids) are commonly recommended at 1-2% product for control of scale insects and mealybugs on actively growing plants. Limonene, a component of citrus peel oil, can be used as an active ingredient in place of soaps or oils to kill mealybugs, scales, whiteflies and other insects. The efficacy of limonene as an insecticide is related to several different mechanisms, but a crucial factor is its ability to initially penetrate the waxy exterior of pests. This ability depends in large measure on the types of adjuvants used to ensure uniform mixing of the limonene with water.

Limonene is used in a variety of foods and beverages and is classified by the U.S. Food and Drug Administration as a GRAS (Generally Recognized as Safe) compound. Limonene is registered as a pesticide active ingredient in more than a dozen products, primarily those used on pets or for control of household pests. The degree to which limonene is used to control plant pests will depend in large measure on whether new formulations can be developed which reduce phytotoxicity without a loss in efficacy.