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Hello growers!

Today, we are going to talk about scale insects and their biological control with beneficial predators and parasites. Scale insects are known to cause heavy yield losses in many field crops, vegetables, fruits, and ornamentals.

They look like bumps on the plant surfaces. However, farmers often notice them only after they cause serious damage to their crops. Scale insects are sap-sucking pests that stick to leaves, twigs, branches, and fruits.

They have a simple life cycle that usually begins when eggs are laid beneath the protective body of the adult female. After hatching, the young nymphs, called “crawlers,” are the only mobile stage that move to find a suitable feeding site on a plant. Once settled, they insert their mouthparts into plant tissue, begin feeding on sap, and gradually lose mobility as they develop a waxy or hard protective covering. The insects pass through several immature stages before reaching adulthood. Adult females typically remain stationary, while adult males, if present, may develop wings and live only briefly to mate.

Scale insects cover themselves with hard or soft layers, appearing as brown, white, or cottony masses. Common types include armored scales, cottony scales and soft scales.

Once settled, they continuously suck sap and gradually weaken the plants. Infested plants turn yellow, grow poorly, and show reduced flowering and fruiting, leading to lower yields. Soft scales produce honeydew, which promotes the development of black sooty mold on the leaf surface. This black coating reduces photosynthesis, diminishes aesthetic value, and severely affects plant health. Plants infested with scale insects produce small, deformed, and unmarketable fruits. Heavy infestations can even kill young plants.

Ants increase the population of scale insects because they protect them in exchange for honeydew. Chemical control often fails because the insects are protected by their covering. Also, repeated spraying of pesticides kills beneficial insects and causes scale insects to rebound.

Therefore, biological control is the safest and most effective solution. Biological control uses natural enemies that feed on or kill scale insects. Important predators include scale-eating lacewing larvae like Chrysoperla rufilabris and the mealybug destroyer, Cryptolaemus montrouzieri beetles that are highly effective in controlling scale insects. Also, a tiny parasitic wasp called Aphytis melinus kills scales from inside and reduces their population.

In conclusion, farmers should avoid unnecessary pesticide use to protect these beneficial insects. Ants should be controlled using sticky bands to prevent them from protecting scale insects from natural enemies. Heavily infested branches should be pruned and destroyed to reduce spread of scale insects. When natural enemies are protected, scale insects stay under control. Threfore, farmers should encourage beneficial insects for healthier crops and better yields.

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