Mealybug on Papaya
White cotton-like masses made of flocks of bugs appear on the underside of leaves, stems, flowers and fruits. They are very active and even though low numbers have very little impact, infestations can lead to yellowing and curling of young leaves, stunted growth of plants and early fall of fruits. Older leaves are less likely to become deformed or distorted. The bugs excrete honeydew during sap sucking and this makes the tissues sticky and prone to be colonized by opportunistic bacteria and fungi. Fruits are particularly susceptible to be attacked and may become deformed or completely coated by wax secretions. Ants may be attracted by the honeydew and may spread the pest to other plants.
Mealybugs are oval, wingless insects found in warm or temperate climates. Their body are protected by a layer of thin mealy wax that give them a cottony appearance. They insert their long piercing and sucking mouthparts (stylets) into plant tissues and suck sap out of them. The symptoms are a reaction to the toxic substances that they inject into plants while feeding. The eggs of the mealybug are also laid in the soil. After hatching, nymphs and adults can crawl to neighboring plants. They can also be dispersed over more or less longer distances by wind, ants, animals, birds or simply during field work activities such as pruning or harvesting. They have an array of alternative hosts such as eggplant and sweet potato, as well as many weeds. Warm temperatures and dry weather favor their life cycle and the severity of the symptoms.
At the first sign of slight infestation, smear the colonies of mealybugs with a cotton bud imbued with oil or spirit. You can also wash the plants with warm water and a small amount of detergent, petroleum oil or insecticidal soap. Nearby plants should be sprayed with neem oil in order to prevent spread of the population. Natural antagonists include the green lacewing, parasitoid wasps, hover flies, ladybird beetles, mealybug destroyer and the predator butterfly Spalgius epius.
Always consider an integrated approach with preventive measures together with biological treatments if available. Treatments against mealybug are difficult because they are protected from adverse environmental conditions by their waxy layers and fibers. However, foliar spray with solutions based on acephate, bifenthrin, chlorpyriphos, thiamethoxam, deltamethrin and pyrethrins can be effective against mealybugs.