Infested leaves may look distorted and curled, eventually, fall off during the premature stage. Sticky honeydew deposits accumulate on leaves and stems and usually develop black mould fungus, giving the foliage a sooty appearance. Ants may be attracted by the honeydew. The insects are most noticeable as groups of very small, black spiny lumps on leaf undersides. The combination of feeding damage and sooty mould growth weaken the trees and reduces fruiting.
The citrus blackfly (Aleurocanthus woglumi) is a serious citrus pest of Asian origin and infests various host plants. It is a member of the whitefly family but the adult has a dark, slate blue appearance that led to it being given the name blackfly. The adult is a very sluggish tiny insect with limited flying range, but is active at dusk and rests on the lower leaf surface during the day. Females produce around 100 golden coloured eggs that are laid in spiral patterns on the lower side of the leaves. Thy nymphs are flattened, oval in shape and scale-like in their appearance. The cell sap is sucked from the leaves through the blackfly's piercing stylet. Simultaneously the fly secretes honeydew in large amounts. The optimal conditions for development are met at a temperature around 28-32°C and relative humidity of 70-80%. A. woglumi cannot survive in cold environments, where frost occurs.
Encarsia Perplexa, Polaszek and Amitus hesperidum silvestri have been identified as parasitic wasps of Citrus Blackfly. The wasps are known to parasitize only the citrus black fly and closely related whiteflies, but will not harm plants and people. The insects such as ladybird, lacewing, Brumus sp., Scymnus sp. and Chlysoperla sp. are other natural enemies. Oils such as cotton oil and Fish Oil Rosin Soap (FORS) are effective and eco-friendly in nature not only to reduce the blackfly population but also reduces sooty moulds on leaves. Use neem seed extract spray (4%) to reduce the pest population.
Always consider an integrated approach with preventive measures together with biological treatments, if available. Avoid the use of wide-spectrum pesticides to conserve natural enemies of A. woglumi. The insect can be controlled by fumigation of planting material or with chemical sprays. Spray curative pesticides when more than 50% of the eggs hatch and the younger ones are without any protective cuticle over their body. Quinalphos and triazophos are found promising in reducing the population of citrus blackfly. Spraying must be done on the lower surface of the leaves where the pest thrives. The entire plant canopy should be drenched with the solution.