Spotlight on Mealybug

Mealybugs are widespread pests that affect mostly ornamentals, grapes and citrus fruits but can also sometimes cause problems in greenhouse-grown vegetables and berries. IPM & Pollination Specialist David Abeijon shines a spotlight on what signs and symptoms to look out for when scouting crops. He knows exactly why this pest is such a challenge to control chemically and explains the Biobest range of biological solutions.

Did you know?

Together with the scale insects, mealybugs are members of the Coccoidea superfamily. They also belong to the Pseudococcidae family, whose most important pest species are the Pseudococcus and the Planococcus.

Mealybugs can also be vectors of viruses, including the GLRaV (Grapevine Leafroll- associated Virus) which is becoming an increasing concern in wine producing areas worldwide.

Mealybugs have low mobility, which means that outbreaks of this pest depend largely on climatic conditions.

Signs & symptoms

Mealybug damage can manifest itself in a variety of ways. Mealybugs cover the stems, the leaf and flower buds with a white, woolly wax. Just like aphids, they have piercing mouth parts which allow them to suck the sap out of plants. The mealybugs then excrete any excess sugars in the form of honeydew.

This makes the plant’s leaves, stems and fruit sticky. These surfaces then often become black due to the growth of sooty moulds. This mould thrives on honeydew and has a negative impact on plant photosynthesis. Honeydew also attracts ants. Ants protect the mealybugs from their natural enemies, which sometimes hinders the effectiveness of biological crop protection products.

One thing is clear: mealybugs reduce the aesthetic value of the plant and in cases of a severe infestation, they can also affect the health and growth of the plant. Wilting may be just around the corner.

Monitoring

When scouting it is important to pay attention to joints on the plant – such as axils and fruit calyx - as mealybug colonies tend to appear in parts serving as a comfortable refuge.

Special attention should be paid to outdoor crops, such as vines and citrus fruits, as the pest can hide underneath the bark or even in the roots of these plants. It is from here that new outbreaks tend to occur in spring. Initially, the pest tends to be distributed throughout the tree or bush, before moving to young leaves or newly formed fruits. In some crops, such as blueberries, it may already be hidden inside the unopened buds.

For these reasons mealybug is challenging to control using chemicals, as it is often hard to target every colony with the spray. In addition, these pests are also protected by their own layer of ‘wool’.  Beneficial insects, on the other hand, actively search out the pest and eliminate them.

Pest host range

Mealybugs have a wide host range, colonizing ornamentals as well as outdoor crops including citrus, grapes, raspberries, blueberries, bananas, pomegranates, pistachios etc. Sometimes greenhouse-grown vegetables - such as sweet pepper, tomato and eggplant - can also be affected.

What does it look like?

First, it is important to note that female and male mealybugs look totally different.

Females are oval shaped and are covered with a white waxy coat, giving them the appearance of being covered with a white powder. Some species can be identified by the patterns generated by the white coat.

In contrast, males look like small flies with a single pair of white/translucent wings and a reddish/pink body. They are quite small in comparison to the females. Without mouthparts, males do not feed on plants, and they can be extremely difficult to observe in the crop.

Life cycle

Mealybug eggs develop in waxy masses called ovisacs. Females go through three nymphal stages, with very similar morphologies, before becoming adults.

Male development follows a different path. During the first two nymphal stages, they are identical to females, but during the third nymphal stage, they pupate, after which they develop into a flying adult insect - similar to a fly.

Solutions

To make informed IPM decisions, it is important to use the correct monitoring tools. It is advisable to use yellow sticky traps, or Delta Traps, to monitor the adult males - the only life cycle stage that can fly. If the species is known in advance, it is best to use attractant pheromones in traps and on cards.

Biobest has a range of beneficial insects to help control mealybug outbreaks:

• Predatory beetle Cryptolaemus-System (Cryptolaemus montrouzieri) is called “the mealybug destroyer” for a reason and is quite specific to Pseudococcidae.
• Generic predator Chrysopa-System (Chrysoperla carnea) can be used in high rates for inundative releases.
• It is advised to combine the use of the predators mentioned above with the parasitic wasp Anagyrus-System (Anagyrus vladimiri). It has great searching capacity and parasitizes the second and third nymphal stages as well as the adult female mealybugs.