Mealybugs are a group of small insects that can cause serious problems to plants. Their presence is common in gardens, greenhouses and agricultural crops, and they can cause significant damage to various plant species. In this article, we will explore what mealybugs are, their life cycle, the symptoms and damage they cause to plants, the different types of mealybugs, and how to eliminate them.
# # # What are mealybugs? # # #
Mealybugs are insects belonging to the superfamily Coccoidea, which includes several different families of mealybugs such as Pseudococcidae (mealybugs), Coccidae (mealybugs or soft scales), and Diaspididae (armored mealybugs). Females are wingless and immobile, and some are covered with a hard scale or waxy threads (mealybugs). They are characterized by their small size and by feeding on plant sap through specialized mouthparts. This can cause significant damage to plants, weakening them and reducing their ability to grow and produce. In addition to the damage they cause by sucking plant sap, mealybugs also produce honeydew (on which molds grow), causing considerable damage to ornamental and fruit crops and loss of value. Diaspines do not produce honeydew. Their hiding ability and the protective cover of these insects mean that they are very well protected against natural enemies and also against synthetic pesticides.
Within the broad superfamily Coccoidea we find very different morphologies and colors. In addition, there are mealybugs that are specific to their host, that is, they only feed on one type of plant and other more polyphagous ones that can infect different types of plants.
# # # Life cycle of mealybugs # # #
The life cycle of mealybugs varies depending on the species, but generally follows these steps:
Egg: Mealybugs lay eggs on the surface of leaves, stems or roots of plants. The number of eggs can vary between species, but is usually from a few dozen to hundreds.
Nymph: Nymphs emerge from the eggs and go through several stages of development, known as instars, while shedding their skin as they grow. During this time, they continue to feed on the plant.
Adult: Adult mealybugs can reproduce, laying more eggs and continuing the life cycle. Adult mealybugs are usually small in size and have colors that range from light to dark tones, depending on the species. Females do not have wings, they do not move and their legs are not visible. Males are smaller than females and, unlike females, have two pairs of wings and two long caudal filaments. In the adult phase, the males do not feed and their only task is to fertilize the females and, as soon as the male emerges from the cocoon, he will begin to look for one. Once the males copulate, they die.
# # # Symptoms and damage to plants # # #
Although most species of scale insects and diaspines feed on the aerial parts of the plant, some species feed on the roots. Some species can also transmit harmful viruses. Symptoms of a mealybug infestation may include:
Yellowed or withered leaves: Nymphs and females extract sap from the plant, hindering growth and causing the leaves to turn yellow, wither or fall off prematurely. Consequently, photosynthesis and therefore performance are reduced. Flowers and fruits can also abort and drop.
Poor growth: Infested plants may show poor growth and general weakness.
Honeydew: Many mealybugs excrete a sticky substance called honeydew, which can accumulate on leaves and stems. Plant sap is low in protein and rich in sugars. To obtain adequate protein intake, mealybugs must ingest large amounts of sap, eliminating excess sugars in the form of honeydew. Honeydew can attract other insects such as ants, which is why we see ants climbing the stems of plants, and encourage the appearance of sooty mold. The sooty mold (complex formed by different species of fungi) that usually develops on the honeydew, as well as the white and waxy secretions of the scale insects, reduce the commercial value of the affected plants and causes less photosynthesis in the leaves, which decreases even more the production of flowers and fruits.
Visible damage: An accumulation of scale insects can be observed on the leaves, stems or roots of the plant. In some cases, armored mealybug scabs form and can damage tree bark.
In ornamental crops, the mere presence of scale insects is enough to make the product unsuitable for sale. Therefore, a very small population can cause a considerable loss of value.
Diaspines, unlike mealybugs, do not produce honeydew. They feed by sucking the contents of the epidermal cells, into which they inject toxic substances that cause the appearance of yellow, red or brown spots on leaves and fruits. This can eventually kill the leaf.
# # # Types of mealybugs # # #
There is a wide variety of types of scale insects that can affect plants:
Cottony cushion scale (Icerya purchasi)
The ribbed mealybug is an insect similar to the cottony mealybug, but differs from it by having a reddish-brown shell that keeps the body protected. It is oval in shape, and like all scale insects, it can multiply in large numbers.
-Favorite plants: it is quite common in citrus trees (orange, lemon, mandarin, etc.).
-Symptoms: the fruits turn yellow and may spoil; Affected leaves also lose color.
Mealybug (Pseudococcus viburni)
It is currently present in many regions of the world with a temperate climate. It looks very similar to the cottony mealybug (Planococcus citri), but its body is covered with a thicker layer of wax, the filaments around the body are longer (20-50% of the body size), and the two caudal filaments They are always clearly longer than the others.
-Favorite plants: It is quite common in tomatoes, pome fruit trees and ornamental crops.
-Symptoms: they do not cause significant damage to plants. The damage is related to the presence of molasses that attracts insects and the appearance of sooty mold.
Cottony mealybug (Planococcus citri)
It is a cosmopolitan scale insect and has numerous and varied host plants. In regions with a temperate climate, this cottony mealybug is a problem for greenhouse horticulture and in the tropics and subtropics also in outdoor crops.
-Favorite plants: Fruit trees, citrus and ornamental crops, especially potted plants such as ficus, palm, schefflera, croton and kalanchoe, but also rose and gerbera, cucumber, melon and eggplant.
-Symptoms: malformations or yellowing of the leaves, sometimes followed by defoliation. Flowers and fruits often fall off. Molasses production.
California red louse (Aonidiella aurantii)
The California red louse is a type of scale insect that is nothing like the ones we have seen so far. It is rounded, almost flat, and is protected by a reddish shell.
-Favorite plants: citrus, palm trees and cacti, although it may affect others.
-Symptoms: yellowing of leaves and fruits, general weakening of the plant.
San José scale (Aspidiotus perniciosus)
The San José scale is similar to the previous one: the female measures about 2 millimeters in diameter, which is protected by a shell, and always lives attached to the plant. The adult male has two wings.
-Favorite plants: it affects numerous species, but in particular fruit trees.
-Symptoms: the affected parts turn yellow, and may fall. In severe cases, the pest will dry out the plant.
Carmine mealybug (Dactylopius coccus)
It is a type of mealybug with the particularity of its ability to produce an intense red pigment, known as carmine, which is used in the food and cosmetic industry.
-Favorite plants: cacti and prickly pears mainly, although in their absence it can infect ornamental succulents and other plants.
-Symptoms: they cause chlorosis and necrosis in the blades and fruits, weakening the plant and can cause its premature fall. The new blades are quickly affected by the parasite, which in the medium term causes their death, since it prevents the plant from carrying out photosynthesis and causes the depletion of its reserves. High population densities can cause plant death.
Black scale (Saissetia oleae)
It is a type of soft-scale mealybug, belonging to the Coccidae family, also called lecanine mealybug. The particularity of this family is having a body hardened by waxy secretions. The eggs of this species are laid beneath the female and are whitish to yellowish in color.
-Favorite plants: it is a cosmopolitan pest on citrus and olive trees. It is a serious pest in coffee and citrus. It can also affect many ornamental crops.
-Symptoms: they produce a large amount of honeydew accumulating sticky deposits on adjacent surfaces. Honeydew can attract ants and sooty mold develops in sugary deposits. Sucking large amounts of sap weakens the plant and can cause wilting, tissue desiccation and necrosis.
# # # How to eliminate mealybugs # # #
There are several ways to control and eliminate mealybugs on plants, ranging from chemical methods to ecological approaches and the use of biocontrol agents or natural predators. In the case of low presence or the first signs of the pest, it is recommended to remove them by hand. Well, who says by hand means with a brush, or a rag (if you choose this, soak them with water and a little soap). If the plant is small and the pest is not widespread, it is best.
In the case of large plants or trees or when there is a high presence of the pest:
Authorized chemical treatments in agriculture
-ABAMECTIN 0.0015% + PYRETHRINS 0.02%
-RAPESE OIL 70% + PYRETHRINS 0.7%
-RAPESE OIL
-ORANGE OIL 60g/L
-PARAFIN OIL79%
-ACETAMIPRID 20%
-Azadirachtin 2.6% or AZADIRACTIN 1%
-CIPERMETRIN 50% or CIPERMETRIN 5%
-DELTAMETHRIN 2.5%
-LAMBDA CYHALOTHRIN 5%
-MALTODEXTRIN 47.6%
-PYRETHRINS 0.12%
-PYRIPROXIFEN 10%
-POTASSIUM SALTS OF FATTY ACIDS C14-C20 48%
-POTASSIUM SALTS OF VEGETABLE FATTY ACIDS 13.04%
-SPIROTETRAMAT 10% or SPIROTETRAMAT 15%
Chemical treatments authorized for non-professional use
-ABAMECTIN 0.0015% + PYRETHRINS 0.02%
-RAPESE OIL 70% + PYRETHRINS 0.7%
-RAPESE OIL
-ORANGE OIL 60g/L
-PARAFIN OIL 79%
-ACETAMIPRID 20%
-DELTAMETHRIN 2.5%
-PYRETHRINS 0.12%
-PYRIPROXIFEN 10%
Ecological treatments
Potassium Soap: Potassium soap is a mild solution that can be sprayed on plants to kill mealybugs. It works by dehydrating the insects' bodies, which kills them.
Neem Oil: Neem oil is a natural pesticide that can help control mealybugs without harming other beneficial insects. It works by interfering with the life cycle and reproduction of mealybugs.
Diatomaceous earth: Diatomaceous earth is an excellent alternative. It can be sprinkled through the substrate or by spraying. It is also a 100% ecological and totally harmless insecticide. In addition, it can be used to combat cockroaches and ants.
Mixture for one liter of preparation |
Instructions for use: Mix well until completely dissolved. Its application is recommended during the hours of less sunlight for greater effectiveness since it has photosensitive products, and since it contains oil, intense sunlight can burn the leaves. It is recommended 3 applications in a row every 2 or 3 days and then apply between 8 and 15 days depending on the evolution of the pest. You must ensure complete coverage on the upper and lower sides of the leaves. |
ATTENTION: do not apply directly to flowers, spray only on leaves and stems.
Natural enemies of mealybugs
Ladybugs (Coccinellids): Ladybugs are beneficial insects that feed on scale insects and other pests, helping to control their population. They are usually most effective against mealybugs in their nymph phase.
-Cryptolaemus montrouzieri: It is a natural predator of scale insects and especially for the control of the carmine scale.
-Chilocorus cacti: feeds on different types of scale insects
-Hyperaspis trifurcata: Although it can feed on aphids and other small insects, its main food is Dactylopius opuntiae, the carmine mealybug.
-Rhyzobius lophanthae: It is a small predatory ladybug very useful in biological control of different species of hard-scaled scale insects in all their stages of development, although it can also prey on soft-scaled scale insects and moth eggs.
Hoverflies or small flies
-Salpingogaster cochenillivorus
Parasitic wasps: they are a type of small wasps. The females bite the mealybugs and insert an egg inside the mealybug. From this egg a larva will hatch that will feed on the mealybug until it reaches adult size and goes outside.
- Acerophagus flavidulus: parasitizes mainly Pseudococcus viburni.
-Aphytis melinus: It mainly parasitizes armored scale insects of the Diaspididae family such as the California red louse (Aonidiella aurantii), white lemon louse (Aspidiotus nerii), San Jose louse (Aspidiotus perniciosus).
Moths or butterflies
-Laetilia coccidivora: The larvae are predators and feed on the eggs and young of scale insects.
-Laetilia bellula: It is a natural predator of carmine scale insects.
Lacewings: Lacewings are natural predators of mealybugs, especially in their larval stage. They also feed on other harmful insects such as aphids, making them an environmentally friendly and effective option.
-Crysoperla carnea
-Sympherobius Barberi
-Sympherobius angustus
# # # Recommendations to prevent and control them # # #
• Apply pressurized water as soon as the first colonies of nymphs are observed.
• If the attack is significant, eliminate the affected parts.
• Eliminate seriously affected parts, crushing and burying where possible.
• Monitor for possible reinfestation
• Make preventive applications of potassium soap with neem oil and diatomaceous earth.
In conclusion, mealybugs can cause serious problems for plants, but there are several ways to control and eliminate them. By combining chemical, ecological treatments and biocontrol agents, you can effectively protect your plants from these pests. In addition, it is important to maintain constant surveillance on your plants to detect early infestations and act immediately.
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