Mealybug on Plants: Identification, Damages and How to Control

IDENTIFICATION, CONTROL AND MANAGEMENT OF THE MEALYBUG IN CROPS

Although there are many different types of pests and diseases in crops, there are a few that are true protagonists. We could include some fungi of great agronomic importance , the aphid, the fly and, of course, the mealybug. There are many different types of mealybugs . We are going to study them and learn a little more about this pest that is present in many of our crops.

This installment belongs to one of the first articles dedicated exclusively to a specific type of pest. Well, if you remember we also did one about aphids on indoor plants  where we also showed some treatments and some predators to keep this plant at bay with our plants indoors.

Cochineal present in the shovels of a prickly pear or nopal. Photo from: Producers Fair

MEALYBUG IDENTIFICATION

The family or superfamily of the coccoids  is very broad. They belong to the order of the Hemiptera and include more than 8,000 species.

The problem is that of those 8,000 a large percentage (if not all) are considered pests or parasites of plants. They feed on the crops from the sap that they extract directly from the vascular tissues of the plants. 

PSEUDOCOOKED OR MEALY BUGS

This group of mealybugs has a special impact on crops and surely all of you who are reading these lines have seen it prowling your plants (whether indoors or outdoors).

They are also called cottony mealybug , and they have a white body that resembles cotton. There is no area in the world (except the poles) where this mealybug is not present.

ANTS AND MEALYBUGS, A RELATIONSHIP OF ETERNAL LOVE

We have always been amazed by the intelligence of ants. In a documentary we saw a symbiosis between ants and a strange plant species that, in exchange for the nectar it produced, the ants returned the favor by killing other plants and animals that were in competition. If an insect dared to eat its leaves, a whole army of ants would come to its defense, expelling or killing the invader.

When we see a row of ants climbing up one of our crops, we must look for the origin and explanation. Normally there will be something that motivates them to climb, and it is probably the presence of the mealybugs. This pest produces food for the ants, so they will not hesitate to protect and care for them as much as possible. At times even ants have acted by protecting mealybugs or aphids when the weather was bad, taking them to the ant hills and depositing them back on the plant when the weather returns to normal.

Symbiosis between mealybugs and ants Source: http://macroinstantes.blogspot.com.es/

 THE DAMAGE THEY PRODUCE ON PLANTS

In modern agriculture we are going to find a lot of alterations and problems caused by the cochineal and all the species that make up this pest . In general, they cause a continuous weakening of the plant by sucking the plant material. Sometimes, if we allow the pest to continue growing, it will cause defoliation, loss of fruits (which turn completely white) and, of course, the death of the plant.

The problem does not end here since the molasses they produce (and which drives the ants crazy) attracts saprophytic fungi that take advantage of the weakening of the plant to obtain benefits. They increase their mycelium by leaves and stems, decreasing even more if possible the photosynthetic capacity of the plant and making its recovery much more complicated.

As if that were not enough, some species of mealybug carry viruses of great agronomic importance …

MAIN SPECIES OF MEALYBUGS ACCORDING TO THE CROP

Although this table is not 100% applicable, each species of mealybug has its main host, so it is easy to recognize the origin of the problem and act accordingly. Let’s look at the species and plants that are affected:

Cochineal speciesMain affected plants
Pseudococcus viburniApple tree and ornamentals
Pseudococcus comstockiMulberry, vine and fruit trees
Psendococcus EchinorhynchinaePitosporum
Planococcus vovaeCypress trees
Planococcus ficusAt
Planococcus citriCitrus
Phenacoccus solaniBell pepper and aromatic spices
Phenacoccus peruvianusOrnamental species
Phenacoccus madeirensisEggplant, pepper and ornamentals
Hypogeococcus pungensCactus
Dysmicoccus fattyBanana and fruit trees


LOCATION OF THE PEST ON PLANTS

The mealybug species mentioned in the table above do not all cause the same effects on plants. For example,  Hypogeococcus pungens  does not produce molasses or cause weakening on the plant, but it does manage to deform its tissues and dry out its organs.

In many pests we can easily locate where it is since it has a predilection for these parts. In the case of the mealybug, they invade the entire plant , including the roots (surprisingly so). It can attack leaves, stems, fruits and the aforementioned roots (reaching them easily if the mealybugs are hosted in the «anthill hotel»).

What makes this pest so economically important is that, despite having reduced mobility and a sedentary attitude, they are capable of varying their movements according to the phenology of the plant . They can be housed and protected inside flowers or buds if the weather is not good and carry out layings or move according to their convenience in different parts of the plant, at their convenience.

To occupy another plant, they only need the action of man or the wind, and continue their cycle by increasing the population in a short time.

CONTROLLING THE MEALYBUG

This part of today’s article on mealybugs is dedicated to controlling and eliminating the population already identified on our plants. Luckily there are different options that lead to the same result, either ecological (through cultural work with the use of predators or with natural products) or using chemical products.

CULTURAL PRACTICES AND WHAT WE DO WRONG

As we saw in the article about fertilizers and as it usually happens with water, we are sinful of excess. How many times have we seen a plant moistened with the flooded substrate that makes it impossible for the roots to absorb oxygen and destroys the plant. Well, the same goes for fertilizers. We tell you its influence with mealybugs.

Excess nitrogen , in addition to promoting the growth of new leaves and stems in plants, also facilitates the proliferation of mealybug populations. In the case of pruning , it can also be a means of attraction and propagation of the different colonies of this pest. In this regard, it is convenient to clean the pruning tools and monitor the state of the tree once it has been felled and, of course, control the fertilization of the plant.

Some cultural tasks such as solarization , a completely natural and ecological technique, has been shown to be effective with the colonies of mealybugs found in the subsoil, waiting for their optimal moment to attack the roots. Let us remember that in this sense, it is a conflictive point and difficult to solve, since we do not realize that the roots are affected, and we look for a thousand and one solutions without reaching the core of the problem.

BIOLOGICAL CONTROL OF MEALYBUG POPULATIONS ON CROPS

Nature tends to balance and when there is a very broad genus of insects it is counteracted by a large number of predators. In the case of  pseudococci , this occurs, with a great variety of natural enemies such as predators, parasitoids and even entomopathogenic fungi.

We found the following predators:

  • Group of  coccinellids
  • Neuroptera
  • Cecidomid Diptera
  • Chamaemiidae
  • Lycene Lepidoptera
  • Coccinélidos (as  Cryptolaemus montrouzieri)

Currently, a natural introduction of exotic pests that act against the cochineal populations has been carried out, with quite successful results. The main problem lies in the disproportionate use of pesticides, which kill off predators or parasitoids earlier than with the plague itself.

The elderly farmer is currently a bit reluctant to use biological control , because he is not clear about the success it can produce, relying blindly on the (often disproportionate) use of pesticides and phytosanitary products. It is not the first time that a biological control has been introduced in a greenhouse and the farmer, distrusting the success of such an operation, proceeds on his own to apply broad spectrum insecticides that kill both all biological organisms. The result is a significant economic loss (the acquisition of predators and possible crop losses).

USE OF CHEMICALS AND NATURAL PRODUCTS

There is a wide variety of chemical products on the market , insecticides after all, which have great power to act on the cochineal. This is the case of insecticides of the organophosphate family (chlorpyrifos at the top and neonicotinoids (the main one is imidacloprid).

Among the natural products  for organic crops, the use of potassium soap (or simply a few drops of dish soap on a liter of water) or mineral oils (paraffin oil) stand out. Alcohol applied with a brush has also proven its success, although it is a somewhat heavy technique if there are a wide variety of plants affected (perfect for those located indoors).

DESCRIPTION OF SOME VERY IMPORTANT MEALYBUGS

COTTONY MEALYBUG

Planococcus citri. We can see this specific type of mealybug in many countries, since it has a great capacity to adapt to different climates. Today it has a great host capacity, of which more than 150 plants are known to be susceptible to being attacked by the cottony mealybug.

Planococcus citri
Fuente: Krister Hall

It is very common to see it in citrus (although also in fig trees, vine, coffee, mango, etc.), being located in the fruits of this crop. It emits molasses and attracts the «bold» fungus, producing chlorotic spots and deformations in fruits, when they are located on them.

The way to control this species is  sometimes enough with good cultural work and the natural enemies that the cottony mealybug already has. Potassium soap also helps. If you decide to use chemical products, you have to be careful not to always use the same active material, as you run the risk of generating resistance.

PSEUDOCOCCUS VIBURNI

This species is also known as cottony cochineal or cotonet since it also produces a cottony tissue around it. We can find it in a large number of important fruit trees such as apple, pear, vine and some horticultural trees. It does not usually cause many problems since it acts as a secondary pest (at least in Spain). Some damage from depreciation or aesthetic loss of ornamental species.

PLANOCOCCUS FICUS

This species is easily distinguishable by the filaments that cover its entire body. It is usually of great importance in the  cultivation of the vine ,  although it is also found in some ornamentals (such as in the shade or promenade banana). Special care must be taken as it transmits a large number of plant viruses.

Planococcus ficus  damages the fruits of the vine when it is installed on the grapes, depreciating the product and altering its flavor. As we have said, it can also introduce the vine  virus into the vine , which affects large areas.

Year after year the importance of this species of mealybug has increased. It has some predators to carry out biological control, although they have the protection of ants so the problem worsens.

CYPRESS MEALYBUG

Planococcus vovae. We will see this annoying set of mealybugs acting on cypress trees throughout the Mediterranean territory. Fortunately, they only act on the genus  Cupressus  and  Juniperus, such  as Cupressocyparis leylandii . 

The cypress mealybug begins to suck the phloem from the cypress trees and to dry branches. In addition, it produces molasses that attracts fungi such as “bold”, discussed above.

Planococcus vovae  has a good number of species that parasitize and balance its population. It is not advisable to do chemical treatments unless the population is very high and the condition of the tree worsens.

LONGISPINE MEALYBUG

Pesudococcus longispinus. This species is not as well known as the rest of those we have seen, but it has a great capacity for lodging. In most cases as a secondary pest, attacking about 250 different species.

This is the case of most fruit , citrus, vine and ornamental palm trees.

So far no serious problems related to this pest, which causes its general decline, have been observed. In certain conditions, such as greenhouses where large populations can be found, biological media ( Acerophagus notativentris ) are used to keep the longispine mealybug at bay  .

PEPPER MEALYBUG

Phenacoccus solani. It is a type of “young” mealybug that is in the process of expansion. It has already reached the Mediterranean area, being its origin in the American continent.

Although it tends to attack a large number of species, it has a predilection for the cultivation of peppers and some aromatic species. By sucking the plant tissue, it produces a loss of vigor on the affected plant and some organs dry. It produces molasses so we already know the problems it can cause.

Controlling this pest when it becomes important is not an easy task. The most recommended is the use of parasitoids, since often not all chemicals reach all mealybugs (the young stages that are protected by the mother’s shell). The most indicated is the detection and identification of the problem, to prevent it from spreading and infesting the entire crop.

 

BOUGAINVILLEA MEALYBUG

Source: G. Arakelian

Phenacoccus peruvianus. This type of mealybug, which is distributed over wide geographical areas (including the Mediterranean), usually attacks different ornamentals (especially bougainvillea, which gives rise to the plague) and most Solanaceae .

It begins to suck the plant content of the plant and produces dry plant organs. They produce molasses and favors the appearance of fungi.

The levels of mealybug in bougainvillea are currently low thanks to the action of the genus Acerophagus , which performs a great biological control on this pest.

Before, successful biological control was not known. The problem comes from the mediation of the ants (happy ants), who will act defending the life of the mealybugs to the death. Given this, what we can do is eliminate them or apply potassium soap to the populations of this pest.

BANANA MEALYBUG

Dysmicoccus grassii. Although this mealybug is native to the American continent, there is already a presence in Europe. In Spain we can see it in the Canary Islands, given the production of bananas on the islands. In fact, it is one of the most limiting pests in banana cultivation.

They suck up the vegetable content and secrete a quantity of molasses, deteriorating the quality of the products (in this case, bananas) and making them unmarketable.

To date, chemical products have been used for their control,  but given the restrictive policy on the use of these phytosanitary products in Europe, there is an increasing trend towards the use of potassium soaps,  oils and methods of sexual confusion.

CACTUS MEALYBUG

Hypogeococcus pungens. It is very typical to see cochineal in cacti and nopales in Spain and other countries where this type of species is cultivated, especially in America. It usually attacks a large number of hosts, almost all of them from the cactus family.

It is of great economic importance given the damage it causes, stopping the development of crops and deforming parts of the plant.

Hypogeococcus pungens
Fuente: sel.barc.usda.gov

The main problem that the farmer faces is that it is located in very hidden parts of the plant, such as folds or between thorns.

It also secretes a wax that protects it from products that act on contact. The most appropriate thing is to eliminate the affected parts, so it is important to locate the cacti mealybug quickly.

The potassium soap is a good agent performance, provided that protective wax is not there on the population of this pest.

Here we put you a fantastic video about how human beings are able to take advantage of everything. In this case, to extract carmine from the mealybugs as was done in the past, in the Canary Islands. Do not miss it!

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