Mealybug

Mealybug can be defined as an insect that is generally found in the green house plants, they are also sometimes defined as sap-sucking insects. The mealybug is not a very large group of insects. They are categorized into the family called Pseudococcidae. The body structure of these insects can be defined as oval and sluggish,  a unique characteristic feature is the presence of a cottony wax layer that covers the complete body. Mealybugs on plants are categorized as a pest, although they live on the plant they have a prominent symbiotic association with the ants. 

Ants are another arthropod, it is seen that ants provide protection to mealybugs on plants whereas the mealybugs provide the ants with food resources. This article deals with the general description of the mealybugs, the taxonomic classification, the mealybug life cycle and the control method of the mealybug. The article also deals with the symbiotic association of the mealybug with ants.

General Description of the Mealybug

A mealybug is a small group of insects that are found in a wide variety of landscapes, but they are the prominent inhabitants of greenhouse plants. Since they are found on plants of the greenhouse, the mealybugs on plants have also been termed as a pest. They eat the sap of the plant. Another interesting fact is that they excrete out partially liquid substances, the excrement is known as homey dew. The physical characteristic of the insect can be defined as the small insect that has an oval shape of the body, the body of the mealybug on the plant is covered with a layer of cottony wax. The colour of the body due to the presence of the wax layer seems white. The exact colour of the body can be described as whitish-grey. The complete length of the body is only about 1 cm long. The geographical distribution of these are very wide they are found in almost all the climatic condition except for the extreme cold regions of Antarctica. Since they are found all over the world the specific trees that are infested by this pest is difficult to summarize so as a general rule they are mostly found in citrus trees and ornamental plants.

The mealybug scientific name is Pseudococcidae. the scientific name of the mealybug is derived from the family of the bug according to the taxonomical classification. Mealybug is also categorized according to the colour of the waxy layer, there are approximately 13 different varieties of mealybug based on their colour. Among all these the white mealybug is the most prominent. The mealybug has a segmented body. An interesting fact about the bug is that they have a pseudo tail. The tail is actually an extension of the waxy layer from the hind portion of the body. They have well-developed legs and eyes. 

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Taxonomic Classification

The mealybug in plants is categorized as Arthropods as they belong to the family called Arthropoda. A unique and most distinctive feature of this phylum is the presence of the exoskeleton. The exoskeleton of the members of this phylum is generally very strong as it is made up of chitin. It has important survival benefits, the hard exoskeleton act as a protective covering of the body against predators and other threats. The exoskeleton is also seen as a survival adaptation. Another characteristic feature that defines the arthropods and the mealybug is the presence of a segmented body and paired jointed appendages. Another feature of this phylum is the presence and use of the combinations of compound eyes and pigment-pit ocelli for vision.

The mealybug is categorized as an insect, all the insects belong to the order Insecta. Insects according to the taxonomic classification is defined as the pancrustacean hexapod invertebrate organism. Another important feature of the Insecta order members is the presence of a segmented body, a insect body can be typically be divided into three parts, they are as following, head, thorax and abdomen. Another feature is the presence of the three pairs of jointed legs, compound eyes and one pair of antennae. All these features can be morphologically observed in the body structure of the mealybug. Another common feature of the life cycle of insects is that they undergo metamorphosis. It is important to note that the mealybug life cycle undergoes drastic changes in the morphology of the body but they are considered to undergo true metamorphosis. 

The mealybug is classified in the order Hemiptera, this order is also known as the order of true bugs. An important distinction between the bugs classified under this order and other orders is that the members of these orders do not undergo true metamorphosis, this holds completely true for the mealybug. Some of the common members of this order include mealybug, cicadas, aphids, planthoppers, leafhoppers, bed bugs and shield bugs. An important anatomical modification seen in this order is the presence of the piercing mouthparts. These modifications are really important as the members of this order are primarily dependent on the plant sap as part of their diet. This holds completely true for the mealybugs on plants, which are known as pests due to their sucking nature. The members of these orders are primarily terrestrial like mealybug with some exceptions that are adapted to aquatic life. Another generalisation that holds true in the case of mealybug is that any member of the order is classified as an agricultural pest including the mealybug. 

The order is further classified into the family, mealybug belongs to the superfamily Coccoidea, this superfamily has a unique feature of high sexual dimorphism, that is the male and female differ greatly in the morphology. Generally, the female body is soft and has no limbs that are an exception only to this superfamily. The mealybug is classified under the family called Pseudococcidae, they are considered as Pseudococcidae because they have joint legs, which is not present in the superfamily. The body of the bug is covered with the wax cottony layer, the legs are usually developed and antennae bear 5-9 segments The body colour may vary from yellow to grey to pink and is covered by white waxy powder which imparts these insects their vernacular name. 

The family is further classified into genus under which various species are classified. Some of the common species of the mealybug, with mealybug scientific name, along with their common names are mentioned as the following, 

1. Planococcus ficus (Spherical mealybug).

2. Planococcus vovae) (Cypress mealybug).

3. Pseudococcus cryptus  (Citriculus mealybug).

4. Pseudococcus longispinus (Long-tailed mealybug).

5. Saccharicoccus sacchari (Sugarcane mealybug).

6. Antonina graminis (Rhodes-grass mealybug).

7. Maconellicoccus hirsutus  (pink hibiscus mealybug, hibiscus mealybug).

8. Dysmicoccus brevipes (Pineapple mealybug).

9. Ferrisia virgata  (Stripped mealybug).

10. Nipaecoccus viridis (Spherical mealybug).

Morphological and Anatomical Features

Mealybugs on plants have very unique morphological features, that sets them apart from any other insect classified under the same phyla or order. One of the common morphological features is the presence of cottony wax that covers the whole body. The body shape of the bug can be defined as an ovoid, sluggish, the complete size of the body is about 1 cm (0.4 inches) long. It is very important to note that the female and young ones are considered crawlers whereas the male members of the bug family have a single pair of wings that are used for flying.

It is very important to note that the mealybugs are highly sexually dimorphic animals, that is the male and female of the group differ greatly in morphology. In the mealybug life cycle, the male undergoes hemimetaboly, which is known as incomplete or untrue metamorphosis. The male members develop wings that reduce their body size. The female members of the group lack wings and are generally larger than the males. Another interesting thing to note is the presence of joint appendages as legs which found in females, the legs are generally are not present in the members of superfamily Coccoidea, the mealybug is the only exception to this although they retain the soft and mushy body feature, which common to this superfamily.

The body is divided into head, thorax and abdomen regions but the division is not very clear. The body of the mealybug is also segmented, the segmentation pattern on the body is very prominent. There are 4 (2 pairs) of thoracic spiracles are present, they are termed as anterior pair and posterior pair. The anterior pair are found behind legs I, the posterior pair is in between legs II and III.

The body contains a region called the Circulus, which can be defined as a median, round area, devoid of pores. The position of it is defined as ventrally located on the abdomen, specifically on the segment IV of the abdomen. Another important anatomical region is the ostiole. The ostiole is defined as a unique, round shape dorsal opening. The anatomical position of this opening is on each side near the margin of abdominal segment VII.

The body of the mealybug also has an anal ring structure that is located between the two anal lobes. 

The waxy secretion is produced by the cerarii, which is present on the dorsal side of the body. The cerarii contains glands that secrete these waxy layers of different lengths. The cerarii are located on the margins of the dorsal side of the body. The colour of the body is decided by the colour of the waxy secretions. An important feature is the presence of a segmented antenna, there are approximately 5 to 9 segments present in the Antenna. 

Mealybug Life Cycle

The life cycle of an organism can be defined as the complete set of events and morphological, anatomical and physiological changes that the organism undergoes during the life span. The mealybug life cycle contains 3 to 4 stages, they are very short-lived animals. Mealybugs produce several annual generations. They produce an entire generation every 1 to 3 months. 

The mealybug life cycle is greatly dependent on the temperature, they can lay up to 600 eggs, per mating season. The eggs are yellow coloured present in a protective cottony layer. The number of eggs laid is dependent on the temperature. In high temperatures, there is a comparatively low number of eggs laid. The eggs are placed over filamentous ovisacs, they are then laid at different locations, as the females move from one host plant to another host plant.

The female parent lives on an average of 10 days after laying eggs, the female young one hatch from the eggs. Young female mealybugs that have hatched from eggs undergo three stages of life, they are motile from birth and maintains the legs and remains motile throughout the mealybug life cycle. The males that have just hatched from the egg, are immature. The immature male mealybug is called a nymph. The nymphs are hemimetabolous organisms, they reduce in body size and develop wings during different stages. After hatching they do no move rather they spin a white coloured cottony cocoon. They develop wings inside the cocoon and hatch from the protective coverings. The average life span of a male mealybug is only a few days. 

Mealybug sucks the plant sap of annual or perennial plants especially grasses. They move from one host plant to another host plant. The mealybugs are seen to have a symbiotic relationship with ants. The mealybugs provide ants with food resources and in exchange, to that the ants provide protection against predators.

Symbiotic Relationship

The symbiotic relationship can be defined as an association or interaction between two animals belonging to different species, in which both the participants are benefited. Mealybugs have a symbiotic association with ants. The information about this relationship is scanty, but it is known that the ants provide protection in exchange for food resources. The mealybug produces honeydews which are used by ants as a food source. The ecological importance of this symbiotic relationship is not completely understood so far although ants are known to reduce the effectiveness of natural enemies resulting in population build-up of other mealybugs.

Predators

Mealybugs are small-sized bugs, they are predated by various insects that are large in body size and shape. The predators of the mealybugs include the following insects, lady beetles, green and brown lacewings, spiders, minute pirate bugs, and larvae of predaceous midges. The lady beetles are the most important natural predators of the mealybug. 

There are several parasitoids that live on the mealybug.  Parasitoids are the organism that derives nutrition and is dependent on some other organism, they ultimately kill the host they infect. Some of the parasitoids of the mealybug are as follows, Anagyrus kamali, Anagyrus dactylopii, Scymnus coccivora.

Geographical Distribution

The mealybug is found in almost all landscapes, but the huge amount of species diversity is mainly found in the Indian subcontinent. India and Sri Lanka are some of the countries that have the highest population of mealybugs. In conclusion, the mealybug is distributed worldwide. 

Mealybugs belong to the family called Pseudococcidae, there are about 270 genera that are classified under this family. One of the major facts about mealybug is that they are considered an agricultural pest, the mealybug scientific name is also derived from the family. The mealybug is also known for its unique cotton waxy covering. Another important fact about them is the presence of sexual dimorphism where the males are smaller with wings, while females are large with prominent legs but no wings. They are also seen to have a symbiotic association with ants. The most important natural predator of the bug is lady beetles, they are also important to maintain the pest population to protect the agriculturally important plants. Since they are considered agricultural pests, there are several biological and chemical methods of maintaining their population.