Chemicals, Cotton

Mealy bug: An emerging threat to cotton crop

By Mohammad Ali Khaskheli

Cotton is the most important fiber crop of Pakistan. It plays pivotal role by providing fiber, food and fuel and earns foreign exchange. The cotton provides raw material to all textile mills, ginning factories and oil mills. It is also used for edible oil, which makes about 80% of national oil production. Cotton has much more important utilization in our economy as well as in our culture therefore; it is regarded as the mother of civilization.

The growers of Pakistan are suffering huge losses in yield and quality of cotton crop due to attack of various insect pests and diseases every year. In Pakistan, cotton crop is attacked by about 150 types of insect pests; which act as significant limiting factor in increasing its production. Because of their improper or un-integrated management, our cotton production is very low as compared to many other cotton producing countries of the world.

Cotton crop is easily damaged by pests, so cotton growers are always looking for ways to protect their crops. The present situation of cotton field, with special reference to Sindh province, needs special attention, where about the crop is suffering from an emerging problem of mealy bug pest (fig.1).

Fig.1- Hibiscus Mealy bug

This pest occurs in most tropical areas of the world, including Asia, the Middle East, Africa, Australia, and Oceania. The mealy bug arrived in Egypt from India in 1912 and in Hawaii in 1984. It appeared in Grenada, Trinidad, and St. Kitts in the1990’s and has spread to other islands in the Caribbean, where it attacks many hosts of economic importance.

Mealy bug Maconellicoccus hirsutus is a small, scaled insect 1/5th of an inch long (about the size of a small red ant) that gets its name from its appearance, which looks as if it has been rolled in coarse flour. Female adult is approximately 3 mm in length (1/10 inches), wingless, and have piercing–sucking mouthparts. A white cotton-like wax covers the female’s reddish body. When punctured, the female’s body fluids are also reddish, but it is important to note that some other mealy bug species may have a similar coloration.

Mealy bug belongs to order Hemiptera, sub-order Homoptera, family Coccidae, sub-family Pseudoccidae. The super family Coccoidea includes mealy bugs and scale insects. Mealy bugs overwinter as eggs on stems, in soil, in cracks and crevices in the stem, and inside crumpled leaves. Freshly laid eggs are orange but turn pink just prior to hatch. The crawlers disperse from the ovisac by way of walking, wind, or ants. The nymphs feed and develop into adults in approximately 30 days. The insect has a life cycle of 24 to 30 days. The female mealy bug produces 10-15 generations per year in colonies of 500-600 eggs.

Mealy bug is a serious pest in many parts of the world where it causes serious damage to a variety of crops. This mealy bug attacks more than 300 plant species including rice, sugarcane, cotton, fruits; papaya, carambola, avocado, citrus, sugar-apple, sour sop, mango breadfruit, golden apple, cherry, plum, guava, pigeon pea, passion fruit ,grape, banana; vegetables, tomato, cucumber, pumpkin, peppers, okra, dasheen, lettuce cabbage, beans, squash; ornamentals hibiscus, bougainvillea, croton, oleander, allamanda, ixora, anthurium, ginger lily, heliconia, schefflera, lantana, ficus, seagrape, and numerous weeds etc.

It feeds on the sap of the plant and releases toxic substances causing injury, curling and drying of leaves which, damages fruiting and drastically decrease the yield. Mealy bug also attacks the roots just below the level of the soil, especially where the root and the stem meet. Root mealy bug lays their eggs in sacs of interwoven filaments that resemble cotton wool. Mealy bug also excretes large quantities of honeydew onto the plant that in turn attracts ants and sooty mould. Keep ants under control as they may distribute the pests to other plants. It is also spread by wind, or it can be stuck on clothing or on the hair of animals. Mealy bug can spread rapidly once introduced in an area

In Sindh the minor infestation of mealy bug had been reported on cotton crop since last so many years, but during September 2005, a severe damage of mealy bug was recorded first time on an area of about 3000 acres in Kot Ghulam Mohammad, Tandoallahyar, Mirpurkahs and Sanghar district (fig.2). The problem was appeared late when cotton crop was mature. But this year the attack of mealy bug has been observed in early stage of cotton crop in district Sanghar and spreading very fast (The daily Dawn June 2, 2006).

Fig.2- Cotton crop severely affected by mealy bug at Kot Ghulam Mohammad

Cotton plant with mealy bug damage
Though the infestation still has not reached at alarming situation but if the pest is not controlled it would cause severe damage to the crop. Furthermore it must be remembered that once mealy bug pests become established, it is extremely difficult to achieve acceptable control.

Signs of Mealy bug Infestation

One or more of the following symptoms may be observed:

• Crinkled or twisted leaves and shoots
• Bunched and unopened leaves
• Distorted or bushy shoots
• White fluffy mass on buds, stems, fruit, and roots
• Presence of honeydew, black sooty mold, and ants
• Unopened flowers which often shrivel and die
• Small deformed fruits.

Management Options

In recent days our experience in the district Sanghar has shown that only the chemical control has become very difficult. The mealy bugs produce large amounts of honeydew (similar to that of produced by whiteflies and aphids), which can coat plants and surrounding surface with a sticky or waxy layer of honeydew (fig-3). Pesticides cannot easily penetrate the heavy wax layers. Therefore, applying pesticides only is an ineffective control technique against this mealy bug pest. Thus mealy bugs cost growers and retailers million of dollars per year in control costs and crop damage throughout the world. However the managements should include following integrated control options.

• Weeds serve as host plant therefore they should be eradicated regularly.
• The severely infested plants must be cut and burnt immediately and field should be ploughed to kill immature stages available in the soil.
• Spray as strong a stream of soapy water solution as the plant can tolerate; this should dislodge most of the bugs. This is the easiest way to control mealy bugs. Repeat if you see new egg sacs.
• Spray with a soap/oil (Mix 1 tsp. detergent surf +100 ml neem oil, and 16 liter water in a spray tank) mixture may also give better results.
• The less affected crop at early growth stage should be sprayed with Imidacloprid (120 gram/acre) or Thiamethoxam and may be repeated after 5-7 days followed by water spray. The spray should be done at the crawler stage of mealy bugs, because it is the most fragile stage and the most susceptible to chemical control.
• The foliar spray of Chlorpyrifos, Triazophos, Profenofos, and Bifenthrin may be applied at later stage of crop. (i.e. after 100 days of sowing).
• Prior to the spray of Imidacloprid, Chlorpyrifos @ 2 Liter per acre should also be applied through irrigation as to control the root infestation and suppress the pest population in the soil.
• Biological control offers the safest, most economical and long term solution to this problem. This strategy relies on producing sufficient numbers of tiny wasps (parasitoids) that attack and kill the mealy bug. A number of natural enemies are known, including the coccinellid predator Cryptolaemus montrouzieri and the parasites Anagyrus kamali and Gyranusoidea indica which suppress the mealy bug population. In Egypt and India, biological controls have been quite successful in suppressing the mealy bug. Other coccinellid predators have also been reported in India. At present, 21 parasites and 41 predators are known to attack this pest worldwide.

In last it must be remembered that once mealy bug pests become established, it is extremely difficult to achieve complete control.