Pappaya mealy bug ( Paracoccus marginatus ) causes severe economic damage in cassava yield.
The mealy bugs are white to pink in colour and measure 3-4 mm in length. Adult females are oval and somewhat round, dark green to almost black in appearance.
Mature female lays eggs in an egg sac of white wax, usually clusters on the twigs, branches, or bark of the host plant. Eggs are creamy white in colour and slender in shape.
Egg development takes between 3 and 9 days and nymphs called crawlers hatch which are very mobile. Non-infected plants can be infected from infected plants as juvenile mealybugs can crawl from an infected plant to another plant.
Crawlers
Small ‘crawlers’ are readily transported by wind, rain, birds, ants, clothing and vehicle and may settle in cracks and crevices, usually on new plants.
The wax, which sticks to each egg, also facilitates passive transport by equipment, animals or people. The female mealybug is not active and unable to fly.
In fact, humans help in transport of these bugs. Infested growing points become stunted and swollen. Heavy clustering of mealybugs can be seen under leaf surface giving the appearance of a thick mat with waxy secretion. They excrete copious amount of honey dew that attracts ants and helps in development of black sooty mould which inhibits the plant's ability to manufacture food.
Management
Crop residues in previously infested fields should be removed and burnt.
Field borders should be free from weeds and debris.
Enhancing the natural enemies’ activities such as coccinellids and blue butterflies ( Spalgius apius ).
Crawler is the most susceptible stage to identify easily to manage the insecticides under field conditions.
Plant protection products are of limited effectiveness against mealybug because of its habit of hiding in crevices, and the waxy covering of its body.
Most granular insecticides are ineffective, therefore systemic insecticides are used to control heavy infestations.
Spray profenophos 50 EC at 2 ml/l (or) dichlorvos 76 EC at 2 ml/ l (or) acephate 75 SP at 2g/lit, chlorpyriphos 20 EC at 2ml/l (or) Imidacloprid 17.8 SL at 0.5 ml/l (or) Thiamethoxam 25 WDG at 0.5 g/l in 2ml/litre of water at 7 days interval.
Plant Protection
Saraswathi Krishi VigyanKendra, Karur, Tamil Nadu
