Papaya

Insect Management

Introduction

  • Papaya is not a preferred host for many species of insects, however 35 insects have been reported infesting it.
  • Of these, only four are found to be the major pests, 15 as minor pests and 16 as occasional pests.
  • Of these only a few, however, are destructive pests. Mites and spiral whiteflies are among the most serious pests of papaya.
  • Because of their small size, mostly less than of 1/20 cm in length, the presence of mites on papaya often escapes detection until these pests multiply in abundance and start damaging the plant.
  • Usually they multiply on weeds and when the weeds begin to dry up, they migrate in mass on to papaya.
  • Older plants are able to tolerate a fair number of them, however, young plants immediately after being transplanted can be severely damaged unless control measure is instituted properly.
  • It is important to recognize the different pests as soon as possible so that the possible control measures can be instituted against them.

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Aphids

Scientific name:
Green peach aphid - Myzus periscae Sulzei
Cotton aphid - Aphis gossypii Glover
Cowpea aphid - Aphis craccirorakoch


Biology

  • Aphids are soft-bodied insects of 20 to 30 mm long having long antennae and legs.
  • They may be green, yellow or black in colour with and without wings.
  • An unfertilized female aphid can produce 60 to 100 nymphs in a life span of about a month.
  • The nymphs mature and become adult in about a week.
  • Aphids are one of the minor pests of papaya causing damage to the plant by way of sucking the juice with their piercing-sucking mouth parts.
  • They feed on the undersurface of leaves and cause them to become curled and crinkled.
  • The petioles of heavily infested leaves generally droop downward.
  • They also secrete honeydew which attracts ants and thereby promote the growth of sooty mould on the papaya plant.
  • Besides causing direct damage to the papaya plants by feeding on them, some of the aphids have been reported to be the vector of virus diseases.
  • The papaya ring spot is reported to be transmitted by green peach aphid (Mysus persicae Sulzei) cotton aphid (Aphis gossypii Glover) and the cowpea aphid (Aphis craccivorakoch).
  • In recent years green peach aphid has been shown to be the vector of papaya mosaic virus.

Management

  • Control the aphids to a large extent by way of keeping the papaya orchard relatively free of weeds.
  • In case of severe attacks, spray methyl demeton 25 EC 2 ml/lit. or dimethoate 30 EC 2ml/lit.

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Scale Insects and Mealy Bugs

  • The scale insects and mealy bugs are not serious pests of papaya.
  • However, sporadic incidence of papaya plants infested with such insects have been noticed in papaya growing regions of the world.

Biology

  • On hatching, the young larvae move around the stem and leaf surfaces until they find a suitable place for settling.
  • Once settled, the larvae pierce the plant tissues with their thread like parts and start sucking the sap.
  • Since the adult insects are immobile, dispersal of first instar larvae from one plant to another or from one part of the plant to the other is caused by external agencies.
  • They are carried by wind as well as by physical contamination with ants, caterpillars, cattle and human beings.
  • Birds are also known to carry these insects from one place to another.

Scale insect

  • Armoured scale - Aonidiella orientalis Duration of the life cycle is variable between 25 and 70 days.

Management

  • Control the scale insects and mealy bugs on stem and leaves effectively by spraying Malathion 50 EC 4 ml dissolved in one litre of water (or) Methyl demeton 25 EC 2 ml/litre.

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Thrips

Scientific name:Thrips tabasi Lindeman

Biology

  • Thrips are small slender insects of about 10 mm long.
  • The adults are yellowish.
  • The immature stages, which include two nymphal (instar form) and two resting stages.
  • The eggs are white and beanshaped are laid into the plant tissue.
  • Its complete life cycle is of about 3 weeks. Onion thrips (Thrips tabaci Lindeman) is a minor pest of papaya.
  • The injury to papaya plant by thrips is caused by way of scarifying the leaf surface and sucking the liberated juices.
  • The thrips affected leaves when young, become distorted and show silvery, whitish sunken areas on their surface.

Management

  • Spray methyldemeton 25 EC 2 ml/litre.

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