Cotton Aphid

This pest is distributed all over the country (W. Bengal, Assam, Orissa, Bihar, U.P, Haryana, Punjab, Madhya Pradesh, Gujarat, Maharashtra, Rajasthan, Andhra Pradesh, Tamil Nadu etc). Alternate hosts are Hibiscus spp. and cucurbitaceae.

Appearance:

Aphids are small soft bodied insects with a pair of cornicles, present on the 6th abdominal segment. Nymphs are light yellowish green, or greenish black or brownish. Adults are mostly wingless, but few winged forms can also be seen with thin transparent wings.

Aphis gossypii  (Glover), Aphididae: Homoptera , Kannada name: Henu                                                                                                                                                                                                                                                   

                   Nymphs                                                             Adult

Life cycle:

Females directly produce young ones which mature in about a week, hence population build up is quite fast. Alate and apterous forms multiply parthenogenetically and viviparously and give birth to 8 –22/ day and become adult in 4-7 days. The nymphs moult four times to become adult completing the life cycle in 8-10 days.

              Life Cycle

Nature of damage:

Nymphs and adults colonize on the undersurface of the young leaves or on shoots.Besides sucking the sap from plant they secrete honey dew on which sooty mold develops causing interference to photosynthesis.

                  Aphids on Leaves & Shoots

Damage symptoms:

Curling and crinkling of leaves, Leaves appear shiny and sticky due to honey dew excreted by the insects. Later, sooty mold grows on honey dew and leaves have a black coating and Stunted growth.

 Curling and crinkling of leaves,                       Sooty mold development                Black coating on leaves

Factors responsible for incidence:

Cool weather and humid conditions favour multiplication, while heavy rains wash away the aphid colonies. A dry weather with prolonged drought favors the fast build up of this pest. Outbreaks are common on young plants in spells of dry weather which clear up rapidly on the onset of rain. In contrast to many taxa, species diversity is much lower in the tropics than in the temperate zones. They can migrate great distances, mainly through passive dispersal by riding on winds.