Thrips Egg - Eggs are usually white, bean-shaped, and approximately 0.2 mm long.
Larva - The wingless larvae are usually white or yellow and approximately 0.25 mm long. There are two larval instars.
Prepupa and Pupa - Pupal stages resemble larvae in shape and color. Prepupa have short wing pads and pupae have long wing pads. Pupae usually remain motionless unless disturbed.
Host plants - The respective host range of each thrips species found on cotton is too extensive to list here. Most field, vegetable, flower, and orchard crops are attacked by at least one thrip species. Several trees and weedy plants are commonly infested also.
Damage - Thrips cause most damage to seedling cotton. They rasp tender leaves and terminal buds with their sharp mouthparts and feed on the escaping juices. Leaves may turn brown on the edges, develop a silvery color, or may become distorted and curl upward. This damage may be confused with aphid injury (aphids cause leaves to curl downward). Light thrips infestations tend to delay plant growth and retard maturity. Heavy infestations may kill terminal buds or even entire plants. Damaged terminal buds result in abnormal branching patterns.
The duration and intensity of thrips infestations vary greatly according to season and geographic location. Once cotton plants are 4 to 6 weeks old, they usually outgrow thrips damage and begin to recover. In most areas, plants recover and suffer no yield loss. However, if late infestation persists, plant maturity may be delayed with resulting yield loss.
Life history - In North Carolina, thrips overwinter as hibernating adults in sheltered areas, as larvae on plants, or as pupae in the soil. They resume development in the spring. Winged adult thrips emerge and fly in search of suitable host plants. Depending on the particular species, each female may produce 10 to 100 eggs which she inserts singly into tender plant tissue. About 4 days later, eggs hatch. The larvae usually feed for approximately 6 days before pupating in the soil. Approximately 4 days later, new adults emerge which soon feed and lay eggs. Although the winged adults are weak fliers, they are capable of flying from plant to plant and may be carried long distances by wind. Most thrips species complete five or more generations per year in North Carolina.
