Common Name: Onion thrips
Scientific Name: Thrips tabaci Lindeman
Description: Adult females have slender, yellowish, 1/25 inch-long bodies with hair-fringed wings held over their backs when at rest. The legs end in a small “bladder”, not claws. Nymphal stages are similar to adults but do not have fully developed wings.
Life Cycle: They are parthenogenetic. Adult females and nymphs occur throughout the year on and around host plants. Wingless males are rare. Females can reproduce without mating (parthenogenesis), thrusting bean shaped eggs completely into leaf and stem tissue. Nymphs, hatching from eggs 5 to 10 days later, develop through four stages (instars) including two larval instars, a prepupal and a pupal stage, over a period of 15 to 30 days. The first two instars are spend on the host plant and the later non-feeding stages are spent in the soil. Up to eight generations can occur annually.
Habitat and Food Source(s): Mouthparts are for rasping or piercing-sucking. Although this species is particularly common on onion leaves, they will feed on many other cultivated (vegetable and field crops) and wild (weed) plants. Adults and immature forms use their single sword-like mandible to rupture plant cells on the outer surface of leaves and other plant parts, and then suck out the contents by pressing their mouthparts onto the damaged surface. Winged adult thrips can be attracted to yellow sticky traps. Adults and nymphs can be beaten onto off-white cards from host plants (particularly from wild flowers).
Pest Status: One of the most commonly encountered thrips in the home garden, particularly on onion leaves where feeding activities cause silver streaking. Adult and nymphal thrips can “bite” by piercing the skin with their sword-like mouthpart (mandible). Flying adults occasionally invade dwellings through screens or open windows, biting the occupants. Although irritating, bites are usually not serious and involves no venom.
Damage: Feeding activities produce silver or whitish streaks or blotches on leaves. Injured young, expanding leaves become distorted. Severely injured leaves and plants may turn brown and die. Onion bulb growth can be distorted and diminished. Injury is most severe during dry seasons.
Literature: Metcalf et al. 1962.