**Flower Thrips** (*Frankliniella* spp., primarily the **Western Flower Thrips** (*F. occidentalis*)) are minute, slender insects that are major global pests in floriculture, greenhouses, and high-value fruit and vegetable crops. They cause damage by piercing the plant tissue (especially tender growing points, flowers, and fruit) and sucking out the cell contents. This feeding leads to cosmetic damage, reduced crop quality, and the transmission of devastating plant viruses, making them particularly difficult and economically important pests.
Taxonomy and Classification
Thrips belong to the order Thysanoptera. They undergo a unique metamorphosis involving two pupal-like resting stages in the soil. The Western Flower Thrips (*F. occidentalis*) is notorious due to its wide host range (hundreds of plants), high reproductive rate, and insecticide resistance, and its ability to vector **Tomato Spotted Wilt Virus (TSWV)**, one of the most damaging plant viruses worldwide.
Physical Description
Adult Flower Thrips are tiny and slender, typically less than $1/20$ inch long.
- **Appearance:** Coloration varies but is often light yellow, brown, or black.
- **Wings:** They possess two pairs of narrow, fringe-like wings (hence “fringe wings”).
- **Damage Sign:**
- **Silvering/Stippling:** Fine, silvery streaks or spots on leaves and flower petals caused by the empty, air-filled plant cells after feeding.
- **Black Dots:** Tiny black droplets of fecal matter (frass) left on the feeding surfaces.
- **Flower Browning/Distortion:** Feeding inside buds prevents flowers from opening properly or causes the petal margins to turn brown.
Distribution and Habitat
Flower Thrips, particularly the Western Flower Thrips, are cosmopolitan. Their habitat is diverse, including field crops, ornamentals, and especially protected environments like greenhouses and high tunnels, where populations build up quickly. They prefer to feed and shelter in concealed areas, such as the axils of leaves, under sepals, and deep inside flower buds.
Behavior and Damage
Thrips have a rapid life cycle, completing a generation in as little as two weeks in warm conditions, leading to large, overlapping populations. Females insert their eggs into the soft plant tissue.
Damage is significant, both physical and pathological:
- **Cosmetic Damage:** Feeding on flower petals, especially on light-colored flowers (roses, orchids), causes unsightly white or silver streaking, severely reducing market value.
- **Fruit Scarring:** Feeding on the surfaces of developing fruits (e.g., citrus, strawberries) leads to scarring and corking.
- **Virus Transmission (Pathological):** Thrips transmit TSWV and other tospoviruses. The virus is acquired by the larval stage and transmitted by the adult, leading to severe, often fatal, systemic plant disease.
Management and Prevention
Control requires integrated, aggressive management, especially in greenhouse environments.
- **Monitoring:** Use **blue or yellow sticky traps** placed vertically near the plants to monitor adult populations. Early detection is critical.
- **Biological Control:** Release predatory mites (*Amblyseius* spp. or *Neoseiulus* spp.) or minute pirate bugs (*Orius* spp.) which are highly effective predators of thrips nymphs and adults.
- **Cultural Control:** Remove weeds and old plant debris, which can harbor thrips and TSWV. Prune and destroy infested buds and flowers.
- **Chemical Control:** Due to resistance, chemicals must be rotated. Systemic insecticides or contact sprays (spinosad, entomopathogenic fungi, or horticultural oil) applied thoroughly to reach hidden pests are used, often targeting the nymph stage in the soil.
Conservation and Research
Flower Thrips are high-priority targets in integrated pest management (IPM) research. Efforts focus on developing new biological controls, improving the efficacy of soil-applied treatments against the pupal stage, and finding plant varieties that are genetically resistant to both the thrips and the viruses they vector.