Thrips are miniscule insects, often measuring less than two millimeters, that cause significant damage to plants in gardens and commercial greenhouses worldwide. These slender, rice-shaped pests locate host plants using a combination of sensory cues, including visual perception, chemical signals, and nutritional requirements. Understanding these attraction mechanisms is the foundation for effective pest control and prevention.
Visual Triggers
Thrips rely heavily on their vision to detect and navigate toward potential hosts. The insects demonstrate a strong attraction to specific wavelengths of light, a trait widely exploited in pest monitoring. They are particularly drawn to colors in the blue (420–470 nm) and yellow (570–590 nm) spectrums. This preference explains why blue and yellow sticky traps are the standard for monitoring thrips populations in greenhouses.
The attraction to these colors often mimics the visual signature of new plant growth. Some species, such as the Western Flower Thrips, also show a strong response to ultraviolet-A (UV-A) light (315–400 nm). The optimal color preference can vary by thrips species, light intensity, and the host plant being sought, with some studies favoring blue and others yellow. Higher reflectivity in attractive colors often increases the number of thrips caught.
Chemical Signals and Scents
Beyond visual cues, thrips use their sense of smell, or olfaction, to pinpoint hosts over longer distances. Plants naturally release a complex blend of airborne Volatile Organic Compounds (VOCs) that function as chemical signals. Thrips interpret certain VOCs, known as kairomones, as indicators of a potential food source.
When a plant is damaged or stressed, it releases a different set of VOCs that can be highly attractive to thrips, signaling an easier feeding opportunity. Specific compounds like butyl butyrate and citronellyl acetate have been identified as attractive to the Western Flower Thrips. These volatile chemicals guide the insects to the source of the scent.
Thrips also communicate using aggregation pheromones, a different class of chemicals. These pheromones are typically produced by adult males and serve to attract both males and females to an established feeding or breeding site. For example, the Western Flower Thrips uses the compound neryl (S)-2-methylbutanoate as its primary aggregation pheromone. This chemical communication encourages a mass influx of thrips to a single location, which is why infestations can rapidly worsen.
Host Plant Preferences
Once thrips are drawn to a plant visually and chemically, their final decision to settle is based on the physical and nutritional quality of the tissue. Thrips feed by piercing plant cells and sucking out the contents, so they naturally prefer plant parts that are easy to penetrate. This leads them to target soft, tender, and actively growing tissue.
New shoots, developing flower buds, and young leaves are particularly attractive because they have thinner cell walls and are rich in accessible nutrients. A primary nutritional draw is nitrogen, which is a limiting nutrient for insect growth and reproduction. Plants with higher concentrations of nitrogen are often more susceptible to thrips infestation and damage.
This preference for nitrogen-rich tissue explains why heavy fertilization, especially with nitrogen-based products, can inadvertently increase a plant’s attractiveness. Encouraging rapid, lush growth creates a more appealing environment for these pests. Focusing on balanced nutrition instead of excessive nitrogen is a practical way to reduce the plant’s susceptibility to thrips damage.