Western Flower Thrips (Part 1)

July 3, 2023
2 mins
Sam Rivers

Why is WFT such a challenging pest?

With Western Flower Thrip (WFT) pressure starting to increase, ICL technical manager for controls Sam Rivers shines a spotlight on this serious widespread pest.   

In part 1 he explores the life cycle, symptoms to look out for and what makes this such a challenging pest to control.  In part 2, Sam explains how Mainspring, with its unique mode of action, can play an important part in managing resistance build-up on your nursery.

Once notifiable

One of the most serious pests in protected ornamentals, Western flower Thrips (WFT) can feed on a wide variety of plants including Chrysanthemums, Fuchsias and Primulas. Once considered a notifiable pest, this is no longer the case as they are widespread throughout the UK.

Weakens plants & secondary diseases

WFT cause damage by piercing plant tissue cells and sucking out their contents; this causes necrosis of the surrounding tissue and mottling – which can be silver/grey in colour. While this damage impacts on the plants photosynthetic ability, resulting in a weaker plant, the wounding paves the way for secondary plant diseases, such as botrytis.

Serious virus vector

Thrips are also a vector for the tomato spotted wilt virus and Impatiens necrotic spot virus. Affecting a wide range of plants, these two serious viruses can ultimately lead to plant death.

Rapid lifecycle

WFT issues are often seen in protected environments, especially heated glasshouses. Capable of breeding year-round, when temperatures are 10-30°C, the adult females can survive outside through winter, hiding in various places on the nursery.

A major reason for the success of this pest is its rapid lifecycle, taking just 11 days from egg to adult.  Producing many generations per year, WFT can quickly build-up resistance to a wide range of control products. This makes it important to have a robust IPM plan in place to help control the population.

Hungry larvae

In terms of the lifecycle, the eggs are typically not visible.  Female WFT lay their eggs into the plant tissue, where they hatch into larvae. There are two instar/development stages; the first larval stage is very small and colourless and consumes plant tissue for a few days, depending on the environmental conditions; the second instar larval stage is small and yellow and lasts up to 10 days, depending on temperature.

The larvae then generally drop to the ground and pupate in the growing media – although some may pupate on the plant itself. The two non-feeding pupal stages last approximately 6-8 days in total, depending on temperature, before the adults begin to emerge.

Adults hide away

Compared to males, the female adults are slightly larger and darker in colour.  While the adults can be found on the leaf surface, they prefer to feed hidden away in flowers or buds (if present). This can make WFT challenging to target.  A characteristic sign of thrip infestation is the presence of black ‘frass’ (insect excrement) around damage sites.