Western Flower Thrips (Frankliniella occidentalis) is a very common agricultural pest that affects a wide variety of hosts. It can damage fruit and flowers in different ways, depending on the host, and can also vector a variety of plant diseases.

Researchers have developed the Western Flower Thrips growing degree day model, available on the Pest Prophet app, in order to help predict when different life stage events will occur, based on the weather.

Calculating Growing Degree Day Units

The Western Flower Thrips growing degree day model uses a lower threshold of 45F  and an upper threshold of 104Ffor calculating growing degree day units. The growing degree day units can be calculated from daily maximum and minimum temperatures using these thresholds, or by using the Pest Prophet app, which features this model and is easy to set up and use.

Setting the Biofix date

In order to begin growing degree day accumulation, first a “biofix” date must be set which is the first date, after which growing degree day units will begin to accumulate. In the Pest Prophet app, the biofix date can be adjusted for any observed life cycle stages.

For the Western Flower Thrips model, in order to predict the emergence of overwintered thrips, the biofix date should be set to a default of January 1st, for the Northern Hemisphere. Approximately 20 GDD(F) after this biofix date, adult thrips will emerge. Egg hatch will occur at approximately 399 GDD(F) after this biofix date, and the next generation of adults will emerge at approximately 676 GDD(F).

For best results the biofix should be re-adjusted for each generation, based on scouting observations. This will improve accuracy of later crop stage predictions.

Sources:

Stacey and Fellowes. 2002. Temperature and the development rates of thrips: Evidence for a constraint on local adaptation? Eur. J. Entomol. 99:399-404

McDonald, Bale and Walters 1998. Effect of temperature on development of the western flower thrips, F. o. Eur. J. Entomol. 95:301-306

M.-C. Nielsen, D.A.J. Teulon, R. B. Chapman, R. C. Butler, G. M. Drayton, and H. Philipse. 2010. Comparison of Life History Parameters of Two Frankliniella occidentalis (Thysanoptera: Thripidae) Strains in New Zealand Environ. Entomol. 39(2): 303-311