The Asian Citrus Psyllid (Diaphorina citri) is a major pest on citrus in many regions. It can damage leaves with its feeding and can also be a carrier for bacterium that causes Huanglongbing (HLB) disease, also known as citrus greening disease. After overwintering, they gather on newly formed citrus leaf buds where they feed and mate. Researchers have developed a growing degree day model for Asian Citrus Psyllid to help predict when overwintered adults will lay eggs, when nymphs will emerge, and when subsequent generations will happen.

Calculating Growing Degree Day Units

The Asian Citrus Psyllid growing degree day model uses a lower threshold of 52F and an upper threshold of 90F for 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 Asian Citrus Psyllid model, the biofix date should be set when the first leaf flush is observed. Approximately 630 GDD(F) after the biofix date (when eggs are observed), first overwintering adult egg-laying will begin with the peak at 990 GDD(F). At approximately 1260 GDD(F) after the biofix date, the peak of F1 nymphs will be observed. At approximately 2034 GDD (C) the next generation of adults will be at peak egg-laying. Subsequent generations can also be predicted using the model, up to the F7 generation.

Sources:

Liu, Y.H., and J.H. Tsai. 2000. Effects of temperature on biology and life table parameters of the Asian citrus psyllid, Diaphorina citri Kuwayama (Homoptera: Psyllidae). Ann. Appl. Biol 137:201-206.