Metasiulus occidentalis, also known as Western Predatory Mite, is an important insect used for biological control of spider mites. Researchers have developed a growing degree day model for Metasiulus occidentalis that can help predict adult emergence timing from eggs and nymphs, in order to improve pest management decisions.

Calculating Growing Degree Days

The Metasiulus occidentalis model uses a lower threshold of 48F and upper threshold of 89.6F. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

For this model, the “biofix” date, or date from which to start accumulating growing degree days, should be set to when Metasiulus occidentalis eggs are first observed or introduced to field.

First adult emergence occurs at approximately 430 GDD (F) after the biofix date.

Sources:

Tanigoshi, L. K., S. C. Hoyt, R. W. Browne, and J. A. Logan. 1975. Influence of temperature on population increase of Metaseiulus occidentalis (Acarina: Phytoseiidae). Ann. Ent. Soc. Amer. 68: 979-986.