Aphytis melinus is an important insect used for biological control of California Red Scale. Researchers have developed a growing degree day model for Aphytis melinus that can help predict adult emergence timing from eggs and nymphs, in order to improve pest management decisions.

Calculating Growing Degree Days

The Aphytis melinus model uses a lower threshold of 49.5F and an upper threshold of 86F. 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 Aphytis melinus eggs are first observed or introduced to field.

First adult emergence occurs at approximately 407 GDD (F) after the biofix date.

Sources:

Yu, D. S., and R. F. Luck. 1988. Temperature-dependent size and development of California red scale (Homoptera: Diaspididae) and its effect on host availability for the ectoparasitoid, Aphytis melinus DeBach (Hymenoptera: Aphelinidae). Environ. Entomol. 17: 154-161.