Voria ruralis, is a fly that is an important insect used for biological control of Cabbage Looper. Researchers have developed a growing degree day model for Voria ruralis that can help predict adult emergence timing from eggs and nymphs, in order to improve pest management decisions.

Calculating Growing Degree Days

The Voria ruralis model uses a lower threshold of 45.5F. 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 Voria ruralis eggs are first observed or introduced to field.

Pupation begins at approximately 227 GDD(F). First adult emergence occurs at approximately 425 GDD (F) after the biofix date.

Sources:

Jackson, C. G., G. D. Butler, Jr., and D. E. Bryan. 1969. Time required for development of Voria ruralis and its host, the cabbage looper, at different temperatures. J. Econ. Entomol. 62: 69-70.