The gypsy moth (Lymantria dispar) is one of the most widespread and devastating pests of forests in the United States and other areas. Gypsy moth eggs usually begin to hatch in spring. The larval stage follows and lasts about 7 weeks before pupation begins.  Adults emerge later in summer.

Researchers have developed Growing Degree Day Models for both predicting egg hatch, and for predicting later life cycles. These two models have combined into the Gypsy Moth Growing Degree Day Model, available on the Pest Prophet app. This app can be used to predict life cycle stages, which can be used to direct management decisions, such as larvae or egg targeting insecticide treatment timing.

Predicting Egg Hatch

To properly use the model, the biofix must first be set. For predicting egg hatch, a default date of January 1st is recommended for the Northern Hemisphere. At this stage a lower threshold of 37.4 F should be used to calculate growing degree day accumulation. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. After approximately 509 GDD(F) egg hatch will begin.

Predicting Later Life Cycle stages

For best results in predicting later crop stages, the biofix should be reset after egg hatch and larvae are observed. After this stage, a lower threshold of 45.8F and an upper threshold of 106F should be used. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app.  This app can be used to predict the emergence of different larval instars, pupation and adult emergence.

Source:

Johnson, P. C., D. P. Mason, S. L. Radke, and K. T. Tracewski. 1983. Gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), egg eclosion: degree-day accumulations. Environ. Entomol. 12: 929-932.

Carter, M. R., F. W. Ravlin, and M. L. McManus. 1992. Effect of defoliation on gypsy moth phenology and capture of male moths in pheromone-baited traps. Environ. Entomol. 21: 1308-1318.