Galerucella calmariensis, also known as the Black-margined Loosestrife Beetle, is an important insect used for biological control of weeds in the loosestrife family. Their reproduction is regulated in part by photo-period, with adult males emitting mating pheromones only under long day conditions. Researchers have developed a growing degree day model for Galerucella calmariensis that can help predict egg-laying of overwintered adults and timing of the following generations, and to predict the timing of when the beetles are susceptible to photo-period.

Calculating Growing Degree Days

The Galerucella calmariensis model uses a lower threshold of 50F and an upper threshold of 100F. 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 Jan. 1st for the Northern Hemisphere.

Spring egg-laying begins at approximately 180 GDD(F) and peaks at 461 GDD (F). Peak larvae of next generation occurs at 755 GDD(F). Peak of adult stage of the next generation occurs at approximately 1616 GDD (F) after the biofix date, this stage is susceptible to photo-period. The model can then be used to predict adult emergence for the next 2-3 generations in a season.

Sources:

McAvoy, T.J. and L.T. Kok. 2004. Temperature dependent development and survival of two sympatric species, Galerucella calmariensis and G. pusilla, on purple loosestrife. BioControl 49:467-480.,

McAvoy, T.J., L.T. Kok, and W.T. Mays. 1997. Phenology of an Established Population of Galerucella calmariensis (L.) and G. pusilla (Duft.) (Coleoptera: Chrysomelidae) on Purple Loosestrife, Lythrum salicaria L. (Lythraceae), in Southwest Virginia. Biological Control 9:106-111.],