Our new phenology plotting feature allows you to interactively produce a current/historical development plot for an insect species of your choice using weather data from any US zipcode.
For many organisms, temperature has a significant influence on phenology— the timing of important life events in the natural world (e.g. bird migrations, trees budding, and juvenile insects reaching adulthood). Phenological shifts— interannual changes in the timing of phenological events— have been among the most apparent signatures of climate change. Many phenological events such as the emergence of plants and insects depend on how fast they develop. For example, seeds often require spring temperatures to reach a certain threshold to sprout and begin growing. The plant will develop more rapidly when temperatures exceed the threshold for longer durations and by more degrees, so warm springs accelerate phenology. Insect herbivores often have different developmental constraints than the plants they feed on, so warm seasons can differentially accelerate the phenology of the plants and insects resulting in a phenological mismatch that changes the strength of their interaction. Using insect developmental constraints to predict phenology can inform management decisions such as when to plant crops and when to deploy herbivore or pest control strategies.
The activity and life cycle of insects is highly dependent on temperature. Many insect eggs are laid in the summer and they begin to develop. The insects often spend the winter as eggs or juvenile stages in a state of dormancy termed diapause. Diapause ends and development resumes once spring temperatures exceed their lower developmental threshold (T0,°C).
Development rates can be reasonably approximated by how many heat units an insect accumulates. The rate of development each day is determined by the number of degrees by which temperatures exceed T0, which is referred to as degree days. The insect reaches adulthood once it acquires a sufficient number of degree day heat units, which is referred to as the growing degree days required (G, °C).
Developmental traits (T0 and G) have been estimated for many insect populations by raising them in laboratories at a range of temperatures. Here we use a compilation of development traits for 1493 observations of 682 species to predict phenological timing. We provide two ways of exploring insect phenology:
Note concerning observation plots: The simplifying assumption that offspring are immediately produced upon the emergence of new adults was made, allowing for multiple generations per year. When accumulated degree days equals G, one generation reaches adulthood and the accumulated degree days are reset to 0. This marks the beginning of a new generation. A custom generational lag can be specified below the plot. This is not the case for the phenophase heatmap, which displays phenology for one generation each year.
Note concerning pieris rapae heatmap: The USA National Phenology Network Nature's Notebook Program features observational data of many plant and insect populations' pheology. The NPN database, features P. rapae as an insect species with many historical phenophase obervations around the USA. Observations within 30 days of the current layer date are presented for P. rapae as an additional (optional) layer of colored, clickable markers, and displayed when P. rapae is selected for visualization on the heatmap.
Weather data: We use daily weather data sourced from the two weather stations nearest to an observaton within NOAA's Global Historical Climatology Network (R Package: RNOAA) to create phenology plots and The Climatology Lab's gridMET dataset (R Package: climateR), which features daily, gridded weather data at 4km spatial resolution to produce phenology heatmaps.
Degree day calculation: We use a function for calculating degree days available from the TrenchR package. The TrenchR package's degree day function combines species-specific baseline developmental temperatures with daily temperature minima (T_min) and maxima (T_max) to calculate the GDDs accumulated in a 24 hour period:
TrenchR::degree_days(T_min, T_max, T_0 = NA, T_upper = NA, method = "single.sine")
T0 (°C) - The lower developmental threshold is the minimum temperature required for development to occur, above which an organism is likely to progress forward in development.
Tupper (°C) - The upper developmental threshold is the upper temperature above which an organism will not be able to develop. In practice, this value is likely greater than any temperature the species will encounter during spring development in the United States. Therefore, in this visualization the simplifying assumption that organisms will not actually encounter this temperature was made.
method - The approximation technique used to calculate temperature throughout the day. The single.sine method assumes the temperature curve is normally distributed around the maximum temperature.
The threshold amount of degree days that must be accumulated for an insect egg to reach adulthood is defined as the growing degree days required (G).