Insects and other arthropods respond to environmental conditions such as rainfall and temperature. Cerain species such as chinch bugs and grass hoppers are favored by hot, dry weather patterns while others such as mosquitoes are favored by wet conditions. Collecting efforts during these favorable periods will assure a higher probability of success.
Seasonality, phenology and degree day models
Insects and their relatives are cold-blooded animals with simple to complicated life cycles. Developmental rates are dependent upon temperature conditions through with development occurs, with higher optimum temperatures speeding up development. Depending on species, development can take days (e.g., aphids) to years (e.g. periodical cicada). Certain developmental stages, such as adults, often occur during specific parts of the year. Knowing when to search for insect developmental stages (i.e., being there at the right time) is critical knowledge for the collector.
One way to predict insect occurrence is by calendar dates when species have occurred historically. This information can often be obtained from colleagues, field notes or by visiting insect collections and studying collection data provided on specimen labels. More specifically, some insects are active only during certain times of the day. Those active during daylight like butterflies are said to have diurnal activity. Those active only at night, such as most species of moths, are nocturnal. Some insects such as mosquitoes are mostly active at dusk or dawn. This activity pattern is called crepuscular.
Because developmental times of both plants and arthropods are driven by temperature conditions, biologists and entomologists have made an attempt to correlate visible events such as the flowering of certain plants to the occurrence of certain stages of insects and their relatives. This field of study is called phenology. In Texas, few correlations have been made to date. This is an area where valuable contributions by amateur collectors and naturalists can be made by collecting and recording field observations. Such information is valueable when trying to manage arthropod pests such as scale insects, using information correlating the hatching of eggs into crawler stages related to flowering ornamental plants to time insecticide applications.
Computer scientists have developed software models that uses minimum and maximum daily temperatures available from meteorologists to mathematically predict the occurrence of specific insects, particularly pest insects. These models are called Degree Day Models (sometimes also called heat unit models or phenology models with slight differences in definition). In practice, however, the computer predicted events require confirmation by field observations to assure that any control tactics made are justified by actual pest occurrence.