Modeling egg development of the pest Clavipalpus ursinus (Coleoptera: Melolonthidae) using a temperature-dependent approach

Predicting the population dynamics of insects in natural conditions is essential for their management or preservation, and temperature-dependent development models contribute to achieving this. In this research the effects of temperature and soil moisture content on egg development and hatching of Clavipalpus ursinus (Blanchard) were evaluated. The eggs were exposed to seven temperature treatments with averages of 7.2, 13.0, 15.5, 19.7, 20.6, 22.0 and 25.3 degrees C, in combination with three soil moisture contents of 40%, 60% and 80%. A linear and two non-linear (Lactin and Briere) models were evaluated in order to determine the thermal requirements of this developmental stage. Temperature affected significantly the time of development and egg hatching, while no significant effect was observed for moisture content. Thermal requirements were set as: 7.2 degrees C for lower developmental threshold, 20.6 degrees C for optimum developmental threshold, 25.3 degrees C for maximum temperature and 344.83 degree-days for the thermal constant. The linear model described satisfactorily egg development at intermediate temperatures; nevertheless, a slightly better fit of the observed data was obtained with the Lactin model. Egg development took place inside a narrow range of temperatures. Consequently, an increment of soil temperature could generate a negative impact on the population size of this species or changes in its biological parameters.