Effects of temperature on the fitness of the alfalfa weevil ( Hypera postica )

Temperature directly influences the survival, development and reproduction of insects and limits their biological activity. The alfalfa weevil (Hypera postica Gyllenhal) is a destructive pest of alfalfa crops in Spain and in most of the alfalfa pro- duction countries. The knowledge of how temperature affects the fitness of this pest can be used to predict its activity in current or forecasted environmental conditions and to develop more accurate control strategies. Results: We evaluated the fitness of alfalfa weevil at eight constant temperatures (8–36 °C) at 4 °C intervals by using life tables and models for the description of temperature-dependent development rates. We found that most of the parameters we stud- ied were temperature dependent. Development was observed at all temperatures. However, postembryonic survival was opti- mal at 16 °C but very low at 36 °C. Adults did not reproduce at 8, 32 or 36 °C. The highest fecundity and net reproductive rate were observed at 20 °C, but the highest intrinsic rate of increase occurred at 24 °C. We predicted the phenology of the pest based on the heat needed for development, the cumulative degree days from the beginning of October to the end of May, and the day length in the study region. Conclusion: Our prediction was validated using field data reporting the first occurrence of larval instars and adults, revealing that no more than two generations are possible within an annual cycle. In a hypothetical case where average monthly temper- atures increase by 1–2 °C, the number of generations would not change. We thank Aldahra Europe, Cooperative of Bellvís, Cooperative of Bell-lloc, Granja San José, Osés-Nafosa Group and Josep Piqué for allowing us to use their alfalfa commercial fields for the study. We also thank Marta Franch and Dr. Addy García for technical sup- port. We would like to thank Dr. Richard Twyman for English edit- ing and revision. Special thanks to Prof. Dr. Hsin Chi for helping us using TWOSEX life table software and for his comments to the manuscript. This project was funded by the Ministerio de Ciencia e Innovación of the Spanish Government (project AGL2017-84127-R). A.L-M. was funded by a Jade Plus Grant from the Universitat de Lleida and R.M. was funded by an FPI Grant from the Ministerio de Ciencia e Innovación of the Spanish Government. info:eu-repo/semantics/publishedVersion