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The effects of thermal waves on the biology and immune function of the cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae)

Zienab E. Alshabka, Elsaied A. Naiem, Noha A. Dabour, Amal I. Seif, Wesam S. Meshrif.


Abstract

The climatic changes have been more frequent, thus modern studies focus on examining the biological responses of life forms to thermal waves either cold or hot. Temperature is one of the most important environmental factors affecting the performance and life history of insects. Therefore, this study aimed to investigate the changes occurring in the pest, Spodoptera littoralis after exposure to 5-day thermal waves defined as cold (15°C) and hot (35°C), whereas 25°C was used as (normal) control temperature. Newly emerged adults were used to estimate fecundity, survival and egg hatchability. Third instar larvae were used to assess the effects of thermal waves on the immune function (protein content and phenoloxidase activity) and the susceptibility to infection with potent entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae. The results showed that S. littoralis females experienced cold or hot wave showed less fecundity and egg hatchability as compared to those in the control temperature. Moreover, hot-wave induced shorter longevity, while cold-wave induced longer adult female longevity. The larvae exposed to thermal waves showed contrasting haemolymph protein contents, but lower phenoloxidase activity than those in the control temperature. Exposure of the fungus-infected larvae to thermal waves was able to affect the percentage mortality and time to death. In more details, particularly, exposure to the cold wave induced longer mortality time and lower percentage mortality than those in the control temperature. These results may enhance our understanding of the effect of climatic changes on the biology of S. littoralis and its control programs.

Key words: Climate changes, infection, pest & phenoloxidase.






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