Effect of heat waves on embryo mortality in the pine processionary moth S. Rocha 1 *, C. Kerdelhué 2 , M.L. Ben Jamaa 3 , S. Dhahri 3 , C. Burban 4 and M. Branco 1 1 Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa, 1349-017, Lisboa, Portugal: 2 INRA Centre de Montpellier, UMR CBGP, F-34988, Montferrier-sur-Lez cedex, France: 3 Université de Carthage, INRGREF, BP 10-2080 Ariana, Tunisie: 4 BIOGECO, INRA, Université de Bordeaux, 33610 Cestas, France Abstract Extreme climate events such as heat waves are predicted to become more frequent with climate change, representing a challenge for many organisms. The pine proces- sionary moth Thaumetopoea pityocampa is a Mediterranean pine defoliator, which typ- ically lays eggs during the summer. We evaluated the effects of heat waves on egg mortality of three populations with different phenologies: a Portuguese population with a classical life cycle (eggs laid in summer), an allochronic Portuguese population reproducing in spring, and a Tunisian population from the extreme southern limit of T. pityocampa distribution range, in which eggs are laid in fall. We tested the influence of three consecutive hot days on egg survival and development time, using either constant (CT) or daily cycling temperatures (DT) with equivalent mean temperatures. Maximum temperatures (T max ) used in the experiment ranged from 36 to 48°C for DT and from 30 to 42°C for CT. Heat waves had a severe negative effect on egg survival when T max reached 42°C for all populations. No embryo survived above this thresh- old. At high mean temperatures (40°C), significant differences were observed be- tween populations and between DT and CT regimes. Heat waves further increased embryo development time. The knowledge we gained about the upper lethal tem- perature to embryos of this species will permit better prediction of the potential ex- pansion of this insect under different climate warming scenarios. Keywords: climate change, temperature, heat wave, egg tolerance, Thaumetopoea pityocampa (Accepted 3 January 2017) Introduction During the decade of 2002–2011, the global mean surface temperature was 0.77 to 0.80°C warmer than the pre-industrial average; in Europe, the increase reached 1.3°C in terrestrial areas (EEA, 2012). Climatic models predict that global warm- ing will continue in the coming decades. The mean global temperature is projected to increase by 1.1–6.4°C by 2100, while mean temperatures in Europe are expected to rise by 2.5–4.0°C for the same period (EEA, 2012). Models also predict increased weather variability and increased severity and fre- quency of extreme weather events such as heat waves, droughts and extreme precipitation (EEA, 2012; IPCC, 2014). These climatic events can have major effects on many organ- isms. In particular, increasing temperatures are likely to affect the behaviour, development, reproduction, survival and geo- graphical distribution of ectothermic organisms, as their physiological processes are highly dependent on ambient tem- peratures (Bale et al., 2002; Menéndez, 2007). While an increase in temperature within a favourable range will tend to speed up their metabolism and development, an increase above the op- timal threshold will reduce survival or fitness, due to the dis- ruption of metabolic functions (Bale et al., 2002; Chiu et al., 2015). Further, the response of insects to climate depends on the developmental stage and phenology (i.e. the timing of *Author for correspondence Phone: +351 213653382 Fax: +351 213653388 E-mail: scm.rocha@gmail.com Bulletin of Entomological Research, Page 1 of 9 doi:10.1017/S0007485317000104 © Cambridge University Press 2017 https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0007485317000104 Downloaded from https:/www.cambridge.org/core. INRA - Versailles-Grignon, on 15 Feb 2017 at 08:31:12, subject to the Cambridge Core terms of use, available at