Effect of heat waves on embryo mortality in the pine processionary moth

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 processionary moth Thaumetopoea pityocampa is a Mediterranean pine defoliator, which typically 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 threshold. At high mean temperatures (40°C), significant differences were observed between populations and between DT and CT regimes. Heat waves further increased embryo development time. The knowledge we gained about the upper lethal temperature to embryos of this species will permit better prediction of the potential expansion of this insect under different climate warming scenarios.

Deciphering the demographic history of allochronic differentiation in the pine processionary moth Thaumetopoea pityocampa

“…Interestingly, a period of colder climate known as the Little Ice Age occurred between years 1300 and 1900, including in Portugal, bringing favourable climatic conditions (Abrantes et al., ; Bartels‐Jónsdóttir, Knudsen, Abrantes, Lebreiro, & Eiríksson, ). Other phenotypic trait divergences between the SP and the WP were documented, with obvious adaptations to the environmental changes experienced by the SP eggs and larvae due to the shift in breeding time (Rocha et al., ; Santos, Paiva, Rocha, Kerdelhué, & Branco, ; Santos, Paiva, et al., ), consistent with the concept of “adaptation by time” proposed by Hendry and Day (). Whether such phenotypic changes occurred over ca.…”

“…An alternative approach could be QTL‐mapping, which has proved to be a successful strategy in a number of studies (e.g., Alem et al., ; Franchini et al., ). It is however expected to be tedious in the particular example of the pine processionary moth for which rearing in experimental conditions is a difficult task due to a high mortality, the urticating nature of its larvae and the obligate 1‐year generation time (Berardi, Branco, Paiva, Santos, & Battisti, ; Branco et al., ; Rocha et al., ).…”

Evidence of potential hybridization in the Thaumetopoea pityocampa‐wilkinsoni complex

“…pityocampa (Pimentel et al ., ; Zamoum et al ., ) and in a phenologically‐shifted population of Th. pityocampa in Portugal (Rocha et al ., ). Although our representative populations originated from different latitudes, the weight of hybrid neonate larvae, which can be taken as a proxy of body and egg size, was higher in the WW pure line and the WP hybrid line than in the PP pure line, whereas the other hybrid PW showed an intermediate value.…”

Shifted phenology in the pine processionary moth affects the outcome of tree–insect interaction

“…1), all contributing to plant drought stress, whereas WP larvae feed during fall and winter, when the tree's physiological parameters are supposed to be less stressed. Previous studies demonstrated that the SP has already undergone some ecological divergences in relation to the WP, namely regarding the upper thermal tolerance limits of the larvae (Santos et al ., 2011 b ) and of the eggs (Rocha et al ., 2017), as well as some reproductive traits, such as fecundity and egg size (Santos et al ., 2013). Also, SP larvae had a faster development than WP, with more larvae reaching the 3 rd instar in both treatments.…”