Are heat waves susceptible to mitigate the expansion of a species progressing with global warming?

Abstract

A number of organisms, especially insects, are extending their range in response of the increasing trend of warmer temperatures. However, the effects of more frequent climatic anomalies on these species are not clearly known. The pine processionary moth, Thaumetopoea pityocampa, is a forest pest that is currently extending its geographical distribution in Europe in response to climate warming. However, its population density largely decreased in its northern expansion range (near Paris, France) the year following the 2003 heat wave. In this study, we tested whether the 2003 heat wave could have killed a large part of egg masses. First, the local heat wave intensity was determined. Then, an outdoor experiment was conducted to measure the deviation between the temperatures recorded by weather stations and those observed within sun-exposed egg masses. A second experiment was conducted under laboratory conditions to simulate heat wave conditions (with night/day temperatures of 20/32°C and 20/40°C compared to the control treatment 13/20°C) and measure the potential effects of this heat wave on egg masses. No effects were noticed on egg development. Then, larvae hatched from these egg masses were reared under mild conditions until the third instar and no delayed effects on the development of larvae were found. Instead of eggs, the 2003 heat wave had probably affected directly or indirectly the young larvae that were already hatched when it occurred. Our results suggest that the effects of extreme climatic anomalies occurring over narrow time windows are difficult to determine because they strongly depend on the life stage of the species exposed to these anomalies. However, these effects could potentially reduce or enhance the average warming effects. As extreme weather conditions are predicted to become more frequent in the future, it is necessary to disentangle the effects of the warming trend from the effects of climatic anomalies when predicting the response of a species to climate change.

Mass‐trapping trials for the control of pine processionary moth in a pine woodland recreational area

“…The pine processionary moth, Thaumetopoea pityocampa (Denis and Shiffermüller, 1775), is considered the most important insect defoliator of pine forests and woodlands in central‐southern Europe and North Africa in terms of its temporal occurrence, geographic range and socioeconomic impact (Jactel et al, ; Robinet, Rousselet, Pineau, Miard, & Roques, ).…”

“…The range expansion of this moth is acknowledged to be directly associated with climate warming, as the feeding activity and survival of the larvae are favoured by the trend for higher winter temperatures that has been observed in central Europe (Robinet et al, ). The temperature increase due to global climate warming favours the expansion of T. pityocampa into regions where it could not develop previously (like France, Switzerland, Austria, Germany and England) (Battisti et al, ; Buffo, Battisti, Stastny, & Larson, ; Hódar, Castro, & Zamora, ).…”

Effects of climate on pine processionary moth fecundity and on its egg parasitoids

“…Furthermore, some authors (Robinet et al. ) suggest that the upper temperature threshold for PPM larval development within eggs is actually much higher than 32°C; indeed, these authors did not find any correlation between heatwaves and PPM egg mortality. Regardless, such high summer temperatures were rarely recorded in our study area.…”

“…Increasing winter temperatures, such as those registered during the last two decades in Italy (Kumar et al 2005;Morabito et al 2007), seems to be favoring the PPM. In fact, since 1995 the PPM's range has been expanding constantly, in both latitude and altitude (H odar et al 2003;H odar and Zamora 2004;Battisti et al 2005;Robinet et al 2013;Roques et al 2015a). Moreover, in some areas, outbreaks are becoming more severe, as well as repeating over time (H odar et al 2012), as PPM larvae more readily feed with milder temperatures during the cold seasons (H odar and Zamora 2004;Battisti et al 2005;Hoch et al 2009).…”

Pine monoterpene deterrence of pine processionary moth oviposition

“…In light of those findings, for this paper (1S)-(−)-␤-pinene, (±)-limonene, (R)-(+)-limonene, and (S)-(−)-limonene were tested in 2003 and 2004 in dispensers of different sizes to verify their efficacy as PPM control tools, as well as their stability inside dispensers. Ten years after the above mentioned trials, the resulting data are still useful today, because PPM's range of distribution is constantly expanding due to increasing winter temperatures (Robinet et al, 2013). As a consequence, finding an effective and ecologically sustainable control method, particularly in urban forestry, is increasingly important.…”