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

Abstract

Climate change may be affecting the fecundity of phytophagous insects as well as impacting their natural enemies. However, temperature impacts these two insect groups differently, disrupting population regulation mechanisms, and ultimately, possibly culminating in an outbreak of the host. The pine processionary moth (PPM) is one of the most harmful insects of the Mediterranean basin. Not only are PPM larvae harmful to plants, but they are also dangerous to humans because of their urticating hairs. Although some information is available on climate change effects on the PPM, little is known about its potential effects on PPM egg parasitoids, especially on their distribution range or on their role in controlling PPM populations. The aim of this article was to verify the effects of climate on PPM fecundity and on its egg parasitoids. Our results show that climate warming may affect the PPM positively, but not its egg parasitoids. Specifically, during our study mild winters directly favored the PPM, while increasing summer temperatures (over 30°C) also favored the PPM indirectly, by decreasing parasitism rates. We predict that ever‐milder winters will not only favor PPM development, but also encourage it to spread in otherwise previously inhospitable environments.

Expansion of elevational range in a forest pest: Can parasitoids track their hosts?

“…Furthermore, host tracking is mandatory for specialist parasitoids, but generalist ones could even be present before host arrival, living in alternative hosts (Auger-Rozenberg et al 2015). Previous studies have shown that in areas recently colonized by PPM, the percentage of parasitism is significantly reduced (Alemany et al 1994, Tiberi et al 2015. The conquest of a new habitat could thus be fueled by the lack of natural control against PPM, since egg parasitoids have been repeatedly pointed out as main controller of the PPM populations (Tsankov et al 1996, Zovi et al 2006, Mirchev et al 2012.…”

Response of the egg parasitoids of the pine processionary moth to host density and forest cover at the southern edge of the range

“…In a study conducted by Tiberi et al . (2015), with a 9‐years' time series observed in Monte San Michele, Florence, Italy, the average parasitism varied inter‐annually from 4% to 26%. It was proposed that daily temperatures above 30 °C would explain lower parasitism rates in years with hot summers.…”

“…The two major egg parasitoid species found in this study, B. servadeii and O. pityocampae , are the same observed all over the Mediterranean basin, although in variable proportions ( e.g . Schmidt et al ., 1997; Tsankov et al ., 1998; Perez‐Contreras & Soler, 2004; Arnaldo & Torres, 2006; Mirchev et al ., 2010; Tiberi et al ., 2015). In the present study, overall parasitism by B. servadeii was higher than that of O. pityocampae , with some differences on the species proportion among sites.…”

“…Two major egg parasitoid species, Baryscapus servadeii (Domenichini) (Hymenoptera Eulophidae) and Ooencyrtus pityocampae (Mercet) (Hymenoptera Encyrtidae), are widely found parasitizing the eggs all over the Mediterranean Basin (e.g. Tsankov, 1990;Schmidt et al, 1997Schmidt et al, , 1999Arnaldo & Torres, 2006;Tiberi et al, 2015).…”

“…However, heat waves during summer with extreme high temperatures may compromise their survival. A study made in Italy suggested that temperatures above 30 °C would cause a decrease in egg parasitism (Tiberi et al ., 2015). No other study however addressed this hypothesis.…”