Temperature as a predictor of survival of the pine processionary moth in the Italian Alps

Abstract

1 The pine processionary moth Thaumetopoea pityocampa is expanding its geographical range in Europe, as a consequence of enhanced winter survival under a warmer climate. A combination of daytime nest temperatures and night air temperatures determines the number of hours larvae are able to feed (hours above realized feeding threshold, RFT). 2 We tested the RFT-based model for survival across multiple areas of the insect's range in the Italian Alps over a 2-year period. In a series of translocation experiments using natural temperature gradients as spatial analogues for global warming, we transferred colonies of T. pityocampa larvae to sites within zones of historical distribution, recent distribution, and outside the present range. The sites included traditional ( Pinus nigra , Pinus sylvestris ) as well as novel ( Pinus mugo , Pinus uncinata , Pinus cembra ) hosts. 3 Survival during precold (August to November), cold (December to February) and postcold (March to May) periods were analysed against climatic variables (temperature and rainfall) and predictors developed by the model. 4 Host species did not significantly affect final survival, with the exception of slower larval development, and resulting lower cold tolerance, on P. cembra than on P. mugo at the same site. 5 Across all the sites and hosts, final survival of colonies depended on the number of feeding hours during the cold period (RFT), which explained 82% of the variance in a regression model. We recommend using RFT, or its surrogate daily mean minimum temperature when nest temperature is not available, in predictive models of range expansion of T. pityocampa under climate change scenarios.

Insect overwintering in a changing climate

“…provides an interesting example of a species that has shown a gradual altitudinal range expansion of 230m in the Italian Alps over the past 30 years (Battisti et al, 2005). The larvae of T. pityocampa overwinter in nests spun from silk and, depending on temperature, leave the nest at night to feed on pine needles; winter survival is determined by the number of feeding hours per day during the coldest part of winter from December to February (Battisti et al, 2005;Buffo et al, 2007). One interesting feature of T. pityocampa is that larvae feed in winter, which would normally be considered incompatible with a freeze-avoidance strategy, because food particles in the digestive system are regarded as potent ice nucleators.…”

“…One interesting feature of T. pityocampa is that larvae feed in winter, which would normally be considered incompatible with a freeze-avoidance strategy, because food particles in the digestive system are regarded as potent ice nucleators. Recent research suggests that a proportion of larval population is freeze tolerant to 10°C below the SCP and the remainder rely on supercooling to survive (Battisti et al, 2005;Battisti et al, 2006;Buffo et al, 2007). One of the predicted features of global climate change, alongside progressively higher temperatures, is an increase in so-called 'extreme events' -such as abnormally hot or cold days or longer periods, high precipitation and flooding.…”

Cambio climático y plagas: algo más que el clima

“…La relación entre las defoliaciones por procesionaria y la temperatura, en particular los inviernos suaves, ya había sido puesta de manifiesto hace años (ver, por ejemplo, los trabajos clásicos de Démolin 1969a, b), aunque no ha sido hasta recientemente que hemos entendido la forma en la que las bajas temperaturas invernales limitan el desarrollo de las larvas, así como los mecanismos de tolerancia de las larvas frente al frío (Buffo et al 2007, Robinet et al 2007, Hoch et al 2009). En un contexto de calentamiento global era esperable que la procesionaria colonizara zonas que, en razón de su latitud o altitud, hasta ahora le estaban vedadas, y en efecto, en los últimos años varios estudios han confirmado dichos movimientos altitudinales (Hódar y Zamora 2004, Battisti et at.…”

Forests and climate change - lessons from insects

“…Consequently, if the climatic conditions become fa vourable in higher latitudes or at higher elevations, the insect may expand its range to these areas, often coupled with host switching (Battisti et al 2005, Robinet et al 2007). This relative im portance of temperature over biotic factors in defining the geographic distri bution makes the moth a particularly suitable model to study the range shift in relation to global warming (Buffo et al 2007). An important forest pest in many areas, the moth has shown in the last decades a substantial expansion of the outbreak area both northward and upward (Huchon & Démolin 1971, Hodar et al 2003, Battisti et al 2005, aggravated by extreme climatic events such as the sum mer of 2003 ).…”