Temperature responses of a plant-insect system using a food-web performance approach Sandra Flores-Mejia 1 *, Val  erie Fournier 2 & Conrad Cloutier 1 1 D epartement de Biologie, Pavillon Alexandre-Vachon, Universit  e Laval, 1045 Av. de la M edecine, Qu  ebec, QC, Canada G1V 0A6, and 2 Centre de Recherche en Horticulture, Universit  e Laval, 2480 Boulevard Hochelaga, Qu  ebec QC, Canada G1V 0A6 Accepted: 24 August 2014 Key words: plant-herbivore interaction, biotype, optimal temperature, optimal size, high tolerable temperatures, bell pepper, potato, climate change, Hemiptera, Aphididae, Solanaceae, Macrosiphum euphorbiae Abstract Evaluation of the performance of a plant-herbivore system as a whole is difficult due to the lack of fitness parameters that can be applied to both components. The individual use of traditional mea- sures of performance (e.g., r m , biomass) can provide useful, but incomplete information on the per- formance of insect herbivores and seldom incorporates plant performance. We propose the use of the net generational productivity (NGP) to evaluate the fitness of the herbivore, which can then be compared directly with the performance of the plant in biomass units, to obtain the food-web perfor- mance ratio (φ H/P ). We compared three biotypes of the potato aphid, Macrosiphum euphorbiae Tho- mas (Hemiptera: Aphididae), when raised on three different host plants: potato (Solanum tuberosum L. cv. Norland) and two bell peppers (Capsicum annuum L. cv. Fascinato and cv. Crosby) (all Solana- ceae) at temperatures ranging from 8 to 36 °C. The temperature profiles of the potato aphid biotypes suggest that this aphid is better suited to temperate climates, and its performance generally depends on the particular host-plant/biotype association. Plant growth performance showed that potato has a lower thermal tolerance, but has a faster growth rate than bell peppers, especially in the range of 16– 24 °C. Temperature variation in the φ H/P ratio shows that aphids have a greater performance than plants, especially at lower temperatures, at which they can accumulate biomass up to 148 times faster. Because of the aphid’s biological inability to withstand long exposures to temperatures above 28 °C, plants have a slight advantage over aphids. Nonetheless, as the performance of plants is extremely reduced at high temperatures, this advantage cannot withstand long-term exposures to extreme tem- peratures. This is the first attempt to obtain a parameter capable of determining the climatic profile and performance of a food web in an inclusive yet simple manner. Introduction Temperature is the overriding bioclimatic factor affecting biological processes of ectotherms. Therefore, weather and climate determine the abundance, distribution, and inter- actions of plants and insects worldwide (Messenger, 1959; Speight et al., 1999; Hance et al., 2007; Gutierrez et al., 2008). This is of particular importance for multitrophic food webs based on green plants, as temperature may differentially affect the biology, physiology, and phenology of each of the organisms that form the food web (van Baaren et al., 2010). Therefore, even a small change in the temperature may destabilize the food web, and in the long term change the ecological landscape of terrestrial ecosys- tems (Campbell et al., 1974; Liu et al., 1995; van der Putten et al., 2004; Hance et al., 2007; Houghton, 2009; van Baaren et al., 2010). Meteorologists forecast a rise in global temperature by an average of 1.5–6 °C over the course of the century. Since the beginning of the 20th century, minimum tem- peratures (usually nighttime) increased twice as much as maximum temperatures on average, having a direct impact on the range of daily, monthly, and seasonal *Correspondence: Sandra Flores-Mej  ıa, D epartement de Biologie, Pavillon Alexandre-Vachon, Universit  e Laval, 1045 Av. de la M edecine, Qu ebec, QC, Canada G1V 0A6. E-mails: sandra.flores-mejia.1@ulaval.ca; sandra.floresm@yahoo.com 142 © 2014 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 153: 142–155, 2014 DOI: 10.1111/eea.12234