Heat tolerance in pea aphids: Harmon et al., 2009

March 18, 2009

Journal: Science
Location: ?, USA

It is suggested that some pea aphids, a crop pest, are tolerant to heat stress because of bacterial symbionts, Buchnera aphidicola. Members of a strain of heat-sensitive pea aphids with only a non-resistant symbiont were put in 2x2x2m mesh cages, and heat shocks were simulated by putting plastic sheets over the cages (increasing temperature by ~5°C to what would normally affect pea aphid reproduction but still occur naturally). Introduction of predators does not necessarily cause the number of aphids to drop. The number of pea aphids was reduced when subjected to heat shocks, and the presence of 7-spot ladybird predators made no difference (X2 = 2.4, P > 0.5). However, when harlequin ladybirds were introduced, the effect of heat shock was alleviated (X2 = 41.8, P <10–6) because they only predate when population density of aphids is high.

In pairs of one green aphid clone and one red aphid clone, the population growth rate of both red heat-sensitive clones (0.243 ± 0.009) and green heat sensitive clones (0.269 ± 0.008) was greater than their green (0.214 ± 0.007, selection coefficient 0.25) and red (0.247 ± 0.010, selection coefficient 0.20) heat-tolerant counterpart, respectively. When subjected to heat shocks, the growth rate of heat-tolerant clones was notably greater for both green (0.234 ± 0.023 compared to 0.155 ± 0.027 in sensitive reds) and red (0.208 ± 0.031 compared to 0.129 ± 0.033 in sensitive greens) clones. Although the population growth rate was reduced in heat-sensitive clones upon heat shock, this was less than the decrease in growth of heat-sensitive clones (X2A = 12.1, P < 0.001; X2B = 6.96, P < 0.01). Thus rapid evolution of heat-tolerant pea aphid strains may occur if climate change causes more frequent heat shocks.

Pea Aphid – Acyrthosiphon pisum
Seven-Spot Ladybird – Coccinella septempunctata
Harlequin Ladybird – Harmonia axyridis

Harmon JP, Moran NA, Ives AR, 2009. “Species Response to Environmental Change: Impacts of Food Web Interactions and Evolution” Science 323(5919): 1347-1350, DOI: 10.1126/science.1167396
Affiliations: University of Wisconsin, and University of Arizona

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