The impact of climate change on herbivorous insects can have far-reaching
consequences for ecosystem processes. However, experiments investigating the
combined effects of multiple climate change drivers on herbivorous insects are
scarce. We independently manipulated three climate change drivers (CO2,
warming, drought) in a Danish heathland ecosystem. The experiment was
established in 2005 as a full factorial split-plot with 6 blocks 9 2 levels of
CO2 9 2 levels of warming 9 2 levels of drought = 48 plots. In 2008, we
exposed 432 larvae (n = 9 per plot) of the heather beetle (Lochmaea suturalis
THOMSON), an important herbivore on heather, to ambient versus elevated
drought, temperature, and CO2 (plus all combinations) for 5 weeks. Larval
weight and survival were highest under ambient conditions and decreased
significantly with the number of climate change drivers. Weight was lowest
under the drought treatment, and there was a three-way interaction between
time, CO2, and drought. Survival was lowest when drought, warming, and elevated
CO2 were combined. Effects of climate change drivers depended on other
co-acting factors and were mediated by changes in plant secondary compounds,
nitrogen, and water content. Overall, drought was the most important factor
for this insect herbivore. Our study shows that weight and survival of insect
herbivores may decline under future climate. The complexity of insect herbivore
responses increases with the number of combined climate change drivers.