Abstract:
The combined effect of drought and heat waves on insect-plant interactions is complex and not fully
understood. Insects may indirectly benefit from water-deficit stress through increased plant nitrogen
levels. Heat stress may have a direct negative effect, yet insect performance may be improved when
day-time heat is followed by cooler night temperatures. We show that moderate water-deficit stress
(25–30% pot capacity) and high day-night temperatures (30/20 °C) affected Macrosiphum euphorbiae
on potato (Solanum tuberosum) differently than their interactions. Water stress lowered stomatal
conductance, and both water and heat stress reduced leaf area. The effect of water stress on nymphal
and adult survival depended on temperature. Water stress added to reduced nymphal survival at high
but not current (25/15 °C) day-night temperatures. Adult survival at high temperatures was reduced
only when combined with water stress. Water stress and high temperatures independently but not
interactively reduced the number of daily offspring. Moderate water stress when combined with high
temperatures had a negative bottom-up effect on aphid survival even though lower night temperatures
aided in the recovery from direct heat stress. Our study illustrates the importance of combining multiple
stressors to better understand their impact on insect-plant interactions in the context of climate
change.
