Insect fitness and performance are affected by temperature, but this relation can be difficult to understand when temperature fluctuates. Sometimes fluctuations can fall outside the adequate range for regular insect development (permissive range) and enter extreme temperature ranges that can be harmful to insects. This adds a level of complexity when studying temperature effects on insects. We asked how insects are affected by constant temperatures (CT) opposed to fluctuating temperatures (FT) and if these differences hold in different temperature ranges. We reared pea aphids (Acyrthosiphon pisum) on fava plants (Vicia faba) in different temperature treatments. We used a cooler (20C) and a warmer (28C) temperature range. To properly test for temperature variation, the CT and FT treatments had the same mean temperature within the same temperature range. One set was in a permissive range (CT: 20C and FT: 16C/24C). The second set ranged from permissive to extreme (CT: 28C and FT: 24C/32C). After 9 days, we compared aphid populations reared under the same mean temperature.
Results/Conclusions
In a permissive range (20 vs 16/24), we obtained similar sized populations. But when the FT fell out of the permissive range (28 vs 24/32), populations were ten times lower than populations under CT. Our experiment showed that insect response to FT is not equal to the average CT when part of the range is particularly high. In fact, just a short exposure to that high temperature produced aphid populations as low as when aphids were at that high temperature constantly. Even short periods of time in extreme temperatures can have a strongly negative effect on insect performance. This could mean that in high variability situations, the range of variability may be less important than the maximum temperature.