As different as night and day: How different warming times affect aphid population growth

Although insects have been instrumental in understanding the potential effects of increasing temperatures, much less is known regarding the effect of when changes in temperature occur.  Historical data shows that temperatures at night have increased twice as fast as the rate of warming during the day.  However, there has been little research exploring the effects of increased temperature at different times.  Our research focuses on that difference in warming rates, specifically, the question of when it occurs rather than the degree of warming.  We examined how the population growth rate of the pea aphid, Acyrthosiphon pisum, changed with respect to the time of day in which warming occurred.  Growth chambers were used to simulate three different treatments, night warming, day warming, and a control.  Each treatment exposed eight mixed age groups of aphids to the same amount and length of warming over a 9 day period.  At the end of the experiments, we counted the total number of aphids per plant to observe any population effects.  Our results showed that increasing the temperature at night has a greater effect than an increase in temperature during the day.  The number of aphids per plant in the night treatment was higher than the number of aphids in either the control or day warming treatments.  This effect, while only one part of changing temperature trends, could indicate an important factor to consider as we try to understand temperature effects on different insect species.