Effects of extreme, fluctuating temperature events on life history traits of the grain aphid,Sitobion avenae

Abstract

Altered temperatures affect insects' life history traits, such as development period and fecundity, which ultimately determine population growth rates. Understanding insects' thermal biology is therefore integral to population forecasting and pest management decision-making such as when to utilise crop spraying or biological control. Aphids are important crop pests in temperate regions, causing considerable yield losses. The aphid thermal-biology literature is, however, heavily biased towards the effects of rising mean temperatures, whereas the effects of fluctuating, extreme climatic events (e.g., heat waves and sub-zero cold periods) are largely overlooked. This study assessed the effects of laboratory-simulated heat waves and sub-zero cold periods on the survival, development period, and fecundity of the grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae: Microsiphini), in addition to assessing maternal effects on the birth weight and development period of the offspring of exposed individuals. Exposure to heat stress periods (total of 16 h at 30°C) significantly reduced aphid fecundity and increased physiological development period (in day-degrees) resulting in a reduced population growth rate. Cold exposure (total of 1.33 h at À15°C) reduced population growth rate due to an elongated development period (in days), but did not affect fecundity or physiological development period (in day-degrees). Both cold and heat stress significantly reduced aphid survival. Maternal experience of heat stress reduced nymphal birth weight although nymphal development period was not affected by either cold or heat stress. The results suggest that including the effects of fluctuating, extreme temperature events on aphid life history in population forecast models is likely to be of great importance to pest management decision-making. The demonstration of maternal effects on birth weight also suggests that cross-generational effects of heat waves on population growth rates could occur. § Present address: Additional Supporting Information may be found in the online version of this article:Data S1. Thermal stress regime pilot experiments.Extreme temperatures and aphid life history traits 249

Insects in Fluctuating Thermal Environments

“…However, recent data support the notion that extreme heat events, even of short duration or when occurring only once, are highly detrimental for species' performance and survival, and that averaging daily temperature will not capture these effects (4,56,88,116,126).…”

“…Temperature in the field fluctuates, and the impact of these variations has been recognized in areas as diverse as forensic entomology (18,53), thermal tolerance physiology (9,80,96), biocontrol (13,28), insect-mediated pollination (98,124), disease vector biology (73,87) and simulated climate warming studies (4,10,56,116,126).…”

Daily temperature extremes play an important role in predicting thermal effects

“…When natural temperature variation is simulated, T max is often deliberately avoided to minimize mortality (Bradshaw et al, 2004;Whitney-Johnson et al, 2005;Warren and Anderson, 2013;Jeffs and Leather, 2014). Temperature fluctuations that vary in amplitude to approximate extremes in nature depress fitness components such as development, survival and fecundity (Ragland and Kingsolver, 2008;Paaijmans et al, 2010;Carrington et al, 2013;Xing et al, 2014), pointing to adverse effects of T max on organism performance.…”

A temperate pollinator with high thermal tolerance is still susceptible to heat events predicted under future climate change

“…The results of our study bear some similarities to previous studies on the responses of temperate non‐pollinating insects to extreme temperatures (Allen & McCoy, ; Feder et al ., ; Roux et al ., ; Gillespie et al ., ; Jeffs & Leather, ). For example, using Drosophila as a model system, Feder et al .…”