Abstract
Insect populations are prone to respond to global changes through shifts in phenology, distribution and abundance. However, global changes cover several factors such as climate and land‐use, the relative importance of these being largely unknown. Here, we aim at disentangling the effects of climate, land‐use, and geographical drivers on aphid abundance and phenology in France, at a regional scale and over the last 40 years. We used aerial data obtained from suction traps between 1978 and 2015 on five aphid species varying in their degree of specialization to legumes, along with climate, legume crop area and geographical data. Effects of environmental and geographical variables on aphid annual abundance and spring migration dates were analyzed using generalized linear mixed models. We found that within the last four decades, aphids have advanced their spring migration by a month, mostly due to the increase in temperature early in the year, and their abundance decreased by half on average, presumably in response to a combination of factors. The influence of legume crop area decreased with the degree of specialization of the aphid species to such crops. The effect of geographical variation was high even when controlling for environmental variables, suggesting that many other spatially structured processes act on aphid population characteristics. Multifactorial analyses helped to partition the effects of different global change drivers. Climate and land‐use changes have strong effects on aphid populations, with important implications for future agriculture. Additionally, trait‐based response variation could have major consequences at the community scale.
Highlights
Crop area We found a positive relationship between pea crop area and abundance for aphid species preferring Fabaceae hosts: A. pisum, A. fabae, and M. euphorbiae (Tables 3 and S1)
As the resulting overall effects of geographical variables were negative, except for M. persicae (Fig. 5B), it seems that aphid phenology was more closely related to latitude than longitude. Both of the biological parameters studied, aphid phenology and abundance, significantly evolved during the last four decades. Aphids advanced their spring migration at a rate varying between 0.6 d/year and 1.2 d/year, while their average abundance diminished by half in 37 years
Aphid phenological changes were tightly related to temperature increase, while aphid numbers depended more on regional crop area
Summary
In a context of global changes, the distribution, abundance and phenology of insect populations are predicted to be profoundly modified, notably over regional scales, through the permanent alteration of environmental factors such as climate and landscape (Moraal & Jagers Op Akkerhuis, 2011; Eskildsen et al, 2013; Aguirre-Guttierez et al, 2016). Globalization can lead to a sizeable increase in the proportion and area of a given crop in a region, together with higher pest populations (Tilman, 1999; Ouyang et al, 2014; Rand et al, 2014), and increased insect dispersion (Tscharntke et al, 2005; Wallner et al, 2014). Previous studies have shown variable impacts of climate and land-use changes on insect populations at different regional scales (Fox et al, 2014; Aguirre-Guttierez et al, 2016), highlighting the difficulty of disentangling their respective influences. It is important to consider both these factors to understand variation in insect population characteristics in a spatiotemporal context, using appropriate tools and datasets to partition their contributions and their interactions (Juroszek & von Tiedemann, 2013)
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