Environmental drivers of annual population fluctuations in a trans-Saharan insect migrant

Abstract

Many latitudinal insect migrants including agricultural pests, disease vectors, and beneficial species show huge fluctuations in the year-to-year abundance of spring immigrants reaching temperate zones. It is widely believed that this variation is driven by climatic conditions in the winter-breeding regions, but evidence is lacking. We identified the environmental drivers of the annual population dynamics of a cosmopolitan migrant butterfly (the painted lady Vanessa cardui) using a combination of long-term monitoring and climate and atmospheric data within the western part of its Afro-Palearctic migratory range. Our population models show that a combination of high winter NDVI (normalized difference vegetation index) in the Savanna/Sahel of sub-Saharan Africa, high spring NDVI in the Maghreb of North Africa, and frequent favorably directed tailwinds during migration periods are the three most important drivers of the size of the immigration to western Europe, while our atmospheric trajectory simulations demonstrate regular opportunities for wind-borne trans-Saharan movements. The effects of sub-Saharan vegetative productivity and wind conditions confirm that painted lady populations on either side of the Sahara are linked by regular mass migrations, making this the longest annual insect migration circuit so far known. Our results provide a quantification of the environmental drivers of large annual population fluctuations of an insect migrant and hold much promise for predicting invasions of migrant insect pests, disease vectors, and beneficial species.

Windborne migration amplifies insect-mediated pollination services

“…As equally noted for other migratory insects (e.g., Guo et al, 2020), important inter- and intra-annual variation occurred in E. balteatus trap catches. Such variation can possibly be ascribed to agroclimatic conditions or biotic factors e.g., fluctuating prey abundance (Drake and Farrow, 1988; Hu et al, 2021). For aphidophagous hoverflies such as E. balteatus , adults deposit their eggs near aphid colonies where larvae subsequently feed until pupation; the ensuing hoverfly abundance levels are inherently shaped by aphid densities (Honěk, 1983).…”

Parasite dynamics in North American monarchs predicted by host density and seasonal migratory culling

“…NDVI quantifies live green vegetation and is assumed to indicate the availability of plant resources, including the abundance of caterpillar host plants and adult nectar plants (e.g. Graham et al, 2016; Hu et al, 2021; Saunders et al, 2019). We acquired NDVI values for all years available (1980–2019) and averaged the values for year and region (as defined above) for the month of July, when vegetation greenness is expected to be high.…”

Stimulus-dependent orientation strategies in monarch butterflies

“…Orientation in space is an essential ability for animals to find food, escape from predators or return to their nest. To achieve this, insects exhibit a number of different orientation mechanisms, ranging from the simple straight-line orientation of dung beetles ( Dacke et al, 2021 ; el Jundi et al, 2019 ) to more complex behaviors such as path integration of ants and bees ( Collett and Collett, 2000 ; Heinze et al, 2018 ) or long-distance migration of lepidopterans ( Grob et al, 2021 ; Hu et al, 2021 ; Merlin and Liedvogel, 2019 ; Warrant et al, 2016 ). One striking example of a migrating insect is the monarch butterfly ( Danaus plexippus ) ( Reppert and de Roode, 2018 ; Reppert et al, 2016 ).…”