Timing of mating, reproductive status and resource availability in relation to migration in the painted lady butterfly,Vanessa cardui

Abstract

In many migratory insects, migration occurs during the pre-reproductive phase of the life cycle. This trait probably arises from a trade-off between migration and reproduction and in females has been termed as the ‘oogenesis-flight syndrome’. However, the generality of this syndrome has been questioned, especially for monomorphic insects. We studied the relationship between migration and reproduction in the highly cosmopolitan painted lady butterfly, which in the Palaearctic undertakes the longest known multi-generational migration circuit of any insect. We tested for the oogenesis-flight syndrome in both spring and autumn migrants in two regions linked by migration, North Africa and northern Spain. Field observations were combined with laboratory experiments to determine the lifespan and the age at first mating to unravel the reproductive strategy observed in individuals captured in the wild. Females and males wait on average around 5–6 days before mating, and field data revealed that mating frequencies increase rapidly once females reach a medium wing wear category. There were seasonal differences in mating frequencies in the study regions depending on whether the region acted as a source or as a destination for migrants, and in the latter case there were almost twice as many mated females. Moreover, about 80% of females collected during migratory flights were unmated, the remaining females having mated only very recently. Our results thus strongly indicate that the painted lady fulfils the oogenesis-flight syndrome, as migration is concentrated in its relatively short pre-reproductive period. Field data also showed a high positive correlation between mating frequency and host plant abundance, which suggests that mated females have the ability to locate potential breeding areas. This, together with the very high fecundity estimated from over 1000 eggs in laboratory trials, makes the painted lady one of the most successful migratory insects on Earth.

The ‘migratory connectivity’ concept, and its applicability to insect migrants

“…The migrant insect species most under threat tend to be those with highly specialised migration systems that combine migration with diapause at a localised site, such as the monarch. However, most migratory insects appear to not be threatened, combining high mobility with very high fecundity and thus they have the ability to withstand generational mortality of > 99% [48,82]. These colonising, dispersive species with high rates of population growth can (and often do) bear high migration losses.…”

Strong impacts of smoke polluted air demonstrated on the flight behaviour of the painted lady butterfly (Vanessa cardui L.)

“…The wingspan of the male is normally 58–70 mm, and that of the female 62–74 mm (Ukbutterflies.co.uk, 2020). Adult V. cardui live for 3–4 weeks, often up to 5 (Talavera & Vila, 2017; Stefanescu et al ., 2020), providing enough time for experimental treatments such as those detailed here to be completed while the butterflies are in robust health.…”

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

“…unmonitored areas. Importantly, all records of massive emergences come from very local, and sometimes highly isolated, spots of barely a few hectares (21,24,37), which means that egg-laying females have the ability to locate small potential breeding habitats that may be created by irregular episodes of intense autumn or winter rains (40).…”

“…Thus, it is conceivable that nectar availability in the Savanna/Sahel is the primary factor driving the abundance of arrivals in the Maghreb and, ultimately, in Europe, although butterflies might actually originate in the tropical region. However, adult painted ladies typically emerge from the pupal stage with a full fat body (40), and comparative evidence from monarchs (44,45) indicates that a full fat body contains enough fuel reserves for crossing the Sahara without the need to replenish fuel stores via nectar feeding (see next section). We therefore suggest that nectar availability is less likely to be the primary driver than the in situ production of large source populations, but that it may have an additional additive effect.…”