Larval development and diapause induction under climate change: an experimental test with the Wall Brown butterfly

Under climate change, organisms with complex life cycles like insects are
confronted with environmental cues that may interfere with their life
cycle regulation, including diapause induction. Maladaptive responses to
novel conditions may contribute to local or regional population declines
and extinctions. In NW-Europe, the Wall Brown butterfly (Lasiommata
megera) is a multivoltine species whose regional decline has been
hypothesised to be related to recent warming in late summer and autumn
increasing the probability of producing a late third generation instead of
going into larval diapause to hibernate. To test this lost generation
hypothesis, we exposed young larvae of different population origins to
outdoor conditions and in situ warming (i.e., increased temperature at the
level of the host plant by 0.5 to 3°C depending on the month). The warming
treatment resulted in shorter larval developmental times and reduced adult
body size. However, the population origin and the temperature treatment
did not affect the probability to produce a third generation of adult
butterflies at the end of summer. Yet, families showed substantial
variation for the probability to induce a third generation. Overall, we
observed reduced larval survival in the warming treatment. We discuss the
implications of these results for the conservation of the Wall Brown in
NW-Europe and, in a broader manner, for life cycle regulation in insects
under rapid climate change.