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

Abstract

1. A major component of biomass burning smoke is fine particulate matter (PM2.5), which has been shown to generate impacts on insect population dynamics and development. However, little is known about its effect on insect flight behaviour, even though this will influence insect dispersal and distribution, and potentially migration and ecosystem services such as pollination. 2. Here we use a tethered flight mill setup to examine the behaviour of adult painted lady butterflies (Vanessa cardui L.) flying in different levels of combustion-generated airborne PM2.5, comparison this to TFM flying under ‘clean air’ conditions. 3. Descriptive statistics and paired sample t-tests indicate that the smoke had a significantly deleterious impact on flight behaviour, with for example total flight distance covered declining by 65% during the first 20 min of flying in the least smoke contaminated air compared to ‘clean air’ control conditions, whilst average speed declined by 54% and flight duration by 32%. A strongly negative and highly significant linear correlation between flight speed and PM2.5 concentration was also observed. 4. This study represents the first time that smoke effects on insect flight behaviour have been experimentally tested, and the longer the butterflies were exposed to the elevated PM2.5 concentrations the more obviously their flight behaviour declined. We conclude that the month(s)-long episodes of air pollution often associated with agricultural burning and deforestation fires in the tropics may well be significantly affecting the behaviour of the flying insects living in those regions and/or who migrate through them.