Effect of temperature on spring emergence of butterflies: Implications of climate change altering insect phenology

Background/Question/Methods Research to date on the biological effects of climate change on plants and animals in New England has focused almost exclusively on plant flowering times and bird arrivals in the spring. Insects play a prominent role in ecological food webs, yet are underrepresented in phenological research. This crucial missing link has limited the understanding of the complete set of community level effects that climate change has caused. It is extremely important to examine the impact of climate change on insects in order to determine whether phenological mismatches are occurring, or are likely to occur, in plant-pollinator and/or plant-herbivore interactions. In this study we examine the impact of temperature on spring emergence dates of one well-known group of insects, the lepidopterans, in Massachusetts. Using simple linear regressions we analyzed yearly emergence data collected for the period between 1995 and 2008. The data were collected by a butterfly enthusiast who methodically recorded daily Lepidoptera sightings on her property in Newbury, a coastal town in eastern MA. Sixteen species of butterflies and one species of moth were studied, eleven of whose emergence dates occur in the spring, which we define as the time between April and June. Results/Conclusions The appearance dates of three of the eleven spring species were significantly correlated with the average temperature of the month before emergence. Our analysis did not find any significant changes in emergence date over time. However, because the phenologies of certain species are dependent on temperature, emergence dates have likely become earlier over the past few decades as a result of global warming. This result agrees with the findings of studies from Europe, where butterflies have been emerging earlier over the past quarter century. Our analysis suggests that for every 1°C increase, butterflies whose emergence dates are significantly affected by temperature are likely to emerge an average of two days earlier. Previously published research from Massachusetts shows that the flowering times for many plant species are changing similarly, flowering approximately three days earlier for each increase of 1°C, while arrival dates of migratory birds in Massachusetts have been highly variable, with some species arriving later, some arriving earlier, and others showing no significant change over time. Further investigation in this study will examine more closely the link between the phenologies of the three groups of organisms, to estimate the possibility of temporal mismatches of interdependent species caused by climate change.