A group of academics funded by the Australian Research Council has researched this issue. Members of the group studied caterpillars bred at the old and new temperature in the laboratory and noted the change. Observation of the butterfly in the wild has confirmed that caterpillars are changing into butterflies earlier.
If butterflies are coming out sooner then other insects must be doing so as well. This means that crops will have to be planted earlier to be fertilized by insects. Bees are not the only insects needed to grow crops. People in cities do not understand the importance of pollination on food crops.