Hi there
I am a bit the opposite though -- i find in warmer weather my insulin needs actually increase -- but many
people on the forum report that their needs decrease during warmer weather.
Have you either spoken with your DSN about making adjustments or have you ever looked at doing some basal testing to see how much if any your back ground might be adjusted.
here is a link to basal testing
http://www.salforddiabetescare.co.uk/index2.php?nav_id=1007
it is aimed at people on a pump but the principles are the same for people on MDI.
all the best !