I've heard that the bugs are bad in Costa Rica during a certain time of year. When is that time of year?

We are planning a trip to Costa Rica and would prefer to avoid the "buggy" season that we have heard about. Not sure if it coincides with the Green season, or if it is only at the beginning of the Green season, or if it is some other time. Also, we might expect that it might be different for different parts of the country. Any help would be appreciated. Thanks.