The Blakestone buzzer is a very successful pattern for imitating chironomid pupae. Fish the blakestone buzzer all year but best spring to summer. Long leader will bring success.
 
Predominantly a Spring / Early Summer fly, the buzzer can induce some savage takes from trout, epecially when competing for food. Make sure you hold on to your rod when fishing buzzers, as it is common for rods to fly off in to the water after a trout takes one and runs !