The Rustbug Hoop is the latest piece of Decepticon weapons technology for handling extremely small flying opponents. It is just a coincidence that it looks like an electrically charged fly swatter. Oh yes.
Starscream was on monitoring duty at Shockwave's base when he spotted a visitation by the Insecticons, spying for Megatron as part of the Decepticon Civil War. After a quick trip to the armoury, Starscream was ready. The Insecticons attacked him, so he pulled out the Rustbug Hoop and casually swatted them all.