A bottletop plug device for trapping flying insects. The bottletop plug device is a reversibly attachable accessory that converts a consumer-supplied narrow-neck bottle into a trap for flying insects. The plug device has a generally tapered body that includes a lower body segment and bottom tip insertable into a baited bottle, a middle body segment having a stack of resilient protruding circumferential ribs sealable against an inside wall of a bottle neck, and an upper body segment having a wide mouth entrance to an internal passageway or chamber that runs down the length of the body and through the bottom tip. At the bottom of the channel, a narrow “insect sized” orifice allows insects to have essentially one-way ingress into the bottle. The protruding ribs are circumferentially stacked like a stack of coins, but the stack is typically tapered top to bottom from greater diameter to lesser diameter so that the plug self-seatingly fits into and plugs various bottle neck sizes while allowing the central insect passageway to remain open. Alternatively the stack may be untapered. The bottle and bait may be supplied by the user.
