PROBLEM TO BE SOLVED: To provide a technique that prevents dictyoptera insects such as cockroaches being creeping sanitary insect pests safely and efficiently.SOLUTION: The present invention provides aqueous baits containing a boric acid of 1-5 mass% for preventing dictyoptera insects. The present invention further provides a pest insect control instrument including a bottle part receiving the aqueous baits, a bait receiving part provided with a liquid suction part for bringing the inside of the bottle part into communication with the outside thereof through a first opening part provided on an upper surface of the bottle part, and a cover part for covering the upper part of the first opening part and locked with a gap between the bottle part and itself, in which the aqueous baits are boric acid solution.
