Walmart offers the Mosquito Dunks 30-oz. Mosquito Bits for $11.78. Opt for in-store pickup to dodge the $5.99 shipping fee. (Amazon charges the same with free shipping via Subscribe & Save.) That's tied with last week's mention and the lowest price we could find by $4. It purports to kill mosquitoes within 24 hours and is suitable for use in water gardens, flower pots, and bird baths.