Gravid traps attract gravid females of some species using mixtures of oviposition stimulants. Which substance is mentioned as an attractant?

• A. Hay
• B. Sugar solution
• C. Fruit juice
• D. Water with yeast

Answer: (A)

Gravid traps rely on cues that signal a suitable place for offspring to develop. A hay infusion—made by soaking hay in water and letting it ferment—releases a mix of volatile compounds produced by microbes. These odors mimic natural standing-water environments and attract gravid females looking to lay eggs, guiding them to the trap. The other substances don’t provide the same oviposition cues in this setup: sugar solution and fruit juice are more about feeding adults, and water with yeast isn’t the standard oviposition attractant described for these traps.