I tried the vegetable oil on water idea that i've been hearing about and it worked really well. Even flies that landed on the layer of oil died. It's quite an insect mass grave.
I'm just curious though, because i had some nearby plants and there leaves touched the oil and became thin and translucent. So i guess the leaves died.
I'm growing lotus tubers in there so I'm wondering, will the vegetable oil ruin the leaves of plants or kill plants. Does it kill aquatic animals too like fish?