It's so rare (in my limited experience) to see negative results like this published. "We tried this novel use for x and it didn't work" is a useful contribution to the body of knowledge.
"We tried to use kava as an insecticide but the results were catastrophic. In our controls, fruit flies damaged the fruit by sucking on them, leaving little pinpricks in the skin of the fruit that hastened spoilage. However, we found that fruit sprayed with kava disappeared altogether. It's suspected that a large mammal has been attracted to the kava-flavoured mangoes."
