When you go through all the trouble of importing non-native insects into your state as a biological control, you want to be sure they're doing their job. That's why researchers were relieved to discover what's been behind the decline in effectiveness of two South American weevil species that were introduced to control burgeoning populations of water hyacinth (Eichhornia crassipes) in Florida. According to this report in Agricultural Research magazine, the culprit is a strain of microsporidia that is infecting the weevils (Neochetina eichhorniae and N. bruchi), causing loss of life and a major decrease in reproductive rates. Now that scientists know what's killing the weevils, they are looking into ways to control the microsporidia, including cold treatments and drugs. Microsporidia themselves are sometimes employed as biocontrol agents.