After picking another 2 dozen or so black blister beetles off my tomatoes again this morning (the photo to the left has both black blister beetles and gray blister beetles on a "hot spot" on one of my tomato plants), I decided to do a little web research and find out more about their life cycle. What could I look for as far as their larval or pupal stage went? Was there something I could do to interrupt their life cycle at an earlier stage?
Well, I came away with yet more respect for the web of life.
It turns out that the larvae of black blister beetles feed on grasshopper eggs, specifically the eggs of short-horned grasshoppers (family Acrididae). Thus black blister beetles are more common during or after grasshopper outbreaks.
Just this afternoon, while I was at the Master Gardener office, we were discussing grasshoppers. Several people in the area are having major trouble with grasshopper outbreaks in their gardens. I was (rather smugly, I'm afraid) noting that I was seeing some, but not any more than usual. It would appear that I may very well owe my "normal" grasshopper population to those same black blister beetles that I've been cussing under my breath as I painstakingly examine my tomato plants to hunt for them.
Other rather interesting facts I learned about black blister beetles (Epicauta pennsylvanica):
* The eggs are laid in the ground or under stones, in clusters of 50-300. The females lay several clusters of eggs throughout their adult life.
* Blister beetles undergo "hypermetamorphosis" - a type of metamorphosis with several different larval forms, rather than the normal single larval form with several "instars" or growth stages. The first larval stage in blister beetles is quite mobile, while the later stages are much less mobile.
* Some of the other blister beetle genuses feed on bee larvae or stored food in bee nests during their larval stage. All blister beetle larvae appear to be predatory.
* Adult blister beetles live about 3 months.
* Blister beetles produce a toxic chemical, cantharidin, in their hemolymph ("blood"). This chemical causes blistering on human skin...so don't crush blister beetles if/when you handle them!
* Cantharidin is very stable and remains toxic even after the beetles die. Horses are particularly susceptible to cantharidin. One of the biggest problems that blister beetles cause is illness or death in horses who eat dead blister beetles in their alfalfa hay.
* The good news is that black blister beetles are one of the least toxic of the blister beetle family.
So now I'm left with the conundrum of "Do I want to minimize the black blister beetle adults that are eating my tomato plant leaves, or do I want to let their populations follow normal fluctuations as their larvae feed on grasshopper eggs in the soil?"
The more I learn, the harder this sort of decision becomes.