Monday, August 20, 2012
Sure enough, we had pegged the genus and from there it wasn't hard to determine its identity as the ninebark beetle, Calligrapha spiraea. Going by the scientific epithet, it would seem that the creature was misnamed - its host is the shrub ninebark, Physocarpus opulifolius, which was growing in profusion where we found the beetle. But there is a rational explanation for the apparent misnomer - back when the beetle was originally described and named, ninebark was placed in the genus Spiraea, which is another group of shrubby rose family members.
The beetles lay their eggs on the underside of leaves of its ninebark host plant, and when the larvae hatches, they (anthropomorphically speaking) happily chew leaf tissue. All would seem well. The larva is essentially living on an inexhaustible supply of food, and their tiny size may make them less of a target to the legions of bad guys lurking about.
As we moved ever closer to our subject, we saw that it had picked up a most unwelcome guest. A tiny parasitoid wasp has lit on the beetle's shell, and is in the act of depositing an egg. Parasites are generally annoyances, like mites or ticks; parasitoids generally kill their victims, often in gruesome fashion. I don't know the wasp species, or even the family, although I wonder if it may be a chalcid. Considering that the beetle is only about 7 mm in length, the wasp is incredibly small, and photographing it taxed the limits of my 100 mm macro lens. The wasp egg will eventually spawn a tiny grub, which will work its way into the beetle's soft inner tissues, and feed upon its host. Presumably, it - and maybe other wasp grubs also within - will eat their host alive.
All seems well, and we were pleased to move in and make interesting photos sans the ghoulish disruptions of parasitoid wasps.
Same old story here. Those eggs will hatch grubs that'll bore within the caterpillar and eat it alive.