While recording as part of the North East Ladybird Spot, Sam Gemmell encountered more than he bargained for when he stumbled across the ladybird parasite, Dinocampus coccinellae.
On 21 April, I found a 7-spot Ladybird sitting on a fence post. At first, this seemed to be a familiar sight- most of my observations for the North East Ladybird Spot, so far, have been of this species on fence posts. However, a closer look revealed that this was no ordinary ladybird sighting. There was something fuzzy and orange nestled underneath the ladybird. I suspected parasitism, but was not sure as I expected the ladybird to be damaged in some way, as a parasitised caterpillar would be. My thinking was proved right, however, after I was told by someone at the NHSN Twitter account that the ladybird had probably been parasitised by a wasp called Dinocampus coccinellae.
This wasp belongs to the family Braconidae, the second-largest Hymenopteran family after Ichneumonidae, another group of parasitic wasps. Like other parasitic wasps, the female has a long ovipositor with which she injects eggs into a living host. If you are lucky enough to find one of these tiny adult wasps, it will probably have an ovipositor; the species is mostly parthenogenetic, with males being very rare.
When a wasp successfully pierces the heavily armoured cuticle of the ladybird, she passes on an egg as well as a virus named Dinocampus cocinellae Paralysis Virus. This infects the ladybird’s nervous system and, as the name suggests, paralyses the helpless ladybird. Once the egg hatches, it will feed on the ladybird’s insides, avoiding the vital organs to ensure that the ladybird remains a living, fresh meal throughout the larva’s life. Once fully grown, the larva emerges from the soft membranes between the beetle’s abdominal segments. The wasp will then spin a cocoon between the ladybird’s legs and begin to pupate. The virus-induced paralysis forces the ladybird to stand guard over the vulnerable pupa, but allows the ladybird to move just enough to protect the cocoon from predators.
When I poked the ladybird to get a better look at the cocoon, it resisted my touch, steadfastly standing guard. Some ladybirds can survive this ordeal, and go on to live normal lives, but more likely than not the process is unsurprisingly fatal.
It is a grim end for an adult ladybird which otherwise enjoys being a top arthropod predator, but from a wasp’s point of view, the process is an ideal life history strategy. Feeding internally means that the larva never has to search for food and is always protected from predators. And having a ladybird bodyguard as a pupa is really important during such a vulnerable time in an insect’s life. One study found that 85% of D. coccinellae pupae that were protected by a dead ladybird were eaten by predators, whereas only 33% of those protected by a living ladybird were predated.
By observing ladybirds for the ladybird spot, I’ve not only learned so much about the target beetles, but also about other insects that I otherwise would not have known anything about!