Photographer in residence at St Cyrus National Nature Reserve, Pauline Smith, not only takes awesome wildlife photos, she writes fascinating blog posts too! Today she looks at the intricate adaptations and evolution of mind and body-controlling parasites, through the very specific relationship between a wasp and a ladybird…
I found this lovely seven-spot ladybird posing on the Ceanothus in the garden but suspected something unusual was going on when I saw it again the next day in exactly the same spot. A closer inspection revealed the sinister truth: the ladybird was`standing guard’ over a cocoon (among the fibres you can see under the ladybird), the cocoon of a parasitic wasp (Dinocampus coccinellae).
This wasp is a specialist parasite of ladybirds and has a very interesting life cycle.
The female parasitic wasp (about 3mm), using her ovipositor (the `spike’ at her rear end), injects an egg into the adult ladybird. On hatching inside the ladybird, the wasp larva first kills any other parasitoid eggs/larvae already present inside the ladybird (to have the host to itself!). As it develops, the larva derives all of the nutrition it needs from the ladybird, and by taking nutrients only from non-essential parts of the ladybird, the wasp larva ensures that the ladybird survives, at least for the duration of the parasite’s larval development.
After a few weeks, the larva, still inside the ladybird, is fully developed and ready to move to the next stage, where the plot takes an even more sinister twist! After burrowing out of the ladybird’s`undercarriage’, the larva spins itself a cocoon – incredibly, the ladybird is still alive but now rooted to the spot, where it stands guard over the cocoon (which is what I witnessed above). While the wasp larva develops inside the cocoon over the next couple of weeks, the ladybird remains in place, providing shelter and protection against predators for the cocoon; the ladybird even twitches if anything gets too close!
Almost immediately after emerging from the cocoon, the adult wasp will be on the lookout for a new victim, into which it will inject an egg, and the whole cycle will begin again. Interestingly, these wasps are primarily parthenogenic; the female is capable of reproducing without the input of a male wasp, which occur only rarely.
Amazingly, the story doesn’t always end there for the ladybird: one-third of ladybirds make a full recovery, and may reproduce … and they may even be parasitized again! This almost unbelievable recovery of the ladybird is also a testament to the parasite’s `care’ to not kill the ladybird, at least while the wasp develops – and any surviving ladybirds are then available for future `use’ by another parasitic wasp.
The wasp’s strategy is as clever as it is cunning! The ladybird provides all that the wasp needs to comfortably progress from the egg to the adult stage. It acts as a protective shelter for the egg and the larva, and also a source of food for the larva, and it then continues to provide shelter and protection for the pupa; all of this is strengthened by the ladybird’s striking colouration, which warns potential predators of its ability to release unpalatable and poisonous chemicals.
Curious as to why the ladybird would stand guard over the cocoon, in 2015, researchers found evidence suggesting that the female wasp also injects a `mind-controlling’ virus along with her egg into the ladybird. This virus is thought to be responsible for the zombie-like state of the `locked down’ ladybird. Much more is yet to be discovered.
I find these types of inter-species interactions absolutely fascinating, and can never quite get my head around how this would all have begun!