Bees, Parasitic wasps and Biodiversity Day

 

There was an old lady who swallowed a fly

[fill in the rest yourself!]

She swallowed the cow to catch the dog,
She swallowed the dog to catch the cat,
She swallowed the cat to catch the bird,
She swallowed the bird to catch the spider,
She swallowed the spider to catch the fly;

I don’t know why she swallowed a fly

What nonsense we still teach our children. Surely, every child would know that a cow would never catch a dog! In my two previous posts about the mason bees, Osmia bicornis, in our garden I have mentioned the other players on the biological stage. Beetles, spiders, flies and kleptoparasitic bees have all put on a show as well as the mason bees themselves. Sally’s picture shows a single cell of the leaf cutter bees (these have not started flying yet but it should be soon). Look more closely and you will see three black beetles – the Six-spotted spider beetle that I mentioned earlier. Each beetle is in a white cocoon made by its pupating larva. We have reared large numbers of these beetles on our kitchen table and released them outside. But I have not yet seen any of them near the mason bee nests. The beetle larva is a very messy feeder and when it is ready to pupate it makes a cocoon in a small cavity it has cut in the bee cell and eventually becomes the adult beetle. Well sometimes. I have been following what happens when the beetle larva is attacked by a parasitic wasp.

 

This picture, taken through a microscope, shows the fat, creamy white, beetle larva in situ. It is basically a swollen bag of resources ready to become a beetle. But you can see one parasitic wasp larva sucking out the body fluids for its own use. It is an exoparasitoid because it feeds on its host from the outside of the body.

 

 

 

I have several beetle larvae under observation – this one shows more of the parasitic larvae but the beetle larva is less well seen. It is just possible to see the empty bag of the beetle’s body in the lower part of the picture. But what really amazed me was that when I looked again 24 hours later the wasp larvae had really grown!

 

Only the hairy head of the beetle is left  (top right corner of photo)-  every bit is being gobbled up!

 

The wasp larvae then seemed to rest for two or three days without doing much. I was becoming concerned that they were going into diapause ie do nothing but remain in the larval state for some time. It’s difficult to keep larvae alive if they diapause for a long time – the conditions need to be just right. Fortunately they have pupated. Brilliant! Shrink wrapped pupae.

To help orientate – the pupae are upright (more or less on their backs) with their round heads at the top. You can make out the eyes. The long string of segments (looking like a string of short sausages) starting from the face are the antennae. You can see the enclosed wings (short oval structure pressed against the body) and some of the legs. When the pupae start to darken I will know that they are getting ready to burst out of their pupal skins. How exciting. And I don’t even know what species I have!

I have also got a different parasitoid that has eaten the body of a bee. It too has pupated and is now a dark green colour – something is going to happen soon. And this is why the children’s song that I started with is really not quite scientifically correct. Food chains are short – three to four levels only. But they are interconnected, to form a network of species that is hopefully resilient to change. However, the International Day for Biological Diversity should remind us that we should not take this resilience for granted. Bees need flowers and lots of them. No flowers in the countryside becomes no bees, no beetles, no wasps, no hedgehogs, no birds (———–) fill in the spaces yourself. Perhaps the song is not so bad after all.

Malcolm