Parasitoid wasp threatens Scottish Seven Spot ladybird The parasitoid wasp Dinocampus coccinellae is threatening to cause severe problems to agriculture and horticulture in Scotland. Studies by Irene Geoghegan of the Scottish Crop Research Institute in Dundee have shown that in the Dundee area, up to 70% of the seven spot ladybird (Coccinella septempunctata) is infested by this native wasp species.

by Anne Bruce

(The author would like to thank Irene Geoghegan, researcher at the Scottish Crop Research Institute, Dundee for providing materials for this article and to Andrew Syred for transferring the images to a digital format.)


The Wasp Life Cycle

One of the parasites that infects the British Coccinellidae is D. coccinellae. It has been found in 13 of the British ladybirds, irrelevant of size or colour, but the seven spot has the highest incidence of attack. The two spot (Adalia bipunctata) and the ten spot (A. decempunctata) seem to be immune to the wasp and another 8 species are known to be rarely parasitised.

Male wasps occur very rarely, the female reproduces by parthenogenesis, laying a single egg inside her ladybird host. On hatching, usually after about 5-7 days, the first larval stage is armed with large mandibles enabling it to remove any eggs or larvae already present. Once this competition is disposed of, the larval wasp obtains its first supply of food via specialised trophic cells which absorb nutrients directly from the ladybird. Later, the larva feeds directly on its host's fat bodies and gonads.

Having passed through 4 larval stages (which takes around 18-27 days) the parasite severs the main nerves to its host's legs. With its host immobilised, but not dead, the larva then burrows out of the ladybird and spins a cocoon between the ladybird's legs. This ensures that the pupating wasp enjoys the protection provided by the ladybird's bright warning coloration as well as the deterrant properties of "reflex bleeding"; a mechanism whereby ladybirds produce toxic and foul tasting fluids from their joints to put off would be predators.

Pupation takes about 6-9 days. An hour after the new wasp emerges from the pointed end of the cocoon she is ready to lay eggs and continue with the destruction of ladybirds.

 

Adult wasp emerging from cocoon

Wasp (Dinocampus coccinellae)

Seven Spot ladybird (Coccinella septempunctata)

Life History of Dinocampus coccinellae

Immobilised ladybird with pupa

Larva about to pupate

Wasp laying egg in ladybird

The implications

The action of a single wasp allows up to 55 million aphids to survive


So what is being done about this?

Irene Geoghegan is so concerned about this alarming threat to agriculture that she is running a research programme in her own time to attempt to determine how widespread wasp infestation is in Scotland. Information packs are being sent out to schools and people are being asked to send live seven spot ladybirds to Irene so that she can continue the research programme. The information packs contain many interesting facts about ladybirds and details as to how the insects may be sent without harm. Once examined, those ladybirds free of the parasite will be released into the wild.

Further studies are being carried out which focus on determining those factors which influence the wasp's preferences for laying eggs. For example, results from research already carried out suggest that female seven spot ladybirds have a higher incidence of infestation than males.

Nuclear magnetic resonance (NMR) microscopy is also being used as a technique to assess interactions between parasite and host. The advantage of this technique is that it is "non-invasive" it can therefore be carried out without harming the ladybird. A comparison of uninfected and infected ladybirds can be seen from the NMR images below.

Uninfected ladybird

Infected ladybird

The head of the larva can be seen (pink structure at left side of image), as can the change in bulk brought about by the production of trophic cells

 


Comments on the article to the author Comments to the author sent via our contacts page quoting page url plus : ('abruce','')">Anne Bruce

If you live in Scotland and would like an information pack or are willing to take part in this important piece of research, then please write to: Irene Geoghegan, Research Scientist, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA (enclosing a large self addressed stamped envelope).

 

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