Caterpillar identity

[mikebriggs]

These caterpillars are destroying our fennel crop - eating the bulbs from the inside with no damage to the leaves and no obvious entry hole. They grow to about 4cm long. What are they?

[GuyF]

Welcome to the site Mike!
I'm fairly sure that these are Brindled Ochre (Dasypolia templi) caterpillars, and if it's any consolation you might be the first person to have recorded these feeding on Fennel I can't find any reference to them using it anyway - they usually feed on Hogweed but will apparently accept other umbellifers in captivity, so Fennel is probably a good substitute if Hogweed isn't available! It's quite a local moth in the UK, restricted to moorland in the north and coastal areas in the south west, would that fit with your location?
Guy

[mikebriggs]

Many thanks for your answer, Guy. We are on the Isle of Harris in the Outer Hebrides, so I guess this is about the limit of this moth's range. We have loads of other umbellifers in the immediate vicinity so it is a shame it has chosen our fennel. Any idea how the bug gets in the fennel bulb: does the moth hibernate in the ground? The plants were planted out as seedlings this spring, so I don't think the moth would have been around to lay eggs on the plants themselves.

Mike

[GuyF]

Originally Posted by mikebriggs

Many thanks for your answer, Guy. We are on the Isle of Harris in the Outer Hebrides, so I guess this is about the limit of this moth's range. We have loads of other umbellifers in the immediate vicinity so it is a shame it has chosen our fennel. Any idea how the bug gets in the fennel bulb: does the moth hibernate in the ground? The plants were planted out as seedlings this spring, so I don't think the moth would have been around to lay eggs on the plants themselves.

Mike

This species has quite an interesting life cycle. The adults hatch out and mate in the autumn, the males then die off while the females hibernate for the winter. These then reappear in the spring, and I'd imagine that this would be when they lay eggs. Apparently the female lays her egg on the stem of the plant, and then the newly hatched caterpillars bury their way down into the bulb. These caterpillars must be tiny, so I'd imagine that they wouldn't leave much of an entry hole at this point!
Guy

[mikebriggs]

Guy, thank you so much for this. It will be interesting to see if our later crop of fennel is free of the caterpillar.