Bug hunt and rosemary leaf beetle

by Richard Jones

"So what are these things on my lavender?" said the complete stranger, plonking down a jam jar full of beetles on the table.

Richard Jones"So what are these things on my lavender?" said the complete stranger, plonking down a jam jar full of beetles on the table.

Ordinarily I would have been pleased, but slightly surprised, to be accosted like this, but Saturday 17th May was open season for me to name whatever was brought my way.

It was the Nunhead Cemetery Open Day (it's more like a fete really) and for the umpteenth year we ran the now famous Bug Hunt. It's very easy: the kids collect a plastic container, look for bugs in this now beautifully rambling and overgrown Victorian cemetery, bring it back to the stall to have their finds identified, and receive a splendid certificate to take away as a souvenir.

It's a great day, and wonderful to be at the centre of so many curious and inquisitive children, eager to find out all about the wildlife they have found and held in their own hands. Their eyesight is so good, and they're all immensely proud of the often tiny specks of protoplasm which would be passed over in a blink by their parents. It's always fascinating to see what they can find and so rewarding to be able to tell them how many legs a woodlouse has (14) or how a hoverfly larva skewers an aphid then sucks out its guts. The more gruesome, the better.

Unfortunately this year it was more of a slug hunt rather than a bug hunt, as the cold drizzle set in for most of the day. So when a local gardener brought out her bottle of beetles, she was just joining in the fun of it all. Of course, they were rosemary leaf beetles, Chrysolina americana. I hope I countered her worries that they would kill the plant. Although they're now very common in the London area, the rosemary, lavender and sage bushes they eat are so vigorous that I've never seen any serious defoliation. And they're such pretty insects too, with their metallic domed bodies, coloured golden/brassy with contrasting reddish stripes.

This beetle has a curious history in Britain. It was first found here in 1963, crawling about in a kitchen in Disley, Cheshire. The conclusion was that the beetles had been accidentally brought back in some pretty pine cones, collected on the family holiday in Portugal. Despite its scientific name it is a Mediterranean, not an American, species. Then in 1994 it appeared in the RHS Garden at Wisley, this time outdoors, feeding on garden rosemary. It was not long before it started turning up all over the place.

I first saw it when an old friend of mine spotted one, crushed, on the pavement near Waterloo Station. I went up to have a look and sure enough, there were the beetles scoffing the many hundreds of small lavender bushes that had only recently been planted to decorate the paved walkways around the Shell building there.

Entomologists are always a curious sight as they crawl around on all fours, bottom in the air, head down to the ground, fingertip searching, so it was not long before a passer-by asked me what I was doing. I told them I was looking for a beetle. Without hesitation came the next question: "Where did you lose it?"

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Gardeners' World Web User 28/05/2008 at 08:48

Although the others you describe are probably the harlequin ladybird, Harmonia axyridis, your metallic stripy 'ladybird' is almost certainly a rosemary leaf beetle, Chrysolina americana. Look out for the pale grey grubs, up to 10 mm long, sitting hard up to the stems, nibbling the edges of the leaves. The beetle rarely does much damage and it is such a wonderful looking insect.

Gardeners' World Web User 01/06/2008 at 18:36

I have just discovered a multitude of rosemary beetle on my rosemary. Is it the cause of frothy collections at the base of some of the sprouting shoots?

Gardeners' World Web User 02/06/2008 at 22:24

You say these plants are resilient,but our small rosemary bush was almost destroyed last year, and this year,with only a tiny amount of greenery visible, once again is covered in them. It has no chance!

Gardeners' World Web User 03/06/2008 at 21:05

I think that sophie's frothiness at the base of the plant's stems is probably cuckoo spit which is made by the froghopper, nymph of the broad-headed bugs (red and black backed).

Gardeners' World Web User 05/06/2008 at 08:39

Claire is right you have cuckoo spit. Which of course is a terrible slight on cuckoos, which I am sure never expectorate in public. The froth is made by the nymph of a plant hopper, Philaenus spumarius (from the latin for spume/ froth). It sucks plant sap and whips up its watery excrement into a protective coating of bubbles. They keep it warm when it is cold, cool when it is hot, hide it from predators and parasites and are a useful byproduct from its liquid diet. Many sap-suckers have the problem of sucking so much food to get enough protein to grow that they have to find some way of getting rid of the copious liquid that must pass through their bodies. Aphids give off honeydew to ants to solve the problem. The adult 'froghopper', 3.5 to 5.0 mm long has a wide variety of patterns from pale beige, mottled grey/ brown to black and is very common. I'd like to say that it never causes any problems, but I said that about rosemary beetles and as you can see felix says different. All I can say is that they are not pests unless they reach pest proportions.

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