Pesky pests I

Funny how one thing leads to another …

I posted a comment on the Garden Dum website (based in Australia) to the effect that the yellow and black ladybirds (Illeis galbula) we find on cucurbit leaves and that are thought to control powdery mildew, actually spread it, don’t they?

The article author, Jennifer Stackhouse, politely queried where I might have got such an odd notion from, so I linked to this Royal New Zealand Institute of Horticulture article about powdery mildew by Jane Wrigglesworth that says: “But if you think these beetles will help control powdery mildew, think again. They actually carry spores of the disease under their wings from plant to plant.”

I also quoted from the 2005 book, Backyard Battlefield (Random House), by entomologist Ruud Kleinpaste who says, “Sadly, observing these elegant creatures in my veggie garden I think I have gathered enough evidence to accuse them of spreading the fungus from leaf to leaf and plant to plant.”

Illeis galbula on a courgette leaf. Photo: Sandra Simpson

So far, so good. Jennifer double-checked my information against that available in Australia and came back with information from Denis Crawford, an insect photographer and garden writer.

“I have heard this story before,” Denis says, “but it is not supported by any scientific literature I can find.” He quotes an excerpt from a paper (one of the few, he says) which examines the biology and behaviour of the fungus-eating ladybird Illeis galbula:

“Feeding behaviour is remarkably uniform, both larvae and adults graze fungal spores and hyphae from surfaces of leaves. When Oidium sp. is dense, they feed on a front and visibly clear large areas of the leaf’s white fungal covering; if infestation is light, both larvae and adults search leaf surfaces at random and if nothing is found, adults fly off.”

Denis suggests it may be possible that the beetles spread the fungus as would any other insect which walks over the spores and moves to another leaf, as would water drops, wind, etc. “The ladybirds almost certainly do more good than harm.”

So I contacted Murray Dawson, RNZIH webmaster, to share this information and wonder if he knew any more … and Murray was kind enough to let me know that Denis who, it turns out, is writing a book on garden insects had also been in touch seeking clarification.

I wonder if it’s one of those things that has been said often enough that people now accept that the ladybirds spread the fungus, and repeat it as a truth to other gardeners. If any readers have any ideas or knowledge, I’d be pleased to hear them. Just click on the “reply” tag underneath this post.

PS (May 5): In the latest edition of the weekly Get Growing email newsletter I find Lynda Hallinan also repeating the story that the ladybirds are pests.

Wasp-ish

Amusing letters in the Bay of Plenty Times this week about what not to do with a wasps’ nest. First up (on February 4) was someone who offered the advice “where german wasps are concerned don’t try to deal with them yourself unless you know what you are doing” and was probably written in response to this story in the paper on February 1.

He/she (I suspect he) writes that fly spray only provoked them and a hose even more so! “I ran like hell.” The parting advice is get in a professional, so here is some advice from a professional.

A wasp nest under construction. Photo: Sandra Simpson

Ruud, “the bugman” Kleinpaste, in his book Backyard Battlefield (2005, Random House), says of paper wasps:

“Established nests are easy to terminate at any stage. All the wasps are home after sunset and later in the evening temperatures are lower, so the reaction time is longer as they sit – head first – in their cells. Approach is easy and should be swift – either spray the face of the nest thoroughly with an aerosol (fly spray will do) or sever the nest’s stalk, dropping it into a plastic bag (without holes). Tie the bag up before the dozy buggers back out of their cells and chuck it into the freezer overnight for a cool kill.”

His advice for german wasps involves evening or night-time, two people (one to carry the torch) and kerosene or diesel, or chemical products bought expressly for the purpose. The fumes of the diesel/kerosene will kill the nest – Ruud suggests carrying the liquid in a bottle and jamming the bottle into the nest entrance to block it. NEVER light it and DON’T linger, the wasps will be attracted to the torchlight.

His other stern piece of advice, too late for our letter writer, is NEVER use a garden hose to try and flood the nest.

The other correspondent (February 7), oh, let’s call him Gordon (cause that’s his name) suggests putting your chemical of choice in the end of a  metre-long piece of garden hose, approaching the nest at night (with someone to hold the torch), getting the hose just inside the opening of the nest and … blowing!

“Warning – make sure you get the hose the right way round,” Gordon advises in a somewhat redundant fashion, but then he has form. “We once used this system for drenching horses – only the horse blew first”. Priceless.

Ruud also makes the point that you should identify your target as there are a dozen or so beneficial parasitic wasps in this country preying on pests such as the cabbage white butterfly. Environment Waikato offers a useful set of identification drawings.

And while we’re on the subject of flying, buzzing things – did you know there aren’t any bumblebees in mainland Australia? Tasmania has bumblebees (Bombus terrestris), thought to have arrived from New Zealand but that’s as far as Australia would like them to advance, thank you very much.

They are such useful, and charming, workers in the garden. I haven’t seen as many honeybees this year so the bumblebees may have been doing the bulk of our pollination. Here’s a whole website (originally) dedicated to bumblebees only.