Biological control in the rose bed...

Prompted by something Deb (Cree) said in one of here posts I decided to make a forum where the science of roses can be discussed. This may not be everyone's cup of tea but for those of you with a penchant for science, you may find something here of interest. To kick it off, getting back to what Deb said, she mentioned parasitic wasps that control aphids in rose gardens... so I went and did a bit of digging and found a lot of interesting information...

Firstly not all aphids are the same. Here I was thinking and aphid was and aphid was an aphid! Well that could not be further from the truth. Roses are affected by a type of aphid known as the rose aphid (Macrosiphum rosae). These, and others in the genus Macrosiphum can be distiguished from other aphids by the pressence of much longer legs and less rounded body.

The next interesting thing I learnt was this... when rose plants are infected with aphids it gives off alarm signals that we cannot see. These are like the batman symbol lighting up the sky calling all predators of aphids to come and clean up the infection. This is pretty nifty I think. These signals are capable of being seen, by these aphid predators, from a long distance allowing them to find infestations of aphids even though they may well be widely scattered. At a close range these aphid predators are able to switch from visual cues to chemical ones as the aphids sucking the plant's sap produce a sticky sweat substance called honeydew (more on that later) that gives off a sweet aroma. The picture I get in my head is like old cartoons when the smell of freshly baked pies wafts out of a window like an outstretched hand embracing a passing character and carrying them on a wave of smells to its source where they proceed to devour it in ecstacy The effect of the smell of the honeydew on these aphid predators is similar to the effect of hot chips on seagulls!

We are all familiar with the ladybird as being aphid enemy number one, but there are others like lacewings and birds that also take their toll. To me the most interesting of these aphid predators is a tiny wasp that is effective in controlling whole populations of aphids in a very short time! It's name is Aphidius rosea. It's not a native to Australia, originally coming from Italy. This tiny wasp is no bigger than the aphids themselves, for reasons that will become obvious soon. There are many different species of Aphidus and each one specifically controls a different group of aphids. Aphidus colmani is one of the most common but it cannot parastise the rose aphid because of rose aphids have these long legs. But Aphidus rosea has no trouble and the rose aphid is its culinary target of choice. It's quite fascinating but in many ways macabre and sinister The adult wasp, having honed in on the visual and chemical signals positions itself next to the adult or juvenile (nymph) aphid and curls its abdomen under its body extending a sharp ovipositor that it sticks into the aphid with surgical precision injecting a single egg into the aphid. In just a few days the egg hatches and the wasp's larvae begins to eat the aphid from the inside out, starting with the non-vital body parts first. After about 10 days the larvae sticks the now dead aphid to the leaf and spins a silken cocoon inside the aphid's abdomens. After a very short metamorphosis of 4 days the adult wasp chews a hole out the back of the aphid, which is now chillingly referred to as an 'aphid mummy', and crawls out looking to mate and continue feeding. The size of the adult wasp is limited by the size of the aphid that it crawls out of! Its whole lifecycle can be broadly divided into a few different stages; egg larvae metamorphosis adult. The whole cycle lasts about 4 weeks. When the adult emerges it mates and begins laying eggs itself, most of which it lays within four days of emerging from its 'mummy' ( ) . Each adult will lay between 200 and 300 eggs in its 2 week stage as an adult to start another cycle and while in the adult stage it will eat about one aphid a day for 2 weeks, the honeydew from other aphids, and the nectar from some flowers. Honeydew is a sugary substance that aphids secrete from their abdomen. The phloem containing the sugary products of photosynthesis is under high pressure inside the plant and when the aphid pierces the plant's dermal layer the pressure of the phloem in the plant forces the sugary substance to flow through the aphid and squirt out the rear of its abdomen in drops The wasp comes along and drinks it up and gets a carbo loaded energy drink... before it eats the aphid

So where can this little baby be found? Well according to the CSIRO this little wasp has spread quickly since the early 1990's and their confirmed distribution is all of NSW and all of South Australia. These are the only two continents where they have been confirmed but it is expected that they are present in small numbers in other states and that they will continue to expand their range. In NSW and VIC they can now be found in most gardens that don't go overboard with insecticides.

So what's the moral to this story? Be clean... be green... and let nature give you a helping hand

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My hoyas often get the orange aphids on them ??

That's an interesting read TasV, thanks
Val

The most important thing to get and keep these wasps in your garden is to provide the right flowers for them to feed on, which was what I was talking about in the previous thread on companion plants. With out the right flower to feed on they can not live in your garden. This is where it is important to track and share the information of what flowers they feed on. As I was trying to point out, the right flowers also need to be there before the aphids arrive in spring, so that the wasps are able to feed..and then are ready to breed. The flowers need to have a certain type of construction, where the pollen is exposed and give a flat area to land on. They can not crawl around inside flowers looking for it. It does no good to plant any flower if it is the wasps you are trying to bring to your garden can not feed on it.
This past year after working on getting the right flowers into the garden blooming prior to the aphids arrival, the wasps were here in large numbers right when the aphids first appeared. There was no delay as had been the case in previous years. Was wonderful to see this working. Biological controls are only going to be considered effective if they work quickly and when needed.
So knowing that these wasp exist is the first step, the next step is to make it work in your garden. Brings us back to providing dinner in the garden. Snow daisy, Feverfew and German Chamomile so far have proven very effective for feeding the wasps in late winter and early spring.

Well... Tasmania has rose aphid wasps I took this photo about 30minutes ago after finding mummies on the undersides of some rose leaves this morning. This morning this aphid was well and truly dead... but I could see the wasp larvae wriggling around in side it and it hadn't spun a cocoon yet. By this afternoon it had the silk base attaching the aphid to the leaf. I've got it in a small container and am hoping to photograph the adult in a few days.

Not the adult from the above mummy but one I found on the plant a little while ago:

This will give you some idea of scale:

I have never seen a web on the aphids before, so you might want to check this a bit further before you make your statement of fact. Might be a different bug or perhaps my eyes are just not good enough to see the webs. As said before in the posts you deleted, contact some of the experienced rose growers in Tassie for local information.

Thankyou Cree. I have already done this and am waiting confirmation from Dr Paul Horne, IPM Technologies. You will notice I didn't identify them as "Aphidius rosea" but as general rose aphid wasps (of which there are a few different ones).

I have just received confirmation from Dr Paul Horne that he feels these are in fact Aphidius rosea.

Hello Simon,

I am fairly confident that the aphids are rose aphids and the wasps are rose aphid parasitoids Aphidius roseae.

I have copied this message to James Altmann and Lionel Hill who may be able to comment further.

Regards,

Paul


Dr Paul A. Horne
Director/ Entomologist
IPM Technologies Pty Ltd

ph: 61 3 97101 554
mob: 0419 891 575
fax: 61 3 97101 354
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As soon as I get the reply from the other two I'll be emailing the CSIRO so they can update their website.

Hi Simon, great pix would love to have a camera like that. The wasp we seeing in our rose gardens are not like the ones shown in your pix.
The mummies are rather round like a bead and fairly firm, even the wasp does not look like the one in the pix.
YOU DO NOT HAVE THE SAME WASP AS NSW. Better keep looking and ask around the experienced rose growers in your state.

In the last 5 years we have seen the introduction of the African Small Hive Beetle. This was first sent to the CSIRO for identification when first noticed in the Richmond district. Everyone breathed a sigh of relief when their experts identified it as not being the African Small Hive Beetle. Everyone was on alert to go and destroy it in that small area as they are the worst pest imaginable for the beekeeping industry.
As a result of the CSIRO experts stuffing up ( Incorrect Identification ) and the government Apiary experts sitting on their hands doing nothing we now have the African Small Hive Beetle destroying 90% of bee boxes all up the east coast of Australia.
This has eroded my confidence in the experts in our government departments and when I see you writing how their reply will be 100% correct and the last word on the identification subject I think visiting some of the very experienced rose growers in your state the best course of action.

At the moment I don't have any Aphids, wasps or a good close up lens camera to send you a pix.

Mushroom

Possible insect causing web in photo
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could this be the aphid conditon
..The young "nymph" aphids go through several growth stages, moulting at each stage into a larger individual. Sometimes you can see the delicate pale white aphid skins or "casts" after they are shed. ...
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Photo of what I have been taught by experienced gardeners of aphid mummies from parasitic wasp larva. Aphid is creamy then tan in colour and, smooth shinny and hard to touch, hollow inside.
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Just thought this was a great photo of a lacewing's egg
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Hmmm Bruce... I think you are a little too premature to write them off. As for categorically stating they are different... well this too is a little premature I think. I think you are assuming too much from what I've actually said and from what I've actually quoted. Nowhere have I, or anyone, stated anything for certain nor did I say I was relying on them for a 100% identification. I sent them the photos and I would have fallen over backwards with shock if they had categorically said yes that's them from photos alone. That would be the worst science I could imagine. I was out inspecting the plants again this afternoon and found those hard little beady cocoons you mentioned as well:

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On the same plant were also loads of these, also taken today:

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What does this prove? Nothing at all. What does it suggest? Lots. It suggests that maybe there is considerable variation between the mummies of these wasps. What I have subjectively noticed is that the mummies with the webs seem to be smaller aphids than the hard shiny ones... maybe the larvae inside the smaller aphid doesn't have enough room and must extend its cocoon out through the bottom of the aphid. It might also suggest that there is more than one species of parasitic wasp here. Also subjectively I have noted that there seems to be a slightly larger wasp around too. Given that there are several species of aphid parasitoid wasps around and that they are not entirely exclusive in their diet (Aphidius colemani is advertised for use on a range of things from fruit and vegtable crops to ornamental plants in greenhouses all of which would have different aphid species), this is a big possibility. Cree... those little lacewing eggs look similar, however, you can clearly see the exoskeleton of the aphid in the first photo and not in the link you posted. Very cool pic though. I think your statement about the aphid going through different stages could be worth investigating further so it will be interesting to see what comes out of the mummy with the web. Before I categorically state anything... I have collected both lots of mummies pictured above and when they emerge I will be able to compare both lots of wasps. I have since received an email from the entomologist from TAS DPI who also said he would not be able to positively ID them from the photos but would defer to Dr Paul Horne's better judgement because he is a non-government expert in this field. The photos have now been sent away to Adelaide University and they have said it would be a good idea to have sample sent to them for a positive identification...

Enjoy the pics