Monday, 9 April 2012

Parasites? (09 APR 2012)

The word parasite, originating from Ancient Greek parásītos : one who eats at another's table, refers to an organism which relies on another organism for nourishment and shelter to survive. A subgroup, parasitoids progess to predation, eventually biting the hand that feeds them.

A couple of weeks ago, the first siting of green fly on the tulips snapped my attention out of the reverie where there are just plants and I inhabiting the garden - I warned myself that precautions needed to be taken to prevent the black bean aphid infestation that ruined the foxglove display last year. Poking around the foxgloves wondering if they would benefit from being sprayed with soapy water sooner rather than later when the buds emerged, I sensed that I was not alone. Out of the corner of my eye, I saw greyish, green aphids lined up on the lupin stems. (I knew there had to be a down-side to planting perennials.)  After the horror had subsided, I was intrigued at their orderly queue, tracing the stems so completely that they almost merged into them.


Black bean aphids feasted on my foxgloves last year.                                                    lupin aphids leave traces this week.

If my garden was a balanced environment, the aphids would breed and feed on my host plants, and in turn they would be eaten by ladybirds and other insects or kept under control by tiny parasitoid wasps which grow inside gradually drawing life from them. It occurred to me that if I left the aphids in situ, over time, the ecological balance might develop. After all, when I first arrived in the garden, there were no foxgloves, lupins or aphids; ivy, brambles and weeds filled the spaces between inherited bushes. It might be my interference with the garden that has caused this problem.

However, my newly acquired gardener's instinct directed me to sacrifice the occupied lupin for the sake of the rest. It duely received a pre-chelsea chop down to the ground. There's a chance that it might grow back this year, fuelled by the storage nodules located at intervals along its roots, though it probably makes more sense to abandon lupins and try growing a different plant that doesn't have its own aphid. It's too late to back-out of growing foxgloves ...

Aphids are usually labelled as plant pests, sometimes plant lice but they aren't described as parasitic - I'm not sure why. I presume that plants that live off other plants or creatures that live off other creatures are generally called parasites but a creature living off a plant isn't.

Mistletoe is hemi-parasitic because even though it is capable of photosynthesising by itself, it can't grow roots in soil, attaching itself to a tree with a root-like organ to obtain mineral salts and water. Its sticky seeds are usually smeared or pooped onto tree bark by birds, if a number of these  plants attach themselves to a tree, they can kill it by sucking out its sap.

Ivy is not a parasite. It roots into the ground and does not draw nutrients from trees. It doesn't try to impede their growth, merely tracing them as a means of support. If a tree suffers damage from ivy its more likely due to its weight rather than strangulation. In its juvenile state ivy forms vines which seek rite of passage until they obtain enough sunlight to trigger puberty, a genetic transformation into its adult, arboreal form. Then, its days of creeping over, it settles into life as a flowering bush producing black berries.


ivy in a local wooded park                                                                                   .... traces nearly every tree

Today I'm linking up to Donna's meme @ GardenWalkGardenTalk : TRACERY

©Copyright 2012 b-a-g. All rights reserved. Content created by b-a-g for http://experiments-with-plants.blogspot.com/2012/04/parasites-09-apr-2012.html

16 comments:

Donna@Gardens Eye View said...

Wonderful post...for learning something not for your poor lupins...I have aphids that appear on my heliopsis but never do any damage..they are eventually consumed by someone so I leave them. The worst damage is caused by Japanese beetles in my garden...they leave holes in the leaves so it almost resembles tracery.

Donna said...

Thanks for linking. As soon as I saw the ivy I thought of it tracing the tree. I too think any sucking animal would be a parasite, but it makes sense I guess they would be plant on plant and animal on animal. Aphids and slugs are my garden nemesis. I hate the little buggers.

David Marsden said...

My cardoons had a spectacular aphid infestation last year and I had it in mind to walk all the way to the greenhouse to fetch the soapy spray and all the way back again. Never did though and then one day, I noticed the aphids were gone and in their place were a dozen or more self-satisfied looking ladybirds. Seems the garden does balance out for us sometimes. Dave

Elephant's Eye said...

In South Africa ivy never has flowers or berries. I only believe it, because I've seen pictures. I wonder, is it our not cold climate, or do we only have castrated varieties?? I guess the Christmas carol we sing - the Holly and the Ivy - is about winter berries.

Mark and Gaz said...

I have to start keeping an eye, making sure that aphids don't start taking over. On the bright side we have loads of ladybirds this year and I'm hoping they will be enough to keep the aphids at bay and not cause damage :)

Alberto said...

Actually I've never lost a single plant because of aphids. They're just a little annoying to see in those sticky and pulsing colonies, often patrolled by aunts, who literally grow aphids for their sugary and honey crap. Who's the parasite of who then? Looking closely I often found several ladybirds' larvae hunting for aphids. Ladybirds larvae doesn't look as good as their grown-ups though!
I've been taught not to exceed with nutrients in plants as they grow bigger but tender shoots, which are more suitable to aphids attacks. So I almost never give anything to my garden plants.

HolleyGarden said...

Those aphids would make me run for cover! I don't think I've ever seen black ones before! We have lots of mistletoe here - it is a horrible parasite and we have a few trees that will not make it much longer. I didn't realize the different stages of aging in ivy. I love seeing it growing over trees, but would never plant it that way in my garden. Next time I see some, I'll look for the black berries!

Bridget said...

I've not seen either of those parasites. Our Foxgloves never get anything on them. Our worst pest is Badgers. We have to keep them out or they do just damage snuffling about looking for slugs.

croftgarden said...

The definition of parasitism is not affected by whether the host or parasite is plant, animal, fungus or anything else. A parasite has a high specialised and intimate relationship with its host(s)in which the parsite derives benefit from the host and it may or may not kill the host. Although aphids suck plant sap they are not parasites because they can travel from plant to plant, they can usually feed on more than one species and the relationship between aphid and plant is not particularly specialised. In the same way mosquitos are not parasitic on humans but the plasmodium they carry (which causes malaria) is.
Bet you wish you'd never asked. Nothing is simple in biology.

b-a-g said...

Thanks Donna GWGT - I'm not so disgusted by the slugs since I discovered aphids.

Thanks Bridget - If a badger came into my garden looking for slugs, I wouldn't get in its way. I bet the badgers licked off the aphids too!

Thanks Donna GEV, Allberto, Dave, Mark & Gaz - I would be happy to leave aphids to get on with their thing if there were a few of them scattered about, but last year they over-crowded the foxgloves so much that the females grew wings. Having said that, even though they crumpled the leaves by congregating on the undersides and even though they traced the stalks up to and around the florets, they didn't stop the foxgloves growing, flowering and seeding. Damage was only done to the gardener's pride.

Thanks Diana (EE) & Holley - I've scanned woods covered in ivy but I've never seen the flowers or black berries either - I've just read about them. Some varieties of ivy never pass their juvenile state. The varieties that do (if they get enough sunlight) can become invasive. Apparently, if you take a cutting from an adult ivy, it forms a flowering bush straight away - it doesn't start as a creeper again.

Thanks for the clarification CroftGardener - This was literally bugging me during the weekend, even fluffy bunnies and easter eggs couldn't distract me.

patientgardener said...

You are right it is all about getting the balance right but this takes time and patience. You need the pests so the predators will come so you have to expect the pests to build up first. You can encourage wildlife in by planting things that the predators like - such as poached egg plants which lacewing love and lacewing love aphids etc.
Dont despair as you say you have introduced lots of new plants to an area previously neglected so you are starting from scratch. Cutting back the lupin will make it regrow but tougher and more resistant. You could also try garlic spray (boil garlic bulb in water and use liquid diluted) or I am told diluted milk is also good, though I am yet to try it

Christine @ The Gardening Blog said...

The two tree photos are really gorgeous!
I used to spray aphids (with organic stuff) but this year I decided to stop all spraying. I occasionally blast them off with a hose, but they always reapper, so now I ignore them (or cut the affected leaves/stems/blooms off. And I find I have less of them now. Maybe the balance is back in my garden. I hope so :)

Crystal said...

Most of the aphids in my garden are eaten by the birds or ladybirds. However, the lupin aphid is not eaten by anything, I think it's one of those imported species, not a native bug. My organic solution is not to grow lupins anymore, sad but true.

Carolyn @ Carolyn's Shade Gardens said...

Aphids can't crawl so you can wash them off with a strong atream of water. I usually use a sponge and soapy water.

Malar said...

I hate aphids! They have kill many of my vegetables in the past!
Thanks for sharing the information! ;)

b-a-g said...

Thanks Helen - your comment gives me hope. You're right, the lupin is regrowing. I saw a recipe the other day for a pest deterrent on SageButterfly's blog - garlic spray with chilli powder and washing-up liquid thrown in too.

Thanks Christine - I was trying to write a post about tracery for a couple of weeks then I saw those trees in the woods ...

Thanks Crystal - I'm surprised that lupins are imported because they grow so easily here. They flowered in their first year, their seeds were the first to germinate. So far only one of three planted last year has succumbed to aphid attack.

Thanks Carolyn - I tried washing off aphids last year, but that didn't stop them returning.

Thanks Malar - Maybe you should try using the garlic, chilli powder, washing-up liquid spray on your vegetables. Here it is : http://thesagebutterfly.blogspot.com/2012/04/natural-garden-recipes-for-pest-and.html

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