This is a story that has the makings of a block buster…..
Picture this….. a lush and bountiful land is invaded and pillaged by villains who take over the kingdom by shear numbers. The villains prevent the locals from harvesting and consuming their crops without the accidental consumption of a large number of these villains (okay, so perhaps that does not happen in your standard story plot!). Secretly there is evidence of heroes starting to emerge, not enough to organise a coup d’etat yet, but enough to inspire the locals that help is coming. Just when it looks like the villains might destroy the crop once-and-for-all, and that failing to “napalm” the landscape with chemicals has cost the locals their key iron supply (okay so they’re not starving, but Brassica’s are pretty important in our household!)….. Fortunes turn…..Lady Luck changes side….. Heavy rain and winds reduce the numbers of the villains and put them on the back foot. Then the heroes finally get themselves organised (hatch!) and rise up. The villains fall like…like….well like (aphids and white-) flies really, and a new balance is restored where there is plenty of iron for everyone. Hurray!
All over the garden epic battles are waged, hard fought, won and lost. “Luck” comes in all sorts of forms, but nature has a way of making her own luck – good old supply and demand…. all you need is faith and patience.
Having said that, mess with her to remove the bad bugs and, depending on the method you use, you might destroy the good bugs too, leave space in the ecosystem for an alternate bad bug to move in, or she might even move your good bugs to a new backyard which respects her more. As the voice of reason keeps telling me when I ask what you do about ….well anything….
(a) look to add life not take it away. You might put in a plant that attracts predators, or keep a sacrificial crop to provide food for predators (i.e. food for the villains and hence villains for the predators) before you plant your favourite green. There are heaps of ways you can help nature if you understand her mechanics and the interacting influences….
(b) take the time to observe and learn – we’ve impacted so much to make the world conform to our desires without realising its capable of delivering our needs.
Today let’s talk about a Villain featuring in one/many of these epic battles.
THE “OH-TOO-COMMON” APHID – KNOW YOUR ENEMY!
Aphids are in the superfamily Aphidoidea in the Sternorrhyncha division of the order Hemiptera. Hmmmm, not sure what that means, but for those of us who don’t speak latin…. Let’s do some Aphid Taxonomy. We will learn in the Soil Blog Episode 2.2 – Organic Matter, that there are 5 Kingdoms, but for now, just trust me on this. (Source)
- KINGDOM – One of the Kingdoms is called Animalia – the villain resides here with us. (Let’s keep it simple and skip all the sub-kingdoms, superphylums etc)
- PHYLUM – The Kingdom Animalia is split into 35 Phylums, one of which is Arthropoda (invertebrates with segmented bodies; jointed limbs and an exoskeleton, made of chitin, a derivative of glucose).
- CLASS – One of the classes in the Phylum is the Insecta Class (a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes ( thousands of individual photoreceptor units) and one pair of antennae.)
- ORDER – We’ve finally reached the Hemiptera Order in the Insect Class. These guys are what we really should call bugs, a name referring to insects with straw like sucking mouthparts called a proboscis (To impress friends, the official plural as derived from the Greek is proboscides…. Useless Trivia 101 – how many creature have multiple proboscides?), which stabs into flesh (in our case plant tissues) to then suck out the liquids (in our case sap).
- SUBORDER – Sternorrhyncha are the ones who have “rearward position of the mouthparts relative to the head.”
- SUPER FAMILY – This suborder contains 5 super families – Aleyrodoidea (the infamous White Fly of which there are 1550 species identified you’ll be pleased to hear!), Aphidoidea (Aphididea FAMILY – Aphids – arrived at last!), Coccoidea (Scale Insects – we’ll learn more about them at a later date), Phylloxeroidea (Closely related to aphids, but no one seems to care enough to write about them! mainly found in Spain and Western Europe it would seem) and Psylloidea (A Super Family of Jumping Plant Lice, but bad as that sounds, they are thought to be the most benign of the Sternorrhyncha super families).
- Of the known ~4,400 SPECIES in 10 FAMILIES about 250 Aphid species are serious pests.
The species seen in WA range from yellow to green to black in colour and within the Swan Coastal Plain the species include: (Source)
- Currant lettuce aphid (CLA, Nasonovia ribis-nigri)
- Green peach aphid (GPA, Myzus persicae)
- Potato aphid (Macrosiphum euphorbiae)
- Corn aphid (Rhopalosiphum maidis)
- Cabbage aphid (Brevicoryne brassicae)
Our Aphid….(Very excited, just received our new USB digital microscope just today…. get ready to get up close and personal!!!)
Looks like a Cabbage aphid who’s feeling lonely, poor love!
Why Aphids are a Problem:
Aphids (and scale insects, mealybugs and white flies) suck the sap out of the plant leaf through their proboscis. Once the sap has been digested, it is excreted as honeydew. This honeydew allows a fungus to grow called Sooty Mould (the black/grey ashy type dust) which reduces the plants ability to photosynthesis and hence thrive or defend itself against other predators or diseases. (Source)
Also, serving aphids (or sooty mould come to that) in your salad is generally not a good start (or should I say finish) to a dinner party. The aphids specialise in new shoots and buds, having devastating effects on the smaller plant’s productivity by preventing fruit setting. However it is not the sooty mould that kills the weaker plants. Whilst they suck the sap from the plants, the aphids are also known to transmit plant diseases. The leaf distortion/malformation/discolouration seen when aphids are present, which again impacts the plant’s ability to photo-synthesise, is evidence of this effective spread of disease.
Aphid “Features” (why they are able to be a problem in such numbers!):
In my corporate world past we use to call stuff-ups in design “Features”. Here are a few “features” we love about aphids….
In Western Australia, most aphids are females which are able to give birth to living young without the need to mate – asexual reproduction which delivers little clones. Up to 12 live young per day per adult female can be born. With the average lifespan being about 30 days and them reaching sexual maturity after 4 to 10 days depending on the species – the maths gets scary! Aphids are said to reproduce faster than any other insect. (Source)
Reproduction slows in cold weather and accelerates in warm weather…. so I’m guessing they’re well on their way given the days are warming up!
(Elsewhere in the world some Aphids require a male to reproduce and some lay eggs. Normally the need for eggs in the lifecycle is to bridge the gap between suitable growing seasons. I.e. where winters are more severe.)
When conditions are favourable and aphids have no reason to migrate, most adults will be wingless. However, when plants become unsuitable habitats, or when overcrowding occurs, winged aphids are produced and migrate to other plants or crops.
In Summary the Life Cycle (Source) – apologies for the American tone…. fall etc…
- Birth to maturity ~ 4-10 days depending on species.
- Total Life Span ~30 days average.
There two main modes of longer distance transport are wind and humans relocating plants. Amazingly in 2004, the currant lettuce aphid (CLA) found its way to Tasmania. The Tasmanian Government determined that “may have resulted from wind assisted dispersal from New Zealand” (Source)
Most aphids can release a liquid from their abdomen which hardens like a wax and acts to protect the aphid when under attack.
For some information on other chemical defense mechanism employed by the aphids and the impact on our poor predators…..you might want to have a read of this blog: Not all aphids taste the same. Less relevant to those of us here in Perth, however it proves an exceptionally entertaining read.
Interesting Aphid/Ant Relationships:
Some species of ants “farm” aphids, protecting them and eating the honeydew released by the aphids. This is a “mutualistic relationship”. The ants “milk” the aphids by rubbing them with their antennae. Aphids are moved to new plants and unaffected areas rapidly by ants as they grow their herd.
Some farming ants store aphid eggs in their nests over the winter and deliver them back to the plant in spring for the next harvest. Some manage “herds” of aphids in the soil and graze them on the plant roots growing through colony. Queen ants leaving to start a new colony might take an aphid egg to start a new herd for her new colony. These farming ants actively fight off aphid predators.
An extension of this involves lycaenid butterflies and Myrmica ants. The butterflies lay eggs on plants where ants are grazing the aphids. The eggs hatch and the caterpillar feeds on the aphids and the ants then carry the caterpillar to their nest and feed on the honeydew it produces. When ready the caterpillar crawls to the colony entrance before creating its cocoon. The butterfly emerges and the cycle begins again.
Some bees in coniferous forests also collect aphid honeydew to make “forest honey”.
Insects that attack aphids include predatory Coccinellidae (lady bugs or ladybirds), hoverfly larvae (Diptera: Syrphidae), parasitic wasps, aphid midge larvae, “aphid lions” (the larvae of green lacewings), crab spiders and lacewings (Neuroptera: Chrysopidae).
Entomopathogenic fungi like Lecanicillium lecanii and the Entomophthorales also kill the Aphids. Having brushed against the fungi spores, the spore penetrates the skin and grows in their equivalent of blood.
Creating systems that attract these control factors for the Aphids is a proactive way of turn the tables.
We are lucky enough to have multiple micro-climates in our garden and each follows a different timetable mainly due to sun exposure. Our front yard is north facing and exposed, so it is our winter garden. Being warmer, it has seen very few aphids, but its fair share of whitefly already this year. Previous years of battling has seen the aphid as the longer term loser – perhaps because of their absence of wings compared to the whitefly (which we’ll discuss in the future) as the predators are similar. We are now seeing out the front, these gorgeous little guys:Meet your friend and mine, the Ladybird Nymph (poor love was hiding from the weekend’s storm before the paparazzi found him!) – an awesome predator with the looks to match. Don’t underestimate this little guy nor his friendly looking parent….. the hero will enter stage right just in time to save the crops (not Brassicas this time, broad beans!).
Eggs look like very organised yellow rice grains standing of their end….. okay, poor description…. like this:
It is interesting to note that the ladybird nymphs eat more pests than the adults.
The most obvious place in our garden to see the battle between aphids and the various incarnations of the Ladybird is on our big ancient hibiscus out the back. This area is shaded by a huge gum and therefore takes a little longer to feel the warmth of the spring sun. As a sacrificial anode, this beautiful huge bush (or tree – depending on what mood the pruner was in at the time and what the plan is for the ground below it!) is the perfect attractor of aphids – the poor new flowers get hammered in bud form! Back in our – the royal “our”, of course – early years of gardening, we grieved its imminent death but then these angry looking black bugs started to appear….. I suspect they had been protecting it all these years in the backyard wasteland of what was a uni student rental. The story will play out again this year as the spring springs and the sun’s arc rises to warm the backyard for more time during the day in advance of another long hot summer. When the aphids decimate the tree, the Nymphs (and not the voluptuous blond type!) will emerge and, as they take control of the hibiscus, they spread to other parts of the garden in search of food, saving the other plants before they are threatened. As far as we can tell, they have won the longer term battle against the aphids in our back yard….. with the bonus of the delight of the children when the adult Ladybirds emerge in great number.
There are various posts around the internet regarding the relocation of ladybirds to stricken plants from other gardens. All appear to be very positive in results, but remember to have several for the propagation of your species and obviously too long in a jar will not go well!
Also naturally occurring in Perth gardens are parasitic wasps (e.g. the Aphidius species). The females sting the aphid and lays its eggs directly inside the body, causing it to swell and turn bronze. (As I said….. close and personal!!! What a ripper!)
The poor blighters (never thought I’d say that about an aphid, but what a horrid way to go) blow up in size as the wasp larva hatches and develops until eventually the aphid dies and stops being a food source. Then the larva pupates which causes the mummification appearance of the aphid. Finally the wasp emerges to start the cycle again. (Source)
Like the Ladybird Larvae, the Lacewings and the hover fly larvae simply just chow down on the aphids. (In addition to the below options to attract the predators, lacewings love night time and can be attracted by lighting in the garden….. those good ol’ mozzie zappers are therefore not an aphid sufferer’s friend. But more on Lacewings another time).
I was going to write you a list of the plants that might attract each of the predators, but there is so much useful information dotted around the internet, that I will just point you toward a few sites that I found useful/interesting:
- Plants that Attract Beneficial Insects (Not an aussie site, but dill and coriander are similar the world over! Plus it’s simple and to the point.)
- Gardening Australia Forum (Closer to home discussion but thinking about attracting lizard life is an option – perhaps warm rock and other “sunning” areas might also be good?)
- Flower use to attract predators (just something to think about with planning year round flowering or pre-emptive flowering in later winter to attract your predators in advance of / or in sync with the villains)
- Attract Bees and Good Insects to a Garden – Starts on the topic of bees, and meanders through some great information and ideas. Brings us the very important aspect of permanent water for dragon flies, but I would add to this wasps and anyone else who likes a drink and is adept at standing on water based plants without falling in! They are brilliant attractors of insect life in a long hot summer. Whilst fish might be great in some ponds its good to have one without fish or heaps of plant as refuge from the fish to encourage frogs, dragon fly nymphs and other predators). There are also a few great (some disturbing) links for a newbie to the scene.
- Companion Planting – Great Australian list of what helps what and how. Looks like we will be in for a massive experiment next year.
- Beneficial Insects – Runs through several actions you can take to attract beneficial insects by different means. They use nettles as an example of a nursery plant (i.e. one that supports pests, but has no ill effect). It attracts the nettle aphids which will not devour the other plants, but can be eaten by the common predators and hence attracts them in advance of a potential future onslaught of more widely foraging villains.
Other ways of influencing aphid numbers:
The use of commercial or home made sprays may kill your aphids, but they are non specific and will kill natural predators too. It is likely that spraying as the aphid numbers increase will kill your heroes in their early stages – you may win the battle, but not the war. There may be no heroes left when the season brings on the next villain.
It is also critical to consider where the spray goes once you have walked away. Should the plant be watered or it rains, then portions of the spray will enter the soil, thus impacting the life existing to feed the plant…… Whilst this use of spray is a much more serious problem for water ways, soil and animals/birds in the large scale agriculture, effecting your plants growth systemically is never a good thing.
Healthy soils make healthy plants and healthy plants can resist pests and disease. An interesting point is made in this link – “When a plant is out of nutritional balance, internal pressures cause some cellular components like simple sugars or incomplete proteins to seep out to the surface of the leaves and stems. Voila! Free lunch for pests!” I would also guess that the weaker the plant, the weaker its membranes and easier to get a free feed from within the plant too.
Plants that repel aphids can be planted as companions to those at risk. Some plants suggested to achieve this are: (Source)
Ladybirds and lacewings are also thought to prefer moist warm conditions so long frequent watering during dry periods is suggested. Obviously this is not possible in Perth, so mulching is a great way to make the most of what water you use.
It is understood that aphids will “preferentially land on yellow (to the human eye) coloured surfaces” (Source) so removal of yellowing leaves (if you don’t already have a problem) or use of sticky yellow traps (more to prevent the spread of winged aphids, again if you don’t yet have an aphid problem and your not concerned about other life being caught – not really our thing, but you can might use vaseline on a yellow Vegemite lid or similar – can be helpful in a sealed greenhouse (but more for white fly) where you don’t have the benefit of predators entering…. but I digress again – I have white flies on the brain and the Brassicas!) are potentially selective means of reducing your risk without adding chemicals. Having said that, our aphids seemed to love a fresh hibiscus with pink flowers, so I am not really convinced that they are selective….. if they can grow wings to move on to a new plant, they can cope with a little blue mixed in with that yellow!
Assuming we can pretend that we have helped our garden by (a) not putting our old girl, the hibiscus out of her misery so many years ago, (b) planting predator attractors which hit several of our pesky pests, (c) a manual squishing expedition to make us feel better, or (d) watering them off the delicate new plants…. The next battle to help mother nature help our heroes in is the one against the white fly! This one is not going as well as the aphids…. looks like we need to focus a little more on our companion planting……. Curse it….. next time, Gadget next time…..