Tuesday, 29 April 2014

Tamarisk - Tamarix tetrandra

A beetle from the Scarabaeidae family
Wandering around the garden this morning I brushed past a Tamarisk branch sending a flurry of winged insects into the air.  The plant is always stunning at this time of year, each branch adorning candy floss pink flowers, but until today I hadn't realised the enormous diversity of insects that the plant attracts. A brief count up revealed at least eight different species, some nectar feeding, others hunting the nectar feeders, all seemingly as mesmerized as I was in this spectacular plant.

Robber Fly - Asilidae (i think )


Eristalis tenax - European Hoverfly

As well as being a good biodiversity plant, Tamarisk branches can be used for basketry, the nectar is forage for honey bees and the plant is relatively unique it that it can tolerate saline soils and actually concentrates salt within the plant. This makes Tamarisk a good choice for planting around gray water outlets. Overtime, gray water systems often accumulate salts in the surrounding soil and this can be damaging to nearby plants. This is due to the fact that water in the soil spaces is taken into the root hairs of a plant by the process of osmosis (see below), there being a higher water concentration outside than within the root hair cells. If the water concentration outside the plant becomes less than inside the plant  (i.e the salts have dissolved in the water) the higher concentrated water from within the plant will move into the soil and the plant will desiccate and die. By planting a few Tamarisk shrubs on the fringes of your gray water outlet,  you may help reduce the accumulation of salt in the soil.

Quite a circus act. Suspending mating whilst the mate is feeding!


 For more info on Tamarisk tetrandra click here


definition of osmosis - the movement of water from a region where there is a high concentration of water to a region where water concentration is lower, through a selectively permeable membrane.

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Sunday, 6 April 2014

Garden Allies - Wasps

Welcome to part two of a series of posts looking at a range of beneficial organisms commonly known as bugs, critters or creepy crawlies that can contribute to a healthy, productive and pest free growing environment in your temperate garden(For part one click here ). As well as identifying key species that serve as allies to our efforts in the garden, we will look at ways to attract and keep these organisms around.

Here we look at the different types of wasps we commonly interact with in the garden and although it may sound bizarre to want to encourage wasps, they do us a great service .



The wasps are insects placed in the order Hymenopteran, along with bees and ants amongst others. This is a huge order containing over 40,000 known species in Europe alone, and is the only order that we find truly social insects (termites are the exception). I have selected three superfamilies of wasps to talk about here that highlight the behavioral diversity of these organisms as solitary hunters, social beings and parasites. 

Digger Wasps - Sphecoidea 

The Digger Wasps are all solitary creatures, many of them burrow in sandy soils while others excavate small nests in dead wood such as tree stumps and fence posts. In the later case their presence can be detected by little piles of coarse sawdust. Some species prefer not to dig their own burrows and will nest in the old hollow stems of herbaceous perennials and garden canes. The nests typically consist of several cells in which an egg is laid and provisions are made for that egg. Unlike bees who provide nectar and pollen for their young,  wasps fill their nests with meat. The wasp, using its sting, paralyses its prey rather than kills it. This is so that it will not rot before the larvae gets a chance to eat it. Prey such as caterpillars, flies, crickets, aphids and spiders all feature in the diet. Wasps do eat nectar and pollen but they do not feed this to their young.
Some species will place meat provisions in with the egg, seal the cell and fly away to build a new nest never to meet the young. Other species hang around bringing food to the larvae and continuing to feed them until they pupate, later emerging as adults. Some species in this family do not make nests at all, instead they have developed a cuckoo habit laying in the nest of other wasps.

There are many different species, some looking similar to what we most commonly think of as wasps, others  entirely black lacking yellow bands. The majority of the black digger wasps provision their nests with aphids.

Image from www.chrysis.net
For citation purposes
Agnoli G.L. & Rosa P., Chrysis.net website, interim version 03-May-2011 , URL: http://www.chrysis.net/. - See more at: http://www.chrysis.net/chrysis/intro/hosts.htm#sthash.a6CH
Benefits
The wasp's feeding habit is a service to the grower as it consists mainly of pest organisms.  These wasps are not aggressive and will only sting if handled so do not pose a serious threat to people. The digger wasps are also known to play a role in the transfers of pollen from plant to plant whilst they feed on the nectar and pollen grains.  
 
Habitat - Areas of  bare ground and piles of old and new logs will provide nesting sites. Species rich grasslands will provide a valuable source of nectar for the adult wasps. (For more info on plants to attract wasps see below)
Herbaceous perennials with hollow stems (see below for species), can be left uncut to provide nesting sites. The hollow stems can also be cut and stacked horizontally and placed in a sheltered position. As with all organisms water is an essential requirement and necessary for nest building. A pond with a shallow edge is ideal.
  

 

True Wasps - Vespoidea

The true wasps include both solitary and social species. Several of the solitary species make their homes in our gardens frequently digging holes in vertical banks and in the old mortar of old walls. They are called the mason wasps. They're similar to the Digger wasps in that they paralyse their prey to stock their nests, generally hunting small caterpillars.

Common Wasp, Hornet and Cuckoo Wasp

The social wasps are the most familiar wasps and are considered the wasps as far as most people are concerned. They may strike fear into you as they buzz around your food on a sunny day but they are not aggressive by nature, just looking for a sweet treat. They resemble bumble bees in forming annual colonies and only the newly mated females or queens survive the winter. The queens awaken some time in April on a quest to find a new nesting site. Less than 1% of the queens manage to start a new nest. To start with, nest building is the solo project of the queen. The nest is built from paper manufactured from wood and mixed with saliva, often underground and always undercover. An old mouse hole, under a tree stump or under roof tiles are all possible locations. After the queen has built a nest containing around 6 cells she lays eggs and continues to build. When the eggs hatch the queen, as well as managing the build, hunts and feeds the grubs with chewed up caterpillars and other insects. Unlike the solitary species, the social wasps do not sting to paralyse their prey but pounce and bite. The grubs pupate and emerge as adult workers when they immediately set about enlarging the nest and take on the task of feeding their sisters. The queen kicks back and occupies herself with egg laying, filling the ever expanding nest.


The completed nest may have up to 12000 cells and during a season a colony may rear up to 25000 wasps although the average is probably nearer to 15000.  Towards the end of the season, males and new queens will be produced. The queens will leave the nest, mate and hibernate until the following year. Meanwhile, the rest of the colony will die when cold weather arrives. The old nest will not be re-used.                

Benefits
It takes little imagination to consider the quantity of would be pests a wasp colony will consume throughout the season. The wasps themselves will also provide a small but not insignificant source of nutrients with their own bodies decomposing around the garden come late autumn. They also contribute to the pollination of the different plant species they visit when feeding.
As mentioned above the social wasps are not aggressive, however a nest too close to the house is probably going to cause discomfort and may need to be removed.         

Habitat
Old stumps, rodent holes, dense vegetation and old sheds or outbuildings are all suitable locations for nesting. Having piles of logs and sticks will provide a source of wood needed for nest building. Flowers from the Umbelliferae familly are commonly utilized by wasps for nectar as are many fruits such as plums and blackberries etc.(see below for plant list) I always leave a few fruits on the trees and shrubs, or left on the ground for the wasps and other insects to enjoy.  Nearby water will be attractive to the wasps. A pond with a shallow edge is ideal.

True Wasps - Image from www.chrysis.net

Parasitic Wasps - Ichneumonoidea 

 Technically, these insects are parasitoids rather than true parasites; parasites allow their hosts to live, while parasitoids eventually bring death. Though there is great diversity in the physical appearance and life cycles of these fascinating and important insects, they have one thing in common: they use other insects to house and feed their developing young.

A common parasitic wasp from the Ichneumon family Ophion luteus
The host, typically a caterpillar (larva), is selected by scent. Once located, the wasp will lay a number of eggs inside the body of the caterpillar -  some species can lay more than 100 eggs. The eggs will hatch and the grubs inside a  grub will proceed to eat the organism from the inside carefully saving the vital organs until last. The grubs now pupate around what is left of the host and will emerge as adults.

Benefits 
Many of the insects these wasps parasitise are considered garden pests, making them an incredibly important ally for gardeners who wish to keep pest populations in check. The vast majority of  these wasps are incapable of stinging humans, and since they are so very small, most gardeners aren’t even aware of their presence. Specifically these wasps help reduce the number of Large White - Pieris brassicae larvae that can cause significant damage to Brassica crops. As with other wasps they make a contribution to the pollination of plants.  

Habitat
Adult parasitic wasps of all species require not only host insects for their young but also nectar and pollen for energy. They lack mouth parts capable of extracting nectar from tubular flowers and so require plants with shallow, exposed nectaries to feed. Members of the Apiaceae (or Umbelliferae) family , such as angelica, chervil, fennel, dill, are known to attract beneficial wasps. Other plant families that are attractive to parasitic wasps include the mint family (Lamiaceae) and the aster family (Asteraceae). (see below for plant list). Nearby water will be attractive to the wasps. A pond with a shallow edge is ideal.

 Multifunctional Plants that attract Wasps

We are growing some great perennial vegetables and herbs at our nursery, plants ideally suited for a productive ecological garden grown entirely naturally. Below is a list of perennial vegetables and herbs that we have available commonly utilized by wasps and many other insects.

Armoracia rusticana - Horseradish
Foeniculum vulgare - Fennel 
Levisticum officinale - Lovage  
Sedem telephium - Orpine 
Tanacetum vulgare - Tansy
Melissa officinalis - Lemon balm
Mentha pulegium - Penny Royal
Allium tuberosum  - Garlic Chives 
Rubus fruticosus cv. - Blackberry
Vitis vinifera cv. - Wine Grape
Ocimum x citriodorum - Lemon Basil
Origanum majorana - Sweet Marjoram





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