Insects and Oak trees { A study of Trees}-22

English oak

geograph.org.uk
geograph.org.uk | Source

Introduction.

The British Oaks,probably on account of their large size,and the peculiar nature of their juices,is attacked by a far greater number of insect enemies,than any other tree in this country. Many of these insects ,are, of course,confined to this tree,but many feed indiscriminately upon the Beech,Birch and Hazel as well as upon the Oak.

With respect to the number of insect species which we find upon the Oak, I commence with the work which began in the 1800's with the authority of Mr.Stephens, { who was generally considered as the most general practical collector of English insects. he states that nearly half the Phytophagous { insects that feed on green plants,they include species that attack roots,stems,leaves,flowers and fruit},of England are either exclusively ,or partially inhabitants of the Oak.

Louden, in his 'Arboretum et Fruticeum Britannicum ', 1800's, states, " perhaps, if we give 2,000 as the number of Oak feeders and their parasites,we shall scarcely run the risk of over rating the quantity"

The Goat Moth Coccus coccus

Taken in Germany.
Taken in Germany. | Source

Insects feed on the various parts of the tree

The solid wood of the Oak serves for the food of various insects,chiefly while in their larva stage. Among these are the Goat Moth Coccus coccus { pictured above}, the Wood leopard moth Zeazera pyrina, the Small Stag Beetle,Dorcus parallelipipedus are all occasional inhabitants of the Oak.

Insects which live under the bark-- There are many species of insects that live under the bark of Oak { chiefly small Coleoptera},without boring into the solid wood. Of these Weevils can cause much damage.

Insects that live on the leaves-- It is on the leaves that the majority of insects find their nourishment and it is chielfy among the larvae of Lepidopterous insects that the greatest number occurs. Of these the Tortrix viridana The Green Oak Moth is prominent. Pictured below.

The Green Oak Moth , Tortrix viridana

Source

Eggs of Tortrix viridana on a winter branch

Uploaded to Commons by Ruigeroeland.
Uploaded to Commons by Ruigeroeland. | Source

Caterpillar of the Tortrix viridana

Uploaded to Commons by Edithsme
Uploaded to Commons by Edithsme | Source

Tortrix viridana, pupa

Uploaded to Commons by Ruigeroeland
Uploaded to Commons by Ruigeroeland | Source

Green Oak Moth Tortrix viridana

History informs us that an infestation of the Larvae of this species can defoliate an oak tree and they were regarded as the most obnoxious of insects. According to Louden -" Even the smaller sorts of caterpillar,become from their multiplicity,sometimes as destructive as those which are of considerable magnitude. During the summer of 1827,we were told that an extraordinary blight had suddenly destroyed the leaves of all the trees in the Oak of Honour Wood,Kent.{south east England} On going thither, we found that the report but little exaggerated,for, though it was the leafy month of June, there was scarcely a leaf to be seen on the Oak trees,which constitute the greater portion of the wood."

" But we were rather surprised when we discovered, on examination, that this extensive destruction had been effected by one of the small solitary leaf rollers,Tortrix viridana,for one of these sort seldom consumes more than four or five leaves,if so much,during its existence. The number,therefore, of these caterpillars must have been almost beyond conception,and that of the moths, the previous year,must also have been very great. For this moth only lays 50-100 eggs,which are glued to an Oak branch and remain there during the winter. It is remarkable , that in this wood during the two following summers, the caterpillars did not abound."

The caterpillar of this moth rolls up the oak leaf in a very ingenious manner,so as to form a very commodious retreat,in which, indeed, it ordinarily resides, the centre of the roll being open.,its diameter is proportional to the body of the insect,and the roll is secured by various little patches of silk attached to the body of the leaf and to the adjoining part of the roll.

The caterpillars were so numerous in Kensington Gardens in May and June ,1832, that " The excrementitious matter from them kept falling and tinkling on the grass below,so frequently as to give the idea of a sprinkling of rain being then fallen"

Other moths and Butterflies that inhabit the Oak tree.

Among the butterflies ,the Purple hairstreak is a species which feed upon the Oak in their larval stage . The larva have a superficial resemblance to a woodlouse. One which a Mr. Lyonnet,reared ceased to eat on the first of June. It then assumed a rounded form,and in three days arrived at the chrysalis state,without spinning any cocoon,and on the 27th of the same month the butterfly appeared.

Caterpillars of many more moths feed on Oak leaves. Among the leaf-feeding species, the majority are external eaters,neither concealing themselves in cases,nor rolling themselves up in leaves. Some especially among the smaller species do not agree with these in their habits, and adopt various methods of defence, which render an examination of the different inhabitants of this tree an object of diverse interest. Of these some roll up the leaves into a ball of considerable size,such as the larvae of the Scarlet underwing moth,{ pictured below }, while others again,construct their boat shaped cocoons of strips of Oak leaves.

Larvae of others feed upon the Parenchyna of the leaf,raising,as it were, large circular blisters, the upper and under surfaces of the leaf remaining unconsumed.

Red underwing moth

Uploaded to Commons by Olei.
Uploaded to Commons by Olei. | Source

White grub of the Cockchafer

Transferred from de.wikipedia
Transferred from de.wikipedia | Source

Cockchaffer in the hand

Source

Coleopterous insects -The Cockchafer.

Among the Coleopterous insects, the common Cockchafer is the most prominent of leaf eating species. The egg of this devastating insect is white and deposited in the ground,where it soon changes into a soft white grub with a reddish coloured head,it is about one to one and a half inches long.

It continues in this state for about four years,during which time it commits the most destructive damage to the roots,not only of grass but all other plants and young trees. When full grown the larvae dig into the earth to incredible depths,spin a smooth case and change into a chrysalis. In this state they remain until the following spring,when the perfect insect emerges from the soil and commences an immediate attack on the leaves of trees.

I came across this historical account given by Molyneux, in one of his early volumes of the 'Philosophical Transactions', in which their appearance in County Galway, Ireland, in 1688,is narrated.

" They were seen in the day time,perfectly quiet,and hanging from boughs in clusters of thousands,clinging on to each other like bees when they swarm. However, they dispersed towards sunset,with a strange humming noise they made in devouring the leaves so great, as to resemble the distant sawing of timber. In a very short time the leaves of all the forest trees, for some miles were destroyed,leaving the trees as bare and desolate in the middle of summer as they would have been in winter."

" They also entered gardens and attacked the fruit trees in the same manner. Their multitudes spread so exceedingly, that they infested houses,and became extremely offensive and troublesome. They were greedily devoured by swine and poultry,which watched under trees for their falling and became fat off the unusual food. towards the end of the summer they disappeared silently and no traces of them were perceived of them the ensuing year"

In the magazine of Natural History, a story is told of a gentleman,who, finding his oak trees stripped of their foliage in the middle of summer,suspected some Rooks of having destroyed them.

" That the Oaks were nearly bare there is no dispute,and he had himself seen the Rooks settling upon them,and pecking away right and left with their bills. War was therefore declared on the Rooks, but fortunately before hostilities commenced, the gentleman was convinced by someone, who knew more about natural history than himself, that the Rooks were not at fault. On the contrary, they had only flocked to the trees for the sake of devouring the myriads of Cockchafer's,and the larvae of moths,which were the real culprits.".

Female Cockchafer

Source

Oak apples

Source

Ichneumon wasp

Source

Artichoke gall caused by Andriscus fecundator.

Source

Oak Marble galls

These are often confused with the oak apple galls
These are often confused with the oak apple galls | Source

Knopper gall-caused by Diplolepsis quercus

Source

Gooseberry galls, caused by the wasp Andriscus grossulariae.

These are very similar to the Knopper gall pictured above.
These are very similar to the Knopper gall pictured above. | Source

The Young Stems and Buds of the Oak

The young stems and buds of the Oak tree are also attacked by various insects,chiefly belonging to the order Hemioptera,furnished, with long elongated rostrums,with which they penetrate without difficulty into the soft substance of the young growth. Among the weevil's many species do damage to young growth.

Oak Apples are the work and nursery to a species of Ichneumon wasp. The adult female lays her eggs in the developing leaf buds. The wasp feeds on the gall tissues resulting form their secretions. The development inside this globular abode of the larvae will depend on the diversity of the season. For example the egg, the larva,or perfect wasp may be detected and often, another species entirely as the Ichneumon wasp and their larvae are also preyed upon by parasitic flies.

The Oak apple calls must not be confused with the Artichoke Oak gall Andriscus fecundator, which look like the head of an artichoke or even the cone of a Larch tree. This one is caused by the Parthenogenetic gall wasp which lays a single egg in the leaf buds using their ovipositor. The larva lives inside a smaller hard casing inside the visual external body and this is released in autumn.The wasp emerges in spring and lays her eggs in the oak catkins.

Another type of gall The Oak Marble gall,may also be encountered on the twigs and branches of Oak species.These are produced by Andricus kollari,a wasp. they develop as a chemically induced distortion of the leaf buds. This wasp lays her eggs within the leaf bud using her ovipositor.

At first the structure is green becoming hard brown and approximately an inch in diameter. Although nearly round they have a number of little flattened nodules. The word marble derives from the shape of the gall. they can be told apart from the Oak apple gall,with which they are often confused.That gall grows much somewhat larger, and often with little red markings, but does not grow on the axillary or terminal buds. each marble oak gall which matures in August has a central chamber, with a single female wasp larva,which emerges through a tiny hole as an adult winged gall wasp in September. These galls may remain on the tree for several years.

Another structure,again made by a wasp is the Knopper-gall,Andricus quercuscalis. these are produced by chemicals which induce distortion on growing acorns and are generally thought to be much more of a threat to the productivity of the tree than all the galls which are produced on leaves twigs and branches.It was only discovered in England in the 1960's. This must not be confused with the Acorn Cup gall made by the wasp Andricus grossulariae,those galls are some times referred to as the Gooseberry gall.

The Knopper gall are formed of flattened projections which often enclose the immature acorn. these galls are at first a pinkish colour then as they mature turn red then green and finally brown. Under certain conditions this and the former species can easily be confused with each other. Although generally found on the acorns it can also be found on the buds. It was first discovered in Britain in the year 2000 in Berkshire, southern England.

Oak Spangle galls. --These are found on the under side of the Oak leaves and appear as reddish blisters which are caused by the larva of a Cynipid wasp, Neuroterus quercusbaccarum. these detach themselves and fall to the ground before the leaves themselves. The larvae continue developing in the fallen spangles and are protected by the leaf litter where they over winter.

There are several types of spangle galls that live on oak trees and a detailed inspection may be required to identify the exact species.


Common Oak spangle galls on the under side of Oak leaf

Source

Leaves of Quercus lobata The Valley oak

From a Tree in Caswell Memorial State park in San Joaquin Valley California.
From a Tree in Caswell Memorial State park in San Joaquin Valley California. | Source

Young and old galls on Quercus lobata. Caused by Andricus californicus

Andricus quercuscalifornicus is sometimes referred to as as just Andricus californicus
Andricus quercuscalifornicus is sometimes referred to as as just Andricus californicus | Source

The pest on American Oaks-a couple of examples.

So far the species have been those that inhabit English oaks,American oaks have their own set of problems. An example of this Quercus lobata,often referred to as the Valley oak and is endemic to California. The deeply lobed foliage of this hardwood is good identification indicator.

Acorns and leaves---The acorns of this tree are eaten by animals ,both mammal and bird species. The acorns`are attacked by Bruchid beetles {bean or seed beetles}. Globular galls up to several centimetres in diameter are frequently found attached to the twigs of mature specimens of this species. These are home to the larval stage of the indigenous wasps. The Californian Gall wasp induces galls on the Valley O. These galls range in size from 2-14 cm across and may contain multiple larvae.

The adult female lays her eggs in the cambium layer of Quercus lobata twigs during the autumn. If the twigs are vigorous they may contain many galls. The eggs over winter on the twig and then hatch in the spring,this generally occurs in the month of April. The resulting larvae induce galls immediately, where they seem to be created overnight on to the twigs.

It is at this stage of development that most of the parasitoids enter the gall, while it is still soft enough and small enough for their ovipositor { in the case of parasitoides it is capable of piercing as well as depositing eggs.}, to reach the larvae.

After a few weeks, the gall stops growing and begins to turn brown or a tan colour. The larvae pupate and begin to bore their way out in mid to late summer. Then they fly off to lay eggs on other trees of the species. It is known that some larvae over winter in the galls and do not emerge until the following spring, however, the true reason for this is still unknown.


Quercus alba -The White oak

Quercus alba is an hardwood of eastern North America and is a long lived tree. This species is the only known food plant of the Bucculatrix luteelia,along with Quercus macrocarpa. The caterpillars of this moth feed on the foliage.

The moth itself usually has a wing span of 5-6 mm. The forewings are creamy white or pale yellow shading to pale orange in the middle of the wing. The hind-wings vary from yellowish white in some females to pale fuscous in males. They are on the wing from May to September.

So as we have seen the Oak species play host to a plethora of diverse insects with untold numbers of bird and animal species that also feed upon the fruits of these trees. here we have but scratched the surface of this subject , but hopefully the reader will have gained a better understanding of the types of creatures that inhabit the Oak.

You may also be interested in my hub 'The Mighty Oaks of England'

Ovipositor in action

1- Tapping with her antennae,the wasp listens for  vibration which will indicate a host is present.2- With her log ovipositor the wasp bores a hole in the bark.3-The wasp inserts her long ovipositor inside the bark which contains the larvae.
1- Tapping with her antennae,the wasp listens for vibration which will indicate a host is present.2- With her log ovipositor the wasp bores a hole in the bark.3-The wasp inserts her long ovipositor inside the bark which contains the larvae. | Source

Ovipositor in Action

The photographs above are to demonstrate how the insects use their ovipositors. The insect shown is a parasitic wasp Dolichomitus imperator. Picture number four shows the wasp doing corrections. Photographs five and six -depositing the eggs.

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3 comments

D.A.L. profile image

D.A.L. 2 years ago from Lancashire north west England Author

aviannovice,

Hi Deb, even when their are the usual number of insects on the oak they generally suffer little visible damage. Yet they play hosts to thousands of insects every season. Best wishes to you.

DDE,

Hello Devika, as I said to Deb it rare to see an oak tree defoliated even though there may be thousands of insects on the tree. the oak feed a plethora of wildlife throughout the season. Thank you for your votes always much appreciated from you. Best wishes to you..


DDE profile image

DDE 2 years ago from Dubrovnik, Croatia

Hi D.A.L. interesting about the Oak tree. I had not much of an idea about these issues. Our oak tree seems fine thus far. Voted up, interesting, useful.


aviannovice profile image

aviannovice 2 years ago from Stillwater, OK

Our oaks have a few problems, but for the most part, it is the maple that tends to suffer greatly. While living in Oklahoma, I have been introduced to more oaks that were not in the northern climes, like I was used to seeing.

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