612
EFFECT ON VEGETATION.
10. The caterpillars damage the trees by eating their leaves, commencing on the old leaves, and when these are consumed going on to the younger ones. When the trees have been entirely denuded of leaves, they are practically dead, as leaves are the principal organs where the conversion takes place of various inorganic substances into organic matter, for the food and building up of the plant. There are very few trees, however, which have lost all their leaves, and these few are located in various parts of the Island. There are some around Aberdeen, at Deep Water Bay, at Causeway Bay and North Point, at Shaukiwan and near Chaiwan. Many trees have been stripped of their old leaves and are consequently in a rather sickly condition. I am of opinion, however, that they will recover in time, as most of them have sufficient young leaves to enable them to make new growth, in fact, a good number of them are already starting to grow.
PREVIOUS VISITATIONS.
11. If the Chinese are to be believed, this caterpillar has been known on the mainland for several years past, and the natives regarded it as an annual visitor with no very great destructive powers. A few leaves were eaten yearly, but no practical damage done. It was not observed in this Colony until the end of the summer of 1892. Little damage was then done to the trees, which may be explained by the fact that the number of insects was comparatively small, only two or three being seen on each individual tree. The localities which they appeared in were Deep Water Bay and Kowloon.
12. The second appearance was last year, at Quarry Bay and Kowloon, towards the end of July. Their numbers had very much increased on the previous year's, as twenty or thirty were sometimes found on a single tree. At Quarry Bay upwards of 30,000 trees were killed, as the Chinese from various reasons could not be induced to collect the pest. One of the chief objections to take part in the work was the pain caused by the hairs of the caterpillars stinging their hands and feet, as well as other parts of their bodies. Another objection was the great difficulty in finding the insects after they had fallen amongst the long grass underneath the trees. Great numbers were collected by our own staff, but owing to the unhealthiness of the district the men had to be taken away, and, as it was, two of the men died from fever contracted whilst at work in that neighbourhood.
PROBABLE CAUSE OF PLAGUE.
13. The cause of the very great increase in the number of the insects this year on anything previously known is, in my opinion, as follows. The winter of 1892-93 was exceptionally severe, and it is quite probable that the natural foe of the caterpillar succumbed to the extraordinarily low temperature. What its enemy is, or was, so far has not been discovered, but no doubt one existed. This idea is very much strengthened by looking at the colour and markings of the caterpillar. When it is full grown its colour closely resembles that of the Pine tree branches, and its markings correspond with the scars left on the branches after the leaves have fallen away. On account of this, in examining Pine trees, it is most difficult to see the caterpillars on them, until the trees have been very closely scrutinised for a few minutes; this too when the caterpillars have attained their maximum size nearly three inches in length and a quarter of an inch in breadth. This close resemblance to the branches of the trees on which these insects thrive, undoubtedly points to a form of protection from some other insect or bird. Another point in favour of the above suggestion is, as mentioned before, that the caterpillar had been known on the mainland for several years past, but previous to the winter of 1892-93 it had not been known to do any damage.
14. If the enemy of the caterpillar was destroyed in the way suggested above, it is quite easy to account for the great increase in the numbers of the pest last year and the still greater increase this year. The chrysalids formed at the end of the summer of 1892 would become moths, and the female moths would probably deposit their eggs in the spring of 1893. One moth is capable of laying an enormous number of eggs, but a good percentage of these do not hatch. The caterpillars hatched in the spring of last year would, in their turn, become chrysalids about the beginning of June, and these chrysalids would become moths about the latter end of the same month. The moths would then deposit their eggs in July, and the caterpillars seen last year at Quarry Bay and Kowloon would, in all probability, be the second hatching. As previously mentioned, many of these were collected, and those which remained formed chrysalids and afterwards moths, and these moths would be the ones which deposited their eggs on the trees this spring.
15. The history of the life of the insect since the end of the summer of 1892 is based chiefly on observations made this year which are as follows:-The first eggs were laid at the end of April, and the caterpillars which escaped the collectors became chrysalids at the end of May or beginning of June, the moths appeared in the middle of June, and now they are depositing the second lot of eggs. It is very gratifying, however, to be able to state that very few eggs or caterpillars have been seen of this second lot, although the plantations have been well examined.
16. Another probable reason for the very large number of the insects which appeared this spring, is the drought which prevailed at the time they were hatched. At this stage of their existence they are extremely small, being only a few lines in length and about the fiftieth part of an inch in breadth, so that it may readily be imagined what the effect of a tropical shower would be upon them at this early period of their life. On several occasions, when I was examining the plantations, it was raining very heavily, and underneath the trees full-grown caterpillars were lying on the ground, in hundreds, in a half-dead condition. A prolonged heavy rain would undoubtedly have killed them.
REMARKS.
17. The eggs of the moth are deposited on the upper part of the leaves, and thus the caterpillars have food to go upon as soon as they come out of the shell. The eggs are pink in colour and oval in shape, about the sixteenth of an inch in length and the twenty-fifth part of an inch in breadth. The size of the moths varies, the largest of the females being 21/4 inches across the wings, and 11/4 inches long, whilst the males are 2 inches across the wings, and an inch long. Both sexes are fawn-coloured, but the male sometimes has a few white and black markings on its wings. The chrysalids are enveloped in a stiff papery cocoon, which is fastened very firmly to the leaves or other parts of the trees. It will thus be noticed that from the time the eggs are laid until the moths are produced, the insects remain on the trees.
18. In conclusion, it is satisfactory to know that the methods employed for the extirpation of the scourge have been decidedly successful. Of the many thousands of trees which were attacked, only a very small percentage have been killed, and many of those which have had some of their leaves destroyed, are in a fair way towards recovery. The pest which at one time threatened the destruction of all the Pine trees in the Colony has, for the present at any rate, been most successfully coped with.
I have the honour to be,
Sir,
Your most obedient Servant,
W. J. TUTCHER,
Acting Superintendent, Botanical and Afforestation Department.
612
EFFECT ON VEGETATION.
10. The caterpillars damage the trees by eating their leaves, commencing on the old leaves, and when these are consumed going on to the younger ones. When the trees have been entirely denry of leaves, they are practically dead, as leaves are the principal organs where the conversion takes place of various inorganic substances into organic matter, for the food and building up of the plant. There are very few trees, however, which have lost all their leaves, and these few are located in various parts of the Island. There are some around Aberdeen, at Deep Water Bay, at Causeway Bay and North Point, at Shaukiwan and near Chaiwan. Many trees have been stripped of their old leaves and are consequently in a rather sickly condition. I am of opinion, however, that they will recover in time, as most of them have sufficient young leaves to enable them to make new growth, in fact, a good number of them are already starting to grow.
PREVIOUS VISITATIONS.
11. If the Chinese are to be believed, this caterpillar has been known on the mainland for several years past, and the natives regarded it as an annual visitor with no very great destructive powers A few leaves were eaten yearly, but no practical damage done. It was not observed in this Colony until the end of the summer of 1892. Little damage was then done to the trees, which may be explained by the fact that the number of insects was comparatively small, only two or three being seen on each individual tree. The localities which they appeared in were Deep Water Bay and
Kowloon.
12. The second appearance was last year, at Quarry Bay and Kowloon, towards the end of July a Their numbers had very much increased on the previous year's, as twenty or thirty were sometimes found on a single tree. At Quarry Bay upwards of 30,000 trees were killed, as the Chinese from various reasons could not be induced to collect the pest. One of the chief objections to take part in the work was the pain caused by the hairs of the caterpillars stinging their hands and feet, as well as other parts of their bodies. Another objection was the great difficulty in finding the insects after they had fallen amongst the long grass underneath the trees. Great numbers were collected by our own staff, but owing to the unhealthiness of the district the men had to be taken away, and, as it was two of the men died from fever contracted whilst at work in that neighbourhood.
PROBABLE CAUSE OF PLAGUE.
16. Another probable reason for the very large number of the insects which appeared this spring, is the drought which prevailed at the time they were hatched. At this stage of their existence they soat it may readily be imagined what the effect of a tropical shower would be upon them at this are extremely small, being only a few lines in length and about the fiftieth part of an inch in breadth, early period of their life. On several occasions, when very heavily, and underneath the trees full grown caterpillars were lying
was examining the plantations, it was raining and thousands, in a half dead condition.
on the ground, in hundreds them.
A prolonged heavy rain would undoubtedly have killed
REMARKS.
17. The eggs of the moth are deposited on the upper part of the leaves, and thus the caterpillars have food to go upon as soon as they come out of the shell. The eggs are pink in colour and oval in shape, about the sixteenth of an inch in length and the twenty-fifth part of an inch in breadth. The size of the moths varies, the largest of the females being 24 inches across the wings, and 14 inches long, whilst the males are 2 inches across the wings, and an inch long. Both sexes are fawn-coloured, out the male sometimes has a few white and black markings on its wings. The chrysalids are enveloped
a stiff papery cocoon, which is fastened very firmly to the leaves or other parts of the trees. will thus be noticed that from the time the eggs are laid until the moths are produced, the insects remain on the trees.
It
18. In conclusion, it is satisfactory to know that the methods employed for the extirpation of the scourge have been decidedly successful. Of the many thousands of trees which were attacked, only very small percentage have been killed, and many of those which have had some of their leaves destroyed, are in a fair way towards recovery. The peat which at one time threatened the destruction of all the Pine trees in the Colony has, for the present at any rate, been most successfully coped with.
THE ACTING COLONIAL SECRETARY.
13. The cause of the very great increase in the number of the insects this year on anything The Honourable previously known is, in my opinion, as follows. The winter of 1892-93 was exceptionally severe, and it is quite probable that the natural foe of the caterpillar succumbed to the extraordinarily low tempera ture. What its enemy is, or was, so far has not been discovered, but no doubt one existed. This idea is very much strengthened by looking at the colour and markings of the caterpillar. When it is full grown its colour closely resembles that of the Pine tree branches, and its markings correspond with the scars left on the branches after the leaves have fallen away. On account of this, in examining Pine trees, it is most difficult to see the caterpillars on them, until the trees have been very closely scrutinised for a few minutes; this too when the caterpillars have attained their maximum size nearly three inches in length and a quarter of an inch in breadth. This close resemblance to the branches of the trees on which these insects thrive, undoubtedly points to a form of protection fro some other insect or bird. Another point in favour of the above suggestion is, as mentioned before, that the caterpillar had been known on the mainland for several years past, but previous to the winter of 1892-93 it had not been known to do any damage.
year.
14. If the enemy of the caterpillar was destroyed in the way suggested above, it is quite easy account for the great increase in the numbers of the pest last year and the still greater increase this The chrysalids formed at the end of the summer of 1892 would become moths, and the female moths would probably deposit their eggs in the spring of 1893. One moth is capable of laying enormous number of eggs, but a good percentage of these do not hatch. The caterpillars hatched it the spring of last year would, in their turu, become chrysalids about the beginning of Jane, and these chrysalids would become moths about the latter end of the same month. The moths would the deposit their eggs in July, and the caterpillars seen last year at Quarry Bay and Kowloon would, in all probability, be the second hatching. As previously mentioned, many of these were collected, and those which remained formed chrysalids and afterwards inoths, and these moths would be the ones which deposited their eggs on the trees this spring.
15. The history of the life of the insect since the end of the summer of 1892 is based chiefly o observations made this year which are as follows:-The first eggs were laid at the end of April, an the caterpillars which escaped the collectors became chrysalids at the end of May or beginning of Juue, the moths appeared in the middle of June, and now they are depositing the second lot of ege It is very gratifying, however, to be able to state that very few eggs or caterpillars have been such of this second lot, although the plantations have been well examined.
I have the honour to be,
Sir,
Your most obedient Servant,
W. J. TUTCHER, Acting Superintendent, Botanical and
Afforestation Department.
No comments yet.
Private notes are available after approval.