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40654

No. 90.

MEETING OF THE HYPERICUM SUB-COMMITTEE OF THE IMPERIAL BUREAU OF ENTOMOLOGY, HELD AT THE COLONIAL OFFICE ON 4TH JUNE,

1919.

Present:

PROFESSOR POULTON (in the chair).

MR. FRYER.

DR. MARSHALL.

DR. NEAVE.

PROFESSOR NEWSTEAD.

MR. THEOBALD.

THE three questions raised by the Australian Government were considered, and the following conclusions arrived at:--

(1) The wisdom of the policy of introducing insects to destroy weeds. The Sub-Committee are of opinion that, though the greatest care must be exercise. the policy of introducing insects to destroy plants might sometimes be advisable. Instances are on record of marked success in such cases.

They consider, however, that no species of insect should ever be introduced which is known to attack any natural order of plants comprising either cultivated crops or forest trees of the country into which it is to be introduced.

(2) Nature of experiments to be made.

The Sub-Committee make the following suggestions:

That the insect in question should be introduced in the first instance into an Island, and there tested as to its possible food plants: (a) under laboratory condi- tions, (b) in the open, with special reference to useful plants of the same natural order as that which it is desired to exterminate.

(3) As regards the insects suitable for combating :-

-

(a) Hypericum.-A seed-infesting insect only should be selected, and not a leaf-destroying one such as Chrysomela hyperici, the introduction of the latter being considered to involve too great a risk, and also unlikely to achieve success.

(b) Opuntia.-The Sub-Committee are not aware of the existence of insects suitable for destroying this plant, other than those already tested in Queensland.

40654

No. 91.

A REPORT ON THE DESIRABILITY OR OTHERWISE OF INTRODUCING INSECTS INTO AUSTRALIA FOR THE DESTRUCTION OF WEED PESTS.

CERTAIN inquiries in relation to the above-mentioned subject that had been received from the Advisory Council of Science and Industry, Melbourne, were brought up for consideration at a meeting of the Honorary Managing Committee of the Imperial Bureau of Entomology held at the Colonial Office on the 22nd May, 1919.*

In the general discussion that took place there was a consensus of opinion that the matter was one that should be approached with the greatest caution, and that no scheme of this nature should be undertaken except with the most stringent safeguards. It was then decided to leave the detailed consideration of the question to the following Entomological Sub-Committee, under the chairmanship of Pro- fessor E. B. Poulton, F.R.S., Hope Professor of Zoology, Oxford; Major E. E. Austen, Entomological Assistant, British Museum; Mr. J. C. F. Fryer, Entomol- ogist to the Board of Agriculture and Fisheries; Professor R. Newstead, F.R.S.. Professor of Medical Entomology, Liverpool; Mr. F. V. Theobald, Vice-Principal of the South-Eastern Agricultural College; and the Director of the Bureau.

The questions referred to this Sub-Committee were as follows:-

(a) The wisdom of the policy of introducing insects for the eradication of

weed pests.

(b) The nature of the experiments that should be made with such insects

before they are liberated.

(c) The points raised in (a) and (b), with special reference to insects to

combat Hypericum and Opuntia.

With regard to the first of these questions, the Sub-Committee are agreed that, as a general principle, the introduction into a new country of any insect that feeds upon plants is in the highest degree risky and undesirable; but they think that it would be foolish to carry this principle to such an extreme as to prohibit such introductions absolutely and without exception. Where a noxious weed con- stitutes a serious menace to the agricultural industry of a country, and when a thorough trial of other methods of eradication has proved of no avail, they think that it would be justifiable to take the risk of utilizing for this purpose an insect enery of the plant, under reasonable safeguards.

The Sub-Committee find support for this view in the results of the two well- known cases in which this policy has actually been carried into effect, namely, against Lantana camara and Õpuntia monacantha

In 1902 Mr. A. Koebele successfully introduced into the Hawaiian Islands no less than eight species of insects that attack Lantana : a fly that lives on the seeds two moths and two butterflies, the caterpillars of which all feed on the flowers, the caterpillar of a moth and a bug that attack the leaves; and a gall-fly that attacks the stems. Such a wholesale introduction certainly seemed to be fraught with great risk; yet thirteen years later Mr. O. H. Swezey wrote that not one of these insects had ever become injurious to any cultivated plants, and the weed was being satisfactorily controlled. Subsequently the seed-fly was sent from Hawaii to various other countries, including Queensland, Fiji, and New Caledonia, without harmful results.

Again, a cochineal insect, introduced from Queensland into South Africa, has been remarkably effective in killing Opuntia monacantha; yet so highly specialized does it appear to be that it will not thrive even on other species of the same genus. Seeing that in these cases the introductions appear to have been effected with- out any very special precautions having been taken, it seems reasonable to suppose that the inevitable element of risk might be reduced to a minimum under stringent control. It is difficult to lay down any general rule on the subject, for each case must be judged on its own merits; but the Sub-Committee consider that no species of insect should ever be introduced which is known to attack any natural order of plants that comprises either cultivated crops or forest trees of the country into

hich it is to be introduced.

With regard to the experiments that should be made before any introduced insects are liberated, the Sub-Committee suggest that, in the first instance, the insects should be taken to an island on which the flora is approximately similar to Here purely that of the district in which they are ultimately to be released. laboratory experiments might be undertaken in order to ascertain whether the species in question is really able under favourable conditions to do sufficient injury to the plant to make it worth while trying it on a larger scale. If the results are satisfactory experiments might then be made (still under strict control in the laboratory) to see whether, in the absence of its natural food-plant, the species is capable of maintaining itself effectively on any cultivated or wild indigenous plants. Should there be any likelihood of this all the insects should at once be destroyed, otherwise, they might then be turned out in experimental plots of the weed, and careful observations could be made of their behaviour under these more Tatural conditions.

So far as concerns insects that might be suitable for combating Hypericum. the Sub-Committee is not yet in a position to make any specific recommendations, but a search will be made during the present summer for enemies that are likely to be useful. They are of opinion that it would be undesirable to introduce any leaf- eating species such as the beetle Chrysomela hyperici, as these would involve too great a risk and would be unlikely to affect the weed to any serious extent. effective seed-destroyer would offer the best chance of success, and as such an insect has a somewhat specialized mode of life, it would be much less likely to adapt itself to other plants.

An

With regard to Opuntia, the Sub-Committee regret that they are unable to suggest any likely enemies in addition to those already recommended by Messrs. T. H Johnston and H. Tryon in the Report of the Prickly-pear Travelling Commission published in 1914.

* No. 88.

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