THE BLACKBERRY PEST.

New Zealand Journal of Agriculture, Volume XXXVI, Issue 4, 20 April 1928, Page 261

THE BLACKBERRY PEST.

111. CONTROL - continued.

E. F. Northcroft,

M.Sc., Biological Laboratory, Wellington.

(2) BIOLOGICAL CONTROL : INSECTS AND FUNGI.

The possibilities of biological control in connection with the blackberry pest were taken into active consideration by the Department of Agriculture several years ago, and various local investigations, weie made. In 1924-25 as complete a study as possible on insect and fungous parasites attacking the genus Rubus in all parts of the world was undertaken, entomological and mycological authorities in many countries being communicated with. Some results of local work, and an account of the wider investigation, including the part taken by the Cawthron Institute, will now be given.

Parasites attacking Blackberry in New Zealand.

There are already in New Zealand a number of insects and fungi attacking blackberry to a greater or lesser degree. Occasionally one notices in newspapers statements concerning large areas of blackberry which are being completely killed out ” by some fungus. On investigation, however, there is, as a rule, not much foundation for such reports beyond the fact that a few patches in a large area are badly infected, having their canes partly or entirely withered, but without evidence that the plants would not send up fresh shoots in the following year. Unfortunately, this is practically always the case ; the vines are killed for a season, and twelve months later the plant is as healthy as ever ; only very occasionally is a small plant completely killed.

One of the most important of the fungi attacking blackberry is Leptosphaeria Coniothyrium- — unfortunately, being also parasitized by this fungus. In the life-history of Leptosphaeria there are two stages, and of these it is the conidial stage which does all the damage. This stage has been named Coniothyrium Fuckelii. Sacc., and it is more severe on raspberries than blackberries. Infection is effected by means of a spore which germinates and penetrates the epidermis, underneath which a mass of hyphae is soon formed. These very quickly penetrate to all parts, including the conducting system of the stem. Here they develop to such an extent, and so rapidly, that in a very short time the vessels are entirely blocked, and as a result the stem dies above the point of infection. "Though this disease in some localities, and in some seasons, gives the' appearance of having caused the death of many blackberry-bushes; or having prevented the ripening of the fruit, on others, actually the real damage does not amount to very much, for its ravages are far too spasmodic ; it is severe in a locality during one season, then next season practically non-existent. The disease is much more vigorous on raspberry.

The most interesting of -these reports came from Feilding, and on investigation it was found that the suffering blackberry was situated on the banks ,of a stream and on the flat low-lying. adjacent land.

Here the weed was found to be attacked by a number of parasites, the following being the most evident :

(i) Rose scale (Aulacaspis Ro see) : This insect was conspicuously abundant on the more sheltered stems, and has been reported from several other localities in New Zealand, but it does no more than restrict the. growth of. the infected plant.

(2) Bronze beetle (Eucalaspis -brunneus) : This had caused a considerable amount of damage to most of the leaves, but it does little real harm to the plant.

(3) Leaf-tying caterpillar (Tortrix excessana) : This was present only to a very slight extent. -

(4) Cane-wilt {Leptosphaeria Coniothyrium) : This fungus was more or less abundant. In other parts of New Zealand it has been found to weaken the plant. 'Here it was common on the. long terminals, and was probably the cause of so many of these tips withering.

(5) Leaf-spot {Septoria rubi) : This was also very much, in evidence, but not causing any damage. It is common wherever blackberry is found, and produces no more serious damage than a spotting of the leaves. .' ■

(6) Tip-wilt: .The cause of this is unknown, and it is far from common, this. particular area having it more in evidence than any I have ever seen. The manner in which the fruiting shoots are attacked is quite striking, and in some cases the wilt extends for 1 ft. or more down the shoot. It causes a premature withering of the developing fruit, which as a rule remains on the stalks in a dried condition. The fungi found in association with these . diseased fruiting shoots are so weakly parasitic that at present they are not regarded as being the cause of the wilt.

This flat land, according to the owner, had not been flooded .but it was evident from the silt on the old leaves of the bushes growing along the banks of the stream that they had been submerged, and here there was no sign of the “ tip-wilt.” On a later visit to this area the spring was well advanced, and it was very evident , that the flooded creek-side bushes were greatly in advance and in a much, more healthy condition than .those' on the flat, in spite, of the fact that they had been subjected to a somewhat lengthy submergence during the winter and early spring. . -

At this visit it was noticed that there was something attacking the young shoots here and there, and this proved to be a stem-boring insect known as (Ecophora pseudo-prutella, which itself is so heavily parasitized that it is not likely to do very much harm. Even in this locality it was not. in great abundance. It seems that the parasite doing. the greatest amount of damage is rose scale but this, as in the case of. Leptosphaeria, only attacked the vines which were considerably advanced —there being no evidence of. infection on the younger stems —though on all the old. stems from the crowns to the terminals there was dense covering of Leptosphaeria, while only the protected stems low down near the crowns were infected with rose scale. •:

SURVEY OF BLACKBERRY AREAS.

As complete a survey as possible of all the blackberry areas in the North Island and a few parts of the South was made, and in this

I paid special attention to parasites attacking blackberry under the following conditions :

Permanent swamp. Temporary swamp-lands, Flooded areas. ■ . Flat well-drained lands.

Hill country. Roadside. . Plantations (well shaded).

Each of these will be considered separately.

Permanent Swamp.

Blackberry growing in areas of this nature was examined at Te Awamutu, Reweti, Woodhill, Kaukapakapa, Opotiki, and. Wairoa. In none of these areas was tip-wilt visible, and the only parasites in evidence were bronze beetle (Fig. 26) and cane-wilt, both of which were abundant, while the plants were most healthy. . ' ;

Temporary Swamp-lands.

These were examined at he following places : Te Awamutu, Ohaupo, Frankton (Waikato), Taupaki, Kaukapakapa, Maungaturoto, Hikurangi, Otiria, Tauranga, Opotiki, Wairoa, Tangoio, and Puketitiri. The only parasites found were the same as in permanent swamps, there being no sign of any borer or tip-wilt of the fruiting shoots.

Flooded Areas.

. . Plants growing on areas which had been flooded under very silty conditions were examined at the following places : Te Awamutu, Ngaruawahia, Mercer, Waimauku, Reweti, and Opotiki. Again the same two parasites were in great evidence, but the leaf-eaters (bronze beetle) had done far less damage. There was no sign of tip-wilt, and though in some cases —for instance, at Te Awamutu —the plants had been flooded (a process which seems of yearly occurrence here) just previous to the time of flowering, and all the stems and leaves had been thickly coated with a pure silt, flowering was general, and growth particularly dense and luxuriant. ’ Farmers I talked with on the subject of flooding were most emphatic that long periods of flooding did- not in any way damage the plant, even though the waters might leave large quantities of silt covering stems . and all green parts; in fact, . the bushes in every case seemed even more vigorous than under normal conditions. This is certainly what I found to be the case.

Flat well-drained Land.

Many areas of this class of country were visited, among others Te Awamutu, Hamilton, Taupiri, Huntly, and Auckland ; and many places in North Auckland, including Henderson, Swanson, Waitakere, Helensville, Whangarei, and Otiria ; other, visits were made to Tauranga, Clive, Whakatane, Opotiki, Wairoa, Esk Valley, and Tangoio. Here again cane-wilt and bronze beetle were everywhere much in evidence. In addition, rose scale was present at Opotiki, Hamilton, and Auckland, while the rust Kuehneola albida was noticed to a small extent at Opotiki and Tangoio. This causes the wilting of shoots, sometimes as far as the crowns in some seasons in varied localities, but even in dense masses there is no general attackonly a few scattered stems here and there being infected. Another parasite in evidence to a small. extent in Auckland, Waitakere, Otiria, Opotiki, and .the Esk Valley was leaf-spot, a parasite which does little or no damage.

Hill Country.

Blackberry growing on hill country was examined at Ngaruawahia, Waitakere, Kaukapakapa, Otiria, Wairoa, Opoutama, Mohaka, Tangoio, Esk Valley, and Puketitiri. In these places cane-wilt was everywhere abundant, as also was evidence of bronze beetle, but this was much more evident on the less exposed parts. Rose scale was in evidence at Opoutama and the Esk Valley, the rust Kuehueola albida was found at Tangoio, while leaf-spot was fairly common at Waitakere, Otiria, Esk Valley, Puketitiri, and Napier.

Roadside.

Roadside blackberry was very much in evidence in almost every town I visited, being particularly noticeable in Auckland, Wairoa, and northern Hawke's Bay generally. Here again the two persistent parasites, cane-wilt and bronze beetle, were by far the most abundant, with the addition in Auckland of rose scale and at Napier, of rust. Here another factor comes in—the effect of dust. In many places the plants were very densely covered with dust, which in no way seemed to inhibit the vigorous growth of the plant or the flowering, the dustcovered bushes being just as healthy as the clean ones.

Plantations well shaded.

Plants growing in the bush were examined at Auckland, Glen Eden, Tangoio, and Patoka. The evidence of bronze beetle was slight, but cane-wilt was general. At Tangoio silver-leaf . fungus (Stereum purpureum) was quite abundant, but doing no apparent harm.

BLACKBERRY PARASITES RECORDED.

In the North Island blackberry parasites have been recorded as follows :

Taranaki— Longhorn beetle (at Midhirst). . Rhizopus arrhizus. ■ Leptosphaeria Coniothyrium (cane-wilt). Aulacaspis Rosa (rose scale). From the South Island : Picton — Carposnia adroptella (blackberry - seed moth) Chenochilon perforatus (scale insect). Blenheim— Stereum purpureum (silver-leaf). Nelson— Leptosphaeria Coniothyrium.

Thames — Kuehueola albida (rust). Waihi—„Leptosphaeria Coniothyrium. Hastings—■ Rosellinia radiciperda. TasmanAulacaspis Rosa. . <. Hokitika— Aulacaspis Rosa. Christchurch— Aulacaspis Rosa.

In no case were the bushes observed to be suffering in any way from these parasites. SUMMARY.

To summarize, the following insects and fungi have been found to attack blackberry in various parts of New Zealand :-

Rose scale (Aulacaspis Roses'). Bronze beetle (Eucalaspis brunneus) . Leaf-tying caterpillar \Tortrix excess ana). \

I Cane-wilt (Leptosphaeria Coniothyrium). ■ Leaf-spot (Septaria. Rubi). | Stem-borer (CEcophora pseudo-prutella}.

Rust (Kuehneola albidd). Tip-wilt. Silver-leaf (Steyeum purpuyeuwi). Longhorn beetle.

• Rhizopus arrhizus. I Rosellinia radicipersa. i Bud moth {Carp osina adroptella). ' Scale insect (Chenochiton perforatus).

" None of these is found to be harmful to any great extent, and even where a plant is attacked by two or three of the parasites the-damage is only very slight.

Parasites in England and France.

After insect and fungous parasites infesting blackberry in New Zealand had been investigated and none found to .damage the plant to any extent, entomologists and mycologists in many countries abroad were circularized with a view to finding the parasites attacking blackberry and related plants throughout the world and to ascertaining if any could be -utilized to combat the pest in New Zealand. Replies were received from over forty entomologists-and mycologists/but from none was any information received concerning parasites which would be sufficiently effective to warrant their introduction.

In June, 1925, an entomologist connected with the Department of Agriculture (Dr. J. G. Myers) was abroad, and he was communicated with and asked to inquire into the matter of insect parasites as a means of controlling blackberry. He found that the natural enemies of blackberry in Europe are less conspicuous than those in New Zealand. . .They were studied in Suffolk and Kent, and again in France at Versailles. The information then available was practically negligible, and concerned usually only those raspberry pests of which blackberry is the original host. No root-attacking species were found. Insects affecting the rest of the plant included a few Lepidoptera (largely polyphagous), the raspberry-beetle ’ (Byturus tomentosus), some Typhlocybid leaf-hoppers, a species of thrips, and certain gall-forming Cynipids and Cecidomyiids .

Taking the foregoing in detail, we may first reject the Lepidoptera (butterflies and moths) as insignificant. - Practically only the leaves are attacked, and the damage to the plant is small.

The raspberry-beetle, as a larva, attacks the fruit and renders it more or less unpalatable, but does not injure the seed. It is one of the worst pests of raspberry in England, and the adult beetles attack appleblossoms and other flowers in early spring. Dr. D. A. Imms, of Rothamsted, while admitting the practical certainty that it would also attack our raspberries, thought that the question of introducing this beetle might be considered. . . '

Several species of Typhlocybid leaf-hoppers live on the under-surface of the leaves, causing spotting and yellowing, as in the case of the species found at Wairoa, Hawke’s Bay, and mentioned elsewhere. The damage as seen in Europe is more or less negligible, but Typhlocybids can become very destructive at times.

A thrips species causes a certain amount of castration by “ blighting ” the flowers. ' ' *

There remain the gall-makers —forms which are likely to be more specific and thus safer than any of the preceding. There are three Cecidomyiidae and one Cynipid. Of these four forms three concentrate on the vegetative parts, while the fourth attacks the reproductive

organs. The Cynipid Diastrophus rubi Hartig produces galls in the shape of swellings on the stem. Similar damage is committed ,by . the Cecidomyiid Lasioptera rubi Heeger, a gall-former , which attacks raspberry and blackberry. It is parasitized heavily by several Hymen (ants, bees, &c.). ' Concerning this insect Dr. R. J. Tillyard says, As far as I can find out, these galls rather tend to stimulate than check the growth of the plant, the insect . acting as a natural pruner.”

Perrisia plicatrix H. Low is a midge whose larvae roll and twist the young leaves. It has never been recorded from raspberry. There are several broods each year.

Contarinia rubicola Rubsamen' in the larval stage does the same damage as thrips, destroying-the stamens in the young flowers .'"'y It has been recorded once from raspberry in Germany, but is not known to attack it in England. To quote .from Dr. Myers : “If any insect enemies were introduced against blackberry the Cecidomyiids, especially Perrisia and Contarinia by reason of their specificity, would be the most promising. At the worst they might attack nothing more than raspberry, and at the best they might make some impression on the blackberry pest. . Plant control by means of natural enemies is, however,, a very dubious matter and one in which the utmost circumspection should be used.”

However, if proper precautions are taken as regards transport, and later in testing, there should be no objection to the introduction of possible enemies of the pest. When the experimental work was commenced it would have been very unwise to introduce parasites into the Dominion, as there were not the necessary insectaries for the proper confining of the insects under strictly experimental conditions, and consequently the risk would have been far too great. At the present time we are in a very different position, since the Cawthron Institute, at the instigation of Dr. Tillyard, has been provided with large, well-equipped insectaries where parasites can be thoroughly tested without fear of accident. Any parasite now introduced into New Zealand is tested under the most rigid conditions, and it is determined definitely to what extent the insect will parasitize plants of economic importance.

Natural Enemies in other Countries.

The result of correspondence with entomologists and mycologists overseas was far from hopeful. The following list of parasites, compiled from these replies, gives the insects and fungi attacking the genus Rubus in all parts of the world : •

(l) FUNGOUS PARASITES. Norway.

Gymnoconia peckiana. Phragmidium rubi-idaei. Phragmidium violaceum. L Phragmidium rubi. ■ ■■■: - Phragmidium rubi var. canicanti. Phragmidium perjorans. Kuehneola albida. Pucciniastrum ardicum. . Italy. ■■ ■■ L- ■ Septoria rubi. ■'>' .

Sphaerotheca humuli. Coleroa chaetomium. Leptosphaeria Coniothryium. Didymella applanata. Plectodiscella veneta. . Septoria rubi. > P&ronospora ntbi. Egypt. No record.

India.

Cercospora rubi. Phragmidium Barclayi. Hamaspora longissima. Septaria rubi. Phragmidium orientals.

Phragmidium rubi. Phragmidium assamense. Phragmidium incompletum. Phragmidium burmanicum.

Ceylon. Phragmidium sp. "Credo.

South Africa. Phragmidium sp. Cronartium sp.

Australia. Victoria. ' . ’ No record. South Australia. Septovia vubi. Phvagmidium subcorticium. Phragmidium barnardi. Western Australia. . New South Wales No record. . No record.

Phragmidium imitans. Gymnoconia peckiana. Septaria rubi. Phytomonas tumefaciens.

Canada. Saskatchewan. Septaria. Mosaic. Ottawa. sphagna Conioihryium.

United States of America. North Carolina.

Gymnoconia peckiana (Howe) Trotter. Fusarium rubi. Septoria rubi. Gymnoconia peckiana. Cercospora rubi.

New York. Plectodiscella veneta. Mosaic. Vevticillium sp.

Michigan. Gymnoconia peckiana. Plectodiscella veneta.

Kansas. Kentucky. Septoria sp. Mosaic. Minnesota.

Gymnoconia peckiana. Kunkelia sp. Microsphaerella rubina. I.eptosphaeria Coniothyrium. Septaria rubi.

Plectodiscella veneta. ■ Phytomonas tumefaciens. Mosaic. Leaf-curl.

California. Gymnoconia peckiana. • Phytomonas tumefaciens. Septoria rubi. Botrytis sp.

Washington. Gymnoconia peckiana. ' Armillaria mellea. Jamaica. Hawaii. No record. No record. Trinidad. Fiji. No record. No record.

Regarding fungous parasites, Dr. C. K. Shear, of the United States Department of Agriculture, Washington, stated :

In so far as we are aware little or no practical success has ever been attained in destroying weeds by means of fungous parasites. We have no fungous parasites of Rubus sufficiently active to destroy any of our native or introduced species of Rubus. Of course, it is possible that some of these parasites might be more destructive in your country and on the species you are dealing with, but on the other hand it is possible, if not probable, that they might be less injurious to your species, and again if once introduced they might attack other species of Rubus or other plants which are of commercial value. It is very difficult to predict how any organism will behave when brought into contact with new hosts and a new environment, and in this case it seems to us possible, if not probable, that the danger would be greater than any benefit likely to be derived from the introduction of new parasites. Of course, it may be possible that there is some fungus which would be as destructive to your Rubus as the chestnut blight fungus is to our chestnuts, but I think the chances are small and the risks too great.

(2) INSECT PARASITES.

Italy. No data. British Guiana. No data. Barbadoes. No data. Cyprus. No data. Hawaii. No data.

Khartoum. No data. India. No data. South Africa. No data. Bermuda. No data. Ceylon.' Natada Nararia (Fringed nettle grub).

Canada.

Byturus unicolor. Oberea bimaculata. Phorbia rubivora. Synchlora aerata. Monophadnus rubi. Pamphilius fletcheri.

Prionus laticollis. Bembecia marginata. (Ecanthus niveus. Agrilus ruficollis. Metallus rubi. Synanthedon (Aegeria) rutilans.

United States (Washington State).

Agvilus ruficollis. Oberea bimaculata. Bembecia marginata. Phorbia rubivora.

Hartigia abdominalis. Monophadnus rubi. (Ecanthus nigricornis. Tetr any telarius.

, Concerning the foregoing. insects . the following notes will be of interest : - '

Byturus unicolor Say. —This is a small Dermentid beetle which feeds as a rule on the young leaves and buds of raspberry and blackberry. The larvae feed on the mature fruit and sometimes cause a considerable amount of damage.

' Oberea bimac/ulata Oliv. The raspberry-cane ; borer, . a slender, black Cerambycid beetle. The larval stage is spent burrowing in the raspberry-canes. It also has a fondness for roses to a limited extent, and each year is recorded as being very much in evidence.

Phorbia rubivora Coq. —The raspberry-cane maggot, a small greyishblack fly the larvae of which tunnel in the raspberry-canes.

Synchlora aerata Fab. —The raspberry spanworm. The larvae of this sometimes injure the fruit of raspberry and blackberry, but not to any great extent or to• the extent of rendering the seed sterile.

Monophadnus rubi Harris. —The raspberry sawfly, whose larvae work havoc on the foliage of raspberries and blackberries.

Pamphilius fletcher i Macq. —The raspberry web-worm, an insect which causes considerable destruction by webbing the terminal leaves together.

Prionus laticollis Drury. giant root-borer, one of the large long-horned beetles the larvae of which bore into the roots of blackberry, grape, apple, and cherry. It may cause a considerable amount of damage, but favours too many hosts of economic importance to warrant a trial in this country.

Bembecia marginata -Harris. The blackberry-crown borer. The larvae of this moth attack blackberries, timpleberri.es, and loganberries by boring into the roots and girdling them. In-some places it becomes a very serious pest, and there seems every likelihood of it turning out a very useful parasite. Regarding this insect Dr. Tillyard says, “It can be controlled in raspberry by carefully cutting- out the infested canes. Does not. attack roses or any other plants. A vigorous insect of great potential value.”

(Ecanthus niveus DeG.The snowy tree-cricket. ■ Damage by this insect is done through the egg-punctures, but it is not of any great importance. .

Agrilus ruficollis Fabr. —The red-necked agrilus. The larvae of this attack blackberry, raspberry, and dewberry canes, causing gall-like swellings and at times doing a considerable amount of damage by killing the stems.

Concerning the insects listed from America attacking blackberry and raspberry, a very large range of orders is represented — e.g., Coleoptera (beetles), Hymenoptera (ants and bees), Lepidoptera (butterflies and moths), Diptera (flies, mosquitoes, &c.), Hemiptera (cicada, aphids, lice), and Orthoptera (dragonflies, mayflies, earwigs). The most likely to do damage are ruficollis and Bembecia marginata (both mentioned elsewhere). In the United States damage by these is not so very extensive on account of the vigorous control exercised against them, so it is impossible to say what damage they might cause, if introduced into New Zealand where these control measures are absent. It is more than likely, however, that they would find blackberry a . very palatable host.

Work of the Cawthron Institute.

In 1926. Dr. R. J. Tillyard, head of the biological branch of the Cawthron Institute, visited America and Europe, and took this opportunity to investigate fully the insect parasites of our noxious weeds, with the idea in particular of introducing into New Zealand those which seemed likely for the control of blackberry. Dr. Tillyard went on the understanding that permits for the introduction of parasites would be granted provided the following conditions, drawn up by the Department of Agriculture, were strictly adhered to :

(1) No species to be forwarded from any country to New Zealand except such as are known to feed on species of the genus Rubus only.

(2) All shipments on arrival in New Zealand to be taken charge of by an officer of the Department of Agriculture, who shall examine the cages to see that they are intact, and that no insects can escape from them while being forwarded to Nelson. (This would allow of broken or damaged consignments being either destroyed or their cages repaired before forwarding.)

(3) Dr. Tillyard to furnish to the Director-General of Agriculture an account of the life-history of each species selected for study.

(4) The permits granted for introduction of all I? ceding species to be permits restricting the study and rearing of such insects to closed insectaria and cages in the Cawthron Institute grounds and laboratories. ,

(5) All such insects to be thoroughly tested within such insectaria or cages on all important economic plants, particularly introduced Rosaceae, such as apples, pears, stone-fruits, roses, &c. ' ■

(6) If considered necessary similar tests to •be made • in country of origin before shipment. ■

Opinions regarding the introduction of fresh parasites differ very widely. Some people are strenuously opposed to importation under any circumstances. Others (generally those with large areas of blackberry) are clamouring for the Government to introduce any insect at all and set it free, no matter what the effect may be on the fruit industry so long as the blackberry will materially suffer.’ A third class consists of those who have given the matter much more mature and reasonable consideration, and consequently are willing that possible insect controllants should be very carefully studied in their natural habitat and an exhaustive investigation made concerning their range of hosts before they are introduced into this country ; further, that with as full information at hand as possible the insects should be introduced under the strictest conditions of confinement in transport, and then kept under very rigid experimental conditions in specially constructed insectaries, where they may be tested on weed pests and also on all likely hosts of economic importance as laid down by the Department. On his return Dr. Tillyard furnished a report in which he suggested that the. following insects should. be imported and studied, his remarks on the various species being given in abridged form : (i) Insects which attack the Crown and Stem by boring or Gall-forming. Coroebus rubi Linn. A Buprestid beetle which destroys up to 60 per cent, of the new stems in some seasons. Its larval attack on other members of the family is almost negligible. Only very occasionally does it attack the rose Frau Karl Druschki, while raspberrythe nearest relation of blackberry—is not parasitized at all.

Agrilus ruficollis Fabr. —-A Buprestid beetle found in North America, which attacks blackberry, dewberry, and raspberry. , • .

Bembecia marginata Harris and Bembecia hylaeiformis Lasp. The larvae of these moths attack the crowns by the formation of galls. They will attack raspberry as well as blackberry.

(2) Insects attacking Twigs.

Diastrophus rubi Htg. —A small gall-forming Cynipid which favours the same hosts as Agrilus ruficollis.

(3) Insects attacking Leaves and Shoots.

Thyatira bails Linn. Attacks., both blackberry and raspberry. Its only damage is that caused by the larvae feeding on the leaves. Habrosyne derasa Linn.—Feeds, as in the case of the preceding, on both blackberry and raspberry, but only to a very slight extent on the latter. Cidaria albicillata Linn.—Has a number of hosts, the most noticeable damage being the larval attack on the leaves.

Tischeria margined H. W. —A -miner which has been reported to attack blackberry and many other plants. Notocelia uddmanhiana Linn.—The larvae of this cause rolling of the leaves of blackberry and raspberry. . Schreckensteinia festaliella Hb. —A leaf-feeding Tineoid. Typhlocyba tenerrima H. S.—This small European leaf-hopper is not known to feed on any plant other than blackberry. Monophadnoides rubi Harris. —A North American sawfly which attacks both blackberry and raspberry. Metolius rubi Forbes. —Also a North American sawfly which mines the leaves of blackberry only. (4) Insects attacking Flowers and Fruit. “ I have not been able to find any insect so far which is effective in these parts on the blackberry. Various species of Byturus attack the fleshy receptacle of the fruit of species of Rubus, but they all seem to prefer the raspberry to the blackberry, and in any case they do not prevent seeding, but only make the fruit unpleasant to eat. The Anthomyiid fly, Phorbia . rubivora Coq., known in America as the raspberry-cane maggot, is very deadly on raspberries, and prefers them to blackberries. There may be other species of this genus which will only attack blackberry, but I have no record of them so far. “ The blackberry-fly, Petrandrus rubivorus Coq., found in South Africa, is stated to never attack raspberry or any other fruit.” Of the above species provisional permits were granted for the introduction of' the following : Coroebus rubi, Agrilus rubicollis, Bembecia marginata, Bembecia hylaeiformis, Diastrophus . rubi, Thyatira batis, Tischeria marginea, Notocelia uddmanniana, Schreckensteinia festaliella, Typhlocyba tenerrima, Monophadnoides rubi, and Metallus rubi. Habrosyne derasa, Cidaria albicillata, and Typhlocyba tenerrima have been collected and left at Rothamsted, in England, for close study. ' By March, 1927, eleven small insectaries, six being for this special work, were in commission at Cawthron Institute.' They were very carefully constructed to ensure the proper and safe keeping of the insects for experimental work. Later in the same year Dr. Tillyard designed a new insectary, 50 ft. by 42-5 ft., costing about £2,000, and to be used mainly for work on blackberry. It was brought into use towards the end of the year. The whole scheme has been assisted by financial support from the Empire Marketing. Board and the New. Zealand Government.

METHODS OF TESTING PARASITES.

The three generally accepted methods for the -proper testing of insects used for the control of noxious weeds are as follows : (1) Oviposition, (2) starvation tests, (3) preference tests. In the case of the insects introduced into New Zealand for the control of noxious weeds these three tests are being carefully carried out under the best and safest experimental conditions possible. . .

(1) Oviposition Tests

Fertile females are tested in closed cages with portions of . the plant on which oviposition is required, and it may be found that («) oviposition takes place on the plant ; (&) the insect refuses to oviposit on the plant, but oviposition takes place somewhere else in the cage ; (c) the insect refuses to oviposit. ' ‘

(2) Starvation Tests.

These tests are carried out on the larvae and adults of all phytophagous insects, and consist of confining them with the plant alone ; consequently they have to eat it or starve. If in.oviposition tests eggs have been laid on the plant, then these are allowed to hatch in situ ; if they are not fertile, then fertile eggs are placed on the plant. Where the larvae and not the eggs are being used for transference they are selected from their natural food plant and placed on the plant under investigation, the insects being tested in the four following stages : (a) First larval instar, newly hatched ; (&) half-grown larvae ; (c) beginning of last larval instar ; (d) imago when necessary. These tests may result in any of the following : . (a) Feeding on the plant ; (&) feeding, but without vigorous attack ; (c) feeding, followed by death ; (di) refusal to feed and consequent starvation. (3) Preference Tests. These are used to show to what extent an insect favours a certain plant. Under starvation tests it is determined whether the insect is positive or negative to a large number of closely related plants, while under preference tests the degree to which each of these plants may be parasitized in the presence of others is readily determined. For instance, blackberry may be the natural food plant of a certain insect, but it is necessary to determine to what extent loganberry may be parasitized. A number of insects are placed on loganberry which has been proved positive, and then blackberry is introduced into the same cage. The following results may be obtained : The insects may persist on loganberry and not attack blackberry at all; a certain number may go over to blackberry, the rest remaining on loganberry ; or they may all leave loganberry and commence feeding on blackberry. '

PARASITES RECEIVED AND RECENT OPERATIONS.

■Early in 1927 the following insects were received for the Institute : (1) Thyatira batis Linn., .(2) Agrilus ruficollis Fabr., (3) Bembecia marginata Harris, (4) Coroebus rubi Linn.

Seventy-eight pupae of Thyatira batis were received, and fifty-two of these emerged, twenty-two being males and thirty females. The moths were placed in egg-laying cages, and 340 larvae resulted. These, on account of very heavy mortality and starvation tests," were reduced to sixty-four. The starvation tests showed that they were positive towards raspberry and loganberry, but negative to strawberry. Preference tests were also carried out, resulting in the following : (a) Raspberry versus blackberry — larvae returned to blackberry, showing a very strong preference for it. (b) Loganberry versus blackberry The larvae again returned to blackberry. .

Dr. L. D. Howard, of Washington, sent blackberry-canes with Agrilus ruficollis and Bembecia marginata. All the canes did not grow ; those which survived showed two specimens of Agrilus, .which commenced to feed on blackberry but did not survive. No specimens of Bembecia survived. ■ '.

The most hopeful insect for the control of blackberry is Coroebus rubi. The larva of this bores down from the crown into the root and then returns to the crown, by which time it is fully fed. It then forms a large cavity within the tissues, where pupation occurs. This insect shows a great liking for Rosa indica, which, in Europe, is used as stock for' many varieties. Exhaustive inquiries, however, have proved that it is seldom made use of in New Zealand. The following are commonly in use as stocks in this country : Rosa canina (dogrose) and Rosa simplex (multiflora or polianthd), mainly in the North Island ; Rosa laxa, to a very small extent; Rosa manetti, to a great extent. Stocks' of all these are now being grown so.that Coroebus rubi might have a thorough test.

Unfortunately, at date of writing, all the imported specimens of this insect have failed, but a further supply, is expected, and when these are received a very complete, study is to be made of this parasite.

For information as to the progress of this work at the Cawthron Institute I am indebted to Dr". Tillyard, who kindly placed his reports on the subject at my disposal.

General.

With such a formidable list of insects, exhibiting such a variety of methods of attack, the biological control of blackberry may be regarded as distinctly encouraging. There are several points worthy of comment : Firstly, it is not likely that a parasite can be found which selects blackberry exclusively for its host; . secondly, all the insects which attack blackberry [Rubus fruticosus Linn.) ' also parasitize the very closely related raspberry (Rubus idaeus) ; thirdly, the range of hosts, as far as is known, in the natural habitat, appears very limitedfew hosts being outside the genus Rubus. If an insect or a collection of insects, or the combination of an insect and fungus, could be found to eradicate or control blackberry at the expense of raspberry, it would seem reasonable to sacrifice the latter; for it is hard to see that the loss of the small raspberry industry can in any degree be compared with the tremendous yearly loss caused to the country by the ever-recurring necessity for clearing roadsides and drains' of blackberry, and attempting to prevent its. further spread, together with the loss of good farming-land already rendered useless by blackberry infestation. Probably the cost to the country of the first of these items is far greater than the value of the whole of the raspberry crop for the Dominion.

. Moreover, it must be pointed out that the insects likely to cause damage to blackberry and which also attack raspberry are comparatively easy to control. In the case of the gall-formers the infected canes can be cut out; while with the others a spray, applied sufficiently early to leave the fruit undamaged or without any adherent poison, should effect control.

It is interesting to note that up to the present insects have been found which attack the crown, the vines, the leaves, and the young shoots of blackberry, but no insect, has been reported which feeds on the

flowers and young fruit. Hence, unless further investigation reveals such a parasite, if all else in the way of control fails, we cannot hope to prevent spread by biological means. Attack on the leaves and young shoots is an important point, for in this way the food-supply can be stopped and so in time the plant will become weaker and weaker ; but the most reasonably hopeful parasite is the one which attacks the crown, for attack on this point is likely to more greatly damage, if not kill, the plant than at any other point. Attack above the crown cannot give much hope of rapid or effective eradication, though it would be a means of control. • . ' ■ . ' '