THE PROGRESS OF ECONOMIC ENTOMOLOGY IN AUSTRALIA AND NEW ZEALAND.

New Zealand Journal of Agriculture, Volume XXXII, Issue 3, 20 March 1926, Page 173

THE PROGRESS OF ECONOMIC ENTOMOLOGY IN AUSTRALIA AND NEW ZEALAND.

Presidential address to the Biology Section of the New Zealand Institute Science Congress, Dunedin, January, 1926, by Dr. R. J. Tillyard, Cawthron Institute of Scientific Research, Nelson.

In this address I have purposely excluded references to the progress of economic entomology, except en passant, in other parts of the world, but have just as deliberately included Australia —-firstly, because the attempt to deal with that progress in the whole world would occupy far more time than can be devoted to this address, and, secondly, because the problems of Australia and New Zealand are inextricably interwoven, and if we turn our eyes away from Australia we shall fail to learn half our lesson. An apple-orchard in Australia and an appleorchard in New Zealand possess far more points in common than they possess differences. Ecologically, one is no more a part, of Australia than the other is a part of New Zealand, but both are little pieces of Old England transplanted to a new environment, with the same old pests—codlin-moth, woolly aphis, and the rest of themand the same problems of cultivation, spraying, picking, and marketing. The new environment, however, modifies the conditions to a considerable extent in so far as there are soil and climatic differences to be considered and a certain number of pests native to the country added to those brought in from outside. The same is true of a pine forest or of a dairy farm ; it is not, ecologically, a bit of New Zealand or Australia, but an exotic development upon a native soil very differently occupied until the white man came on the scene. It is a piece of disturbed country, like that of a nation through which the scourge of war has passed. Never again can it settle down to its original condition, and never can it continue in the artificial condition apportioned to it by man unless he himself is prepared to give it constant supervision and attention. In respect of any such piece of ground innumerable problemsagricultural, chemical, horticultural, entomological, and mycological —press upon him for solution, and the final success of his experiment depends on how he is able to deal with. them.

Now, in this address I propose to examine the progress which has been made in recent years purely as regards entomological problems only, and to try to indicate the lines on which future progress must be made. In doing this I shall divide the subject into two main sections —namely, (1) the control of injurious insects, and (2) the utilization of insects to control noxious weeds.

I. THE CONTROL OF INJURIOUS INSECTS.

The outstanding feature of the past few years, to my mind, has been the marked increase in the application and success of the biological method of control of injurious insects by means of their natural enemies, both parasites and predators. Only six years ago, at the First Imperial Entomological Conference in London, there were more speakers opposed to this method than in favour of it, and the great majority were in

a position of doubt, not knowing what to think about it. This was inevitable, of course, in. so conservative a centre as London and in view of the backward state of entomology in the Empire as compared with America. The best speech in favour of the biological method was made by a visitor, Dr. L. 0. Howard ; and I am not ashamed to own, ■ for my part, that he carried me with him entirely, and that I am now an enthusiastic supporter and worker for this method. New Zealand already owes more to Dr. Howard than to any other living entomologist, for it was through him that we have been enabled to introduce a number of most valuable enemies of some of our worst insect pests and to make marked progress in the work of establishing them permanently within the Dominion. One of the curses of entomology, as, indeed, of all branches of science to a greater or less degree, is facile generalization from insufficient facts. My experience with biological control leads me to state here that no generalizations are worth anything in this particular case, for the simple reason . that the amount we know about the habits and psychology of insects is so small compared with the vast amount still unknown that there is only one safe method of procedurenamely, to test every case on its own merits and as thoroughly as possible. To illustrate this I will outline the recent history of the control of woolly aphis in New Zealand and Australia’. There are in America, the original home of the pest, three types of insects concerned in its natural control — (r) certain syrphid flies, (2) the ladybird Hippodamia convergens, and (3) the chalcid wasp Aphelinus mali. As closely similar syrphid flies already exist in New Zealand I did not make any attempt to introduce the American species. In considering the other two all the evidence was in favour of Hippodamia. This ladybird has a wonderful record in California, and is rightly looked upon as one of the most valuable of known beneficial insects. Large sums of money are spent in rearing, collecting, and distributing it, and every fruitgrower is fully convinced of the benefits it confers upon him. Aphelinus mali, on the other hand, is not thought much of. Moreover, it had already been introduced into South Africa, where it was a failure. Anybody with a ready faculty for generalization might have been tempted to concentrate on Hippodamia and write Aphelinus down as foredoomed to failure. I confess that I was on the verge of making this decision, when a conversation with a Canadian scientist on the apparently unrelated subject of biological strains or races gave me a new idea about it. We were studying two races, exactly similar morphologically, of a small dipteron, one of which lived only on one host plant and was of economic importance, and the other lived on an entirely different host plant and was of no economic importance whatever. In spite of apparent absence of morphological differences, experiments proved that you could not make the progeny of the one race live on the host plant of the other, and vice versa. My Canadian friend wanted to argue that they were therefore distinct species ; but I would not agree, and countered his argument by asking him what he would do in the case of two morphologically similar races of a single species, one living, say, in a cold climate, on a given host plant, and having a single brood annually, and the other living in a much warmer climate, on the same host plant, but having two or three broods a year. The argument was left unfinished, but it suggested to my mind that the

value of a beneficial insect might, be greatly increased in a new country if, instead of introducing consignments from one locality only, two or three localities with widely different climates were to be selected, and the biological races received from these were to be crossed before liberation in the new country. With this end in view I arranged with Dr. Howard to send supplies of Aphelinus mali from three States — Connecticut, Georgia, and Arkansas having very different climates. We have no evidence that any progeny containing the Georgia strain survived the first winter, but individuals from the other two strains were observed to pair, and their progeny was recovered in the following spring from the tree on which they were placed. It will always be a matter of some doubt how far this crossing has been responsible for the success of Aphelinus mali in New Zealand, but that it has been one of the factors making for success I feel certain.

At-the present time woolly aphis is'well under control in New Zealand owing to the work of this parasite, which has proved of the greatest help to orchardists throughout the Dominion. Hippodamia convergens, on the other hand, though liberated in thousands throughout the Nelson Province, has not since been seen or heard of, and it is probable that this insect's known habit of seeking the tops of high mountains on which to hibernate has proved its undoing in New Zealand and in every other country in which it has been tried.

The New Zealand strain of Aphelinus mali has been sent across to Australia, and has already done splendid work in the apple districts of the States of Queensland and Western Australia, while the latest reports show that it is beginning to make its mark in the other States, where its propagation was greatly hampered by severe quarantine restrictions. The same strain has also been sent to South Africa, where it will be interesting to note whether it does any better than the original pure strain introduced there some years ago.

I think it may be claimed that Aphelinus mali is the first case •of outstanding success with an internal parasite of an injurious, insect present in New Zealand: In the case of predators — i.e., beneficial insects which prey upon their host from outside marked successes at least had been obtained previously in New Zealand by the Department of Agriculturenamely, Novius cardinalis in controlling cottony cushion scale, and Rhizobius ventralis in controlling blue-gum scale. Of these, the experiment with Novius is now of long enough standing for us to be able to answer the oft-repeated question, “ What happens to the beneficial insect when its host is exterminated ? ” In the Nelson District cottony cushion scale was practically exterminated for a number of years, and Novius disappeared with it. But the cottony cushion scale had one refuge where Novius either failed to follow it or only followed it —namely, on gorse —and from this refuge, when the local population of Novius was almost extinct, the scale has again made its appearance and spread abroad on to wattles, kowhai, boronia, and other plants. At the present time this pest is doing quite a fair amount of damage in Nelson, and a room has been set apart in the Cawthron insectaria to rear it and to study its enemies further. Not only Novius cardinalis, but a small fly, Cryptochaetum iceryae, attacks the cottony cushion scale, and both of these can be made use of for the control of this pest when required.

The question may be asked here, Is the internal parasite preferable to the external predator in the control of a pest ? The answer I would give is that again we must not generalize, but must take each case on its merits. Other conditions being, equal, we should not be biased in favour of one or the other, but should be prepared to utilize that one which shows best, by experiment, its ability to exercise control of its host. In the case of orchards, however, or other areas which are regularly sprayed, it is obvious that the internal parasite will have an advantage over the external • predator, since the latter may well be killed by the spray, while the former will, at any rate, escape during part of its life when it is sealed safely up within the body of its host.

The success with Aphelinus mali was the direct result of the sending by the New Zealand Government of a representative to the First Imperial Entomological Conference in London. Five years later, in June last, a second similar Conference was held, and New Zealand again sent a representative in the person of Mr. J. G. Myers. This brilliant young entomologist has already justified his mission by the discovery of internal parasites of the pear-leaf-curling midge, Pirrisia pyri, and the first supplies of these insects are already in the hands of Mr. David Miller, the Government Entomologist. This is another case of a most serious pest to orchardists, and one which defies all attempts to control it with sprays. lam sure you. will all agree with me when I say that we hope Mr. Miller will have with these little insects a success as great as that which attended the introduction of Aphelinus mali.

I now wish to bring before your notice two related problems in the biological control of insect pests. One of these is illustrated by the work done with the Australian ladybird, Cryptolaemus montrouzieri, in the control of mealy bug in orchards, and the other by the attempt to introduce into New Zealand the chalcid wasp, Habrolepsis dalmanni, for the control of oak-scale, Asterolecanium variolosum. In the' first case it is found that, even in the comparatively warm climate of California, the ladybird starts too late in the season to make any impression on its host. But if the ladybird is reared artifically in warm insectaria it can be sent, out in great numbers earlier .in the season to all points where mealy bug threatens to become a serious pest, and in this manner the pest is regularly checked. What is true of California has been proved true of New Zealand, both by Mr. Miller and myself. But neither he nor I have a staff of assistants large enough to enable us to carry on work of this sort and at the same time to attend to the numerous other pressing problems which are calling for solution. We may state definitely at the present time that if mealy bug becomes in any given season a serious pest in New Zealand the early and abundant distribution of Cryptolaemus ought to be undertaken in order to check it as soon as possible. Fortunately, our New Zealand climate is not so favourable to this pest as is that of California, and an exceptionally severe winter, like that just past, gives it a severe set-back. At present there is very little, mealy bug in Nelson orchards, but it is highly probable that the pest will reassert itself after two or three more favourable seasons.

The other problem is one of considerable scientific —namely, the difficulty of dealing with insects which reproduce parthenogenetic-

ally when introducing them into a new country. In the case of Habvolepsis dalmanni nothing was known of its life-history when the attempt to introduce it into New Zealand was first made ; but we now have enough evidence to make it highly probable that in the case of this chalcid, as in some other Hymenoptera, the unfertilized females produce males only, while the fertilized females produce either wholly or mostly females. Now, you will appreciate the delicacy of the situation when you learn that, after repeated trials with consignments of oak-scale from which few or no parasites have been obtained, the last lot received by the Cawthron Institute has yielded a single male and no less than 427 females emerging over a period of more than a month ! If the progeny of these become acclimatized in our insectaria and emerge in the spring of the present year it will all depend on that solitary male whether ,we shall get a mixed brood or an immense number of males only. If the latter event happens, then that is again the end of the attempt. The only solution seems to be to time a further consignment from America in such a way that the females derived from it may pair with the males derived from the present lot of 427 females. And even then our difficulties are not at an end, -for if we overdo the business, so that all these new females become paired, we may obtain only females at the next brood, and only males from the second brood following ! You will see from this how great a difficulty parthenogenesis introduces into these economic problems, and how delicate must be the balance in nature which, in its natural habitat, enables an insect like Habrolepsis dalmanni to continue year after year without running out entirely to one sex or the other. The very fact that from one consignment of oak-scale only a single male was obtained to 427 females shows how nearly, even in a state of nature, such an insect can come to extermination in one locality or another, and suggests to us that it may possibly be only by the interaction of a number of thriving colonies that we shall at last attain success.

■ While on this subject of parthenogenesis I may as well mention a second instance due to it of failure to establish a beneficial insect in New Zealand. Three years ago the Cawthron Institute received from Dr. Imms, Chief Entomologist of the Rothamsted Experimental Station, England, a consignment of cocoons of the well-known pearslug Caliroa limacina parasitized by the ichneumon fly Pevilissus luteolator. In the spring of 1923 not a single insect emerged from these cocoons, but a year later, during a much wetter spring, a number of pear-slug adults emerged, followed by about forty of the parasites, both sexes being represented. Most of these were liberated in the insectarium, with a plentiful supply of well-grown pear-slugs on small plum-trees, while a few were set free on two cherry-trees in the open. In both cases the ichneumons were seen feeding on the slimy exudation of the pear-slug, and the females were observed attacking them and laying their eggs in them. But it is sad to relate that every single ichneumon which has appeared in our cages this season has been a male. Either -no pairing took place between the males and females, of last year’s brood, and the unfertilized females attacked the pear-slug, laid their eggs in them, and have produced only male progeny, or else all the females paired and produced .male offspring only !

One lesson to be learnt from the above-mentioned failure is the great difficulty of obtaining success with small consignments. One might think at first that the liberation of, say, ten males and ten females would be practically certain to ensure pairing. This is not so. In many cases females and males of the same. species do not even frequent the same places or have similar habits, and their meeting and pairing may only take place when certain fixed conditions of feeding and maturation have been fulfilled. What these conditions are in the case of Perilissus is not known. We hope to continue the attempt to introduce it, but it is clear that very much larger initial supplies will be needed for success.

It is inevitable in the case of experiments such as these that a large percentage of failures should be recorded. Some of these are absolute failures, without a single redeeming feature, as in the case of Hippodamia convergens. Others, like those cases of parthenogenesis mentioned above, are failures from which we may learn valuable lessons with which to pave the way to future success. There are many causes of failure which are not within the control of the workers themselves. One of these, a very sad one, I have to record in the case of the attempt to introduce parasites of the earwig into New Zealand.

The European earwig, Forficula auricularia, is, as most of you know, a serious pest in New Zealand, particularly in Otago. In the Central Otago orchards it is the worst pest of stone-fruit present. The Imperial Bureau of Entomology in London took up this question, and arranged with Dr. Imms at Rothamsted for a student to be given complete charge of this work. Mr. H. M. Altson was selected, and as a result of his work initial supplies of two parasites were sent out to the Cawthron Institute. These consisted of 120 puparia of Digonochaeta setipennis,' and, later on, 1,400 live earwigs stated to be parasitized with Racodineura antiqua. Owing to the great difficulty of the work, a continuance of supplies over at least two whole years was essential. But, unfortunately, Mr. Altson fell ill, and there was nobody who could carry on the research. We now learn with the greatest sorrow that his illness is quite incurable, and that he will never again be able to take up this important work.

As this question of control of the earwig is of special interest to Otago I hope I may be pardoned for discussing it somewhat more fully. The insects mentioned above, the only two parasites known which are likely to offer a chance of successful control, are both flies of the family Tachinidae, and neither of them is easy to handle under insectarium conditions. Digonochaeta setipennis is larviparous, depositing young living larvae in the haunts 'of earwigs ; these larvae move rapidly about, seeking for their prey, the latter showing evident signs of fear in their presence and hiding in dark corners. When the young Digonochaeta larva reaches an earwig it bores into it and feeds on its internal tissues, finally issuing fully fed from the destroyed host and forming the usual barrel-like puparium near its remains. In the case of Racodineura antiqua the procedure is very different. The females seek out leaves and vegetable remains which have been nibbled by earwigs, and deposit on them minute, black, seed-like eggs. These are swallowed by the earwigs, and the young larvae hatch out

inside them and devour the internal organs of the host, finally pupating much as in the case of Digonochaeta. Under insectarium conditions we succeeded in taking both these flies through two complete broods, but we were not able to keep the percentage of parasitism high - enough to ensure success of the experiment. The second brood in each case consisted of so few individuals, emerging at wide intervals apart, that the work could no longer go on without fresh supplies. Further, in the case of Racodineura it was noted that only eighty out of the original 1,400 earwigs sent from England yielded puparia i.e., the amount of parasitism was under 6 per cent. This percentage dropped still lower when we worked with Nelson earwigs.

, One unexpected . difficulty was met with in the case of Racodineura, but was overcome by the ingenuity of Mr. Tonnoir, who was at that time working in the Cawthron Institute as research student in Diptera. The earwigs were given slices of potato or apple to nibble, and when these were put into the cages where the fertilized females of Racodineura were confined the latter laid a great number of eggs on them. The slices were then returned to the earwig-cages, when it was found that the earwigs ate them readily enough, but left each little egg standing up on a high pinnacle untouched ! This most unexpected set-back was countered by Mr. Tonnoir, who, knowing the fondness of earwigs for dandelion-leaves, tempted them with these. They fed readily enough, and the flies laid their eggs on the nibbled pieces ; these, when returned to the earwig-cages, were finally devoured, and thus parasitism was at last secured.

The experiments with these two flies appear to indicate. that, given adequate supplies to start with, and working as close as possible to nature i.e., not with closed cages in insectaria, but with baited traps in the open, into which the earwigs could be attracted by hundreds —Racodineura and possibly also Digonochaeta could be permanently established in New Zealand. But whether either of these flies, or even both together, will give a sufficiently high percentage of parasitism to control the pest to any great extent our experiments do not enable us to say. The attempt must certainly be made, and it will be one of the. principal objects of my forthcoming visit to America and Europe to try to arrange for abundant supplies of both parasites in the near future.

New Zealand is the only large area of land in the world, exclusive of the frigid zones, in which the green lacewings, family Chrysopidae, are not represented by native species. These insects feed on various species of aphids ; their larvae have peculiarly formed sucking mouthparts and are very voracious. In most parts of the world they are only sporadically beneficial, owing to the large number of parasites from which they suffer. If these insects could be acclimatized in New Zealand without their own parasites it seems highly probable that they would prove of very great benefit in the control of a number of introduced aphids, such as those of pine, spruce, and oak. Attempts have been made from time to time to introduce various species of Chrysopidae into New Zealand from America and Australia, but all have failed' from one cause. or another. More recently a large shipment of 1,900 hibernating green lacewings has been received by the

Cawthron Institute from Canada, through the co-operation of the Dominion Entomologists in Ottawa and the State Entomologists of British Columbia. These insects arrived in excellent condition, only about fifty being dead. A large number were sent down immediately to Christchurch in order to make an attempt at controlling the oakaphis. Both in Nelson and Christchurch a considerable number of eggs were laid, and the larvae hatched from them are at present feeding vigorously on various species of aphids. Further consignments are being arranged for in. the near future.

. The problem of saving the oaks in Canterbury is a difficult one, as it appears to be the damage done by the combined attacks of oak-aphis and oak-scale which is the cause of their serious condition. The solution to be aimed at must be efficient control of both these pests. This should be attained to a large extent by the successful acclimatization of both Habrolepis dalmanni and a suitable species of Chrysopa; but there is still a considerable way to go before this desirable end is achieved.

The codlin-moth, Laspereysia pomonella, is, as you all know, one of the worst pests which orchardists have to contend with in all parts of the world. Only the most careful and’ rigid attention to the spraying schedule will ensure to an. orchardist freedom of his crop from the injury done by it. In New Zealand there are known to be two distinct broods of this moth, and the main effort of the orchardist is in the direction of getting his arsenical sprays on to the trees at the right times to check the newly-hatched larvae of these two broods before they can enter the apples. Recent observations, however, indicate that there is a more continuous succession of moths throughout the summer than is generally . supposed. The two broods are, in fact, only the crests or maxima of the wave-like curve on the graph' indicating the number of emergencies week by week from October to May. Two entomologists in the University of Colorado discovered a few years ago that codlin-moth could be easily trapped by means of fermented apple-juice placed in jars hung in the upper third of the trees. This experiment has been repeated recently in a Nelson orchard, and also by a South Australian grower. Both got closely similar results, which are rather remarkable when we consider that the experiments were carried out on clean orchards where codlin-moth has been controlled by careful spraying for many years.

In the Nelson orchard fifty-five small tins were used, hung between the upper limbs of consecutive trees in one section of the orchard. During November and December, when the experiment was being carried on, high winds prevailed nearly all the time, a most unusual state of affairs for Nelson. A number of tins were blown about violently and their contents spilled, so that the total recorded falls short of the actual catch. The supply of apple-juice gave out on the 23rd December. For the period of seven weeks the following catch was secured : Number of codlin-moth, 305, of which 218, or 72 per cent., were females ; number of leaf-roller moths, 198 ; number of other insects, 5,468, of which 7 per cent, could be classed as beneficial, the rest being either injurious species such as cut-worms, ’ &c., or of no account.

In the South Australian experiment sixteen large tins were used, and four of these were placed near a neighbouring orchard whose owner had neglected to spray carefully. In three weeks during the latter part of November and first part of December 442 codlin-moth were caught, 66 per cent, being females. More than half of these were trapped in the four tins near the neglected orchard !

I mention these results particularly on account of the recent outcry in Great Britain against the sale of apples having arsenical sprays on them. At the present moment there does not appear to be any reason to think that New Zealand apples which have undergone the full spraying programme will come under the ban. The scare, however, has started, and I think we ought to be considering whether we might not reap a great advantage by substituting either a spray harmless to man, or else a trapping method for the later sprays in January and February, which are the ones which leave arsenic on the exported apples. The country which could place the label "No arsenical spray on these apples ” on all exported cases of that fruit would undoubtedly reap the benefit over other countries in higher prices and a more ready market.. So I shall express the hope that next year some groups of orchardists will take up this question of trapping more extensively and carry on larger experiments right through from one end of the season to the other.

You will see from the above account that much has been done in the past few years towards an increase in our knowledge of economic entomology in New Zealand, particularly as regards the biological method of control of insect pests. There is,. however, a hundred times as much left undone, for lack of the trained men and resources needed to carry out the work. Even the preliminary work, such as the workingout of life-histories, is still undone in the case of some of our worst pests. The valuable work done by Mr. David Miller in his study of the life-history of the pear-leaf-curling midge and the New Zealand grassgrub must form the essential basis on which any scheme of attack on either of these two pests must be built up. The life-history of the New Zealand bronze-beetle is still to a great extent unknown. Many examples could be given of pressing pioneer work which badly needs to be done. ■ ' .

(To be continued.)

Farmers’ Field-days. Writing on a field-day held at the Merredin State Farm, the editor of the Journal of the Department of Agriculture of Western Australia thus defines a farmers’ field-day : “It is an annual exposition of results from patient effort harnessed to trial, experience, experiment, and condition; an education in a nutshell ; bovrilized farm science. It is a gift from the Government of the day to its husbandmen of knowledge painstakingly acquired, and a plan scientifically designed for the opening-up and development of fields and pastures to the limit of the State’s soil and climatic capacity. It is also a signpost at the cross-roads of success and failure.”

Forty per cent, of the bulk of a fertile soil should be air and not stagnant water. Oxygen in the soil is necessary for the establishment and maintenance of the highest-class plants that a soil will carry. Drainage provides oxygen to waterridden soils. t