The Coconut Grasshopper.

Advice on Its Control.

We are indebted to Mr. George H. Murray, F.E.S., Director of Agriculture in the Mandated Territory of New Guinea, for this article on a pest which has worried copra planters in New Guinea. We publish it in full in the hope that it will be of benefit to planters in other territories.

THE most serious pest of coconuts in the Mandated Territory of New Guinea is the large tree locust com monly known as “grasshopper”

(Sexava sp) belonging to the family Tettigoniidae. It would seem as if the pest is becoming even more widespread, as nearly every mail brings letters to the Department from planters report ing new districts seriously attacked, and it is thought therefore that the following notes with excerpts from Mr.

Caldwell’s Progress Report would be of value to the planting community.

In some instances the outbreaks have been so severe that coconut palms have been stripped of all leaves except the central “spear,” which apparently is never, or rarely, attacked. So far, all attempts to control the pest by poison baits have been ineffective, and to spray or dust the palms would be an economically unsound proposition. The Department of Agriculture has also made many experiments with tangle foot mixtures, proprietary and other wise, to trap the nymphs (the wingless stage of the insect) as they ascended the palms. Large numbers have been trapped by this method, but it has proved far too costly for extensive use and had to be abandoned.

For the past fifteen months an entomologist, Mr. N. E. H. Caldwell, B.Sc., has been specially employed in studying its life history and carrying out experiments for its control. His

field of operations has been on several plantations in Manus (Admiralty Group) which have been severely attacked for years by this pest, and much useful information has been ob tained, full details of which will ulti mately be made known when the history of the campaign against Sexava has been written. It has been estimated that the losses caused by this pest amount to 10,000 tons of copra per annum, a loss of fully £100,000 per annum to the Territory.

The eggs closely resemble grains of oats in shape, size, and colour, and the natural site for oviposition in Manus, would seem to be the ground, the epiphytes on the palm trunks being also favourite places for egg-laying.

The site of egg-laying would seem to vary in different districts, as in some places numbers of eggs are sometimes laid in the crowns of palms, and the writer has even found them in shallow holes in the trunks of palms.

Mr. Caldwell states: “The epiphytic growth on palms will always be found to contain a number of eggs in an infested area. A mat, perhaps half an inch in thickness, would appear to be the most favoured when the eggs will be found on the inner surface against the ‘trunk.’ A thinner mass probably does not afford sufficient protection. Thick masses are sometimes utilised, the eggs being found embedded in the centre of the material. Usually, however, the egg’s are placed so far into the mass that they are either partially or wholly exposed on the trunk side of the growth. In the ground the eggs may be found almost anywhere in an in fested area. They have not been found anywhere here (Manus) but in the ground itself, i.e., not in decaying timber, bomboms, husks, or any other material. The insects do not appear to show any marked preference for any particular type of soil for oviposition, and thus probably deposit their eggs wherever they happen to alight at the end of their downward flight. Avery thorough examination of wet black ground with a heavy covering of bracken fern, pepper vine, etc., has re vealed the eggs to be about as numerous as in sandy parts, taking into consideration, of course, the com parative density of infestation.

“The nymphs immediately they have hatched appear to make their way to the nearest palm and climb it. In areas of dense infestation where nymphs are hatching in large numbers every night—as shown by adhesive bandages on the palm trunks —one very seldom finds a first stage nymph on the ground, on the grass, or low down on the palm trunks. Occasionally one will be brushed off on one’s clothes, and by sweeping the grass with a net a few specimens may be obtained on occasions. From these considerations one is led to the belief that the nymphs ascend the palms within forty-eight hours at most of their emergence from the egg. Further, the ascent takes place at night.”

Mr. Caldwell also states: “In this connection I put forward the tentative suggestion based largely on specula tion, that the ‘increase of the pest is dependent on the fate of the first stage nymphs.’ It appears that there is a normal high rate of mortality amongst these nymphs. It has been observed that the great majority of newly

hatched nymphs liberated on isolated small palms have disappeared. It is not likely that they would be able to travel th e 30 feet to the nearest palm tree, or rather, would not undertake to do so; a certain number of nymphs do reach maturity on palms of say three years of age, thus proving that the conditions are not unfavourable.

Also the number of nymphs caught ascending the palm trunks by ‘Ostico’ bands—up to 300 in slightly less than five months —is much greater than the population of an infested palm.”

It is quite evident from the above, therefore, that there is a greater chance of keeping the pest under con trol if immediate action is taken as soon as the insects are seen on the plantation. On well managed planta tions there are ‘“Beetle-Gangs” regu larly employed in collecting “rhinoce ros” and other beetles, but it is even more important that they should col lect Sexava or “grasshoppers” also.

During the day the adults remain more or less inactive, and are usually found on the underside of the leaflets or on the upper side if it happens to be more sheltered than usual. Owing to the greater amount of protection afforded by the broader part of the leaflet they will be found towards the base, rather than near the tip. They are much easier disturbed than any of the nymphal stages and will take to flight easily.

Feeding is largely a night activity, though they may regularly be seen feeding on the late afternoon, especially on dull days. ... It is probable that feeding is entirely dependent on the weather, and on very dull days the in sect probably feeds at intervals through the day.

Natural Enemies.

No egg parasites of Sexava have been found in the Manus district, but a few have been bred by Mr. Frog gatt, Entomologist of the Department, from the eggs obtained in New Han over, though not in sufficient numbers to have any appreciable effect in re ducing the pest.

Mr. Caldwell states that two species of hawks, two herons, and a king fisher have been observed feeding on the “grasshoppers.” These naturally confine their attention more to the larger nymphs and adults.

The species of birds have not been identified, but planters would be well advised not to molest any insectivorous or even predaceous birds noticed on their plantations.

Plague Outbreaks.

With reference to sudden outbreaks of the pest Mr. Caldwell reports: “The idea of plague outbreaks comparable with those of locusts would appear to be erroneous. There has been no evi dence to support this idea forthcom ing in this district (Manus) for the last eleven months. All increases in the pest have been fairly gradual nothing at all like the conditions per taining to the locust plagues, i.e., a sudden appearance of large numbers of the pest, the complete eating out of an area, and the equally sudden dis appearance of the pest.”

Control Measures.

Many experiments have been made to discover some effective method of controlling the pest, but hand collect

ing appears so far to be the most satisfactory. Mr. Caldwell states: “For young palms up to 10 feet in height the ‘grasshoppers’ may be either picked off by hand or dislodged with a short stick. For palms greater than ten feet up to twenty-five feet the use of a long light stick, to the end of which a tuft of coconut leaves has been tied, is probably the best. ‘Teasing’ the grasshopper will result in its either fluttering down from the palm, or transferring itself to the leaves on the end of the stick, whence it may be picked with the hand. For palms greater than twenty-five feet in height fires must be used to dislodge the ‘grasshoppers.’ ”

“Very tall palms are beyond the reach of fires. The action of the fires is definitely dependent on heat and not smoke. The efficiency of fires will de pend largely on the leather condi tions as well as on the actual height of the palm. Wind is the chief factor in rendering fires inefficient. If the force of the wind is such, that in order for the blast of hot air to reach a palm

the fire has to be made in the next line of palms (about 30 feet away) it will have little effect. A slight breeze is better than a perfect calm, as then the blast of air will travel across the palm head instead of straight through it vertically, and thus effect a greater area. It is difficult to get a fire to affect the whole palm head. The average diameter is at least 30 feet.

To obtain a pillar of hot air of this width would require a considerable blaze. . . . The contention that burn ing the fallen bomboms destroys valu able plant food does not apply to the majority of plantations, which have a luxuriant growth of grass and weeds, ample for the provision of humus, etc.

Burning of course will not destroy the mineral constituents of the fuel.”

A variation of the ordinary collect ing practice is collecting at night.

This has been done at Mokerang Plan tation. The number of “grasshoppers” caught per unit of labour is not greater than each unit on Pak Plantation, where collecting is done during the day. But two facts must be considered; (1) 95

per cent, of the catch were females and (2) this plantation contains noth ing but very tall palms, and the other methods of collecting are impracticable.

Fires were found to be effective only on the calmest days and then obviously only partially so.

Traps.

The traps have consisted mainly of bands of “Ostico,” a trade tanglefoot preparation, applied in bands round each palm. Many experiments have been made with this preparation, but the cost would be prohibitive on a plantation scale. “Ostico” costs 3/per 51bs. tin in Australia, and the cost of application for one treatment is 6d per palm.

From Mr. Caldwell’s and my own observations, it would seem that digging the around for the purpose of destroying “grasshopper” eggs has not proved practicable, for the reason that the cost is not warranted by the small number of eggs destroyed.

A species of Sexava closely akin, if not identical with our coconut pest, is found in Amboina, Netherland East Indies, but is there largely kept under control by a minute wasp parasitic on the Sexava eggs.

Efforts made to introduce this wasp from time to time during the past four years did not materialise, but on Feb ruary 2, Mr. J. L. Froggatt, B.Sc., Entomologist to the Department of Agriculture, was despatched by the Administration to Amboina, on the motor schooner “Hermes,” for the pur pose of bringing a shipment of parasites to the Territory, the Dutch authorities very kindly agreeing to co operate in the work. It is proposed to introduce the parasites to Mokerang Plantation where they will be in charge of Mr. Caldwell. When suffi cient have been bred they will be re leased in an infested area, and after they are thoroughly established will be distributed in other parts of the Ter ritory infested with Sexava.

In the meantime, however, planters should not relax their efforts to keep the pest under control as far as pos

sible by the method recommended by the Department of Agriculture.

On many plantations “grasshopper” drives have been carried out under the supervision of Agricultural Inspectors, or, in accordance with the Depart ment’s recommendations, and in many instances with very satisfactory re sults. It is advisable to make thorough arrangements for carrying out the drive beforehand. Plentiful supplies of dry coconut leaves (bomboms) should be provided along the lines intended for the flares or fires, and the assistance of native children should be sought for collecting the insects as they are brought to the ground.

A day with a gentle or moderate breeze should be selected for the drive and the “bomboms” should be stacked upright as far as possible and the whole line lighted simultaneously.

Many letters from plantation man agers have been received by the De partment of Agriculture stating that these methods have been successful in reducing the pest but it is absolutely necessary that no time be lost in taking active measures before the pest has had time to become serious.