1 in sugar from borer control was 21.4 pounds per ton of cane. Calculating sugar at a value of lc per pound, and cane production at a rate of 40 tons per acre (the average production on the hacienda was 45 tons per, acre), we may figure the gain in sugar at $8.56 per acre of cane. This is gross gain, at a very low valuation for sugar; the net gain would in any circumstances considerably exceed the cost of borer control, and the lower cost of milling alone makes borer control a profitable undertaking. The chairman presented a paper prepared by W. F. Jepson and L. A. Moutia. PAPER THE PROGRESS OF APPLIED ENTOMOLOGY IN MAURITIUS DURING THE YEARS 1933 TO 1938, WITH REFERENCE TO INSECTS OF THE SUGARCANE W. F. JEPSON, Ph.D., Entomologist, Maz~ritiz~s and L. A. MOUTIA, Di$. Agr. (Maur.), Assistant Entomologist, Mnzlriti~ls / The principal features of the past five years, in regard to the insect pests of the sugarcane have been the steady extension of the area of infestation by the Melolonthid white grub, Plzytalus smithi Arr., in the central, southern, and eastern portions of the island, and the great decrease of the infestation in the northern plantations; the added prominence of damage by the "moth borers" Diatraea venosata Wlk. and Olothrez~tes schistacaena Sn. Intensive efforts to control the white grub pest by biological means have been made since 1932, and continue unabated. A coinprehensive scheme for the biological control of moth borers has been submitted to the authorities for consideration. 1. Phytalus Smithi Arr. The period under review has been one of growing conviction that the hand collection of beetles, as practiced by the general public for more than twenty years, under a bounty system is quite ineffectual, and does not justify the large sums expended upon it. A policy of gradual voluntary abolition, led by several prominent planters, was adopted in the campaign, and was succeeded in the following season by legislative measures to prevent the collection of beetles over 80% of the infested area. The annual larval survey, recently concluded, gives an indication of a marked general decrease in the intensity of infestation for These have been considered sufficient grounds for suppressing completely the hand collection campaign during the coming beetle season, thus saving a sum of between &5000 and &6000, the amount of the annual disbursements over many past years.
2 It is generally recognized that the only practicable methods of control of Phytalus under conditions obtaining in Mauritius lie firstly, in the importation and the establishment of effective natural enemies, and secondly, in the development of varieties of cane with great vegetative vigor, and with specialized root systems, capable of resisting the attacks of Plzytalz~s larvae. It is with the first named method that the writer, a Phytalus investigation officer, working in close cooperation with Mr. A. Moutia, and the officers of the Entomological Division, has been chiefly concerned. The five-year period has been one 01 steady progress in the importation of natural enemies of Melolonthines from all parts of the world. Much of this parasite work in Madagascar, Puerto Rico, Netherlands East Indies, Philippine Islands, and Malaya, has been reported elsewhere (1, 2, 3, 4, 5). Work is in progress in South Africa, Zanzibar, Northern Africa, and England, and foreign parasite importations are regarded as part of the normal routine of officers of the Division of Ehtomology. The following parasites and predators have been imported and released in Mauritius, from 1953 to 1938: Campsomeris annulata F.", from East and West Java; Negros. Campsomeris asiatica Sauss, irom E. Java. Campsomeris aureoloides Brad., from Natal, South Africa. Campsomeris erythrogaster Dalm.," from Nossi-bC, Madagascar. Campsomeris felina Sauss., from Natal. Campsomeris dorsata F., from Puerto Rico. Campsomeris javana Lep.," from West Java. Campsomeri leefmansi Betr., from East Java. Campsomeris lindenii Lep., from West Java. Campsomeris madonensis Du Buyss., from Natal (Zululand). Campsomeris marginellasub. sp. modesta Sm., from Negros, P. I. Campsomeris minutalis Brad., from Madagascar. ~ampsomeris phalerata Sauss.," from West Java. Campsomeris fiilosella Saws.,* from Madagascar. * Campsomeris pfeiflerae Sauss., from Madagascar. Campsomeris pocillator Brad., from Madagascar. Campsomeris firismatica Sm., from Malaya. Campsomeris quadrifasciata F., from West Java.. sub. sp. fimbriata Burm., from East Java. sub. sp. negrosicola Betr., from Negros. Campsomeris quadriguttulata Burm., from East Java. var. sericeps Cam., from East Java. var. bendoredjoensis Betr., froin East Java. var. nov. from East Java. * Recovered. 378
3 Scolia carnifex Sauss., from Madagascar. Scolia rubea Brad.,* lrom Nossi-bC. Myzinidae Myzine (Mesa) nodosa Guer., from Madagascar. D~~~~~~-Tachinidae (incl. Dexiidae) Prosena siberita F., from West Java. Urodexia uramyoides Tns., from Banka, N. E. I. Hamaxia incongrua Wlk., from Banka, N. E. I. Paratamiclea pallida, var. Houa Vn., from Madagascar. Dexia rustica F., from England. Pexopsis pyrrhaspis Villen., froin Natal. Pyrgotidae Adupsilia latipennis Wlk., s. sp., froin Natal. COLEOPTERA-E~U~~~~~U~ Pyrophorus luminosus Ill., from Puerto Rico. 1 AMPHIBIA-Buf onidae Bufo marinus L.,** from Puerto Rico. The latest discovery may be reported of Dexiid parasites of both larvae and adults of the clove chafer, Entyposis impressa Arr., at Zanzibar. The beetle closely resembles Phytalus in size and general facies, a fact which is sufficient to warrant the shipment of large numbers oc these parasites for trial in Mauritius. It must be admitted, that with the exception of Paratamiclea pallida, of which over 17,000 specimens were released, only a few hundreds of the other Dipterous species were available for distribution, and there is pressing'need for further shipment work in Banka, Africa, and England. The two latter countries are being worked during the present year, and shipments are expected from Zanzibar and North Africa, where Mr. Moutia is carrying out systematic searches for material. As to the results of the parasite work, it inay be stated that the two Scoliids Campsomeris ibilosella and C. phalerata are now to be found in nearly every infested canefield, the case of C. fihalerata being particularly interesting in that it is present in enormous numbers, even in the winter season. The role of these parasites in control is almost iinpossible to determine, since parasitized larvae are practically never met in ordinary survey work, due to the habit of the female wasp of dragging her prey deep down in the earth. When male wasps can be found congregated on the flower heads of common canefield weeds, so as to impart a black patchy appearance, one cannot but conclude that this source ol larval mortality must aid considerably in reducing high grub populations. The results of various experiments in the direct control of the larvae of Phytalus in cane plantations do not offer any great hope of success. Mechanical * * Release pending.
4 tillage of the soil in the earlier stages of development of the larvae cannot be carried near enough to the cane stool to kill a significant proportion. In practice, the stony or rocky nature of many infested soils renders hand forking the only economic method of cultivation. This is beneficial in stimulating root formation, but its effect on Phytalus is negligible. Newly planted cane has been covered with a two foot layer of trash, without affecting the ability of Phytalus to oviposit, and to develop successfully. Burning a thick trash layer before planting, at the time of beetle flight, may possibly stimulate cane growth, but it has no effect whatsoever on Phytalzu. The application of white arsenic at the rate of 75 Ibs. per acre produced an insignificant decrease in group population, and any increase on this rate is econoinically out of the question. 2. Diatraea Venosata Wlk. The spotted borer, as this species is called in Mauritius, is responsible for insidious damage, both to young and to maturing canes, which must be comparable in magnitude with that done in a more conspicuous fashion by Phytalus. An annual survey has been initiated, with the object of obtaining as it were, a cross section of the general infestation throughout the colony. 200 canes of each of the varieties White Tanna, and B.H. 10 (12) are closely examined at the cane carriers of 24 factories, the results being expressed in the familiar terms of per cent stalk infestation, per cent joint infestation, and intensity index. The figures for the per cent joint infestation for 1936 and 1937 are 12.6% and 11.7% respectively, the years being reckoned by planters as relatively light infestation years. It must be stressed that the figures for Mauritius tend to include a greater proportion of ratoon cane, since this represents nearly 5/6 of the total area under cane. Ratoons are universally less infested than plant canes. The estimated loss according to the 1933 survey (Moutia 1934) was 2.3% sucrose per cent cane, representing a gross loss of one million and a half Rupees. The local parasites of this borer are totally inadequate to prevent this serious degree of infestation, which in a dry year becomes almost ruinous for coastal estates. The practice of cutting out of deadhearts, though sometimes practiced with certain success, is thoroughly undependable as a means of control. In view of the promising attempts to control the moth borer in Barbados by means of Trichogramma it has been established that the indigenous species T. australicum Gir. can be reared on the rice moth Corcyra cephalonica in Mauritius. Meanwhile a comprehensive scheme for biological control investigations in Ceylon, the home of the borer, and in India, has been submitted to the authorities. If this be approved, it should form the starting point of an onslaught on a pest which is common to many sugar countries in the Orient. For our region, however, there is only one practicable line of fundamental reasearch into this problem, namely a search in the home of the wild Saccharum and Sorghum species, New Guinea, by an exploratory biologist of repute. This could only bk accomplished by financial and technical cooperation between several interested countries, both in the East, and in the neotropical sugar regions. 3. Nomadacris septemfasciata Serv. The red-wing locust of Africa, once so destructive in Mauritius, is now con-
5 fined in its depredations to two or three patches of a few acres in extent. This is thought to be due chiefly to the Mynah, Acridotheres tristis. The last minor outbreak was in the dry year Recently the egg Pedator, Stomatorrhina lunata has been recognized as one of the commonest canefield Diptera, though its influence on the locust population remains to be evaluated. 4. Oryctes tarandus 01. The large white grub of this Dynastine is still found at the rate of about 2,000 per acre in localized areas, though it is apparently held in check by the Scoliid, Scolia oryctophaga Coq., whose maximum season of abundance is July and August. I 5. Aphis nzaidis Fitch. This Aphid is very coininon on maize, bul is rarely found on sugarcane. Mosaic of cane is absent from Mauritius. 6. Aphis sacchari Zehnt. Tended by the ubiquitous black ant, Teclzno~7zyrnzex detorquens Wlk., this Aphid is universally present in canefields. An outbreak has recently occurred, the death of the cane being brought about largely by the development of sooty mold on the infested leaves. Eventually, the outbreak was controlled by an entomogenous fungus, aided by the Coccinellid, Chilomenes lunata F., at the onset of the cool winter season in May. 7. Gryllotalpa africa?za Pal de B. This mole cricket has been recorded as causing severe local damage to sugarcane, and, as far as we can ascertain, it is free from insect predators or parasites. Baiting with Paris green and bran has not given any appreciable control. 8. Perlzinsiella saccharicida Kirk. The presence of this insect in Mauritius has recently been recognized, by the finding of several adults in a light trap, by Mr. Jean Vinson, scientific assistant of the Entomological Division. It has probably been in the island for many years, since 0. H. Swezey records having seen a specimen from Mauritius. The typical ovipos:tion scars on the midrib of cane leaves are met with fairly frequently, but no damage which could be ascribed to the insect has ever been observed. 9. Aulacaspis tegalensis Zehnt. Long recorded in Mauritius, this white encrusting scale has only during the past two years, 1937 and 1938, been the subject of complaints addressed to this Division. Starting from the nodes, the scale forms a compact white crust over the stalks and leaf bases of maturing cane. At present the infested areas do not exceed a few acres in extent, but the only recommendations that can be made are the burning and cutting of the fields at the earliest possible date in the grinding season. The Coccinellid, Lindorus loplzanthae Blaisd., preys on the scale, but is quite insufficient in the present instance, to prevent serious infestation. Recently, a number of old larval skins of the newly established Coccinellid, Chilo-
6 corus politus Muls., have been found in fields infested by this scale, and there is some hope that this Javanese importation may prove of value in checking the pest, although its primary object is to control Aspidiotus destructor Sign. on the coconut palm. 10. Leaf Roller (Marasmia sp.). In April, 1938, an infestation of the hearts of young cane shoots arising from the stools of maturing ratoons, was reported. On examination, the trouble proved to be due to a delicate green Pyralid larva, which stripied the upper surface of the first free leaf, the edges of which were securely glued together. Chlorosis and death of the enclosed shoot frequently ensued, giving the appearance, at first sight, of deadhearts due to the moth borers. In other cases, pokkah boeng symptoms were apparent, the young shoot succeeding in penetrating the surrounding affected leaf. This insect has been noted before in Mauritius, upon rice, and has now been found on a number of wild grasses, but no records of economic damage exist. No advice as to control by direct methods can be given, but it is thought that when the cane is growing vigorously, the young leaves are being pushed out of the heart so quickly, that the larva is forced to confine its attentions* to the tip of the leaf on which it has developed, and cannot cause the strangulation of the shoot. Elimination of wild host grasses is also desirable. 11. Nematodes, Heterodera and Tylenchus spp. During 1937 and 1938, a number of complaints of growth failure in young canes, particularly in the variety P.O. J. 2878, have been received, which could not be ascribed to Phytalus. Root examinations have shown the presence of nematodes in the tissues. In the case of Heterodera, the typical root knots occur, within which are often found the sac-like female worm. The presencd of Tylenchus is revealed by the red lesions seen on new roots. The infestations are, at the moment, sporadic, and no control measures have been attempted, but it remains LO be seen whether there is varietal resistance to these attacks, which will provide a welcome means of obviating them. It will thus be seen that, apart from Phytalus and L)iatmea, which are of widespread importance, there are a number of pests which, under the system of numerous individual ownerships, cause considerable loss on Mauritius sugar estates. In cases where cultural measures cannot be applied, it is the policy of the Division to strive for the increased natural control of the insects by the importation of parasites and predators whenever the opportunity occurs. REFERENCES (1) Moutia, L. A. Report on Entomological Missions to Madagascar. Port Louis (2). Bull. Ent. Res. 24: (3) Jepson, W. F. Report on the Search for Parasites for Phytalus smithi, Arr. Port Louis (4). A Summary of the Results of the Phytalus Investigations Port Louis (5) Jepson, W. P., and Regnard, L. P. The Parasites of Melolonthines at Nossi-bC. International Sugar Jour. February 1937.