A Review of twenty-five Years of economic Entomology in the Island of Mauritius

Abstract

The practical results achieved in the past twenty-five years' work on the major insect pest problems of Mauritius are discussed.The major insect pests studied are the white grubs of sugar-cane, Clemora smithi (= Phytalus smithi) and Oryctes tarandus; the sugar-cane moth borers, Proceras sacchariphagus, Sesamia vuteria, and Argyroploce schistaceana; the coconut scale-insect, Aspidiotus destructor; the pineapple mealybug, Pseudococcus brevipes; the cochineal insects of the prickly pears, Dactylopius tomentosus and D. indicus; fruit-flies; the biting flies, Stomoxys nigra and S. calcitrans; the red ant, Solenopsis geminata; the black ant, Technomyrmex detorquens; and termites.The actual status of these pests is given in detail. Clemora smithi, which was first recorded in 1911, is still a major pest of sugar-cane in spite of the 43 species of parasites and 2 species of predators introduced to check it. Oryctes tarandus very seldom causes severe damage now to sugar-cane plantations. It is a sporadic pest, and has been definitely held in check since the Scoliid wasp, Scolia oryctophaga, was introduced from Madagascar in 1917.The status of the three moth borers of sugar-cane and that of their parasites is fully dealt with. Of the five species of parasites introduced from Ceylon and Madagascar in 1938–40 to control Proceras sacchariphagus, only one has so far been recovered and its beneficial effect is very limited. An account is given of experiments on the mass liberation of the egg parasites, Trichogramma australicum and T. evanescens. The results were in both cases deceptive. The spotted borer, P. sacchariphagus, is a major pest of sugar-cane in some localities and further introductions of parasites from other cane-growing countries are recommended.The coconut scale, Aspidiotus destructor, which, since 1927, threatened all the coconut plantations of the Island, is now under control, owing to the introduction from Ceylon and Java, respectively, of the predacious Coccinellids, Chilocorus nigritus and C. politus. The bionomics of the various parasites and predators of this scale in Mauritius are fully described.A historical review is given of the introduction of the cochineal insects of prickly pear, Dactylopius indicus and D. tomentosus in the Island. The completely successful eradication of Opuntia tuna and O. monacantha, by these two Coccids is given as a typical example of the biological control of noxious plants by insects.The pineapple mealybug. Pseudococcus brevipes, which is responsible for wilting disease, is considered to be one of the factors limiting the development of the pineapple industry in Mauritius. Spraying with a diesel-clay emulsion, though checking this pest, is limited in its application. Further introductions of parasites and predators are desirable.The common white mealybug, Icerya seychellarum, is still a major pest of orchards and ornamental plants in spite of the presence of the local Coccinellid predators, Rodolia chertnesina and Exochomus laeviusculus. Practical control can be achieved by the use of banding grease coupled with the attacks of predators. No local parasite has been recorded in Mauritius.Six species of Trypetids are recorded. Of these, the flies attacking cucurbitaceous fruits are the most harmful. Experiments with numerous attractants for fruit-flies are mentioned. The only bait showing any success in the control of the Dacus flies is the Mally fruit-fly bait. Parasites have been imported from South Africa and Ceylon without success. Further attempts should be made.The bionomics and breeding places of the blood-sucking fly, Stomoxys nigra, are described.The Red Ant, Solenopsis geminata, is a major pest of seedlings in Mauritius. It is now destroyed by the use of a diesel-clay emulsion. Baits containing thallium sulphate have been tried without success.The rôle of the Black Ant, Technomyrmex detorquens, in preventing development of the Coccinellid predators on Icerya seychellarum is emphasised. Barber's poisoned bait has been found very useful against this household pest.A review of the species of termites found in Mauritius as well as the various means of control used against them are given. An insecticidal powder containing arsenious oxide has given the best results.During the last 25–30 years, 64 species of parasites and predators have been imported for the biological control of eight species of insects of major economic importance and of two species of noxious plants.The results achieved indicate that the introduction of parasites and predators in insular countries like Mauritius should be carried out only after a thorough investigation of the various ecological, biotic and climatic factors existing between the country of exportation and the country of importation.The rôle of cyclonic disturbance in the fluctuation of the parasite population is mentioned. Scoliid parasites, for instance, are generally scarce after violently disturbed weather and may sometimes remain so for two or three years after the disturbance.