Studies on the biology, ecology and economic importance of the sugar-cane scale insect, Aulacaspis tegalensis (Zhnt.) (Diaspididae), in Mauritius

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Abstract
Aulacaspis tegalensis (Zhnt.) (Diaspididae) infests the stems, and to a lesser extent the leaves, of sugar-cane. It is indigenous to Malaya and the islands of S.E. Asia, and has been introduced to the Mascarene Islands and East Africa. Its biology and economic importance were studied in Mauritius. Development and construction of the scale in both sexes are described. The life cycle takes 3–9 weeks, the female laying 700–800 eggs over 10 weeks in summer and 14 in winter. Feeding in the stem is in the parenchyma; the path of the stylet is intracellular and vascular bundles are avoided. Stem surfaces are essential for population increase. The leaf sheaths which invest stems tightly or loosely according to their age, have a decisive role among factors that influence intensity and pattern of stem infestation. Field infestations may be severe in dry coastal areas. Populations increase in March-May, and decline in July-November. The determining factors are seasonal weather, crop growth, harvesting and natural enemies. Dispersal, by the eggs and crawlers, is passive. Adelencyrtus miyarai Tachikawa (Encyrtidae) is constantly associated with Aulacaspis tegalensis and is heavily hyperparasitised by Tetrastichus sp. (Eulophidae). The most frequent predators are Lindorus lophanthae (Blaisd.) (Coccinellidae), Cybocephalus mollis Endrödy-Younga (Nitidulidae) and mites. Predators are important only in the regulation of large A. tegalensis populations. Reductions in the sucrose content of the cane juice are directly proportional to the numbers of scales present on each interaode; growth of canes is not obviously affected, but grown canes may die before harvest. Reduced germination and growth may result from use of infested propagative material. Practicable control measures comprise use of clean or hot-water-treated propagative material, field hygiene and block harvesting, removal of dry leaves to expose the stems, and varying the date of harvest.