The ecology of a scale insect, Aulacaspis tegalensis, on sugar cane in East Africa

Abstract

SUMMARY The scale insect, Aulacaspis tegalensis, invaded a sugar estate near Moshi, Tanzania, in 1969. The number of fields affected and scale abundance were estimated weekly by weighing eggs sifted from samples scraped from infested cane. Abundance increased exponentially with the age of the cane, once mature cane began to develop at the age of six months, and it was also affected by the cane variety. The principal source of temporal variation in abundance was weather, especially mean maximum temperature eight weeks before sampling, when the crawlers which gave rise to the females were settling. The behaviour of crawlers is affected by temperature, humidity and sunshine. Up to 25% of the crop was lost at the height of the infestation. Wild natural enemies could not reduce scale numbers to an acceptable level. Lindorus lophanthae (Coccinellidae) was introduced from Mauritius in 1971 and may have been responsible for the decline in scales which began after it had become abundant throughout the estate. Since 1972 loss of yield due to scale has been undetectable in the factory. The results are discussed in relation to the situation in Mauritius, where L.lophanthae is ineffective and the implications of the studies for the reduction of losses by agronomic methods are detailed.