Observations on the ecology ofSaccharosydne saccharivora(Westw.) (Hom., Delphacidae) in Jamaican sugar-cane fields

Abstract

Between 1961 and 1967 intensive and extensive field studies on the sugar-cane pestSaccharosydne saccharivora(Westw.) were carried out in Jamaica (with supplementary observations from British Honduras). Egg populations were scored for size, and egg mortality and nymph-adult parasitism were estimated directly. In epidemic, but not endemic, populations, successive generations of the pest were segregated and their development was synchronised over areas of up to 80 miles2despite its 6½—7-week life-cycle and potential for continuous breeding. Segregation was due to the sterilising action of the parasiteStenocranophilus quadratus Pierce (Halictophagidae); in the drier months this spread so rapidly through the nymph and adult population that oviposition ceased until the first adults of the next generation reached maturity. In the wet season this effect was complemented by the entomogenous fungusMetarrhizium anisopliae. Synchronisation was ensured by the dispersal of parasitised adultSaccharosydne saccharivorabefore oviposition. In ratoon cane there were six or seven generations between successive annual harvests; egg populations were highest in generations 1–3 (up to 1·0×106/chain-row (≡2O·2-m row-length)), and declined in old cane irrespective of season. In plant cane, egg populations did not show a decline with age and sometimes increased. In epidemic areas a factor associated with older cane sometimes caused over 90% egg mortality; elsewhereTetrastichussp. (Eulophidae) was the leading cause of egg mortality (ca30%). Data from extensive surveys showed that the early stages of outbreaks were invariably associated with plant cane; heavy infestations rarely occurred on cane subjected to adverse growing conditions; and populations were smaller on the variety B42231 than on B4362 and B41227. Outbreak periods since the 18th century have been associated with periods of prosperity within the sugar industry, when presumably more attention was paid to improving production. Rainfall, in that it improves cane growth, is beneficial toS. saccharivora, whereas drought is detrimental; published records of outbreaks in dry periods are due to the preference of migrating adults for young cane which is most prevalent in the dry season. It is concluded that the essential prerequisite for an outbreak is plant cane growing under favourable climatic and agricultural conditions; present conditions, namely the long harvest period, high standards of cultivation, irrigation and fertiliser practice, and favourable cane varieties together offer the minimum chance for a natural end to outbreaks.