Studies on the effect of the nutrient status of sugar-cane on the fecundity of Saccharosydne saccharivora (Westw.) (Hom., Delphacidae)

Abstract

An account is given of glasshouse experiments in Jamaica to determine the effects of agronomic practice on the fecundity of the sugar-cane pest Saccharosydne saccharivora (Westw.). Eggs (up to one egg per ovariole per day) develop throughout adult life. On young vigorous plant cane the pre-oviposition period was 5·3 days; egg production was highest during the first six days of the oviposition period and declined markedly after 12 days. Mean daily egg production per female over 12 days was taken as an index of fecundity.The effects of fertiliser application (ammonium sulphate and potassium chloride), wet and dry water regimes, variety (B41227, B42231 and B4362) and crop cycle (plant and ratoon cane), all at different stages of crop development, were observed in four series of experiments involving 1 000 female S. saccharivora. Potassium (K2O) and phosphorus (P2O5) per cent lamina dry matter varied comparatively little, but nitrogen content declined with the age of the plant, increased with application of ammonium sulphate, and was unaffected by crop cycle or variety. Egg production was highest on young cane (up to a mean of 12·0 eggs per female per day), but declined on older cane; it increased with the application of ammonium sulphate but was unaffected by potassium chloride. A direct linear correlation between egg production and the nitrogen content of the leaf (r2 = 0·69, 0·81, 0·52 and 0·69 in series I–IV, respectively) suggested a causal relationship. The pre-oviposition period lengthened and the proportion of females failing to lay any eggs increased in the absence of fertiliser and with increasing plant age. Variation in leaf nitrogen under field conditions could affect egg production.