The occurrence of Eldana saccharina (Lepidoptera: Pyralidae) was monitored in grids represented by plots in 12 nematicide trials in South African sugarcane fields. The trials encompassed a total of eight plant cane crops and 22 ratoon crops and were situated within commercial cane fields. Several measurements were made to characterize the damage caused by E. saccharina. These included the number of internodes per stalk, the percentage of internodes damaged and the percentage of stalks damaged. The mapping of E. saccharina infestation in plant crops of sugarcane showed that the borders of the trials were as infested as the centre, indicating invasion from outside the field plus internal spread within the field. Ratoon crops were less infested than plant crops. This could be explained by a shorter ratoon crop cycle and by the fields having areas that were more suitable for the borer than elsewhere. The location of these preferred areas could be predicted from one ratoon crop to the next but was not related to the distribution of the borer in the plant crop. This situation was thought to explain the apparent stabilization of E. saccharina infestation in ratoon cane. Because the borer was found at harvest only in stalks with more than 14 to 16 internodes, it appeared that the oldest shoots, or the shoots with the greatest growth potential, attracted the insect, possibly due to their higher nitrogen content, which would stimulate growth. All the trials were on sandy soil, and crop loss from nematodes was greater than that caused by E. saccharina.

Zea mays L. and Rottboellia exaltata L. were the main graminaceous plant species infested by Eldana saccharina Walker, the major pest of sugar-cane in southern Ghana. Other stem-borers of sugar-cane, Sesamia botanephaga Tams and Bowden, Sesamia penniseti Tams and Bowden, Sesamia calamistis Hampson and Chilo zacconius Bleszynski, were recorded on Zea mays, Echinocloa pyramidalis (Lamk.) et Chase, Rottboellia exaltata, Panicum maximum Jacquin and Oryza sativa L.

All the stem-borer populations except E. saccharina on Rottboellia exaltata increased on their host plants. Sesamia and Chilo species were present from January to December on Echinocloa pyramidalis. It is concluded that these alternative host plants provide a potential source of stem-borer infestation on sugar-cane at Asutsuare in southern Ghana.

Studies on damage by larvae of Eldana saccharina Walker, Chilo zacconius Bleszynski and Sesamia spp. to sugar-cane stands revealed a high degree of correlation between internode damage and stalk damage as well as between internode damage and sugar content of the canes. For every 1% increase in stalk damage there was a corresponding increase of 0.214% in the internode damage. The distribution of larvae inside the internodes was found to depend on the level of infestation. At low field infestation level (below 25 larvae per 100 canes) the distribution was random. As the level of infestation increases, the distribution becomes more aggregated. The distribution of damage in the sugar-cane field was found to depend on the overall stalk damage. The distribution tends to be more contagious when field level of stalk damage was less than 45%. The damage became evenly distributed when stalk damage rose above 60%. An estimation of average loss of sugar caused by stem-borers to the variety NCO 376 (at the field damage rate of 8.6, 10.6 and 3.1% damage for bottom, middle and top parts respectively of the cane) was U.S.S332.10 per ha of field.

Female Eldana saccharina Walker was found to lay 327 ± 17.1 eggs within a period of 4 days and required three surfaces to lay eggs which were mainly deposited on the inner side of leaf sheaths fitting tightly on to the sugar-cane stalk. The mated females laid more eggs per female (327.0 ± 17.1) than virgin females (212.3 ± 5.5). The incubation period of the eggs of E. saccharina was found to be 5.64 ± 0.01 (5–7) days in the laboratory and 5.82 ± 0.03 (5–7) days in the field. The mean larval duration was 31 days and pre-pupal period lasted 2.05 ± 0.05 days. Larvae were found to exude a brownish liquid from their mouth in the direction of the invading predators. The newly hatched larvae spread out in 1–3 days of hatching. The mean growth ratio of the larval instars was 1.54 ± 0.05. Pupae frequently occurred very close to the exit hole (less than 5 cm) and the pupal period varied from 7 to 13 (9.76 ± 0.05) days. The life cycle of E. saccharina was completed in 49 (36–62) days. The pre-oviposition period was 2 days and the female reproductive life lasted 4 days. It takes about 53 days for a succeeding generation to be produced. Adults of E. saccharina survived from 6 to 13 days. Adults reared from field collected larvae snowed a sex ratio of 42:51 which was significantly different from 1:1 in the laboratory bred stock, at the 5% level of probability. A comparison of the life cycle of E. saccharina populations in Ghana and Uganda suggests the existence of two biotypes of the pest.

Population dynamics of the larvae of Eldana saccharina Walker, Chilo zacconius Bleszynski and Sesamia spp. on sugar-cane was studied over a period of 3 years, by regular sampling. Analysis of results indicated that during the first rainy season (March–June) the borer populations were low. However, the larval population increased considerably during the dry season and declined gradually during the second rainy season (September–November). Rainfall in Southern Ghana is typically bimo-dal, but it is occasionally evenly distributed throughout the year. When rainfall was evenly distributed. borer populations remained consistently low throughout the year. Flooding reduced the population of E. saccharina larvae in the field. Though the stem-borers showed preference for relatively younger canes, the type of borers present and their proportions varied with the sugar-cane phenology.