Susceptibility of stored sorghum grains in Renk area to infestation by the Khapra beetle and the Lesser grain borer

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Talib Selim Doka Beshir, Beshir
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ABSTRACT Insect pests of stored products cause much damage to stored sorghum grains. Considerable losses were recorded at Renk, Upper Nile State, Southern Sudan, and the surrounding areas. The objectives of this study were: To test susceptibility of two sorghum varieties to insect infestation, to conduct a general survey in order to identify the main stored grains pest in Renk area, to study the biology, ecology of the key insect pests of stored grains in the area and to evaluate local and improved storage facilities used by small farmers. A survey of insect pests of stored products was carried out in season 2008/2009 at four localities around Renk (Guwzrum, Geigar, Gelhak and Wadacona) by interviewing farmers. The survey showed that there were 13 species of insect pests of stored grains in Renk County. Trogoderma granarium (Everts) and Rhyzopertha dominica (F.) caused most of the damage to stored grains. The results showed that the lesser grain borer Rhyzopertha dominica (F.) did more damage than the Khapra beetle Trogoderma granarium (Everts) to the two studied sorghum cultivars, Fetterita and Gadam Alhamam, and it laid more eggs than Khapra beetle. The results also showed that the mean number of eggs, larvae, pupae and adults increased with time of storage. More eggs were laid by the Khapra beetles in Fetterita (466) than in Gadam Alhamam (247), but the lesser grain borer laid almost the same number of eggs in both cultivars (467 eggs in Fetterita and 469 in Gadam Alhamam). The maximum developmental period (from egg to adult) of the Khapra beetle was 43 days in Fetterita and the minimum was 26 days, while the maximum developmental period of the lesser grain borer was 44 days in Fetterita and the minimum was 26 days. Laboratory results showed that Fetterita cultivar had higher percentage of proteins and fat content than Gadam Alhmam , while Gadam Alhamam contained more crude fiber than Fetterita. This may partly explain why Gadam Alhamam was more resistant to infestation by both the Khapra beetle and the lesser grain borer than Fetterita. During 12 months, the percentage weight loss of the infested Gadam Alhamam grains was about 5.2%, while that of Fetterita was 9.1%. The results also revealed that there was a positive relationship between coat hardness of the grains and degree of grain resistance to infestation by insect pests. The percentage weight loss of infested Fetterita grains was 14.4%, while that of Gadam Alhamam was 8.1%. The degree of the seed coat resistance of Fetterita was 2.88 kg/mm, while that of Gadam Alhamam was 3.12 kg/mm. The results of the survey showed that small farmers preferred Gadam Alhamam and Fetterita to other cultivars and that they stored grains for a period of 6 months and that the traditional (Gugu = Sweiba) was more preferable for storage (54.3%), as compared with Guttia (Hut) (37.1%) and small warehouses (5.71%). It was also found that improved (gugues) were better storage structures than the local gugues, guttias and small warehouses because there were less insect infestation, decreased weight losses of grains and better seed quality in the improved structures. The losses of grains due to insect infestation were approximately 1.62% in an improved (gugu), 4.92% in a local (gugu), 8.5% in a (Guttia = Hut) and 8.87% in a small warehouse
Susceptibility of stored sorghum grains in Renk area to infestation by the Khapra beetle and the Lesser grain borer