Susceptibility of Soybean, Glycine max (L.) Merrill, cultivars to Callosobruchus maculatus (Fab.) (Coleoptera: Bruchidae) and Oryzaephilus mercator (Fauvel) (Coleoptera: Silvanidae) Infestations

PESSU, P. O. and UMEOZO R, O.C

ABSTRACT: A study was undertaken to assess the susceptibility of five soybean cultivars (TgX 1t061-IE, TgX 536 – 02D, TgX 306 – 036, TgX 1072 – 2E, TgX 1019 – 2E) to Callosobruchus maculatus (Fab.) and Orvraephilus mercator (Fauv.) infestations. Results indicated that the five cultivars showed similar levels of susceptibility to C. maculatus attack. The mean percentage seed damage in the cultivars varied from 9.3 – 14.3, mean weight loss from l.1 – 1.7 g per sample size of 25 g, and index of susceptibility from 2.6 – 3.2. There was a significant decrease (P <0.05) in the mean percentage viability in two of the five cultivars after 70 days. The heavier seeds lost viability faster than the lighter ones. The mean developmental periods among the five cultivars were prolonged, and varied from 53.8 – 60.5 days. Furthermore, the emerged C. maculatus adults from the five soybean cultivars were underweight and undersized. There was no emergence of O. mercator adults observed in any of the five cultivars. Thus, C. maculatus, and O. mercator may not pose a serious threat to stored soybeans. It remains to be seen how other soybean cultivars would respond to C. maculatus infestation.

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