A survey on pest insects of fiber and grain sorghum in northern Italy

In the Po valley plain grain sorghum (Sorghum bicolor) has been introduced in the last decades for cattle feed production. More recently fiber sorghum has been tested to be used for electric power production. Since little is known about the sorghum insect pest community in northern Italy, a research was carried out in a study area located in the central western area of the Po valley. Grain sorghum plots and fields were studied between 2008 and 2011. No insect pest of economic importance was recorded in grain sorghum cultivations. Population density of the aphid Rhopalosiphim maidis was very low, as well as the one of the European Corn Borer (ECB, Ostrinia nubilalis, Lepidoptera Crambidae). Lygus rugulipennis (Hemiptera Miridae) tended to colonize grain sorghum after panicle development, but densities were not a matter of concern. In fiber sorghum plots ECB populations did not result noxious, while R. maidis density was higher than the one on grain sorghum, but infestations did not significantly affect the development of the stalks, being localized only on panicles during their first stage of development. The production of cyanogenetic compounds by young sorghum plants is likely to be an effective protection against ECB first generation larvae, while earlier harvest time of both grain and fiber sorghum compared with maize later harvest time prevents significant damages caused by ECB second generation larvae. Sorghum requires less water than maize. Such a condition, joint to the weak susceptibility to insect pests, could favour a further increase of sorghum cultivations in northern Italy.