Influence of Ostrinia nubilalis larval density and location in the maize plant on the tachinid fly Lydella thompsoni

A three years research (2008-2010) was carried out in the Po valley (northern Italy) on Lydella thompsoni Herting (Diptera Tachinidae), an important parasitoid of ECB (European corn borer - Ostrinia nubilalis Hubner, Lepidoptera Crambidae). Several factors can affect the action of L. thompsoni against ECB. This case of study was focused on the influence of ECB larval density and position in maize plant organs. Wintering ECB larvae and parasitoid puparia were sampled from maize plants and reared. O. nubilalis density ranged from 0.2 to 3.2 larvae/plant. L. thompsoni was the only parasitoid regularly reared from ECB larvae. Parasitisation rates were 17.9, 16 and 11% in 2008, 2009 and 2010 respectively. It was noticed that ECB larvae distribution in the maize plants was related to infestation degree. ECB larvae preferably colonized ears; however, when their density increased, their proportion in the stalk did, as well. The density of L. thompsoni was higher in stalk tissues, below and above the ear. Among the range of ECB densities recorded as a result of this study, it was not observed a density dependent relation between ECB and L. thompsoni.