Secondary contact and admixture between independently invading populations of the Western corn rootworm, diabrotica virgifera virgifera in Europe

The western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), is one of the most destructive pests of corn in North America and is currently invading Europe. The two major invasive outbreaks of rootworm in Europe have occurred, in North-West Italy and in Central and South-Eastern Europe. These two outbreaks originated from independent introductions from North America. Secondary contact probably occurred in North Italy between these two outbreaks, in 2008. We used 13 microsatellite markers to conduct a population genetics study, to demonstrate that this geographic contact resulted in a zone of admixture in the Italian region of Veneto. We show that i) genetic variation is greater in the contact zone than in the parental outbreaks; ii) several signs of admixture were detected in some Venetian samples, in a Bayesian analysis of the population structure and in an approximate Bayesian computation analysis of historical scenarios and, finally, iii) allelic frequency clines were observed at microsatellite loci. The contact between the invasive outbreaks in North-West Italy and Central and South-Eastern Europe resulted in a zone of admixture, with particular characteristics. The evolutionary implications of the existence of a zone of admixture in Northern Italy and their possible impact on the invasion success of the western corn rootworm are discussed

Powder blown laser cladding of vertical surfaces

Powder blown laser cladding is widely applied in industry to achieve functional surface modifications for corrosion or wear resistance. Commonly this is deposited in the 1G flat position in accordance to the ASME BPVC Section IX (equivalent to the ISO 6947 PA position). For certain applications, however, especially large and heavy components which are difficult to manipulate, the cladding of vertical surfaces would be beneficial – cladding in 2G horizontal position in accordance to the ASMCE BPVC Section IX (equivalently to the ISO 6947 PC position). The task of cladding vertical surfaces requires a specially designed cladding head. The aim of this report is to present those initial results observed through depositing powder in this attitude using a high power diode laser (HPDL). It was observed that the change of the position of the cladded surface from flat to horizontal or vertical affects the cladding process. The reason for this is that gravity affects the powder stream and weld pool in a different way. An optimized parameter set for the 1G (PA) cladding resulted in inferior clads with extensive dilution leading to inhomogeneous properties within the clad; therefore a specific cladding parameter set for the 2G (PC) position had to be developed. Different laser beam sizes and cladding parameters were investigated with the aim of achieving well bonded, crack-free overlapping beads with minimal dilution. The results indicate that the amount of transport gas and the position of a laser head critically influence the clad quality and that generally a smaller laser spot gives better results