Did the introduction of maize into Europe provide enemy‐free space to Ostrinia nubilalis? Parasitism differences between two sibling species of the genus Ostrinia

We examined whether maize offers enemy‐free space (EFS) to its pest Ostrinia nubilalis, and may thereby have contributed to its divergence from the sibling species, Ostrinia scapulalis, feeding mainly on mugwort, when introduced into Europe five centuries ago. We collected Ostrinia larvae on maize (70 populations, 8425 individuals) and mugwort (10 populations, 1184 individuals) and recorded parasitism using both traditional (counting emerging parasitoids) and molecular methods (detection by specific polymerase chain reaction). The main parasitoid was Macrocentrus cingulum (Braconidae). On mugwort, parasitism was twice that on maize, and parasitoid‐related mortality was 8 times higher. This suggests that maize affords substantial EFS to Ostrinia feeding on it. The lower Mortality:Infestation ratio in maize suggests that O. nubilalis’ immune response might be stronger than that of O. scapulalis. If so, adapting to maize and diverging from O. scapulalis would decrease the impact of parasitism on O. nubilalis at both ecological and evolutionary levels.     

Growth Dynamics and Morphology of Annual Shoots, According to their Architectural Position, in Young Cedrus atlantica (Endl.) Manetti ex Carriere (Pinaceae)

The influence of shoot architectural position on growth andbranching pattern of young Cedrus atlantica (Endl.) Manettiex Carrière trees were studied. Extension growth andtype of axillary products (lateral bud, sylleptic short or longshoots) of annual shoots of increasing branching order (mainstem, branches and branchlets) were recorded weekly during the1993 growing season. Annual final shoot length, duration ofextension, and maximum extension rate decreased with increasingbranching order. Sylleptic axillary shoots occurred only onannual shoots of the main stem and branches and were producedwhen extension rate was at its highest. Differences in growthrate and final length of annual shoots, according to their architecturalposition, were related to differences in the total number anddiversity of types of sylleptic axillary shoots produced. Itis suggested that types and numbers of sylleptic axillary shootsproduced are linked with threshold values for both final lengthand extension rate of the parent shoot. Copyright 1999 Annalsof Botany Company Atlas cedar, extension growth, sylleptic branching, tree architecture, morphology.