Seasonal abundance and spatial distribution of the predator Macrolophus costalis and its prey Myzus persicae on tobacco

Field studies were conducted to assess the population and the spatial dynamics of the predatory bug Macrolophus costalis Fieber (Hemiptera: Miridae) and of its prey, the aphid Myzus persicae (Sulzer) (Hemiptera: Aphidoidea), on tobacco. From an untreated tobacco field in Tithorea (central Greece), tobacco leaves were collected from the upper and the lower half of the plants from June until September, in 1999 and 2000. The numbers of M. costalis and M. persicae individuals per leaf were counted. Most aphids were observed during July and August (early and mid season), with densities dropping markedly in September. In contrast, M. costalis population densities increased late in the season (September). Significantly higher numbers of aphids were found on the upper half of the plants than on the lower half. In contrast, significantly more M. costalis individuals were observed on the lower half. Iwao's Regression Analysis was used in order to characterize the spatial; pattern of the two species. According to this model, in both sampling seasons, aphids and M. costalis nymphs displayed an aggregated spatial pattern, while M. costalis adults were found to be randomly distributed among sampling units. Although more M. costalis individuals were recorded on leaves with relatively high aphid densities, this species did not react numerically to changes in prey density. In addition, a significant number of bugs were found on leaves with low aphid densities or no aphids at all.