Aerial Spraying of Neemazal®-T/S Against the Forest Cockchafer (Melolontha hippocastani, Col.: Scarabaeidae) in South-West Germany: The Effects of Two Field Trials Performed in 2007 and 2008 on Local Populations

The forest cockchafer Melolontha hippocastani is a serious forest pest whose infestation levels have been increasing in South-West Germany since the mid-1980 s. During the past 25 years several control measures have been taken to manage its populations. In 2007 and 2008, 122 and 73 hectares of forest stands comprising of deciduous trees were sprayed with NeemAzal®-T/S (1% azadirachtin A) by helicopter, respectively. Here we summarize the results of the accompanying research with the aim to evaluate the efficacy of NeemAzal®-T/S in the control of M. hippocastani populations under field conditions. As expected from azadirachtin’s mode of action, no immediate mortality occurred but maturation feeding and oogenesis was interrupted. It appeared that precise timing of the application is a crucial issue regarding the level of its effect on the population density. In 2007, the first application was performed in good synchrony with the climax of female emergence from the soil, resulting in a remarkable decline of the population density in the next generation of beetles in 2011. In 2008, our data suggest that maturation feeding and oogenesis had already been completed when the agent was sprayed. Hence, no significant decline of the population density could be registered in 2012. Practicability of the use of NeemAzal®-T/S against M. hippocastani in forests is discussed.