Biocontrol of the forest cockchafer (Melolontha hippocastani): Experiments on the applicability of the “Catch and Infect”-Technique using a combination of attractant traps with the entomopathogenic fungus Beauveria brongniartii

In the German federal states of Hessen, Rheinland-Pfalz and Baden-Württemberg a massive outbreak of the forest cockchafer, Melolontha hippocastani Fabr. (Coleoptera, Scarabaeidae) endangers approximately 7 500 ha of forests (occurrence on 37 000 ha). As a naturally occurring pathogen, Beauveria brongniartii is a promising candidate for biological control of M. hippocastani. In the present study we investigated, whether spores of B. brongniartii could be spread within the cockchafer population using males as vectors after contamination by passage of an inoculation trap. First, in order to optimise the funnel traps, three different types were compared to a standard trap with respect to their handling in the field and their catch and release characteristics. Each funnel trap was baited with a mixture of the sexual pheromone 1,4-benzoquinone and the sexual kairomone (Z)-3- hexen-1-ol and placed in oak trees (Quercus rubra) infested with cockchafers. Both volatiles are involved in mate finding of forest cockchafers and are attractive to males. During the swarming flight a maximum of 261 males was captured per funnel trap per day. No correlation between the size of the baffle screen and the number of captured males was found. The results suggest that the spatial arrangement of the baffle screen is more important for the capture of males than its dimension. Furthermore, the influence of the position of the funnel trap within the tree on the catching efficacy was studied by placing the traps at different heights. The number of captured males significantly increased with the trap height in the trees. A contamination experiment in flight cages in a forest was performed to evaluate a proposed transfer of spores from (a) trap to male (b) male to female and (c) female to soil/white grubs in the field. Males picked up sufficient spores to become mycosed by B. brongniartii and to transfer the fungus to females successfully. However, spore numbers in the soil did not increase significantly. This confirms that infective spores of B. brongniartii can be disseminated by male cockchafers after the passage through an inoculation trap. Whether the females could transmit the spores in effective numbers into the breeding sites still needs to be proven under field conditions.