Biological Control Of Wood Destroying Beetles With Spathius Exarator (Hymenoptera: Braconidae)

For nearly a decade, the wood pest Anobium punctatum has been effectively controlled in historic monuments with its natural antagonist Spathius exarator. This braconid wasp parasitizes its host species by piercing its ovipositor directly through the wood surface followed by oviposition onto the beetle larva. After development, it hatches as an adult wasp through a hole it gnaws itself. This tiny exit hole, 0.5 mm wide, can be easily distinguished from the 2 mm wide exit hole of A. punctatum, allowing us to monitor parasitation success. Between 2012 and 2021, these parasitic wasps were successfully released into more than 200 different A. punctatum infested objects across Europe. Between 400 and 2000 wasps were released per treatment,
depending on severity of infestation and quantity of infested objects within the building. A monitoring program was established in parallel, and parasitism rates were calculated as the proportion of parasitized A. punctatum. We started in 2012 with a release protocol that included 5-8 individual treatments per year. In subsequent years, the protocol was slightly modified and reduced to up to 4 treatments per year to allow for a longer treatment period. Here we present parasitism rates of A. punctatum infested objects (n=42), treated and monitored up to three years in relation to the number of treatments per year. Parasitism rates increased
significantly after one year of treatment (Wilcoxon rank-sum-test, p=0.0008; n=42) and continued to increase in the second and third year. Corresponding annual parasitism rates, based solely on new exit holes of A. punctatum and S. exarator per year, ranged from 0.66 to 0.74. There were no significant differences in the parasitism rates between the group of churches with 5-8 and 1-4 annual treatments during all three years of treatment. Long-term monitoring data, as shown for church Pa. indicate the need to continue biological control with one or two individual releases per year to maintain infestations at the low levels achieved. These data prove this biological method of pest control as an efficient, sustainable and non-toxic long-term option to
manage the common furniture beetle.