Effective control of anobia through the use of beneficial insects is not just a pipe dream. The nail beetle from the Anobiidae family, often referred to as the “woodworm”, is one of the most potentially damaging species of anobia. It can cause devastating damage to churches, monuments and museums. The risks and costs of toxic treatment methods are well known and […]
Effective control of anobia through the use of beneficial insects – this is not just a pipe dream.
The nail beetle from the Anobiidae family, often referred to as the “woodworm”, is one of the most potentially damaging species of anobia. It can cause devastating damage to churches, monuments and museums. The risks and costs of toxic treatment methods are well known and will not be discussed here. Due to their positive properties, biological methods of pest control are increasingly attracting the attention of those responsible. The development and practical implementation of biological pest control are the declared aims of the company’s CEO, Alexander Kassel, who also initiated and supervises this project. The aim was to find a natural enemy of the rodent beetle that can be reproduced in mass breeding. After a series of tests with numerous beneficial insects, the decision was made in favor of a special type of ichneumon wasp, Spathius exarator. It took around three years to establish stable mass breeding of these useful tiny creatures in the laboratory.
The development cycle
The female of the ichneumon wasp is 5 to 9 millimeters in size. It recognizes the presence of an anobia larva from a distance by its smell and movement in the boreholes and feeding tunnels inside the wood. The body-length ovipositor tube is then inserted through the wood and the larva is initially paralyzed. The female presses the flexible egg through this ovipositor and places it on the larva. An ichneumon wasp larva hatches from the egg after a few days. It finds food in the paralyzed anobia larva, which is kept alive for a while. This is followed by the pupation of the ichneumon wasp larva and the emergence of the finished wasp.
At around 20 degrees Celsius, the entire development period from egg laying to flight-capable wasp is around 30 days.
Three years of practical experience
In summer 2012, the company began putting the positive research results from the laboratory into practice. In the first year, six small to medium-sized churches in the Franconian region, some of which were heavily infested, were selected as pilot applications. Further objects were added in 2013 and 2014. Extensive documentation was compiled to evaluate and monitor success. The project was accompanied and assessed by a publicly appointed and sworn expert for disinfection, pest control and biological damage to wood.
In the period from May to October, 6 to 8 releases of beneficial insects were carried out each year at intervals of 3 to 4 weeks. During each inspection, the level of anobia infestation and its reduction through the use of parasitic wasps was examined in precisely defined areas of the infested objects. The newly created exit holes of the anobes and the parasitic wasps, which differ in size, were counted and documented during each treatment. Each newly created exit hole of the anobia represents one survivor, each exit hole of the ichneumon wasps represents one killed rodent beetle.
These data were used to calculate the reduction in the number of rodent beetle hatchlings per treatment year and the mean predator-prey ratio.
Results and conclusions
There is no doubt that the ichneumon wasps parasitize rodent beetle larvae efficiently based on the available, evaluated results. After just one year of treatment, a reduction of up to 81 percent was achieved, and after two years of treatment, a reduction of up to 100 percent of newly hatched rodent beetles. This was solely due to the parasitization performance of S. exarator, which can be seen in the increasing number of fresh ichneumon wasp emergence holes.
The determination of the results in the form of the average predator-prey ratio shows the drastic reduction in newly hatched rodent beetles after biological control. While an average of one ichneumon wasp and 26.5 anobia hatch per year in untreated objects, the ratio drops to an average of 3 in the first year of treatment, 0.37 in the second year of treatment and 0.13 anobia per ichneumon wasp in the third year, in some cases without treatment.
The author already felt vindicated by the extremely positive report by the expert from 2012 during the first application period. Here is an excerpt from the interim report on the status of biological rodent beetle control in Church I: “In summary, however, it can already be stated that the eradication success achieved so far can certainly be compared with the injection methods with chemical wood preservatives frequently used to date, and very probably even surpasses them; and this without the use of chemical agents that may also be hazardous to health.” The report also confirms: ” Spathius exarator exit holes have now also been detected, which indicates that the egg-laying and subsequent development of the braconid wasps is obviously successful.”
The frequently expressed fear that biological control could lead to infestation by beneficial insects once the pest infestation has been reduced can be refuted: Parasitoids need their hosts to survive. If there are not enough of these, the beneficial insects die off.
Read more about monitoring pest infestations in the current issue of RESTAURO 5/2015.
