The influence of mowing techniques on insects living in grassland is discussed again and again. Previous studies on this subject were not very representative of commercial grassland and agricultural practice.
The primary objective of this project was to investigate the effects of mowing techniques used in agricultural practice on insects living in farm grassland. In addition, “protection and scaring devices” were tested on mowing equipment and investigated whether they can reduce insect losses. Assessment criteria were developed that can be used in future to categorise different mowing techniques according to their impact on insects.
The following mowers were compared in the trials:
‑double-blade mower
‑disc mower
‑disc mower with conditioner
‑Disc mower with conditioner and protection/scouring device „harrow“
‑Disc mower with conditioner and protection/scouring device „deflector plate“
Before mowing, the naturally occurring insects were recorded on transects. After mowing, the insects that flew away, those that remained in the mown material and those that were sucked up from the ground were recorded and separated into “living” and “dead or damaged” insects.
The investigations were carried out on both five-mown grassland and nature conservation areas at typical cutting times once in the morning and once in the afternoon for each variant.
The mean mortality rate for mowing with the double-blade mower was less than 5 %. The disc mower differed significantly and mortality was about twice as high as with the double-blade mower. All three mowing variants with conditioner showed about a doubling of mortality compared to the disc mower. Protective and scouring devices did not significantly improve the situation.
In addition, it was observed that the probability of damage from mowing depends on the body size of the individual, with larger individuals being damaged more frequently.
Since the number of insects found was highest in the summer months and most insects are relatively large during this period, dispensing with the conditioner can make a particular contribution to insect conservation here.
With the applied method of surveying the insects still living as well as dead and damaged in the mown material, a categorisation of the different mower designs with regard to their insect protection is basically possible. |