Decline in populations
Saddle grasshopper (Ephippiger diurnus) occurs in the Netherlands exclusively in nature reserves on the Veluwe and only a few stocks outside it. Despite the protected status of the areas on the Veluwe, there is still a downward trend in the size of these stocks. Some of the potential bottlenecks include food availability and problems with egg disposal. These two possible problems will this year be investigated by the Stichting Bargerveen in collaboration with the province of Gelderland and the central state real estate agent.
Food research with DNA
To identify possible food supply problems, it is important to determine which food sources are used by young and adult grasshoppers. A still large and stable population in the Netherlands is that of the Artillery Shooting Camp (ASK, Oldebroek) on the northern Veluwe. The food situation in this area is apparently fine, making this a good place to start determining the species’ diet. However, there are extraordinary circumstances at ASK; Impacts of heavy ammunition result in soil replacement, supply of chemical elements and occasionally large fires. Further data is therefore collected in Infantry Shooting Camp (ISK, Harskamp), where the area of the saddle grasshopper has decreased, but where a small core population is still left. Juveniles and females are expected to have higher dietary needs than adult males due to growth and egg production, respectively. Therefore, the study distinguishes between immature and adult animals, as well as both sexes. In June, nymphs are gathered by the saddle grasshopper and in September the adults. The captured animals are placed individually in jars and taken away. After a day and a night in the jar, the excrement produced during that time is collected. The animals are then sent back to the place where they were captured. The feces will then be analyzed for the DNA they contain so that the diet can be determined.
The importance of bare sandy soil
In addition to the importance of food availability, an open sandy bottom is regularly mentioned as an important quality aspect of the saddle grasshopper’s habitat. The importance of this will be investigated experimentally in a two-part study. First of all, it was determined whether the animals have a preference for a particular soil type and whether they are willing to lay eggs in a non-preferred soil. Under controlled conditions, trays are provided with substrate for laying eggs, water, food and a few saddle grasshoppers. In different tanks, the animals were given the opportunity to choose between bare and covered soil and a combination of both soils. The number of eggs deposited in each of the available substrates was later counted to map preference for egg deposition. When the saddle grasshopper can choose between bare sandy bottom and bottom that has been overgrown with moss, it always chooses the bare bottom. But when the females do not have a choice, they also deposit their eggs in a moss pack. So after an experiment, we still did not know how important and bare soil is. Therefore, in another experiment, it is determined whether a covered soil is a less favorable environment for egg development. This is done by examining the development of eggs in bare and covered sandy soil under field conditions. To this is added a layer of sand on a series of sieves. Half of the sieves are covered with a top layer of bare sand. The rest is covered by a top layer overgrown with bogs. The sigene with the eggs are buried in open ground in the saddle grasshopper’s habitat. Just before the normal development time for the eggs has passed (two years), the sieves are dug out and the eggs are stored at 20 degrees Celsius so that they can develop. The number of nymphs hatching from the eggs is counted to determine the reproductive success of the different bundles. At the moment we eat debris with mice every day, because the young grasshoppers are in a hurry to leave their nursery.
Expectations and results
These studies from the Bargerveen Foundation will provide more insight into potential problems for the saddle grasshopper with food supply and with laying eggs. As a result, this species can be taken into account in land use and management, and the current stocks can be preserved.
Text: Kevin Geurts, Bargerveen Fonden
Photos: Marijn Nijssen; Bouke ten Cate; Jan Kuper