Insects are disappearing worldwide at an alarming rate. This is not only a problem for biodiversity, but also for agriculture and food production: many insects pollinate crops or help control pests. Lexmond is investigating how we can support insect populations. To this end, she spent three years collecting insects using special traps along 24 field and grassland margins in an agricultural area near the River Waal: the Ooijpolder and the Duffelt.
‘It was essentially a tent about 1.70 metres high,’ explains the ecologist. ‘Insects could get in, but not out. We then weighed the insects that ended up in the trap.’
Some of the margins where the traps were placed had hedges, others had flower strips, and some had no additional vegetation at all. After weighing the insects, the results showed that more than twice as much insect biomass was found near hedges compared to bare field edges. Flower strips performed slightly better than edges without vegetation, but their effect was less pronounced and less consistent.
Lexmond explains: ‘This is probably because many flower strips are ploughed and reseeded every year. As a result, there is a lack of stable winter shelters and early-season food sources.’ Hedges, on the other hand, remain in place for years and provide shelter, food, and breeding sites year-round.
Surroundings play a lesser role
Remarkably, the wider surroundings proved to be less important than expected. Factors such as the type of agriculture, plot size, or the amount of nearby woodland had little influence on insect numbers. There was one exception: areas with more protected natural habitat in the vicinity supported higher insect populations.
Even there, however, the positive effect of local hedges remained clearly visible. Hedges near protected nature still yielded more insects. As the ecologist notes: ‘This is important, because it shows that such measures are worthwhile not only in intensively farmed areas with little nature, but also in landscapes where biodiversity investments have already been made. Every extra metre of hedge counts.’