Flower strips in margins of potato fields: effects on biodiversity, predators and natural pest control

Abstract: In the arable landscape of the Hoeksche Waard, NL, there are approximately 550 km of field margin strips, most of which are flower-rich and designed to support functional
agrobiodiversity (FAB), mainly for natural pest control and pollination. To investigate the
effectiveness of these flower strips and to help arable farmers to profit from FAB, broad
monitoring has taken place for 6 years. About 30 field margin strips of different types and years of establishment were selected yearly, largely along potato fields. Vegetation composition, flower abundance and flower-visiting insects of each strip were monitored three times, and pests and their natural enemies in each field were monitored four times.
Flower density appeared to be a good predictor for the number of beneficial insects. The
density of flowers with nectar accessible for short-tongued insects appeared to be an even better predictor for the number of hoverflies, other predators and solitary bees, as well as for insect diversity, than the total flower density. Annual and young perennial flower strips showed similar numbers of hoverflies, other predators, bees and butterflies, but numbers of hoverflies and bees declined markedly with the age of the perennial flower strips, due to increasing dominance of grasses. Mowing negatively affected the abundances of all insect groups.
In potato fields, the abundance of several groups of predators was correlated with potato
pests, indicating that hoverflies and lacewings were responding to aphids, whereas ladybeetles were also responding to Colorado potato beetles. Only low numbers of aphids remained by the end of July in the potato fields, even where no insecticide was used. If there were more hoverflies and other predators in the field margin strips, the number of aphids decreased even faster, even at 80 m from the field margins, indicating that flower strips contributed to natural pest control.
In all years, aphid numbers remained well below the damage threshold, and informed by
these results, farmers did not apply chemical control against aphids. However, in 2019-2022 an insecticide treatment was applied against Colorado potato beetle in c. 60 % of the potato fields surveyed.
This research provides knowledge that can be used to make flower strips more effective in
supporting biodiversity and natural pest control.