Impact of oilseed rape coverage and other agricultural landscape characteristics on two generations of the red mason bee Osmia bicornis

Abstract

The intensification of agriculture and the related increase in pesticide use and land transformation toward large-scale monocultures are linked to a global insect decline that impacts biodiversity and essential ecosystem services. Apart from direct effects, potential delayed carry-over and maternal effects from past exposure to intensive farming at different life stages may have profound implications for population dynamics. We studied the effects of farming of varying intensity, represented by different proportion of oilseed rape in the close vicinity of nests and, at the same time, by different landscape structure on the life history traits of two generations of the red mason bee (Osmia bicornis) and the sensitivity of bees toward insecticide. Twelve O. bicornis nests with cocooned adults of the parental (P) generation were located at sites representing 6–65% of oilseed rape coverage (ORC, % land cover) within nonoverlapping circles of 500 m radius. The bees were allowed to build their nests during the entire period of oilseed blooming. The following year, part of the newly emerged bees (generation F1) was used to test sensitivity to Dursban 480 EC insecticide, and the remaining bees were transferred to mid-forest meadows and allowed to establish the next (F2) generation in the areas without agricultural pressure. The F2 adults were tested the following year to determine their sensitivity to the same insecticides as F1 adults. We showed that ORC affected the F1 bees by decreasing their emergence success, shortening the emergence time of F1 females, and making them more sensitive toward Dursban 480 EC (topical exposure). However, these effects of ORC and the effect of landscape structure around the nests on emergence time disappeared in the F2 generation that developed in the areas without agricultural pressure. The only significant effect observed in F2 bees was the increase in the female:male ratio with increasing ORC. We also found that with increasing ORC, the survival time of newly emerged F1 males decreased, but the opposite relationship was found for F2 males. The results indicate that larval development under monoculture farming has some carry-over effects, but the effects mostly disappear in the next generation. Implications of carry-over and maternal effects for population sustainability should be considered in pollinator conservation and management decisions to mitigate the effects of agricultural landscape.