To what extent is fennel crop dependent on insect pollination?

Abstract

The importance of insects for global food crop production is starting to be well-known but the level of dependence on insects is less referenced, especially for some aromatic crops. Fennel (Foeniculum vulgare, Mill.) is an aromatic mass-flowering crop cultivated in the south of France for its essential oil that contains anethole. This compound is of food and economical interest because of its anise flavour, which is used to elaborate anise drinks. Here, we have characterized the dependence of fennel on insect pollination. We used four controlled pollination treatments to compare the reproductive success (fruit initiation rate, fruit weight), and the fennel yield (fruit weight and amount of anethole per hectare) between insect pollinated flowers and bagged flowers. We also checked the ability of reproduction by self-pollination in this species, and the existence of a reproductive limitation linked to insect activity. We have shown that pollination without insects leads to reproductive failure in fennel. At the field level, insect pollination is fundamental to improve the fruit initiation rate, the fruit weight and the amount of anethole per hectare leading to an estimated 86 % dependence of fennel on insect pollination. Finally, we showed no reproductive limitation with the current state of insect activity. This study adds new evidence of the importance of insects in agroecosystems to sustain food production.