Insecticide use in hybrid onion seed production affects pre - and post - pollination processes 21 22

28 Research on threats to pollination service in agro-ecosystems has focused primarily on 29 the negative impacts of land use change and agricultural practices, such as insecticide use, on 30 pollinator populations. Insecticide use could also affect the pollination process, through non31 lethal impacts on pollinator attraction and post-pollination processes such as pollen viability or 32 pollen tube growth. Hybrid onion seed (Allium cepa L., Alliaceae) is an important pollinator33 dependent crop that has suffered yield declines in California, concurrent with increased 34 insecticide use. Field studies suggest that insecticide use reduces pollination service in this 35 system. We conducted a field experiment manipulating insecticide use to examine the impacts of 36 insecticides on (1) pollinator attraction, (2) pollen/stigma interactions and (3) seed set and seed 37 quality. Select insecticides had negative impacts on pollinator attraction and pollen-stigma 38 interactions, with certain products dramatically reducing pollen germination and pollen tube 39 growth. Decreased pollen germination was not associated with reduced seed set; however, 40 reduced pollinator attraction was associated with lower seed set and seed quality, for one of the 41 two female lines examined. Our results highlight the importance of pesticide effects on the 42 pollination process. Over-use may lead to yield reductions through impacts on pollinator 43 behavior and post-pollination processes. Overall, in hybrid onion seed production, moderation in 44 insecticide use is advised when controlling onion thrips, Thrips tabaci, on commercial fields. 45