Osmia_phenology.pdf

<em>Osmia cornifrons</em> was imported from Japan in 1976 to Maryland, US, for orchard pollination and since then is expanded to almost all Eastern US. Their impacts on native species are unknown. The invader <em>O. cornifrons</em> and the native <em>Osmia lignaria</em> <em>lignaria</em> have now a very similar distribution, they have a similar biology and nest in the same nest structures. Niche overlap may lead to competition between both species. Here, I analyzed the phenological overlap of <em>O. cornifrons</em> with the native species <em>O. lignaria</em> at Hutchington Memorial Forest, New Jersey, USA. I monitored 125 cocoons of each species that wintered exposed to the same natural conditions. Emergence of both species was monitored along 35 days during spring 2011. As showed in the figure, the invader,<em> O. cornifrons</em>, emerged earlier than the native bee (Cox survival analysis: z = -4.9; p &lt; 0.001). I speculate that this can give to the invader an advantage when choosing nesting sites, but at the same time could increase the risk of the invader to late spring frosts.