Nest contests between farmed species of local solitary bees and wasps. University of Toronto and Department of Natural History, Royal Ontario Museum. Contests within a single nest cavity include: (a) cut-back of an earlier nest to accommodate a later nest; (b) a later nest blocking the emergence of an earlier one; (c) emergence of an earlier nest through a blocking nest. Counts of interspecific attacks at 1 locality for generation 2006 (years ) can be reduced to a few levels of competitiveness. (The data set for the first 10 years of the farming project is available on request.)‏

1 of 2 equipment replicates (“stands”), 3 nest boxes per stand, many nest blocks of mm cavity widths. An “outbreak” of the Mason Bee was countered by partly harvesting it so as to make room for other bees & wasps.

June 15. 2&3 up: Unhatched Isodontia mexicana; new Osmia lignaria. Half cocoons and lost cells mean ‘attack by cutback’.

Aug up: Dead adults of Isodontia & a partly penetrated new Osmia nest. I.E., ‘blocked emergence’, and an ‘attack by exit’.

Aug 15, 2006: 4 up: Leafcutter; Trypoxylon collinum; Megachile campanulae. All died trying to emerge in I.E., intragenerational “block” and “exit” attacks.

Conflicts between successive nests in the same cavity: the ‘blue’ nest can attack or be attacked, or both. Earlier nest Later nest Exit through Cut back Block emergence Blue attacking: Blue attacked:

4sp10117 ol oc1181 lcb11401 mc453 im0040 mclcbocol4sp ol oc0000 lcb23144 mc81161 im150 mclcbocol4sp Interspecies pair-wise attacks Attacking Attacked BAR stand LAU stand st2006-2nd2007-1st2006-3rd2006-4th n =119n =100

Overall success in the above attacks 41loser431loser6I. mexicana O. coerulescens Leafcutters 8 Near balance or varies 1014 Near balance or varies 184 spp. combined O. lignaria 4winner1211winner26M. campanulae AttackedAttacksAttackedAttacks LAU standBAR stand

A few levels of dominance O.lignaria 4 species O.coerulescens Isodontia 2 Megachile campanulae Leafcutters 1B 2 3 1

Conclusions This talk advertises a 10 year data base. There is replicated evidence for 2 bee species being dominant in bee and wasp nest attacks, for 1 generation at 1 locality. Nest attacks are not likely to be a large factor in the dynamics of farmed populations. ( About 26% of cavities have multiple nests; about 16% show evidence of conflict.) About 3 or so generations and 3 localities are available for further analyses of nesting contests.

Related issues The present definitions of interspecies conflict do not include the roles of aggressive mites. Will farming the Orchard Mason Bee (Osmia lignaria) impact on biodiversity in E. Canada? Thanks to Chris Darling and Arthur Weis for for encouragement and facilities. An overly anxious view of the future ?