Ecology and Diversity of Wild Bees and Wasps in An Urban Landscape

Bees are a diverse group of essential pollinators and useful for studying the impacts of urban environmental change on local biodiversity. A subset of solitary bee species widespread in cities the cavity-nesters nest in plant stems and bored holes in wood and readily use human-made nest boxes comprised of these materials or similar ones. Many solitary wasps that predate on abundant and pest arthropod species also use these nest boxes. Nest boxes provide information on diversity, parasitism, and a plethora of other data on cavity-nesting bees and wasps. The main objective was to detect patterns in cavity-nesting bee and wasp diversity using nest boxes and determine the urban factors that impact their populations. A primary goal was to connect urban gardening, land use planning, and policy more directly with bee populations. Nest boxes were set up at 200 home gardens, community gardens, urban parks, and green roofs and each monitored by a member of a large network of citizen scientists. Nest boxes were set out in April and retrieved in October over three years (2011-2013). From October to March, bee, wasp, and parasite larvae were removed, then reared and identified to species. From over 27,000 records, 84 species of bees, wasps, and parasites were identified from three years including new records for the Toronto region. More native species were recorded than exotic ones, however the most abundant colonizers were exotic [Megachile rotundata Fabricius, Osmia caerulescens (Linnaeus)] and half of the colonizers were wasps. The type of urban green space surveyed and increasing habitat availability index (HAI), which included high resolution mapping of seven different land use types within 200m of the nest box, were important for increasing colonization. Diversity and abundance in nest boxes and in particularly that of bees was positively influenced by the luxury effect, while wasps and parasites responded negatively to increasing human population density. Nest boxes are useful tools for study of populations of cavity-nesting bees and wasps and can become catalysts for conversation regarding bee populations, diversity, and declines.