The Squash Bee; Essential Native Pollinator

By Ian Seifried, Summer Research Technician, OMAFRA.

Squash bees are native pollinators. They are directly associated with the cucurbita family of crops (squash, pumpkin, gourd, zucchini, marrow and courgette). This means that the squash bee populations depend solely on the production of these crops to establish their broods as well as feed their larvae.

Cucurbita flowers are synchronized to open just as the sun comes up and to close as soon as the temperature heats up, approximately 3-hours later. Squash bees are similarly synchronized to start collecting pollen as the sun comes up and to stop once the flowers begin to wilt. You can find both solitary male and unmated females in the flowers; you can even touch them, as they are stinger less.

Squash bees are medium sized with a very hairy thorax and black and white horizontal stripes running down the abdomen ending with a smooth point, without a stinger. The specialized hairs on the squash bees’ thorax and legs enable the bees to pick up cucurbita pollen which is larger, stickier and coarser than the other types of pollen (Figure 1). This makes them more efficient than other pollinators such as the bumblebee and honeybee.

The squash bee constructs ground burrows that are a series of lateral tunnels ending in individual brood cells. The cells are connected to a central vertical tunnel (which can be up to 45cm deep) leading to the surface hole. The surface hole is approximately the width of a pencil and can be found either in the field that is home to cucurbita crops or around the edges of fields.

The squash bee burrows are directly affected when tillage is used. Tillage can fill in these burrows, destroying the central tunnel along with several brood cells, and even kill the squash bees trapped inside.

During a recent field survey of squash bee activity in commercial pumpkin fields, the number of bees varied considerably. Total bees observed in 10 minutes (1 minute intervals at each of 10 locations across the field) ranged from 11 to 170, depending on the location.