Look for tiny larvae of  Yellow-headed spruce sawfly feeding on tender new needles of spruce (e.g. Colorado spruce) in the landscape.  Plant phenology indicator:  Robinia pseudoacacia (black locust) in full bloom.  Larvae are green with lighter longitudinal stripes, yellow-brown heads.  There are several insecticides registered including Dragnet, Dylox, Pounce and Success to target young larvae.  This is a damaging pest of spruce just north of Toronto and has caused significant damage to spruce trees.