Hot and humid weather could invite leaf-eating caterpillars that will hatch from eggs and start eating crops as soon as they are out! Watch your crops, especially soybean and canola, for damage from larvae and spray insecticide if the damage exceeds the threshold (usually 20 % or so).
The best insecticide for the first spray would be Chlorpyrifos (trade name Lorsban).
See the product label at: http://msdssearch.dow.com/PublishedLiteratureDAS/dh_08a6/0901b803808a6e57.pdf?filepath=ca/pdfs/noreg/010-21834.pdf&fromPage=GetDoc
Please don’t use synthetic pyrethroids, which will also kill the friendly insects (predators) and eventually aggravate the pest problem. These chemicals should be used only as a last resort.
Second insecticide spray, 10-15 days after the first spray if need be, could be of Malathion. See product label at: http://www.uap.ca/products/documents/Malathion500E-EdatapakJan2008_000.pdf
Remember rotating pesticides and crops helps to check pesticides resistance in the pests!