The need for insecticides on parent seed corn arises from the high value of the crop, and a need to protect the yield, and in Hawaii, there is consistent pest pressure. Among the most significant insect pests here are thrips (that vector a virus that infects the corn), and corn ear worm, the larvae of which attack and feed on the developing kernels. Both reduce yields; both need to be suppressed. The companies do apply pesticides for such insect pests. People have the impression that the sprays are applied continuously, but this impression is largely created by the fact that the sprayers are seen operating frequently. This is the result of operators not being able to complete all their spraying in a single day - if the wind comes up, they need to stop and continue the next morning for example. (They need to stop spraying to avoid pesticide drift.) So you might see them out there “all the time”, but they are not spraying the same fields every day!
That said, thrips do require frequent insecticide applications. They build up huge populations quickly, and this requires intervention in a high-value crop, such as parent seed corn. It may surprise many that the seed companies engage in practices that help reduce insecticide dependence, and they have in fact funded research on biological control options and cover cropping practices, to reduce or avoid sprays.
The fact that a number of restricted use products are used does indeed sound worrying. But bear in mind that most of these products are pyrethroids (originally derived from pyrethrum, an organic insecticide), and theyare restricted because of potential negative impacts on aquatic organisms if they contaminate fresh water. Pyrethorids actually have very low mammal and bird toxicity. You can purchase pyrethroids of the shelf in supermarkets for home-use. Those products have the same active ingredients as the restricted use products!
I am no insecticide fan myself (I work in biocontrol mostly), but I recognize the need for insecticides in many situations. I have been impressed that the seed corn growers go to great lengths to ensure safe application practices, and to use the “softest” possible products wherever possible. I am also impressed that they are prepared to invest research into finding more effective and environmentally safer options for insect management.