> Considering the concept of judicious use, surface spraying
>  as needed might well be preferable to seed coating, 
> which wastes a lot of product

I always enjoy hearing folks who have never had any acreage in cultivation
talk about farming.

I did not need neonics, as I grew 450 acres of high-end horse hay, and if it
did not rain when the hay was winnowed, I made far more off the hay than
from pollinating with 600 hives of bees.  But if it did rain, I had nothing
but "cow" hay, and I was lucky to recover the cost of cutting the hay, which
I outsourced.  (Contracting, rather than buying and maintaining the capital
equipment to harvest hay is the key to profitability.  Counter-intuitive,
but I never argue with spreadsheets.)

But waste?    Let's do the math:

Chlorpyrifos (Lorsban) is spayed on corn and soybeans at 1.0 pound active
ingredient per acre ("lb ai / A") .

To compare the maximum use rate for thiamethoxam applied as a seed treatment
(Cruiser) in corn is 0.156 lb ai/A
Thiamethoxam as a seed treatment for soybean maxes out at 0.083 lb ai/A

This is a 6 and 12-fold reduction in the active ingredient per acre for seed
treatments.
One sixth and one 12th the total amount used implies that the amount used in
seed treatments is lower than the amount of spray that is wasted because it
does not end up on the plants.

Imidacloprid is applied at approximately 0.04 lb ai/A as a seed treatment in
cotton. 
Imidacloprid applied as an in-furrow spray (Admire Pro), the maximum use
rate is 0.33 lb ai/A. 
That's 8.25 times more.

To control thrips with foliar sprayed Imidacloprid on cotton, the maximum
amount is over 0.5 lb ai / A. 

Also, seed treatments don't flare secondary pests like foliar sprays do.
When you spray, you kill both the target insect and beneficial insects.
Spraying broad spectrum insecticides like as acephate or dicrotophos for
thrips control is certain to kill the predators, and suddenly you have
spider mites, which are yet another level of problem, one normally
controlled by the predators that can live to prey on the spider mites if
seed treatments are used.

> and may not be needed (one cannot know beforehand if the crop will be
affected). 

If the pesticide it is on the seed, and only on the crop, the pest
population is unaffected, except for those who encounter the crop itself.
The pests can breed normally and not mutate in the buffers and borders (but
some farmers plant sacrificial plantings so as to avoid breeding teenage
mutant ninja pests).

I was never much of a farmer myself, but I certainly listened to those who
were.

One thing is for sure, the more GMO "RoundUp-Ready" seed is planted, the
more RoundUp is used.

Here's an article on sweet corn I bookmarked a while ago, as sweet corn is a
good example of a crop where GMO Bt makes sense.
http://www.biofortified.org/2012/05/the-frustrating-lot-of-the-american-swee
t-corn-grower/

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