What pollinated this?

Thanks to that's how it happened, I can direct you to this year's new pumpkin record. Dr Pumpkin set a new Circleville Pumpkin Show record with a 1,353 lbs (615 kgs) monster.

According to Science Fair:

[US] pumpkins have historically been pollinated by the native squash bee Peponapis pruinosa, but this bee has declined, probably due to pesticide sensitivity, and most commercial plantings are pollinated by honeybees today. One hive per acre is recommended by the US Department of Agriculture. Gardeners with a shortage of bees often have to hand pollinate.

But according to the rather dubiously-named Mid-Atlantic Apiculture honeybees do have to get up early and work hard to pollinate pumpkins:

Pollination must take place on the day when the flowers open ... Pumpkin and squash pollination is most effective in early morning, primarily before 9:00 A.M. ... Honey bees are normally most active in the field from 10:00 A.M. to 3:00 P.M., with peak flight occurring near noon. Honey bees are not as effective in pollinating squash and pumpkins as the other cucurbits, since the flowers close at noon.

Multiple bee visits of at least eight to twelve per flower are needed to produce marketable fruit. ... In general, as the number of visits increase, so does the fruit set, number of seeds per fruit, and fruit weight. Fruit shape also improves up to a point as the number of visits increase.