All termite members are of the insect order Isoptera. Termites feed primarily on the cellulose and lignin found in plant cell walls; these compounds are the main ingredients of wood and all paper products. Termites cannot digest the cellulose directly so they rely upon symbiotic bacteria and protozoa living within their intestines to supply most of the enzymes needed for cellulose digestion. Termites are sometimes called white ants. They may resemble ants in size, but ants have a narrow waist and elbowed antennae while termites have a thick waist and antennae that resemble a string of beads.

Ecologically, termites play an important role in the environment by helping to break down and recycle dead wood and other plant tissues. They become pests when their appetite for wood and wood products extends to human homes, fence posts, building materials, cardboard, and other valuable products. In tropical and subtropical forests where termites are abundant, railroads must use expensive metal ties because wooden ones are quickly destroyed.

Hope this helps.

Here’s another opinion for you to consider. The white creatures are unlikely to be termites because the most common habitat is dead wood.  Each one would be about a half inch long.

But if the small white creatures in your images are small, less than a 1/4-inch, they are most likely springtails which are common in moist compost and soils with extremely high organic content from food waste and manures. Springtails commonly jump (“spring”) when disturbed but may be less active when soil is cold and wet. Springtails are typically scavenger of dead organic materials but when they are particularly numerous, they can damage roots of seedlings and tender plants. The key to managing springtails is to reduce soil moisture. You didn’t mention how much organic matter you add to your garden but it’s likely that decreasing the amount will also limit the number of springtails.

Please see "Springtails" at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74136.html

Determining why your tomato harvest was below average will require a different conversation. One potential factor was the unusual heat of this past summer which periodically stopped fruit set.