The best, cheapest, and most practical thing to do is to water the pine trees. Simply water the trees. During the last severe drought, homeowners who only watered their pines fared as well as those who tried other means to keep their pines alive. Watering also prevents other opportunistic (and fatal) pests from gaining a toe hold in drought-stressed trees.
Keep the trees well watered by providing at least 1-inch of water per week for the growing season. If nature doesn't supply it, use the garden hose. The top 8 to 12 inches of soil should be kept evenly moist around trees during periods of drought, at least as far as the branches spread (drip line). Avoid using a sprinkler; this just waters the grass and, although you think you're watering the tree, you're not. It's easiest to position the hose near or inside the tree's drip line and let it run for an hour or more, move it slightly, and let it run. Continue doing this until you've watered most of the areas around your trees. Then repeat this next week if 1-inch of rain doesn't fall. If you have many trees to keep watered, a large-diameter soaker hose might be more to your liking.
Mulching will keep soil moisture high. Use needles, bark, wood chips, or other organic materials as mulching material in a layer that is only add 2 to 4 inches thick. Never place plastic under the mulch because this does not allow rain or irrigation water to get into the soil and root system.
Do not fertilize until the drought and bark beetle outbreak is over. A water shortage triggered the bark beetle outbreak, not a shortage of chemical elements in the soil. In fact, the addition of fertilizers will decrease the amount of water available to the trees because fertilizers are salts.
If watering is not an option, another technique can be used to reduce populations of bark beetles that uses a trap baited with bark beetle pheromones. Pheromones are airborne chemicals produced and excreted by insects that attract others of the same species. Pheromones could be thought of as insect perfumes. Bark beetles use pheromones to attract other male and female beetles to a tree so that the tree's defense system can be overcome by a massive number of beetle attacks.
Usually reserved for research purposes, pheromone traps can be economically used on suburban lots, but are too expensive to be used in woodlots and plantations. This technology reduces the local populations of bark beetles by attracting and catching the beetles in funnel traps. You can trap lots of bark beetles using pheromone traps, but whether you trap enough beetles to affect the population and prevent them from attacking other pine trees has not been proven. The traps use no pesticides to kill the beetles; the beetles die from dehydration, starvation, or being consumed by predators. Pheromone traps will not prevent attack by other opportunistic pests.
Pheromones and funnel traps are available from one source, Phero Tech in British Columbia, and they cost about $50.00 each. Shipping and handling are additional costs. Phero Tech Inc. can be reached by telephone at 604-940-9944 or by email at firstname.lastname@example.org. You'll need to provide a 5/8-inch diameter steel rebar to hold up the trap.
The best defense is to keep trees healthy by watering them during droughty weather.