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Good to see this many answer.

Karma arising from clinging to I and mine and the negative emotions, what impede us to realize the nature of the ground or Buddha nature and being trapped in the world of cause and effect. So you should try to learn and train yourself in emptiness and non-dualist, since while you keep the clinging to conditioned self you will continue to create more karmic imprint, even if you don't kill.

Now, about pest control, you should try some alternative way to kill, this book give you some options: http://www.amazon.com.br/dp/B00MQ994VY . However, specialty if you don't leave a life of a monk, it could be difficult to protect the life of family and others without to kill, that don't mean you should go around killing all time, only I high level Bodhisattva could do that, since they realized the union between emptiness and interdependence and know how to act to the benefit of beings.

I would recommend read Shamar Rinpoche's Animal Rights chapter in his Creating A Transparent Democracy: A New Model and also Patrul Rinpoche's 'Nine Considerations and Criteria for Benefiting Beings'.