Answer: One of the problems of growing plants in a greenhouse is that the environment is also perfect for year around pests. Aphids bear live young that are capable of bearing live young. If there's food enough, you can have several generations of aphids feeding on a single plant. Spider mites love the perennial spring-like conditions, too. You can release ladybugs inside your greenhouse and their population will increase enough to seek and destroy, but keep in mind that ladybugs are genetically programmed to go into hibernation in the fall and winter months. They may be confused with year around spring-time like conditions. I suspect they'll die off after a while and will have to be replaced. Both aphids and spider mites are soft-bodied insects and you can kill them off with regular applications of insecticidal soap. Be sure to read and follow the label directions - sometimes insecticidal soap can burn the tender leaves on young plants.
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