Herbs can be technically defined as plants without any wooden stems. There are thousands of plants that do not have any stems and can be classified under the category of herbs. However, only those little plants whose parts and products are used in cooking, fragrance, crafts or medicine are practically recognized as herbs. Even these plants are favorite foods for many pests and insects.
Based on their utility, garden insects can be classified into two types. While one variety of insects causes damage to plants, the other variety feeds on these pests. Harmful pests include insects like aphids, asparagus beetles, Japanese beetles, leafminers, caterpillars, tomato hornworms, spider mites, thrips, slugs, snails, maggots, flies, bugs, wireworms and leafhoppers. Beneficial insects include wasps, ladybugs and praying mantis. One should plant varieties that can attract beneficial insects into the garden. Presence of herbs like lavender, thyme, borage purple coneflower, lemon balm, catnip, yarrow and dill are good source of nectar and pollen for beneficial insects like butterflies and bees.
There are certain herbs that can act as repellants to various pests. Presence of lavender can drive away insects like moths, ticks and mice. Herbs like garlic, onion and chives have the tendency to repel aphids, Japanese beetles, borers and mites. Insects like Tomato hornworms, whitefly, Mexican bean beetles, cabbage maggots, cabbage moths and eel worms are averse to herbs like rosemary and marigold. Leafhoppers and Rose chafers do not like the presence of petunias and geraniums. Cucumber beetles are repelled by radish and tansy. Wireworms do not enter into gardens having mustard and buckwheat. Similarly, cabbage moths can be stopped if you plant alternating rows of mint, tomato, rosemary and sage.