What are some examples of good guy insects?

Beneficial garden insects include pollinators, predators, and parasitoids, or parasitic wasps.

Pollinators visit flowers to collect nectar and pollen to feed their young. In visiting many flowers, they transfer pollen from one flower to another, fertilizing seeds. Some garden vegetables can reproduce without pollinators--corn, for example, is wind pollinated--but in most fruiting plants, pollinators are either necessary for producing fruit, or fruit produced from cross-pollinated flowers is larger and has a longer shelf life than self-pollinated fruit. European honey bees are the most important agricultural pollinators, but orchard mason bees, bumble bees, and other native pollinators also pollinate vegetable crops.

Parasitoids are wasps that lay their eggs in the eggs--or bodies--of other insects. Most are tiny, gnat-sized insects with a wingspan of 1-2 mm, like trichogramma wasps, but some are larger. Larger parasitoids lay their eggs in caterpillars and the nymphs of beetle pests like squash beetles or spotted cucumber beetles. Parasitoids are critical insects in natural garden pest control because they control insect pests at low population densities, before they get out of hand. These tiny garden allies are the first insects to die when pesticides are applied. They're wiped out long before the pest insects.

Predators are the cleanup crew. Predator population increase in response to rising prey populations, but there's always a small lag before their numbers are high enough to control a severe infestation. Wasps, Spiders, preying mantises, predatory flies like robber flies, syrphid flies, and beetles like lady bird beetles (ladybugs) and ground beetles are examples of predatory insects. Ladybugs, and especially their larvae, are voracious predators of aphids, scale insects, and mealybugs.

Pollinators increase crop yields and improve produce quality. In organic gardens, parasitoids and predators work together to keep pest insects in check. They don't wipe pests out--after all, pest insects are the food of predators, and the incubators of parasitoids--but they do keep their numbers low, below the threshold for economic damage. In a healthy organic garden, you'll see many different kinds of insects, just not too many of any single pest.