Good Garden Bugs

Everything You Need to Know About Beneficial Insects

Mary Gardiner

• Publisher: Quarry Books
• Year: 2014
• ISBN:
  9781627880336
• Topic: Biological Sciences
• Subtopic: Horticulture
• Index: Biological Sciences

Your guide to the beneficial insects in your garden!

Good Garden Bugs is an easy-to-follow reference to beneficial insects that provide pest control, allowing your garden to grow full and bountiful.

Aphids, caterpillars, grubs, and slugs are not only creepy-crawlies, they can wreak havoc on your garden and plants. But fear not! You don't need dangerous chemicals to enjoy a lively, healthy garden. The secret? More lady beetles, fewer aphids! Wildlife in your garden--especially insects--can be natural pesticide alternatives. From mantids to beetles to wasps, spiders, and everything in between, entomologist Mary Gardiner tells you how to identify these beneficial bugs, how to enhance your home landscape as a habitat, and how to work with them to grow and enjoy your garden.

1
The Basics: Natural Enemy Lifecycles and Eating Habits

Natural enemy arthropods vary widely in the prey they seek, the environment in which they live, and their lifecycles. Although these specific details are presented in the individual chapters, I wanted to draw your attention to two key distinctions in how natural enemies develop and how they feed.

Knowing the lifecycle of important natural enemies is helpful as you begin to identify these insects in your garden. When armed with this knowledge, you’ll have a better understanding of how natural enemies impact pests in the garden. The natural enemy arthropods can be divided into two different groups: those that develop via gradual metamorphosis and those that undergo complete metamorphosis.

Gradual Metamorphosis

All orders in the classes Arachnida and Chilopoda, as well as the two orders within the class Insecta included in this book—Mantodea (mantids) and Hemiptera (true bugs)—develop via gradual metamorphosis. This means that they hatch from an egg into an immature stage typically called a nymph (spider hatchlings are also referred to as spiderlings and juveniles). These arthropods undergo several molts to reach the reproductive adult stage, but they do not have a pupal stage, so will you will never find a cocoon of a spider or mantid in the garden. The nymphs will become larger following each molt, and if the arthropod is winged as an adult, its wings will gradually form. These partially formed wings are called wing buds and are not functional until the adult stage. Typically, the nymph or immature stages of these groups look similar to the adult, although with some species, picking out the family resemblance is much easier when immatures are close to reaching the adult stage. Both the immature stages and adults of these arthropods will typically feed on garden pests. Often, there is also considerable overlap in the types of prey immatures and adults will consume. For example, nymph and adult minute pirate bugs (Anthocoridae) feed on many common garden pests, including aphids (Aphididae), spider mites (Tetranychidae), and insect eggs. In most cases then, you can find both nymphs and adults foraging within the same habitat, such as on the soil or crawling on plant leaves, and you often will find both nymphs and adults present at the same time in the garden.

Natural enemies that develop via gradual metamorphosis do not have a pupal stage. These arthropods hatch from an egg into an immature stage called a nymph. The nymph will undergo several molts, growing larger each time, and if they will be winged as an adult, their wings will form slowly during their development. After its final molt, a nymph will become an adult able to reproduce, and if winged, its wings will be fully formed. When insects develop via gradual metamorphosis, both the nymph and adult stage typically feed on prey within the garden.

Complete Metamorphosis

Four orders of natural enemies discussed in this book develop via complete metamorphosis: Neuroptera (lacewings, owlflies, and antlions), Coleoptera (beetles), Diptera (flies), and Hymenoptera (wasps and ants). Here, insects emerge from the egg as a larva, which develops through several molts, increasing in size each time. The larvae of insects that undergo complete metamorphosis often look very different from the adult stage. They are usually somewhat worm- or caterpillar-like—they do not have wings (and developing wing buds are not present) and may or may not have legs. Eventually, insects with complete metamorphosis will construct a pupa (or cocoon), and inside this protected case, they will undergo a major transformation. When they emerge, they look much different from their larval stage; most have wings and have a different general body form. They are also able to reproduce.

Arthropods that develop through complete metamorphosis are more likely to vary in what they eat among life stages than those that develop by gradual metamorphosis. The immature, larval stages of these natural enemies are typically predacious. A larva may find its arthropod prey on its own or be provided with food by adults. For example, the larvae of lady beetles (Coccinellidae) actively seek out aphids, whereas an adult female thread-waisted wasp (Sphecidae) will collect arthropods for its larvae to eat. Adults may or may not feed on prey themselves. Also, the larvae and adults are not always found in the same place within the garden and may not hunt in the same way. For example, the larvae of tiger beetles (Carabidae) construct tunnel-shaped burrows into the soil and wait inside to catch unsuspecting insect prey, whereas the adults run along the soil surface searching for prey.

Insects that undergo complete metamorphosis will have egg, larval, pupal, and adult stages. A larva will emerge from its egg and, over the course of this life stage, undergo several molts, gaining size each time. Often larvae are slender bodied. They can appear wormlike without legs, or they may have three pairs of legs present. Eventually, the larva will be ready to construct a pupa and enter this resting stage where major transformation occurs. When ready, the insect will emerge from the pupa as an adult. Typically, insects that develop via complete metamorphosis look very different during the adult and larval stages. Adults may also be found in a different part of the garden than the larva, such as above versus below ground, and may or may not feed on insect prey.

Eating Habits: Predators and Parasitoids

A second major distinction among natural enemies is whether they feed as a predator or parasitoid. Each of the arthropod chapters in this book includes predatory species. Living as a parasitoid is most common among wasps (Hymenoptera) and to a lesser extent flies (Diptera) and beetles (Coleoptera); it is rare to nonexistent within other groups of arthropods.

Predators

Predators are arthropods that actively hunt for their own prey. Most predatory arthropods are generalists, meaning that they will find many different types of insects acceptable as food and will also eat other types of food, such as pollen or nectar from flowers.

Some generalist predators, such as lady beetles (Coccinellidae), consume mainly pest insects, including aphids, scales, and mealybugs. Others, such as many spiders (Araneae), will consume both pests and other beneficial insects. Since pests are often common in home gardens, it is likely that these unwanted insects will make up much but maybe not all of the diet of many of the predators you encounter.

Predators vary widely in their hunting strategy. Many spend their days walking and flying around the garden and other surrounding habitats in search of food. These are called active hunters and examples include wolf spiders (Lycosidae) and minute pirate bugs (Anthocoridae). Active hunters with large eyes such as jumping spiders (Salticidae) may use visual cues to locate prey, whereas others may track prey using olfactory or tactile cues. For example, aphid predatory midge larva (Cecidomyiidae: Aphidoletes aphidimyza) cannot see, thus as they crawl along on leaves, they rely on feeling the leg of an aphid to know they have found their next meal. Then the larva will pierce the leg joint, paralyze the aphid, and ingest the aphid’s liquid contents.

Other predators, such as crab spiders (Thomisidae) and most mantids (Mantidae), wait for their next meal to find them. These sit-and-wait predators are able to remain motionless until prey comes within their grasp; then they move quickly to capture it. Often, these predators are well camouflaged to their hunting grounds. Web-building spiders, such as orb weavers (Araneidae) and sheetweb spiders (Linyphiidae), take the sit-and-wait strategy a step further by creating a trap to catch passing prey.

Parasitoids

Parasitoids live their lives quite differently from predators. This group of insects is similar to parasites in that they live internally during part of their lifecycle. Yet unlike a parasite where the host animal survives, as they develop, parasitoids will eventually kill their host.

The life of a female parasitoid centers on locating a host arthropod for her offspring to feed upon. She will lay eggs within, on, or near this host using an ovipositor, which is a tubular, egg-laying organ. For some parasitoid wasps, the ovipositor is clearly visible and can be longer than the body of the insect! Ovipositor length varies most widely among wasps, and the length can be an indicator of how difficult it is for the parasitoid to get to its host. Those such as the giant ichneumons (Ichneumonidae: Megarhyssa), which attack large prey or prey hidden inside stems, seeds, or even under bark, have longer ovipositors. It’s a good thing that parasitoid wasps cannot sting humans with their ovipositor and only are a threat to their targeted host insects!

Most parasitoids are considered “specialists” in that they will attack only one or a few species of host arthropods. Some females search for a specific species of arthropod, while others will accept several different hosts, but usually in the same arthropod family or order. A small parasitoid flying around in a garden looking for a specific host might seem akin to looking for a needle in a haystack, but female parasitoids use a lot of cues to narrow in and locate their host. When determining where fresh eggs may be located, parasitoids are able to follow odors, such as those from the droppings of caterpillars chewing on a corn plant or even the mating pheromones of adult hosts. For concealed hosts, such as those feeding inside rolled leaves or under bark, vibrational cues are also very important.

1. A female parasitoid seeks a host as a food source for her offspring. Many species attack aphids (Aphididae). This female wasp is inserting one egg inside the pest with her ovipositor.

2. The egg of the wasp hatches within the aphid and the larva consumes its internal contents.

3. The wasp larva will pupate within the dead aphid, which darkens and hardens into an aphid mummy. Often, aphid mummies are the only visible evidence of aphid parasitism you will see in the garden. When ready to emerge as an adult, the parasitoid chews a round exit hole through the dead aphid and flies off in search of a mate.

Once the host is located, th...

Table of contents

• Cover
• Title Page
• Contents
• Introduction
• Chapter 1: The Basics: Natural Enemy Lifecycles and Eating Habits
• Chapter 2: Biological Control in Home Gardens
• Chapter 3: Monitoring and Collecting Good Garden Bugs
• Chapter 4: Mantids (Mantodea)
• Chapter 5: True Bug Predators (Hemiptera)
• Chapter 6: Lacewings and Other Net-Winged Predators (Neuroptera)
• Chapter 7: Beetles (Coleoptera)
• Chapter 8: Predator and Parasitoid Flies (Diptera)
• Chapter 9: Wasps and Ants (Hymenoptera)
• Chapter 10: Spiders (Araneae)
• Chapter 11: Other Arachnids (Arachnida)
• Chapter 12: Centipedes (Chilopoda)
• References
• Index
• About the Author
• Acknowledgments
• Copyright