The Seen and Unseen World of Invertebrates and Vegetables: The good, the bad, and the cute

Written by Joslyn Fousert, Hannah Voye, and Ashtyn Schultz, SDSU Department of Agronomy, Horticulture, and Plant Science graduate and undergraduate students, under the direction and review of Kristine Lang and Amanda Bachmann.

Introduction

From the second we leave the security of our homes and enter the outdoors we find ourselves face-to-face with different communities and ecosystems buzzing with life, continually adapting and striving for sustenance and survival. Within these ecosystems, many invertebrates and microorganisms are thriving and building their own microclimates to sustain and ensure their survival. These organisms are interacting with each other and with humans. This interaction with humans has carved out a path for a way of thinking of organisms in terms of the good, the bad, and even the cute. However, it is key to remember that each invertebrate and microorganism plays a vital role in the systems at place, allowing the ecosystems and microclimates to continue to exist as we know them—both seen and unseen.

Article Topics

• The Good: Red Earthworm
• The Bad: Cabbage Looper
• The Cute: Brown-belted Bumble Bee
• Summary and Resources

The Good: Red Earthworm (Lumbricus rubellus)

Figure 1. Adult Red Earthworm. Courtesy: Missouri Department of Conservation

Earthworms

Earthworms can be found in agricultural fields, forests, and grassland habitats across South Dakota. Earthworms found in South Dakota are nonnative species originating from Europe and Asia. Earthworms are segmented invertebrates belonging to the phylum Annelida. While most earthworms carry both male and female organs, they typically require a mate for reproduction. Earthworms can produce up to 1,000 cocoons per year, depending on species and environmental conditions.

Earthworms are generally divided into three major groups: litter dwellers, topsoil dwellers, and subsoil dwellers. Litter dwellers are typically found in forest habitats, where their presence has been found to negatively affect soil bulk density, soil nutrient levels, and forest ecology. Topsoil and subsoil dwellers are typically found in gardens, agricultural fields, and grasslands, where they improve soil aeration, nutrient recycling, and water infiltration.

Figure 2. Earthworm castings. Courtesy: Missouri Department of Conservation

Soil Benefits

Earthworms do not feed on living plant roots. Earthworms feed on soil and decomposing organic matter, such as leaves, dead plant roots, and soil flora. Once digested, the organic matter is excreted by the earthworms as casts (Figure 2). Casts are rich in nitrogen, phosphorus, and helpful bacteria. Soil that has been digested and excreted by earthworms typically contains more bioavailable nitrogen than mineral soil. The breakdown of organic matter also makes it more readily available to bacteria and fungi. A soil rich in worm casts is likely to have 1,000 times more beneficial bacteria than soil that does not contain earthworms.

As topsoil and subsoil dwellers burrow through the soil, they help move fertilizer and nutrients. Topsoil dwellers produce numerous small, horizontal burrows as they eat their way through the soil. These small burrows harbor nutrient-dense casts, water, and air. The burrows increase aeration and reduce soil compaction, creating better ventilation for plant roots and soil organisms. Subsoil dwellers create permanent vertical burrows up to six-feet deep. Along with aeration, these deep burrows increase water infiltration, reduce erosion, and aid root proliferation.

Courtesy: Canva

Encouraging Populations

The presence of earthworms is an indicator of good soil health, and there are a number of things you can do to support an environment that is ideal for earthworm growth. To encourage and sustain a healthy population of worms, consider the following best management practices:

• Plant cover crops.
• Reduce soil tillage.
• Add manure or compost.
• Reduce pesticide and herbicide use.
• Use mulch to keep soil moist and cool.
• Leave organic matter on the soil surface.

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The Bad: Cabbage Looper (Trichoplusia ni)

Figure 3. Cabbage looper moth. Courtesy: Mark Dreiling, Bugwood.org

Origins

The cabbage looper is native to the United States, and it feeds on all vegetables in the Brassicaceae family (examples include cabbage, kale, and others). Cabbage loopers cannot overwinter in the Midwest, so adult moths (Figure 3) annually migrate to the Northern United States and Canada from early July to late August. One to three generations are possible during the growing season in South Dakota.

Description

The adult moth is grayish brown with a 1.5 inch wingspan with a small silvery white patch in the middle of each front wing. They are nocturnal fliers, but they can be seen resting on the underside of cabbage leaves during the day. On average they lay 200 to 350 eggs over 10 to 12 days. Eggs are white, round and the size of a pinhead (Figure 4). The eggs are usually laid on the outer edges of lower leaves on plants that are not previously infested by loopers.

The larvae are light green and have two white stripes along each side. Loopers move in an inchworm fashion, arching their bodies as they bring their hind prolegs up to their front true legs (Figure 5). Eventually the caterpillars turn dark brown when they mature and enter a cocoon stage.

Figure 6. Row covers are a management option to consider. Courtesy: Canva

Commercial Management Options

Row covers are a good first option to consider (Figure 6); however, on large scales they could become an expensive investment. Monitoring flight habits with pheromone traps to ensure better scouting in advance of insecticide applications should also be considered. Attracting and maintaining beneficial insects through habitat strips and using biological controls, such as Bacillus thuringiensis (abbreviated as BT) are additional options.

Insecticides, such as those containing Spinosad, are available, but always read and follow all label instructions. When considering management options, it is important to take a look at your production system to form an Integrated Pest Management system (abbreviated as IPM) that will work best for your goals.

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The Cute: Brown-belted Bumble Bee (Bombus griseocollis)

Figure 7. Adult brown-belted bumble bee. Courtesy: Illinois Department of Natural Resources

Identification

Bumble bees are easily recognized by their fuzzy, yellow-and-black bodies and clear, black-veined wings. True to name, the brown-belted bumble bee, Bombus griseocollis, has a characteristic brown stripe, or “belt,” on its abdomen (Figure 7).

Habits

The brown-belted bumble bee is a pollinator and feeds on nectar and pollen. It collects pollen from various flowering plants found in farmland, fields, parks, and gardens. This species of bumble bee most commonly visits flowers on thistle (Cirsium), milkweed (Asclepias), and sunflower (Helianthus). It is important to watch out for their ground nests in grassy, undisturbed areas, as they are protective of their home.

Figure 8. Bumble bee ground nest. Courtesy: Iowa State University Extension

Lifecycle

Bumble bees can be spotted in early spring to late summer. In the spring, the queen emerges from hibernating to forage, build her ground nest, and start a new colony. Once female worker bees are produced, they also begin to forage and grow the colony. Male eggs are laid, and the female worker bees develop into new queens. Once the male bees have matured, the new queens mate with the male bees and find a place to hibernate for the winter.

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