Industrial hemp (Cannabis sativa L.) has a complex history in the United States. However, the introduction of the 2018 Farm Bill legalized industrial hemp (hereafter hemp) cultivation in the United States. Since then, growing hemp for grain, fiber and pharmaceuticals has been legal in at least 48 states, including Nebraska. To legally grow hemp in Nebraska after the introduction of LB262, LB657, and LB1152, interested entities must receive a cultivator license from the Nebraska Department of Agriculture (NDA), regardless of the cultivation size or purpose (including grain, fiber and flower).

Hemp is different from other cannabis plants based on delta-9 tetrahydrocannabinol (THC) levels, the chemical responsible for the plant's psychoactive effects. To be classified as hemp in Nebraska, the plant's flowers must have less than 0.3% total THC. If the total THC level in the flowers exceeds 0.3%, the individual plant or fields (as listed with NDA) must be destroyed following the established rules and regulations.

Study Rationale and Importance

With the legalization of industrial hemp for cultivation, the acreage in Nebraska has increased significantly over recent years. Available reports indicate only 10 cultivator licenses in 2019, growing to 62 licenses and 250 acres in 2021 and 280 acres in 2022. This new crop, coupled with limited knowledge about arthropod diversity at the local and state levels, was the motive for conducting a study at the West Central Research, Extension and Education Center (WCREEC) in North Platte, Nebraska.

Understanding arthropod abundance and diversity in industrial hemp in west-central Nebraska will allow us to lay the groundwork for an integrated pest management strategy. Understanding arthropod communities in hemp cultivation areas — both open and indoor — is crucial, as insects from the field can invade controlled environments if proper measures are not taken. Identifying the arthropods associated with industrial hemp provides valuable insights that give growers the tools to develop and implement effective pest management strategies, reducing crop damage and improving yields. Additionally, it supports sustainable practices by promoting more integrated pest control methods, leading to healthier crops, higher quality yields, and ultimately increased profitability.

Materials and Methods

The study was conducted in 2020 at WCREEC in a hemp dual-purpose cultivar grown for grain and fiber. Hemp was planted at 30-inch row spacing at 130,000 plants/acre. Arthropod sampling was performed bi-weekly using pitfall traps, yellow sticky cards, sweep netting and visual observations (Figure 1). The height of yellow sticky cards was adjusted based on the hemp canopy over the growing season.

The collection started in the first week of July and ended at the beginning of September. Collecting was performed at six sampling points across a 0.2-acre field. The results are shown as a combination of all four sampling methods (pooled).

Results

Beneficial Arthropods: 32% of the total number collected

Parasitoid Wasps — 18.6% (Superfamilies Ichneumonoidea and Chalcidoidea)

Parasitoid wasps are diverse in appearance but typically are very small (0.1–1.5 inches long) and can be brown, black, yellow or even metallic (Figures 2 and 3). Females use their ovipositor (egg-laying organ, which can be longer than their body) to insert eggs into or place eggs onto the body of their hosts. Typical hosts include the eggs and larvae of other insects, including agricultural pests such as aphids and caterpillars.

Ground Beetles (family Carabidae) — 3.4 %

Adults are shiny black or brown, but some species have bright metallic colors such as blue, green and red. Ground beetles generally have flattened bodies and big mandibles (jaws) that are used for catching and chewing their prey (Figure 4). Adults and larvae of ground beetles feed on a variety of other insects such as caterpillars, as well as other invertebrate animals (millipedes, slugs and snails).

Minute Pirate Bug (Orius insidiosus) — 2.8%

The adults are approximately 0.1-inch long. Minute pirate bugs have mouthparts like a long, sharp straw, used for consuming prey or sucking plant juices (mostly pollen and nectar) when the availability of the prey is scarce (Figure 5). Nymphs and adults are general predators. Their prey is a wide variety of small, soft-bodied arthropods such as thrips, mites, aphids, whiteflies, scale insects, small caterpillars, and eggs of various insects.

Predatory Thrips (family Aeolothripidae) — 2.4%

Predatory thrips are black or dark brown-bodied insects around 0.06- to 0.1-inch long. Some species might have white to yellow bands on their wings. Overall, predatory thrips are considered predaceous on small arthropods, such as plant-feeding thrips and spider mites. However, some species of this family might feed on pollen and other arthropods, such as aphids and whiteflies.

Long-legged Flies (family Dolichopodidae) — 1.7%

These flies are small (<0.3-inch), usually metallic blue, green, or coppery in color (Figure 6). The legs are long, ornamented, and brightly colored in males. This fly's larval and adult stages are beneficial, and they are predators of other small insects and mites. Adults are predacious, which means that they actively hunt their prey. However, they are only short-distance flyers (from leaf to leaf).

Lady Beetles (Ladybugs) Larvae and Adults (family Coccinellidae) — <1%

The most common species in Nebraska are convergent and pink lady beetles. The larvae and adults of ladybeetles (Figure 7 and 8) are well-known as biological control agents. They feed on soft-bodied insects such as aphids, mites and eggs of other insect pests. Larger larvae may consume 30 to 50 aphids per day, which could greatly reduce aphid populations in hemp.

Spiders (Order: Araneae) — 0.6%

Spiders can be important predators of insect pests such as beetles, caterpillars, leafhoppers, and aphids.

Jumping spiders are relatively small, measuring about 0.14­-inch to 0.5-inch long, and have abundant body hairs (Figure 9). Wolf spiders vary in size, from 0.5-2 inches long.

Jumping spiders and wolf spiders do not build webs to catch their prey but are active hunters —they either ambush or freely hunt their prey.

Potential Pests: 24% of the total number collected

Thrips (Order: Thysanoptera) — 16.1%

The major pest found on yellow sticky cards were western flower thrips and onion thrips.

They feed by piercing the surface cells of leaves and sucking out the cell contents. This results in a small, light area at the feeding site that causes silver scars or white flecks on hemp leaves. This small insect pest can transmit viruses in some types of plants, which might lead to discoloration, deformation and stunted plant growth. For now, there are no cases confirmed in Nebraska of thrips transmitting viruses to hemp in Nebraska.

Western flower thrips, Frankliniella occidentalis, are a commonly seen insect in a variety of plants. They are small, typically less than 0.07-inch, with an elongated body (Figure 10). Under normal field conditions, their life cycle can be completed in two to three weeks, which results in multiple generations per year. Fast reproduction makes this pest challenging to control.

Onion thrips, Thrips tabaci, are cosmopolitan insects — they are pests on a wide variety of plants such as onion, leek, garlic, cabbage, tomatoes, cucumber, alfalfa, small grain, and many more. Adult onion thrips are about 0.06-inch to 0.08-inch long, thin, and pale yellow to brown color. However, their lifecycle is estimated to take 20 to 40 days, depending on temperatures and seasonal conditions.

Aphids (family Aphididae) — 2.4 %

The Cannabis aphid, Phorodon cannabis, is an aphid that only feeds on hemp plants. Cannabis aphids (Figure 11) are small insects about 0.07-inch to 0.1-inch long, and they can vary in shades of green to brown.

These aphids cause injury by feeding on the hemp plants. However, other damage can occur from the transmission of disease during the feeding. Additionally, aphids secrete honeydew, which can become a target for things like sooty mold, further deteriorating the health of the plant.

Potato Leafhopper (family Cicadellidae) — 2.2 %

The potato leafhopper adult, Empoasca fabae, is bright lime green with an elongated body and it is about 0.12-inch long (Figure 12). Adults and nymphs feed with piercing-sucking mouthparts that result in white-flecked injury (stippling) on the foliage. Leaf tips become yellow and scorched. This pest also feeds on a wide host range, such as soybean, clovers, alfalfa, potato, apples, beans, and weeds (pigweed and shepherd's purse).

Tarnished Plant Bug (family Miridae) — 1.9%

The tarnished plant bug, Lygus lineolaris, was the most encountered species within this family. They have a large host plant range in the U.S., including hemp. This insect is about 0.2-inch long and has variable markings that vary from pale yellow, brown, green, and reddish hues. However, all have a light “V” shape on the back.

The adults lay eggs directly on vegetation. They feed with their sucking/piercing mouthparts and extract fluids from the plant. Their feeding can cause direct injury to the plant, including yellowing of terminal growth, necrosis near the feeding site, plant growth disruption, and deformed seeds. Also, they can transmit diseases to the hemp plant during feeding.

Eurasian Hemp Borer (family Tortricidae)

The Eurasian hemp borer, Grapholita delineana, a known invasive pest of hemp, was observed for the first time in Nebraska in 2020 at the WCREEC field. During the summer of 2020, the peak of the adult flight in our field was recorded in early July, while larvae were found one month later in August (Figure 14).

The Eurasian hemp borer is a moth with a wingspan of around 0.5-inch wide. The moths have white lines on brown and gray wings (Figure 15). Older caterpillars have a reddish-orange coloration (Figure 16).

Larvae (Figure 17) are the damaging stage of this pest. Young larvae bore into the buds and plant stem and branches, which can cause wilting, swelling, and eventually death of the hemp plant. Additionally, plants can be stunted or even split due to the damage to the stem. Time to scout plants is from spring until harvest. This pest can also reproduce in feral cannabis (“ditch weed”). Therefore, monitoring and management of feral cannabis patches surrounding the cultivated hemp should be considered.

Conclusions

A diversity of both beneficial and potentially harmful arthropods has been found in industrial hemp grown in west-central Nebraska. Of particular interest is the presence of potential pests, such as Eurasian hemp borer, thrips, aphids, leafhoppers and tarnished plant bugs. However, an abundant community of beneficial natural enemies is also present in hemp fields and is contributing to the biological control of these pests. We encourage hemp growers across the state to regularly scout their fields and any nearby patches of feral cannabis, mainly looking for the presence and crop damage from Eurasian hemp borers. Please reach out to your local extension office with any questions.

For more information about the Nebraska Department of Agriculture, please visit their website.