The Kudzu Bug and The Search for Its Parasitoids

The kudzu bug, Megacopta cribraria (Hemiptera: Plataspidae) (Figure 1), is a shield bug that is native to Asia. This insect receives its name because its main host plant is kudzu, Pueraria montana (Fabaceae). However, kudzu bugs also feed on soybeans and other legumes.

Figure 1. Adult kudzu bug on kudzu plant (Photo: A. Ritchey)

Problems

Kudzu bugs feeding on soybeans and other legumes can cause economic loss to farmers. This has occurred in Georgia, North Carolina, and other states in the South, although in later years, populations of kudzu bugs have decreased. In Kentucky, kudzu populations do not reach threatening levels. During the last 5 years, kudzu bugs were not found in soybean plants while scouting for other pests, except in 2020 when a couple of kudzu bugs were found in soybean fields in at least five different counties (Lyon, Caldwell, Trigg, Todd, and Logan).

Another problem with kudzu bugs is that they invade homes to overwinter. During the winter months, kudzu bugs seek shelter in or around homes. They enter houses through small cracks or crevices that might be in walls, window screens, or door frames. Kudzu bugs release an aggregation pheromone that attracts more bugs. Once in a building, kudzu bugs can cause allergies, and stain walls, fabrics, and other materials. Kudzu bugs release a secretion with a foul-smell that can irritate, if it contacts your skin

Life Cycle of the Kudzu Bug

After the overwinter period, adults become active, fly away, feed on kudzu plants or wisteria, and mate. Eggs are laid around late May or early June. Kudzu bug eggs are laid in two side-by-side rows with approximately eighteen eggs in each row (Figure 2). Immediately after hatching, the first instar nymphs (Figure 3) consume an endosymbiotic bacterium located underneath the eggs; they do this because the bacterium provides them with enzymes to digest the plant where the eggs are laid. There are five nymphal stages before they finally become an adult. The nymphs come in a few different colors: pale orange, olive green, or light brown. After 6 to 8 weeks, these nymphs will develop into adult kudzu bugs. Kudzu bugs in Kentucky, have a bivoltine life cycle, which means that they have two generations per year. So, this whole process will repeat again within the year.

Figure 2. Kudzu bug eggs on kudzu leaf (Photo: A. Ritchey)

Figure 3. Newly hatched kudzu nymphs on kudzu leaf (Photo: A. Ritchey)

Management

Populations of kudzu bugs are very low in Kentucky soybeans, and research conducted in other states has shown that larger populations of kudzu bugs are necessary to cause economic damage in soybeans. There are some ways to go about managing kudzu bugs in soybeans and as structural pests in winter.

To reduce the presence of kudzu bugs in soybean fields, there are some possible options:

  • Remove the kudzu bug’s most important food sources from the edges of soybean fields; these plants include kudzu and wisteria.
  • Enhance biological management.  Native parasitoid wasps were detected in kudzu eggs, as well as nonnative parasitoids, such as Paratelenomus saccharalis (Hymenoptera: Platygastridae).  These species can cause up to 50% egg parasitism in Georgia. In addition, Beauveria bassiana, an entomopathogenic fungus, has been affecting kudzu bugs and causing population reductions.
  • Chemical control has been used in other states when populations are high in bean crops, but it should be used judiciously. There are multiple pyrethroids commonly used for their control, including permethrin, bifenthrin, or lambda cyhalothrin.

For control of kudzu bugs in human structures (barns, houses, etc.), use a vacuum to contain the bugs. Freeze them in a bag or submerge them in soapy water to kill them. Dispose of the insects off-site.

Searching For Parasitoids in KY (Research Findings)

The objective of my project was to determine percentages of parasitism on egg clusters. To do this, egg clusters were collected from kudzu plants and brought to the laboratory, placed in Petri dishes, and percentages of eggs hatched and parasitism were monitored. All egg clusters were found in the petiole or stems of kudzu plants. Our results are shown in Table 1.

Table 1. Mean number (±SEM) of eggs per cluster (n=7), numbers of eggs hatched and unhatched eggs, and their respective percentages.

Nº eggs/clusterNº eggs hatchedPercentages of eggs hatchedNº eggs unhatchedPercentages of eggs unhatched
18 ± 2.0311.43± 2.267.9± 12.7%6.57± 2.732.1± 12.7%

From a total of 7 egg clusters collected during early May, we found that the average egg cluster had 18 eggs. In total, the hatch rate was near 68%, ranging from 14% to 100%. Parasitoids were not found in any of the eggs. Percentages of eggs unhatched were 32%.

A possible reason why some eggs did not hatch was that parasitoids may have tried to lay eggs in them, killing the kudzu bug, but the parasitoids also didn’t hatch. Native parasitoids may not develop in the eggs of this invasive species.


By Avery Ritchey, 11th Grade High School Student at Caldwell County High School in Princeton, KY; and working at the UK-Research and Education Center under Raul T. Villanueva, Entomology Extension Specialist.

Posted in Grains
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