Lygus Bugs

Lots of insects bug plants, but “plant bugs” (Order Hemiptera; Family Miridae) cause extensive damage in the home garden as well as commercial agriculture. In fact, more than 50% of all cultivated plants grown in the U.S. are host plants for the tarnished plant bug (Lygus lineolaris).

In the West, we are (un)lucky enough to have at least three species:

Tarnished Plant Bug – Lygus lineolaris P.d.B

Western Tarnished Plant Bug – Lygus hesperus K.

Pale Legume Bug – Lygus elisus V.D.

Damage

Lygus bugs have a long, beak-like mouthpart that works like a syringe; salivary fluid is injected into plant tissues, and liquefied food returns up. The saliva can transmit disease, and research suggests that stink bugs, plant bugs, and seed bugs may be as equally important as vectors of plant diseases as aphids or leafhoppers, though they are much less studied.
Common hosts include alfalfa, strawberries, tree nuts, dry beans, apples, pears, conifer seedlings, corn, cotton, vegetables (fresh and seed crops), and ornamentals. Symptoms vary by crop but include “cat-facing”(strawberries), “blasting” (canola), “blackheart” (celery), pitting, dimpling, flower deformation, gall formation, and tip dieback.
Damage symptoms on flower petals, celery, and beans
Damage symptoms on flower petals, celery, and beans. All photos used with permission

Identification & Lifecycle

The 3 species we have here in the PNW are similar in appearance. Adults have variable color depending on species and age and overwintered adults tend to be darker. There is usually a pale Y or V shape on the scutellum (the triangular area outlined in sketches above). Nymphs look similar to aphids but do not have the two extending tubes at the tip of the abdomen, as aphids do.

3 species of PNW lygus bugs (C) J. Antwi

Adult bugs overwinter in sheltered or weedy areas. They become active in early April, and begin laying eggs at the base of leaf petioles. Nymphs emerge about 10 days later and develop through five stages of maturity; stage 5 nymphs have evident wing pads. The life cycle takes 30-45 days, and there are multiple generations per year.

Monitoring

Depending on the crop, drop cloth or sweep net sampling can provide a good estimate of Lygus activity within a field. Lygus move quickly, so be aware of approach (keep shadows behind you). Conduct a series of 10, 180° sweeps as you walk through the field. In each series of sweeps, record the number of nymphs and adults found. Sweep netting tends to underestimate nymphs, but monitoring nymphs is important because as the population ages, it is more likely that movement into other crops will occur.

Sticky traps placed every 2 ft. can be used to detect areas where Lygus are aggregated. Beat trays in orchards can be used, but may not be indicative of actual pressure within tree nut clusters2. Because Lygus can be a greenhouse pest, it is possible that transplants are sources of infestation.

Management

Cultural control:Many pests have associations with weed hosts, but Lygus is especially linked. In fact, if excessive rainfall causes a flush of early weeds, Lygus populations will increase2, and as the weeds dry down, movement into crops is common. Weedy hosts like kochia, hoary cress, pepperweed, wild radish and mustards, and fleabane should be monitored.

Biological control: A number of natural enemies attack Lygus eggs and nymphs. Crab spiders, big-eyed bugs, and damsel bugs are common predators. A native braconid wasp is highly effective at parasitizing nymphs, but control will lag because nymphs continue to feed.

Chemical control: Various products are listed in the PNW Insect Management Handbook, search by crop. A recent efficacy trial in seed alfalfa suggests that lower-risk insecticides like sulfoxaflor and flonicamid can reduce Lygus activity during the bloom period3. Make note of adjacent crop hosts and use border treatments as necessary to reduce intercrop movement.

Further Reading

Antwi, J., Rondon, S., et al. Taking a closer look at Lygus bugs in the PNW. PNWIMC 2016 Proceedings

1Schuh, R.T. On-line Systematic Catalog of Plant Bugs (Insecta: Heteroptera: Miridae). http://research.amnh.org/pbi/catalog/; 2P.Goodell and W. Bentley “Lygus Bugs” UCANR Pistachio crop guide ; 3 J.D. Barbour, U of Idaho Ext. Report from 2018 winter crop school meeting; 4S. Mueller, C. Summers, and P. Goodell. A field key to common species in the San Joaquin Valley of California.UCANR Pub. no. 8104, 12 pp.