More than you (probably) ever wanted to know about Lygus

Namyatova et al (2022) reviewed five Palearctic Lygus species: L. gemellatus, L. pratensis, L. punctatus, L. rugulipennis,L. wagneri. This document considers four species on the UK Checklist: L. pratensis, L. punctatus, L. rugulipennis, L. wagneri; the fifth UK species, L. maritimus, was not examined by Namyatova et al but is covered by Nau (2004). Namyatova et al conclude that:

1. The currently recognized Lygus species are poorly supported by DNA studies or are non-monophyletic, thus needing reclassification (L. gemellatus, L. pratensis and L. wagneri appear to be synonymous, as do L. punctatusand L. rugulipennis).

2. However, morphometric analysis is generally a reliable way of separating the currently recognized species. 

3. Until a taxonomic revision of this genus is published, the existing species must stand and can be separated (with some difficulty) based on morphology. 

The morphological characters used by Namyatova et al are: 

• punctation on clavus and corium

• vesical spicule shape

• presence or absence of teeth on the right side of the small lobe of the vesica

• colour pattern

Due to the difficulty of examining the vesica, only punctation on clavus and corium and colour patterns are used in this document. (N.B. All Lygus species have antennae light/light+dark; c.f. Orthops, all dark). In general, the species descriptions given by Namyatova et al (2022) agree with those in Nau (2004). 

Lygus pratensis 

Males 5.1-7.0mm, females 5.1-6.6mm. Scutellum usually with single brown mark or stripe or the medial anterior part. Hemelytra with short, dense setae, often appearing shiny. Punctures on middle part of hemelytra evenly spaced, distance between them equal or less than puncture diameter; anterior half of clavus with some punctures at a distance longer than puncture diameter; punctures on posterior half of clavus evenly spaced and close to each other, but distinctly separate from each other. 

Lygus punctatus

Males 5.9-7.2mm, females 5.1-6.7mm. Scutellum either with two stripes or W-shaped mark on the medial anterior part. Hemelytra with short, dense setae, often appearing shiny. Punctures on middle part of hemelytra and on anterior and posterior half of clavus further apart than the puncture diameter. 

Lygus rugulipennis 

Males 4.9-5.9mm, females 4.5-6.4mm. Scutellum either with two stripes or W-shaped mark on the medial anterior part. Hemelytra covered with dense flat setae, its surface appearing dull and matte. Punctures on hemelytra and clavus very small and almost touching each other;

Lygus wagneri

Males 5.7–6.8, females 5.3-6.5mm. Scutellum either with two stripes or W-shaped mark on the medial anterior part. Hemelytra with sparse setae, often appearing shiny. Punctures on middle part of hemelytra evenly spaced, distance between them equal or less than puncture diameter; punctures on anterior half of clavus spaced further apart than the puncture diameter; punctures on posterior half of clavus evenly spaced and close to each other, but distinctly separate.

Lygus maritimus (from Nau, 2004) 

Punctures on apical region of the corium several diameters apart in each direction. 

References: 

Namyatova, A. A., Tyts, V. D., & Bolshakova, D. S. (2022) Identification and delimitation of the trans-Palearctic Lygus species (Insecta: Heteroptera: Miridae) using integrative approach. Insect Systematics & Evolution, 1, 1-47.https://doi.org/10.1163/1876312X-bja10035

and:

Nau, B. (2004) The Lygus situation. Newsletter of the UK Heteroptera Recording Schemes 3, 11.https://www.britishbugs.org.uk/HetNews/Issue%203_Spring%202004_422Kb.pdf