Plagiognathus arbustorum

Identification & Distribution

The ground colour of adult Plagiognathus arbustorum varies from pale olive-green to light red-brown to almost black (see pictures), but the head and pronotum are usually dark. The dorsal surface of the thorax and forewings is covered in dark hairs. The green larvae can be distinguished when in the second and subsequent instars by the dark brown or black line on the front of the hind femora whilst the basal antennal segment is black; in the later instars additional dark markings are present.

Second image (dark form), Copyright S. Rae under a Creative Commons Attribution 2.0 Generic License

Plagiognathus arbustorum is known to be a plant feeder, especially on nettles (Urtica dioica), and a predator of small insects. The eggs are laid in the autumn and hatch in the following May. It is found in North America, most of Europe, and east to Siberia and Central Asia.

Biology & Ecology

Plagiognathus arbustorum in some situations is a beneficial predator. We have found Plagiognathus arbustorum predating Cavariella aphids on hogweed in southern England. Kelton (1982) recorded it preying on aphids on hazel. It has also been recorded preying on Acyrthosiphon pisum on broom. Davis (2001) found it was the commonest of the univoltine mirid bugs on nettle.

Biological control of Aphids

Plagiognathus arbustorum has not, as far as we know, been used for biological control of aphids, either in terms of encouraging it by environmental modification or augmentative releases. This is probably because, rather than being a beneficial aphid predator, it can be a phytophagous pest in some crops. For example, in strawberries it is the most common pest capsid bug on June-bearing and mid-season strawberries. Capsid bugs cause damage by feeding on the achenes of developing fruits, resulting in deformed or 'cat-faced' fruit which is often unmarketable (Cross et al., 2001).

Taksdal & Sorum (1971) showed capsids, especially Plagiognathus arbustorum, to be the main cause of strawberry fruit malformation. Plagiognathus oviposited in the autumn at the base of the outer leaf stalks of the strawberry plants. The eggs hatched at the beginning of the flowering period, and the first adults appeared shortly before first harvest. In cage experiments 4 larvae per inflorescence caused 94% fruit malformation. The symptoms from feeding in open flowers were strikingly different from those caused by feeding on young fruits. In laboratory preference tests, adult bugs preferred flowers and fruits and were not observed feeding on leaves. Another mirid bug, the European tarnished plant bug, Lygus rugulipennis (see picture below), was the second most important species.

Copyright S. Rae under a Creative Commons Attribution 2.0 Generic License.

Lygus rugulipennis caused severe fruit damage to strawberries in cage experiments. In preference tests it strongly preferred flowers and flower buds and oviposited in the calyx or flower stalk.

Taksdal (1971) demonstrated a reduction of strawberry fruit malformation by chemical control of Plagiognathus arbustorum. One spraying just before flowering with dimethoate, fenitrothion, fenthion, malathion, methomyl or parathion reduced fruit malformation to an average of 8.6% (from 71.5 to 96.0%) in unsprayed plots. Azinphos-methyl was unsatisfactory, as was spraying with dimethoate two weeks before the first flowers opened. The sprays had no significant effect on numbers of larvae of Dolycoris baccarum or Nabidae (damsel bugs). No pesticide residues were recorded in fruits taken at or just before the first picking.

Acknowledgements We especially thank Sandy Rae for the images on this page. For the mirid bugs we have used Southwood & Leston (1959) and British Bugs to aid in identification and for the key characteristics. For aphids we have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks

References Cross, J.V. et al. (2001). Review: Natural enemies and biocontrol of pests of strawberry in northern and central Europe. Biocontrol Science and Technology 11, 165-216. Abstract Davis, B.N.K. (2001). The Hemiptera and Coleoptera of stinging nettle (Urtica dioica L.) in East Anglia. Journal of Applied Ecology 10(1), 213. Abstract Kelton, L.A. (1982). New and additional records of Palearctic Phylus Hahn and Plagiognathus Fieber in North America (Heteroptera: Miridae). Canadian Entomologist 114(12), 1127-1128. Abstract Taksdal, G. & Sorum, O. (1971). Capsids (Heteroptera, Miridae) in strawberries, and their influence on fruit malformation. Journal of Horticultural Science 46(1), 43-50. Abstract Taksdal, G. (1971). Reduction of strawberry fruit malformation by chemical control of Plagiognathus arbustorum Fabr. (Heteroptera, Miridae). Journal of Horticultural Science 46(1), 51-54. Abstract