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Identification & Distribution

Adult apterae of Schizaphis holci (see first picture below) are greenish yellow or pale yellow usually with a faint darker green spinal stripe. The apical rostral segment (RIV+V) is 0.8-1.0 times the length of segment II of the hind tarsus (cf. Schizaphis agrostis which has the apical rostral segment 0.75-0.88 times the length of segment II of the hind tarsus). The siphunculi are pale with dark tips (cf. Metopolophium dirhodum,  which has the siphunculi completely pale). The siphunculi are 1.25-1.4 times the length of the pale cauda (cf. Schizaphis agrostis which has the siphunculi 1.3-1.5 times the length of the cauda). The body length of adult Schizaphis holci apterae is 1.6-1.9 mm.

The alates of Schizaphis holci (see second picture above) are brownish-green in colour with black-tipped siphunculi. The pictures below show an adult aptera and an alate in alcohol.

Schizaphis holci is found on the undersides of leaves of Yorkshire fog (Holcus lanatus) and creeping soft grass (Holcus mollis). Colonies are usually attended by ants. Oviparae and apterous males develop in late September and October. In the UK Stroyan (1984)  describes this species as rare but perhaps overlooked.

 

Biology & Ecology

Life cycle

Until recently Schizaphis holci (and Schizaphis agrostis) have been considered rare in the UK (Kati et al., 2013 ). However, suction trap catches suggest they have become more common since around 2000.

The overwintering eggs hatch in April/May to give the first instar nymphs (see picture below).

The younger instars often live inside the rolled new grass shoots where they are largely protected from weather and natural enemies.

Colonies develop on Holcus grass in May, and by June quite large colonies may have developed on a single grass leaf.

All the colonies we found were in early June - so far we have found none later in the year. Suction trap catches show a peak of alate females in late May/early June (Kati et al., 2013 ). Numbers then decline with sexuales produced in late September and October.

 

Ant attendance

Schizaphis holci are often, but not always, attended by ants. Most of the colonies we found in East Sussex were attended by Lasius niger.

There was usually only one ant attending per colony.

None of the aphids found by Kati et al. (2013)  were attended by ants.

 

Natural enemies

Schizaphis holci colonies in Sussex have been attacked by at least two species of braconid parasites (so far unidentified), one producing a brown mummy and the other a black mummy (see pictures below).

Known parasitoids of Schizaphis species include Lysiphlebus testaceipes (most likely the brown mummy above), Aphelinus asychis and Aphelinus varipes, as well as 7 Aphidius species (CABI, 2018 ).

The black mummy was probably produced by an Aphelinus species. Japoshvili & Abrantes (2006)  also listed Aphelinus abdominalis and Aphelinus mali as Schizaphis parasitoids.

 

Other aphids on the same host

Blackman & Eastop list 23 species of aphid  as feeding on Yorkshire fog (Holcus lanatus) and creeping soft grass (Holcus mollis) worldwide, and provide formal identification keys.

Of those aphid species, Baker (2015)  lists 22 as occurring in Britain: Anoecia corni,  Atheroides serrulatus, Cryptaphis poae, Diuraphis frequens, Diuraphis holci, Forda formicaria,  Geoica setulosa, Geoica utricularia, Hyalopteroides humilis,  Laingia psammae,  Melanaphis pyraria,  Metopolophium dirhodum,  Metopolophium festucae, Rhopalosiphum nymphaeae,  Rhopalosiphum oxyacanthae,  Rhopalosiphum padi,  Schizaphis holci, Sipha glyceriae, Sipha maydis,  Sitobion avenae,  Sitobion fragariae  and Tetraneura ulmi. 

 

Damage and control

Damage

Feeding by Schizaphis holci has a phytotoxic effect, and leaves hosting a colony turn a characteristic pinky orange-brown (see picture below) and soon die.

Such leaf discoloration in May or June is usually the best indicator that the aphid is present.

Are they a threat to crops

The increasing numbers of winged (alate) aphids morphologically resembling the greenbug (Schizaphis graminum ) caught in 12.2 meter high suction-trap samples of the Rothamsted Insect Survey (RIS) prompted a study by Kati et al. (2013)  to establish their identity. The results from the host-choice and life history studies performed on the Schizaphis species found in the UK on Holcus lanatus suggested that the species involved was actually Schizaphis holci and hence unlikely to be a threat to crops.

Morphometric characteristics of alatae caught in suction traps indicated that the suction-trapped alatae were Schizaphis agrostis or Schizaphis holci, with no Schizaphis graminum being found. However, two UK specimens had identical cytochrome c oxidase subunit I (COI) sequence to the US sorghum-adapted form of Schizaphis graminum, suggesting this form of Schizaphis graminum may be present in the UK. - However those suction-trapped alatae may have been carried by the jet-stream air currents from North America. There are no records of Schizaphis graminum from field crops in northern Europe.

Acknowledgements

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

  • Japoshvili, G. & Abrantes, I. (2006). Aphelinus species (Hymenoptera: Aphelinidae) from the Iberian Peninsula, with the description of one new species from Portugal. Journal of Natural History 40 (13-14), 855-862. Full text 

  • Kati, A. et al. (2013). Identity of Schizaphis species (Hemiptera: Aphididae) in the United Kingdom: are they a threat to crops?. Bulletin of Entomological Research 103, 425440. Full text