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Aphid Predator (Coleoptera: Coccinellidae)

Scymnus frontalis

Two-spot hairy ladybird

On this page: Identification Biological Control & Distribution

Identification

Scymnus frontalis is a small coccinellid with a body length of only 2.6-3.2 mm. The elytra are black and covered with fine hairs. They usually have two elongate dull red spots towards the front of the elytra which do not extend to the margin of the elytra (cf. Scymnus interruptus which has two orange-brown spots on the elytra which reach the edge of the elytra and then extend along the edge towards the border with the pronotum). There is also a form with four red spots. The pronotum is completely black in the female, but has reddish brown margins in the male. The Scymnus frontalis head is black in the female and brown in the male (cf. Scymnus schmidti which has the head of both sexes reddish-brown). The mouthparts and legs are brown.

The Scymnus frontalis larva is covered with white waxy tufts. Unfortunately the larvae of the different Scymnus are not distinguishable (at least we can find no detailed morphological descriptions of the larvae of the various species under the wax), so our pictures of the larvae above and below that we have found predating aphids may be of any of the UK Scymnus species.

Biological control & Distribution

Scymnus frontalis was imported from Turkey into the United States as a potential predator of the Russian wheat aphid, Diuraphis noxius (Naranjo et al. (1990). Diuraphis noxius lives inside characteristically rolled leaves, refugia which both larvae and adults of Scymnus are able to penetrate. However, the temperature threshold for development of Scymnus frontalis was about 5-10°C higher than that of Diuraphis noxius. Subsequent work by Gibson et al. (1992) to evaluate its potential showed that Russian wheat aphid was a very suitable prey for Scymnus frontalis, which showed a slight preference for Russian wheat aphid over the English grain aphid (Sitobion avenae). Scymnus frontalis was subsequently released in the USA and became established, but it is unclear how effective the control has been.

In Britain we have only found Scymnus adults on one occasion (see pictures above), but have found Scymnus larvae quite frequently. Some observations have been from coniferous woodland where the most likely species are Scymnus nigrinus (adult has upper surface completely black, with the legs also completely black) and Scymnus suturalis (adult has mainly brown elytra, but with black along the front margin and the suture). The larva below was found feeding on balsam woolly adelgid (Adelges piceae).

We have also found Scymnus larvae feeding on Pineus strobi on Weymouth pine (Pinus strobus, see picture below).

Outside of coniferous woodland, there are another nine species of Scymnus found in Britain, and the larvae shown below may belong to any of thereof. The picture below shows a Scymnus larvae predating Aphis grossulariae on willowherb (Epilobium) despite the colony being ant attended.

The white waxy tufts of Scymnus have been shown to provide significant defense against ant aggression (Schwartzberg et al., 2010). Another aphid which is invariably ant attended is Aphis hypochoeridis which lives under ant-tenting on the root collar, the underside of radical leaves and up the lower part of the stem of cat's ear (Hypochaeris radicata).

The picture above shows a Scymnus larva feeding on Hypochaeris radicata.

Acknowledgements

We especially thank the UK Forestry Commission Bedgebury Pinetum for their kind assistance, and permission to sample.

For coccinellid identification we have used Hackston for the key characteristics, together with the latest Wikipediaaccount for each species. For aphids we have made provisional identifications from photos of living specimens, along with host plant identity using 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

  • Gibson, R.L. et al. (1992). Life history and development of Scymnus frontalis (Fabricius) (Coleoptera: Coccinellidae) on four species of aphids. Kansas Entomological Society 65(4), 410-415. Full text

  • Naranjo, S.E. et al. (1990). Development, survival and reproduction of Scymnus frontalis (Coleoptera: Coccinellidae), an imported predator of Russian wheat aphid, at four fluctuating temperatures. Annals of the Entomological Society of America 83(3), 527-531. Full text

  • Schwartzberg, E.G. et al. (2010). Wax structures of Scymnus louisiana attenuate aggression from aphid-tending ants. Chemical Ecology 39(4), 1309-1314. Full text