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Identification & Distribution

The ten-spot ladybird, Adalia decempunctata is a rather small almost round ladybird with body length 3.5-4.5 mm. The elytral colour and pattern is very variable, but there are three main forms all of which occur commonly: The 'typical' form ('decempunctata', see first picture below) has a red, orange or brown ground colour and between 0 and 12 distinct black elytral spots. The chequered form (decempustulatus, see second picture below) has a buff, beige or light brown ground colour overlaid with a dark grid-like pattern. The melanic form (bimaculata, see third picture below) has a dark brown or black ground colour with two red, orange or yellow shoulder flashes. In freshly hatched Adalia decempunctata the elytra are pale brown. The colour of the pronotum varies between white with five darker spots, and black with narrow white edges. The head is black basally and pale anteriorly, sometimes with contrasting spots. The ten-spot ladybird legs are orange, and its abdomen underside is yellow or orange.

Second image above copyright Boris Loboda under a under a CC BY-NC-ND 3.0 creative commons licence.
fourth image above copyright Gilles San Martin under a Creative Commons Attribution-Share Alike 2.0 Generic license.

The larva of Adalia decempunctata is mainly grey, but with pale dorsal areas on the thoracic segments and a light brown head. It also has a pair of conspicuous pale orange to whitish dorsolateral tubercles on the first abdominal segment, a pair of mid-dorsal pale tubercles on abdominal segment IV and partially or completely pale outermost lateral tubercles on most abdominal segments (cf Adalia bipunctata which has the latter tubercles dark). Adalia decempunctata also has fine hairs projecting from the tubercles.

The ten-spot ladybird mainly feeds on aphids, and occasionally scale insects and mites. It also takes pollen and nectar. It is a primarily an arboreal species found especially on broad-leaved trees, but may also be found on conifers, in hedgerows and on low-growing herbs such as stinging nettles. Adalia decempunctata is found throughout the Palaearctic region in Europe, North Africa, European Russia, the Caucasus and most of Western Asia.

 

Biological Control of Aphids

Aphid control in the field

The ten spot ladybird has not been used for augmentative releases, but has been found to be an important predator in some semi-natural field situations. Like the two-spot ladybird, the ten-spot ladybird can be found in any vegetation type, but seems to show a preference for trees, shrubs and bushes.

For example Cecilio & Ilharco (1997) conducted field studies on the walnut aphid, Chromaphis juglandicola, and its natural enemies in Portugal. The most important predators in walnut orchards were the aphidophagous coccinellids Adalia decempunctata and Oenopia conglobata. These could occur with relatively low numbers of aphids per leaf.

Leather & Kidd (1998) reported that both Adalia decempunctata and Coccinella septempunctata have been found feeding on the green spruce aphid, Elatobium abietinum, in addition to the most commonly identified predator Aphidecta obliterata. However, it was thought that the ten-spot ladybird probably preferred deciduous trees, which would reduce its value against the green spruce aphid.

Borg (1919) and Borg (1922) reported seven species of coccinellids including Adalia decempunctata preying on pest scale insects in the Maltese Islands.

Below are a few examples of where we have found ten-spot ladybird predating aphids in southern England.

Predation of Rhopalosiphum padi

The bird cherry-oat aphid, Rhopalosiphum padi, lives in leaf galls of bird cherry (Prunus padus) in spring, where it is subject to predation by a number of predators including the ten-spot ladybird (see picture below).

Predation of Periphyllus testudinaceus

There tend to be rather few predators in evidence around colonies of the common periphyllus aphid (Periphyllus testudinaceus, see picture below) most likely because this aphid is usually strongly ant-attended.

We have, however, found adults of two species of coccinellids, Adalia decempunctata and Calvia quattuordecimguttata, feeding on less closely-attended colonies.

The picture above shows an adult Adalia decempunctata of the melanic form (bimaculata) which was feeding on the common periphyllus aphid.

 

Biology & Ecology

Colour forms

In central Europe Adalia decempunctata occurs in three main morphs: spotted (form typica), chequered (form decempustulus) and melanic (form bimaculata). Honek et al. (2005) looked at the temporal stability of morph frequency in the Czech Republic where geographic variation in morph frequency is low. Morph proportions did not change seasonally, nor did they differ significantly among collections made on different plants. However, there were long-term changes in morph proportions over 12 years (19762004). The proportions of spotted (mean over the years 29.4%), chequered (42.2%) and melanic (21.3%) morphs varied between years. There was a trend toward an increasing proportion of the spotted form in the 2000s compared to the 1970s and 1980s. In Great Britain Brakefield & Lees (1987) found proportions of spotted, chequered and dark forms in central England to be 60.9%, 27.8% and 11.3%.

Searching behaviour

Dixon (1958) looked at the escape responses shown by certain aphids to the presence of Adalia decempunctata. He found that larvae which had encountered the toxic aphid Hyalopterus pruni (at least those that had penetrated the aphid cuticle) subsequently rejected this aphid.

Dixon (1959) then carried out an extensive experimental study of the searching behaviour of the ten-spot ladybird (Adalia decempunctata). Healthy eggs in a batch hatched successively over a period of several hours, and larvae did not eat other larvae hatching soon after them. They did, however, eat eggs which failed to hatch once the majority of the batch had done so - few of these would anyway have hatched successfully. Searching larvae were negatively geotactic and positively phototactic and they spent most time searching the rim and veins. Having captured one aphid, a first-instar coccinellid larva's chance of capturing a second aphid was greater than was its chance of capturing the first. As larvae increased in age their efficiency in capturing the aphids increased, at least when the prey was Microlophium carnosum. Larvae were more efficient in capturing young aphids.

The number of aphids required to be provided daily to the larvae increases with each successive instar. With increasing aphid population density, there was an increase in the rate of development and percentage survival of larvae. There were signs of satiety when approximately fifteen third-instar aphids were provided each day. In each successive instar, unfed larvae were capable of covering a greater distance before succumbing to starvation. Larvae which consumed very few aphids each day traversed an area greater than that traversed by those which received rather more. For survival of 50% of the individuals, first-instar larvae required a prey population density many times greater than that required by fourth-instar larvae, dependent upon the age distribution of the aphid population which is being attacked. Adults were less active and laid more eggs when well fed. In the field, egg batches of Adalia decempunctata were usually found either on leaves infested with aphids or close to infested ones.

Acknowledgements

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

  • Borg, P. (1919). The Scale Insects of the Maltese Islands. Malta Herald Office, Malta.

  • Borg, P. (1922). Cultivation and Diseases of Fruit Trees in the Maltese Islands. Government Printing Press, Valletta (MT). Full text

  • Brakefield, P.M. & Lees, D.R. (1987). Melanism in Adalia ladybirds and declining air pollution in Birmingham. Heredity 59, 273277. Full text

  • Cecilio, A. & Ilharco, F. (1997). The control of walnut aphid, Chromaphis juglandicola (Homoptera: Aphidoidea) in walnut orchards in Portugal. Acta Horticulturae 442, 399-406. Abstract

  • Dixon, A. F. G. (1958). The escape responses shown by certain aphids to the presence of the coccinellid Adalia decempunctata (L.). Transactions of the Royal Entomological Society of London 110, 319334. Abstract

  • Dixon, A.F.G. (1959). An experimental study of the searching behaviour of the predatory coccinellid beetle Adalia decempunctata (L.). Journal of Animal Ecology 28(2), 259-281. Full text

  • Honek et al. (2005). Temporal stability of morph frequency in central European populations of Adalia bipunctata and A. decempunctata (Coleoptera: Coccinellidae). European Journal of Entomology 102, 437442. Full text

  • Leather, S.R. & Kidd, N.A.C. (1998). The quantitative impact of natural enemies and the prospect for biological control. pp. 61-70. In:The Green Spruce Aphid in Western Europe: Ecology, status, impacts and prospects for management. Ed. Day, K.R. et al. Forestry Commission Technical Paper 24. Forestry Commission, Edinburgh.