Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Aphid Predator (Coleoptera: Coccinellidae)
Ten-spot ladybirdOn this page: Identification & Distribution Biological Control of Aphids: Aphid control in the field Predation of Rhopalosiphum padi Biology & Ecology: Colour forms Searching behaviour
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. 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.
Second image above copyright Boris Loboda under a under a CC BY-NC-ND 3.0 creative commons licence.
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
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 (1976-2004). 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%.
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.