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Aphid Predator (Coleoptera: Coccinellidae)Chilocorus bipustulatusHeather ladybird, Armoured-scale ladybeetleOn this page: Identification & Distribution Biological Control of Scales & Aphids Classical biological control Augmentative release Suppliers Scale & aphid control in the field BiologyIdentification & DistributionThe heather ladybird (Chilocorus bipustulatus) is a rather small coccinellid with a body length of 3-4 mm. The elytra are shiny dark reddish-brown to black, usually with a total of 6 red spots in a line across the middle of the elytra (see first picture below). Spot fusions may reduce this to 4 or 2 red spots. The pronotum and head are black, as are the legs. There is a distinct rim around the edge of the elytra.
Second and third images above copyright Gilles San Martin under a Creative Commons Attribution-Share Alike 2.0 License. The fourth instar larva of Chilocorus bipustulatus (see second picture above) is mostly blackish brown apart from a diagnostic pale first abdominal segment. Each thoracic and abdominal segment bears six long spines which give rise to hairs with extensive side branching. The spines are black except for those on the first abdominal segment which are pale. The pupa of Chilocorus bipustulatus (see third picture above) is shiny black with numerous hairs. The old larval skin remains around the lower part of the pupa. Chilocorus bipustulatus seems to favour xeric habitats - in Britain it is mainly found in heathland, coastal dunes and scrub; in mainland Europe it inhabits pine forests, orchards and stone quarries. It is a coccid (='scale insects') specialist, feeding especially on soft scales (Coccidae) and armoured scales (Diaspididae), as well as aphids when available. Chilocorus bipustulatus is found in most of the Palaearctic zone, and has been introduced for biological control purposes to tropical Africa, Hawaii and North America. Biological Control of Coccids & AphidsClassical biological controlHuffaker & Doutt (1965) describe the introduction and establishment of the European coccinellid Chilocorus bipustulatus in olive groves in California, USA to control scale insects. Kaufmann (1977) reviews the initial introduction of Chilocorus bipustulatus var. iranensis for the biological control of the date palm scale (Parlatoria blanchardi) in Niger, West Africa. The ladybird had established itself to a limited extent in the harsh environment of Agadez, a Sahelian oasis town of Niger in the Aar Mountain region of Northern Niger, and its surroundings. The ladybird population had 2 peaks a year: one preceding the dry season (April-June), and the other following the rains (July-August). In the cold period (November-February), the beetle was reproductively dormant but otherwise active, while in the dry period, total aestivation occurred following oocyte (="eggcell precursor") resorption. There were, therefore, a maximun of 6 generations of Chilocorus bipustulatus a year. Changes in microclimatic conditions were the main cause for the migration of this ladybeetle. A few years later Stansley (1984) described how the ladybird had become successfully established in the area, where it had become the major cause of mortality among adult females of the scale insect. This had resulted in significantly lower scale infestation of date palms in a test plot when compared to a control with no introduced ladybeetles. The coccinellids were able to reproduce year-round, but during the hot season were largely confined to natural refuges composed of dense stands of date palms. Dispersal and multiplication occurred primarily during the rainy season, toward the end of which the greatest suppression of scale populations was seen. Hattingh & Samways (1991) evaluated Chilocorus nigritus, Chilocorus bipustulatus and Chilocorus infernalis) as potential new biocontrol agents against red scale (Aonidiella aurantii) in South Africa. Red scale is one of the most damaging pests of citrus fruits. The scale gets its name from the circular reddish brown scale which it attaches to the plant (see picture below). The cover of the female is circular and the female lives under it for its entire life. Males pass through their larval stages under a smaller elongated cover, emerging as winged insects after four months.
Image copyright Dennis Navea, ControlBest, Bugwood.org under a Creative Commons Attribution-Noncommercial 3.0 License. Each life stage of Chilocorus had advantages and disadvantages for field introductions. A number of synthetic materials were tested as egg pads but without success, and introduction of eggs adhering to stiff paper cards was unsuccessful and impractical for all species. The most viable approach was to release the predators into populations of the non-target scale Asterolecanium on stands of giant bamboo (Dendrocalamus giganteus). The adult was the most suitable life stage for establishment followed by older larvae, then younger larvae, with the least suitable being the egg stage. Adults of the three species of Chilocorus were released on to scale-infested bamboo at two sites to evaluate the viability of such introductions and to compare their persistence at these sites. Chilocorus nigritus and Chilocorus infernalis (but presumably not Chilocorus bipustulatus) persisted at one release site through the winter and the hottest period of the summer. When the release sites were adjacent to citrus orchards, the coccinellid readily moved across to reduce population levels of the target prey, Aonidiella aurantii. Not all introductions of Chilocorus have been as successful as those mentioned above. Charles et al. (1995) describes the unsuccessful introduction of three species of Chilocorus (including Chilocorus bipustulatus) in New Zealand. Augmentative release & suppliersThere have been a few attempts at augmentative releases of Chilocorus bipustulatus to control scale insects. The most notable was that by Stathas (2005) who attempted to control three species of diaspidid scale insects which infested olives in Greece - the oleander scale (Aspidiotus nerii), the olive parlatoria scale (Parlatoria oleae) and the apple mussel scale (Lepidosaphes ulmi). Large-scale releases were made of two predatory coccinellids, Chilocorus bipustulatus and Rhyzobius lophanthae. The latter coccinellid species is known as the scale-eating ladybird and is native to Queensland and Southern Australia. It was introduced to the United States for classical biological control of the olive scale (Saissetia oleae) in 1895, and has since spread over half the country. Mass releases of the two chosen coccinellids were made in an olive grove in Southern Greece. Lepidosaphes ulmi populations were reduced, but not by the released coccinellids. They were controlled instead by local populations of the parasitic mite Hemisarcoptes. However, population reductions of Aspidiotus nerii and Parlatoria oleae were attributed to the released coccinellids. After predator releases Rhyzobius lophanthae built up higher populations than Chilocorus bipustulatus, but the author acknowledged that we cannot assume from this that Rhyzobius lophanthae is more efficient. Suppliers of Chilocorus species for augmentative releaseAs far as we know, Chilocorus bipustulatus is not available from any suppliers of biological control agents, although in Europe it is the most likely Chilocorus species you will find predating scale insects in the field. In Europe the related Chilocorus nigritus is available specifically for the control of scales in glasshouses.
In Australia Chilocorus circumdatus is available for armoured scale insect control.
Scale & aphid control in the fieldThe earliest records of the control of scale insects by natural enemies in the Maltese Islands were by Borg 1922, 1932. Two 'mussel scales' (Lepidosaphes spp.) were introduced to citrus groves in 1885, followed by the 'mulberry scale' (Pseudaulacaspis pentagona), also known as the white peach scale (see picture below).
Image copyright Scot Nelson under a Public Domain License. These pests were subsequently controlled by two species of coccinellid, Chilocorus bipustulatus and Exochomus quadripustulatus. Mifsud (1997), in his review of the scale insect fauna of the Maltese Islands, noted that these predators were still present. Chilocorus bipustulatus is known to be an important predator of scale insects in citrus groves in Israel. However, Kehat et al. (1970) found that there was a considerable decline in ovogenesis of Chilocorus females during mid-summer and winter. This decline was thought to be caused by climatic factors, with decreased ovogenesis being to be the main factor governing Chilocorus population decrease during summer. Changes in photoperiod did not hinder egg laying or induce any diapause. Applebaum et al. (1971) also studied the summer decline of Chilocorus bipustulatus in citrus groves of Israel, and came up with a different conclusion. Controlled photoperiodic and temperature regimens, programmed to simulate summer conditions in the coastal plain of Israel, did not adversely affect the fecundity of Chilocorus bipustulatus nor its energy reserves. Infection by the fungus Hesperomyces virescens had little effect on the predator's viability. It was concluded that the summer decline of the beetle may be associated with a change in its diet. Argyriou & Kourmadas (1980) investigated the host range and quantity of scale-insect consumption by Chilocorus bipustulatus. The ladybird was found in various groves, on garden and forest trees, on shrubs and weeds in the coastal and mountain regions of Israel. The adult beetles and larvae preyed, in order of preference, upon: armoured scale-insects, soft-scales & mealybugs. The average consumption during the larval period was 80 specimens of the Florida red scale Chrysomphalus aonidum with the daily average consumption for adults being 5.2. Females consume 30% more than males. Nunez-Perez & Tizado (1996) recorded Chilocorus bipustulatus as a predator of both Cinara pinea and Eulachnus rileyi in the León province (Spain). They noted that the coccinellids were the most abundant predators of the conifer aphids, and that Myrrha octodecimguttata and Chilocorus bipustulatus were the most numerous of the coccinellids. In northern Europe the heather ladybird is primarily known as a predator of heathland and coniferous woodland. The picture below shows a larval Chilocorus bipustulatus predating juniper scales.
Images copyright Gilles San Martin under a Creative Commons Attribution-Share Alike 2.0 License. BiologyAlthough developmental thresholds and day-degree requirements for development of many aphid and mealybug coccinellid predators have been estimated, few data were available as far as diaspidid predators are concerned. Hence Eliopoulous et al. (2010) looked at the temperature-dependent development of Chilocorus bipustulatus. Developmental times were determined at six different constant temperatures. This enabled the calculation of the thermal constant (total of day degrees required for development from egg to adult) at 651.1 day degrees, and the developmental threshold at 5.91 degrees. The results showed that the predator would remain active throughout the year in Antalya, Turkey, and would be able to survive the likely extremes of low and high temperatures. It was therefore an appropriate predator to use for biological control of California red scale (Aonidiella aurantii) on citrus in Turkey.
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