Rodolia cardinalis

Rodolia cardinalis

The Vedalia beetle or Vedalia ladybird (Rodolia cardinalis Mulsant, 1850), is an insect belonging to the family Coccinellidae.

Systematics –
Domain Eukaryota,
Kingdom Animalia,
Suborder Eumetazoa,
Branch Bilateria,
Phylum Arthropoda,
Subphylum Tracheata,
Superclass Hexapoda,
Class Insecta,
Subclass Pterygota,
Cohort Endopterygota,
Superorder Oligoneoptera,
Section Coleopteroidea,
Order Coleoptera,
Suborder Polyphaga,
Infraorder Cucujiformia,
Superfamily Cucujoidea,
Family Coccinellidae,
Subfamily Coccidulinae,
Tribe Noviini,
Genus Rodolia,
Species R. cardinalis.
Its basionym is:
– Vedalia cardinalis Mulsant, 1850.

Geographic Distribution and Habitat –
The cardinal beetle (Rodolia cardinalis) has played an important role in the history of biological control: its introduction from Australia to the United States in the second half of the 19th century gave rise to a modern concept of this control method. Over the course of a few decades, it was gradually introduced to all citrus-growing regions of the world, drastically and definitively reducing to impotence what at the end of the 19th century was expected to be one of the most fearsome plagues of citrus cultivation.
Today, the cardinal butterfly (Rodolia cardinalis) is widespread across all continents: the Americas (USA, Central America, the Caribbean, South America, from Venezuela to Chile and Argentina), Europe (Iberian Peninsula, France, Italy, Balkan Peninsula, Russia), Asia (Japan, India, Philippines, Taiwan, Siberia), Africa (North Africa, South Africa), Oceania (Hawaii, Guam), and, of course, its native Australia.

Morphology –
The adult Vedalia beetle (Rodolia cardinalis) has a hemispherical body, 2 to 4 mm long, covered with dense, short hair. It is reddish-purple in color with black spots on certain parts of the body, forming irregularly shaped patches. The head, the entire width of the posterior part of the pronotum, and the scutellum are black. In its typical livery, there are five black spots on the elytra. Four of these are located on the dorsolateral surface of the elytra; The two anterior spots are oval or slightly crescent-shaped, with a convexity facing the elytral suture; the two posterior spots are more irregular in shape, appearing to be formed by the confluence of two circular spots. The fifth spot develops longitudinally along the elytral suture and widens along the anterior segment.
It has short, slightly clubbed antennae, composed of eight segments, of which the proximal segment is markedly enlarged.
The legs have enlarged and irregularly flattened tibiae, forming a groove in which the tarsi are housed when at rest. The tarsi are composed of three tarsomeres.
The larva is approximately 5 mm long and red at maturity with black spots on the thorax. The back is covered with multiple rows of tubercles, each bearing short setae.
The pupa is 4–5 mm long and red, darkening with age on the abdomen.

Behavior and Life Cycle –
The Vedalia beetle is a mostly monophagous insect, attacking almost exclusively the Icerya purchasi, although it can occasionally prey on other species of the Margarodidae family.
A variable number of generations occurs throughout the year, depending on the climate. In warm regions, up to eight generations occur per year, while in Italy the average is 5-6. The complete developmental cycle is reduced to 20-25 days in the summer months. Overwintering occurs in the adult, larval, and pupal stages, but only in regions with mild winters, as the species is unable to overwinter in cold regions. Fecundity is high: a female can be fertilized multiple times and lays eggs several times over the course of a month or so, with a number varying from 300 to 600 eggs. The eggs are generally laid between the furrows of the egg sac of adult scale insects. Post-embryonic development goes through 4 larval stages and one pupal stage, so during its life a Rodolia undergoes 5 moults.

Ecological Role –
Before discovering the ecological role, and therefore its practical use, of Rodolia cardinalis we must go back in time.
Numerous reports exist of empirical biological control using entomophagous insects; the first dates back to the 4th century, when, as reported by Chi-Han, colonies of the yellow-red ant Oecophylla smaragdina were sold in woven rush bags in southeastern China. The containers were hung on mandarin tree branches to allow the ants to prey on harmful insects, but even beneficial insects were difficult to escape. In 1840, in Poitiers, France, Boisgiraud released the predatory beetle Calosoma sycophantha on poplar trees infested with the odd-leaved silkworm, Lymantria dispar. Villa had a similar experience a few years later in his garden in Desio, receiving the praise of the Society for the Encouragement of Arts and Crafts of Milan.
However, despite these interesting achievements, the emblem of classic biological control is Rodolia cardinalis, introduced in America in 1888, along with the dipteran fly Cryptochaetum iceryae, to control the Australian scale insect Iceria purchasi. As early as 1864, the American diplomat Perkins Marsh had written that the only remedy against exotic organisms introduced through trade was to import natural antagonists from their areas of origin. This concept found practical application thanks to C. Riley, head of the US Federal Entomological Service, who developed a project aimed at tackling the serious infestations of I. purchasi, which threatened Californian citrus cultivation. Government entomologist A. Koebele, who was sent to Australia to search for entomophagous insects, found and shipped to California several thousand specimens of the fly C. iceryae and 160 specimens of R. cardinalis during his four-month mission. Due to the long sea voyage, they did not arrive in optimal condition. On his return to America, Koebele stopped in New Zealand where, thanks to Whight’s report, in just three days he collected 6,000 Rodolia larvae and adults. He placed them in refrigerated containers and personally brought them back to America, where the coccinellid was successfully bred and distributed in citrus-growing areas around the world where Iceria infestations had been reported. Given its complete success, this method, defined as propagative, served as a model for numerous programs based on the introduction of entomophagous insects from the areas of origin of harmful exotic pests. The Rhodolia was introduced to Italy in 1901 by Berlese and, about a decade later, also to Sicily, thanks to the Royal Citrus and Fruit Growing Station of Acireale. This ladybug has acclimated well to southern environments, where, during the winter, it is present in various stages and is less active. In spring, after mating, females lay up to 600 purple-red eggs with sub-elliptical sculpturing within a month. In Sicily, it produces up to six generations per year, which average 20-24 days, while the scale insect produces two to three in the same citrus groves. The adult preys on 300 to 400 eggs from its victim, and the larva, which is red with dark spots, consumes the same number during its development. When the population density of the Iceria decreases, the ladybugs disperse in flight, and only the larvae that prey on younger or molting larvae of their own species are able to complete their development. Adults are 2 to 4 mm long and, in their typical form, are easily recognizable by their reddish-purple dorsal integument, with five black spots on the elytra. They frequently exhibit color variations; about twenty have been described in Italy, characterized by a predominance of black on the elytra over red. These color variations, more pronounced in males, can mislead the uninitiated; but an examination of the genitalia is enough to dispel any doubts. The ladybug has acclimated well in many areas of our country, and even today, introducing 2-3 pairs per plant is the best way to control Iceria, which thrives when favorable environmental conditions occur, whether natural, such as low winter temperatures, or anthropogenic, especially through repeated use of non-selective insecticides.
Today, we know that predatory activity, both by larvae and adults, is very intense and targets the eggs and nymphs of the scale insect. When prey is scarce, predation manifests as cannibalism.
However, the limitations of Rodolia cardinalis lie primarily in its difficulty acclimating to cold-winter regions, which necessarily requires its reintroduction each spring in the event of Icerya purchasi infestations. However, the biological potential of this cochineal insect is such that it allows for the pest’s control in a relatively short timeframe: the scale insect has a limited number of generations (2-3), compared to at least double that of the predator, and the voracity and fecundity of Rodolia are elements that complement its role as an effective control agent.
Furthermore, the use of Rodolia depends on the agro-environmental context and climate. Given that the species is now cosmopolitan, its absence in the event of an Icerya purchasi infestation would be found in one of the following scenarios:
First introduction, in a given environment, of the agricultural species with which the scale insect is normally associated. This insect generally attacks citrus fruits, but in Italy it is also frequently found on pittosporum and various brooms (particularly common broom). The first-time introduction of any of these species can easily be accompanied by a subsequent scale infestation due to the absence of its predator.
Climate pattern with harsh winters. Low winter temperatures prevent the cardinal scale from overwintering, so the predator is unable to acclimatize in these environments. In Italy, these conditions occur, depending on the location, from the central regions toward the north. Since the citrus growing area is also dependent on winter temperatures, this scenario generally occurs in gardens where pittosporum or some shrubby legumes are present.
Environmental degradation caused by indiscriminate use of insecticides. Occasional Icerya infestations are common in citrus groves subjected to repeated treatments with broad-spectrum insecticides. The environmental impact of insecticides is, in fact, the main anthropogenic factor limiting Rhodolia.
Historically, Rhodolia has been successfully used using propagation methods: in environmental conditions favorable to the beetle’s acclimatization, the species has always established itself stably without necessarily requiring repeated introductions. Once established, its population dynamics adapt to that of the scale insect according to ordinary patterns, consistently keeping infestations below the tolerance threshold. Referring to the scenarios described above, the propagation method could be applied in the case of the first point and, excluding the very low probability of a new introduction of citrus fruit, the possibility of an I. purchasi attack is limited to isolated plants in the gardening sector. In other conditions, the inoculation method must be used, with targeted releases of the cochineal during the scale insect’s breeding periods. In contexts that address the third point described above, predator inoculation can prove definitively effective if citrus fruit growing is converted to low-impact techniques. In this case, predator inoculation would be considered a protective measure.
The intensity of the releases depends on the scale insect’s spread. Generally, Rhodolia can compensate for even low-density releases with its reproductive potential: in infestations limited to isolated plants, three pairs of adults are sufficient to quickly bring the pest population below the tolerance threshold, while in widespread infestations, it will be necessary to adjust the release density to the extent of infestation and the degree of fragmentation of the attacks.
Of particular importance is choosing the right timing for releases: predation is particularly prevalent on eggs and nymphs, and conditions of prey scarcity inevitably lead to lower fecundity and increased cannibalism. Therefore, releases must be performed during the periods when Icerya is reproducing: in Italy, these events occur in late spring and in late summer or early autumn.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Pollini A., 2002. Manual of Applied Entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied Entomology. Liguori Editore, Naples.

Photo source:
– https://observation.org/photos/101900706.jpg