Scale insects detected on camellia in Galicia

Rosa Pérez-Otero, Pedro Mansilla, Carmen Salinero

Estación Fitopatolóxica do Areeiro, Deputación de Pontevedra, Subida a la Robleda s/n, 36153 Pontevedra, España

Introduction

Scale insects (Homoptera, Coccoidea) are polyphagous (feed on a wide range of hosts) small insects, usually less than 3 mm long. Many of these insects are frequent and serious pests of trees, shrubs, and indoor plants. These species have a distinct sexual dimorphism: adult females are neotenic and apterous/wingless, whereas males are winged and do not feed. The integument of females is provided with glands that secrete wax or lacquer to protect themselves from adverse weather conditions and natural enemies (García-Marí et al. 1994). They tend to be species with a high reproductive potential that can attain large populations. They are usually oviparous insects. At birth, they are mobile, but later they lose part or all their legs so their movements are limited or they become immobile. They may be found on the leaves, on the bark and on fruits. Scale insects introduce their stylet-like mouthparts into plant tissues and suck their fluids. Damages observed in fruit crops include fruit depreciation, discoloration at the feeding point (in certain species), crop yield reductions and plant weakening. They cause weakening in ornamental plants. The occurrence of insects and the installation of sooty mould fungi in the sugary substance (honeydew) that some scale insect families secrete lead to the loss of the ornamental value of the species; certain species also cause discoloration.

Camellias are highly appreciated plants widely distributed in Galician parks and gardens. This is mainly due to the soil and climatic conditions in Galicia that promote their development. Of the species grown in Galicia, the dominant species is Camellia japonica L. In this region, Camellia plants have been subjected to the attack of several pathogens, such as Ciborinia cameliae, Pestalotia güepini and Colletotrichum gloeosporioides amongst others. Different species of arthropod pests have been also identified, including some aphids (mostly Toxoptera aurantii), mites (mainly eryophid mites) and scale insects (Mansilla et al. 2003).

In this paper the Coccoidea species associated with camellia identified in our laboratory over the past 10 years are presented. Their morphology and biology are described and we provide data on the incidence and the scope of damages they cause.

Materials and methods

Samples were taken at different times over 10 years in different surveys conducted on Camellia with different purposes (specific surveys, study of varieties, phenology, seed collection) in the four Galician provinces (A Coruña, Lugo, Ourense and Pontevedra). The largest number of scale insects was collected in Pontevedra, our main area of influence, which is together with A Coruña the province with more camellias in their gardens. Lugo and Ourense provinces have unfavourable conditions for camellia growth (continental, cold weather in winter), and thus camellias are scarce.

In each survey, camellia plants were examined and when some form of Coccoidea was detected, those plant organs with the scale insect were separated, placed in bags inside a portable cooler and transported to the laboratory. Species determination was carried out using microscopic preparations of adult females. Females were carefully separated from plant organs with the aid of an entomological needle. Then they were clarified, stained and mounted according to the following protocol: the insects were placed inside glass capsules containing 10% NaOH until they were clarified; subsequently they were washed using a mixture of acetic acid (25%), water (50%) and 70% alcohol (25%) to neutralize the NaOH and they were transferred to a recipient with 70% alcohol for at least 15 minutes. They were then dyed using clorazole black for a few seconds and put again in 70% alcohol and later in acid fucsin (at least during 24 hours). Next step was the alcohol dehydration: first using 70% alcohol (15 minutes), then 96% (15 minutes) and 100% alcohol (15 minutes). Finally specimens were put in Euparal essence for 15 minutes and then they were mounted on microscope slides using Euparal. If the insect had an excess of wax on its body, just after the NaOH neutralizing step, a mixture of three parts of phenic acid and one part of xylol had to be used. Species was determined by morphology using taxonomic keys.

Results and discussion

The Coccoidea species found on camellia were three species of the Coccidae family (Chloropulvinaria floccifera Westwood, Coccus hesperidium L. and Ceroplastes sinensis Del Guercio), two belonging to the Diaspididae family (Hemiberlesia rapax (Comstock) Sign. and Parlatoria camelliae Comstock), and one of the Pseudococcidae family (Planococcus citri Risso). No other species frequently detected in other countries has been reported on camellia, such as Ceroplastes rusci, Chrysomphalus dictyospermi, Eulecanium sp. or Parthenolecanium sp. (Ferrari et al, 1999).

Chloropulvinaria floccifera Westwood is the most frequent species. It is usually found in gardens throughout the region, especially in warmer climate zones (coastal and southern parts of Pontevedra and A Coruña). It can be seen all year round as nymphs and females when the weather is mild, or as remains of ovisacs during autumn-winter. The ovisacs are first visible during the spring, when egg-laying starts, but remain on the plant even when the female has completed the annual cycle and dies.

C. floccifera is also the species causing the most severe damages. Immature and adult stages produce plenty of honeydew that serves as a medium for the growth of sooty moulds. These fungi cover the plant completely hindering photosynthesis and respiration and also reducing the ornamental value of the plant. If this happens, at least one or two insecticide treatments are required during the year, and they may not be efficient.

The adult female (3-4 mm in length) is oval and slightly convex, usually widest near the centre. At first it is light green, but when the oviposition is finished it turns greenish-brown. The ovisac is very long, containing more than 1,000 white-yellow eggs. The nymphs are elliptical, somewhat narrowed in its anterior half and flat. They have hairs scattered regularly around its contour and a colour varying from brown to yellowish green.

Body of mounted adult female is elongate oval, widest in the abdomen. Legs and antennae (8 segments) are well developed. Body has short and spiniform dorsal setae with a well developed basal-socket. Anal plates quadrate; each plate with posterior edge slightly convex and apex rounded, with 4 setae. Anal ring has at least 3 pairs of large setae (Hodgson, 1994).

C. floccifera is a highly polyphagous species. It can be found on camellia and on other ornamental plants (euonymus, rhododendron, holly tree, Pittosporum, yew, maple, etc.) as well as on citrus.

Coccus hesperidium Linnaeus is the second species most commonly occurring on camellias in Galicia. It is also more abundant in Pontevedra and A Coruña. Different developmental stages of the species are present in most camellia plants, especially in spring. The female body is oval and flat. It is about 4 mm long. Its color is yellow-green, but shades into yellow-brown at the end of its life. It is almost immobile; the ovigerous cavity is not present: larvae are born directly from the adult female body. The nymphs are yellow and look flat, with well-developed legs and antennae.

C. hesperidium does not usually damage camellias, probably because their populations are not large enough and there is a high natural parasitism. They attack leaves, especially the underside and along the midrib; they also affect buds and tender branches. Both adult and immature stages secrete abundant honeydew. It is a typical species found on citrus fruits and also affects many ornamental plants (it has been reported feeding on hundreds of different plants).

The coccid Ceroplastes sinensis is rarely found on Galician camellias. All detections have been on C. japonica. It has been found only in plants growing in Pontevedra in early spring extending until fall. The adult female is oval and convex; it is 3 mm in diameter. The body is covered with plates of whitish waxy substances whose plates fade at the end of insect´s life. The nymphs are reddish. They have white waxy pyramidal exudates, which are lost during their development. Egg-laying occurs under the female body.

Adult females and Ceroplastes sinensis nymphs

Mounted female presents 7-segmented antennae, with 2 pairs of interantennal setae. Legs are well developed. Along the margins, stigmatic setae are conical or bullet-shaped or hemispherical, with blunt apexes. Tubular ducts have a narrow inner filament. Filamentous ducts are present on ventral submargin. They do not have multilocular pores on abdominal segments 2 and 3 and near coxae of meso and meta-thoracic legs.

It is a very polyphagous species with preference for Citrus.

Hemiberlessia rapax(Comstock) Sign. is also abundant in Galicia. Colonized plants do not usually show damages as their populations are not large enough. It is a diaspidid, so it does not segregate honeydew; consequently sooty moulds do not grow. Scale cover of adult female is 1.0-2.0 mm long, circular to somewhat elongate, convex, and grey to white with yellow-brown central or subcentral exuviae. The body is yellow, like that of nymphs. Mounted females are membranous and pyriform. The pygidium presents median lobes large and closely set; the second and third lobes are often unsclerotized and very small; the third lobes are reduced to small points. Perivulvar pores are not present. The large anal opening is situated near the posterior margin of the pygidium. The paraphyses are shorter than lobes, and are present only on the margin between the third lobes. Only 1 or 2 submedian macroducts are present on each side of abdominal segment 5; segment 4 does not present submarginal macroducts.

Hemiberlesia rapax is a highly polyphagous species that seems to prefer woody ornamental plants. Hosts include camellia, acacia, boxwood, cactus, fruit trees, holly, ivy, laurel, magnolia, pittosporum, pyracantha, willow.

The other diaspidid found on camellia in Galicia is Parlatoria camelliae. It has only been detected on two plants of Camellia wabisuke var.Uraku in a garden in Vilanoviña parish (Meis municipality, Pontevedra). These plants showed evident signs of discoloration at the leaves’ insertion point. This is the last species detected in Galicia. Scale cover of adult female is broadly elongate oval, greyish to brown. Its body is pyriform, purple in color. Nymphs are also faintly purple.

Parlatoria camelliae: female body (left); colony on camellia leaf (right)

Mounted adult female has 5 pairs of well developed lobes. Fourth and fifth lobes are often shorter and broader than the first 3 pairs of lobes. Median lobes do not have sclerosis or parafises; second lobes are simple, about the same size as median lobes. Macroducts on pygidium have 2 sizes: marginal ducts are larger than submarginals. Marginal ducts are on segments 5 to 8, while submarginals on segments 5 to 7. Microducts are present on marginal or submedial areas of segments 5 to 7. Perivulvar pores are arranged in 4 groups. Anterior spiracles present 2-3 pores; posterior spiracles do not have pores. Each antenna has one conspicuous seta.

P. camelliae is a polyphagous species, but feels more attracted to camellias. Their hosts include various species of Acer, Aucuba, Citrus, Euonymus, Ficus, Gardenia, Laurus, Rhododendron and other ornamental plants.

Only one species of mealybug scales was reported on camellia in Galicia: Planococcus citriRisso. The insect was scarcely detected on Camellia japonica in our region. Apart from segregating honeydew, this mealybug does not usually cause important damages.

Adult mealybug female has oval body, slightly rounded in lateral view. Its color is at first yellow, and pink or orange-brown when it is fully mature. It is not visible because it has a mealy wax covering it. It has18 pairs of lateral wax filaments, most relatively short; posterior pair is slightly longer. The legs are well developed. Nymphs are narrow, oval in form and yellow with red eyes. When developed, they are covered by wax.

Planococcus citri: mounted female

Mounted female has more than 5 ventral tubular ducts between antennae; 6 or more ventral tubular ducts lateral of middle coxae (count both sides); translucent pores on hind coxa and tibia; usually with 1 or more dorsolateral tubular ducts that often appear as oral rims; no auxiliary setae; anal bar present; 18 pairs of cerarii.

P. citri may attack camellia, although it is a major pest of Citrus genus. It also attacks other wide range of hosts (grapevine, gardenia, fichus, ivy, rhododendron, begonia ...).

The results of this work indicate that are few species of scale insects associated to camellia in Galicia, but they are common, mainly in those provinces with a warmer climate. Among them, only Chloropulvinaria floccifera, the most widely distributed species, causes damages and requires chemical control.

References

Ferrari, M., Menta, A., Marcon, E. e Montermini, A. 1999. Malattie e parassiti delle piante da fiore, ornamentali e forestali. Vol. 1. Edagricole, Bolonia. 1807 pp.
García-Marí, F., Costa Comelles, J., Ferragut Pérez, F. 1994. “Homópteros” En Las plagas agrícolas. Agropubli-Phytoma España. 375 pp.
Hodgson, 1994. The scale insect family Coccidae: An Identification Manual to genera. CAB International, UK. 639 pp
Mansilla Vázquez, P., Salinero Corral, C., Pérez Otero, R., Pintos Varela, C. 2003. Plagas, enfermedades y fisiopatías de la camelia. Xunta de Galicia. 107 pp.