ADUlt Morphology
The external morphology of adult Coccinellidae is fairly simple to understand. In the case of medium to large species, external characters like colour and other patterns such as spots and markings are sufficient to make routine identifications with the help of a hand lens. However, identification of many smaller species is rendered difficult for an economic entomologist due to the lack of external diagnostic characters. A brief account of the morphology of adult coccinellids is given here with illustrations to enable the users of literature on coccinellid taxonomy to get acquainted with the various characters used in identification. Excellent and exhaustive accounts of coccinellid morphology, with illustrations, by Sasaji (1968, 1971), Hodek (1973), Kovář (1996), Kuznetsov (1997), Vandenberg (2002) and to some extent, Gordon (1985), can be consulted for more detailed information.
General appearance (Fig. 1 a&b)
Lady beetles vary in size from minute (one mm or less in length) to large (10-17 mm long). The shape is usually round or short oval to distinctly elongate. The dorsal surface (dorsum) is weakly to very strongly convex, glabrous or with sparse to dense pubescence. The dorsum has fine to coarse punctures, but never has distinct striations and sculptures. The interspaces between punctures are smooth, matt-like or with microsculpture, which can be observed properly only under a microscope at high magnification. Many species have bright red, orange or yellow elytra with distinctive spots, stripes and other markings/patterns. A few species are brightly metallic blue, green or violet.
The body of a coccinellid is divided into three basic parts: the head, thorax and abdomen (Fig. 1 a&b). There is a usually triangular scutellum between the pronotum and the elytra. In the dorsal aspect, the pronotum and elytra are broadly and compactly joined. The head is usually retracted into the anterior margin of pronotum at rest. In general, males are smaller in size than females.
Fig. 1a. Coccinellidae - Dorsal view
Fig. 1b. Coccinellidae - Ventral view (Redrawn from Gordon, 1985)
The general appearance of a coccinellid head in dorsal (Fig. 2a) and ventral view (Fig. 2b) is illustrated below. Generally, the head (Figs. 2a, 3a-f) is broader than long (transverse) and quadrate, with its corners rounded. A feature that is important in the higher classification of the family is the nature of the clypeus (the portion of the head above the eyes). It is normal (Figs 3c-f) in most species. In the subfamily Chilocorinae, it is broadly and laterally expanded in front of the eyes, covering the antennal insertions (Fig. 3b). The tribe Shirozuellini [Sticholotidinae], which is rarely collected, is the only other group with laterally expanded clypeus. In the tribe Aspidimerini, the genae are very narrowly expanded just above the eyes (Fig. 3a). The area between the eyes (frons) is flat or weakly convex.
The antennal insertions are usually lateral or dorsolateral, in front of the eyes and broadly separated; however, in the subfamily Chilocorinae, antennal insertions are not seen above the head as they are ventral and covered by the expanded clypeal margin (Fig. 3b); in the Epilachninae, they are dorsal (Fig.3e).
Fig. 2 a&b. Head in Coccinellidae: a. Dorsal view; b. Ventral view. An - antenna; Ce - compound eye; Clp - clypeus; Lm - labrum; Lp - labial palpus; Md - mandible; Mp - maxillary palpus; Mt - mentum; pm - prementum
Fig. 3 a-f. Head in Coccinellidae: a. Aspidimerini; b. Chilocorinae; c. Coccinellinae; d. Sticholotidini; e. Epilachninae; f. Ortaliinae
The compound eyes are usually well developed and anterolaterally located. They are entire or divided anteriorly by a post-antennal process (also known as post-antennal emargination or canthus). The post-antennal canthus is very prominent in the tribe Ortaliini (Fig. 3f). The eyes are usually well separated and the narrowest distance between the inner margin of eyes (interocular distance) is an important taxonomic character. The eyes are glabrous (e.g., Coccinellinae) or sparsely to densely pubescent with very short, erect hairs (e.g., the tribes Scymnini, Ortaliini, Noviini, Platynaspidini, and Telsimiini). In some species (e.g., Hyperaspis maindroni Sicard, most Ortalia spp., and some Telsimia spp.), eyes are brilliantly coloured with metallic green or purplish iridescence, especially in live specimens.
The antennae of coccinellids are 6-11 segmented (Figs. 4a-n), the segments being freely movable. The last three or four segments form a loose or compact club in many species. In the tribe Serangiini, the last segment alone forms an enlarged, knife shaped or spatulate club (Fig. 4h). The length of the antennae varies from very short (about 1/5th of the head width) to much longer than the head width (about 1.5X as long as the head width) in different groups. The antennae are occasionally longer in males than in females.
Fig. 4a-n.
Antenna
in Coccinellidae: a. Nephus; b. Axinoscymnus;
c. Harmonia; d. Stictobura; e.Scymnus; f. Pseudoscymnus;
g. Ortalia; h. Serangium; i. Telsimia; j.
Psyllobora; k. Rodolia;
l. Platynaspidius; m. Exochomus;
n. Sumnius
The mouthparts in coccinellids are adapted for biting and chewing. They consist of a labrum, a labium, paired mandibles and maxillae. The labrum is transverse and quadrate with a truncate base and rounded sides (Figs. 5m-r). It is usually narrower than the clypeus and is visible at the top of the head, just above the anterior or clypeal margin. The mandibles are massive, wide and sickle shaped. The mandibular apex is simple (Fig. 5b) or bifid (Fig. 5c&d) in carnivorous or predacious species, and multidentate (Fig. 5a) in phytophagous forms. In many fungus-feeding species, the ventral apical tooth has a series of small serrations (Fig. 5e), which are used for combing out fungal spores. Besides, there is also a basal tooth in most carnivorous species, which is lacking in plant feeders.
Fig. 5a-r. Mouthparts in Coccinellidae: a-e. mandibles: a. phytophagous type; b-d. carnivorous/predatory type; e. fungivorous type; f-l. labium; m-r. labrum
The labium (Figs. 5f-l) has three components: (1) a mentum, that is usually trapezoidal and rarely heart-shaped, and broadly or narrowly joined with the submentum; (2) a subquadrate or apically broadened prementum, with numerous minute hairs and several long setae; and (3) a pair of two- to three-segmented labial palpi inserted into the prementum, usually on the ventral side. In the Epilachninae (Fig. 5l), the prementum is narrowed in front.
The maxillae (Fig. 6a-o) are paired and composed of a basal cardo, an oblong or roughly triangular stipes, an outer galea, an inner lacinia and a well developed, four-segmented maxillary palpus. In the phytophagous species (Fig. 6f), the galeae and laciniae are much larger than those of other groups. The terminal segment of maxillary palpi is an important distinguishing character for the entire family. It is usually large and axe-head/hatchet shaped (securiform) (Figs. 6e, n, o). Its shape varies in some groups, particularly in the subfamily Sticholotidinae. It may be barrel shaped, cylindrical with an obliquely truncate apex (Fig. 6m), elongate conical (Fig. 6a) or apically acuminate (Fig. 6b).
Fig. 6 a-o. Maxilla in Coccinellidae: a-d. Sticholotidinae; e. Noviini; f. Epilachninae; g. Scymnini; h. Hyperaspidini; i. Ortaliini; j. Aspidimerini; k, n, o - Coccinellinae; l. Platynaspidini; m. Chilocorini.
The well-developed, large dorsal plate of the prothorax, namely the pronotum (Fig. 1a), is the dorsally visible part of thorax in all beetles. The anterior margin of pronotum in most coccinellids is weakly or strongly and trapezoidally excavated; it is rarely truncate or straight. In some groups, it partially covers the head and is very rarely produced forward to fully cover the head. The scutellum (a small sclerotized part of mesonotum) is present between the elytral bases and is usually inversely triangular.
The prosternum (the area corresponding to the pronotum, on the ventral side) (Fig. 7a) is strongly transverse and medially convex, with a well developed prosternal intercoxal process. The intercoxal process has a pair of carinae or longitudinal ridges of varying length; in some groups, carinae are totally lacking (e.g., species of the genera Stethorus Weise, Nephus Mulsant and Telsimia Casey). The median portion of prosternum in most coccinellids is T-shaped (Fig. 7a). In the tribe Stethorini, the anterior margin of prosternum has a median semicircular lobe or protrusion (Fig. 7d). Sometimes, it is anteriorly produced (Figs. 7 b&c) to cover the mouthparts partially or fully (e.g., Cryptolaemus Mulsant, the tribes Plotinini and Serangiini).
Fig. 7a-d. Prosternum in Coccinellidae. a. general apperance; b-c. prosternum anteriorly extended to cover mouthparts: c. Cryptolaemus, d. Serangiini; d. prosternum with a median lobe-like projection in Stethorini; e. Prosternum in Noviini. Hm-Hypomeron; Fo - fovea; Ps-Prosternum; Pc-prosternal carina.
External to the prosternum, the hypomeron (Fig. 7a) is present, reaching to the pronotal side margins. The anterior inner corners of the hypomera are flat or shallowly to deeply impressed (foveate or foveolate) in some groups (e.g., several genera of Coccinellinae). The hypomera are replaced by two small sclerites on both meso- and metasterna: an anterior episternum and a posterior, usually more externally placed, epimeron. These sclerites are distinctively coloured (usually creamy yellow or white) in some species, especially in the tribe Coccinellini. The mesosternum (Fig. 1b) is broad and short, in front of the middle coxae. Its anterior margin is weakly to deeply emarginate or flat in the middle. The extent of mesosternal emargination is an important taxonomic character. The mesocoxae are more broadly separated than fore coxae.
The metasternum (Fig. 1b) is large and rectangular and compactly joined with the mesosternum. It is divided by a longitudinal medial suture and has a pair of distinctive postcoxal lines or plates, behind middle coxal cavities.
The elytra or the hard, leathery fore wings (Fig. 1a) completely cover the abdomen and are more or less convex dorsally. Their basal margin is nearly straight and the apices are usually rounded and rarely subtruncate. The elytra meet each other at the middle along their entire length forming the sutural line/elytral suture (Fig. 1a). The humeral callus (shoulder boil in old literature) is distinctly raised near the anterolateral corner, just below the anterior margin and is well developed in many cases. The elytral epipleuron (Figs. 1b, 8a-g) or the continuation of the elytra on the underside, is well developed, with an inner carina that may or may not reach the elytral apex. In some groups, the epipleura are deeply impressed or foveate on level with middle and / or hind pair of legs (Figs.8b, c) to receive the femoral tips of the middle and / or hind legs at rest (e.g., tribes Serangiini, Aspidimerini and Platynaspidini).
Fig.
8a-g.
Elytral epipleura in Coccinellidae
The hind wings are thin and membranous and form the true functional wings, but are poorly developed or atrophied in some genera (e.g., Stictobura Crotch and Nesolotis Miyatake), and altogether absent in the tribe Lithophilini. Wing polymorphism has been reported in some Rhyzobius spp. and Subcoccinella vigintiquatuorpunctata (L.).
The legs are well developed and adapted for walking and running. The femora are usually elongate and shallowly grooved on the ventral side to receive the tibiae at rest. In the tribes Serangiini and Aspidimerini, the femora are plate-like, greatly enlarged and retracted into deep impressions on the ventral side of the body. The tibia is usually slender, sometimes with a median tooth or externally angulate. There may be one or two spurs at the tibial apex. The tarsal formula (the number of tarsal segments in the pro-, meso-, and metatarsi), usually expressed as three numbers, is of great taxonomic significance and is 3-3-3 or 4-4-4 in coccinellids. The number of segments is the same for all legs in both females and males. The tarsi are true trimerous (three-segmented) (Fig. 9b) or cryptotetramerous/pseudotrimerous (Fig. 9a). In the pseudotrimerous or cryptotetramerous condition, the tarsi have four segments, but the third is very small, partially hidden by the strongly bilobed second segment. Only in the tribe Lithophilini (=Tetrabrachini), tarsi are truly tetramerous (four-segmented) (Fig. 9c). The last tarsal segment is elongate and ends in a pair of claws, free from each other and usually armed with a basal tooth (Figs. 9d,e), or bifid (Fig. 9f) or simple, without a claw (Fig. 9g).
Fig. 7a-c. Tarsi in Coccinellidae: a. Pseudotrimerous / cryptotetramerous; b. Trimerous; c. Tetramerous; d-h. Tarsal claw: d, f. with a basal tooth; e. bifid; g. simple; h. apically bifid.
The abdomen has five or six visible segments (=sternites or ventrites) on the ventral side. The number of visible segments is usually the same in both sexes and rarely variable (e.g., in some genera of the tribe Chilocorini, males usually have six and females have only five segments). The last visible abdominal segment (sometimes the last two) is usually sexually dimorphic. It is entire or notched to some degree (Figs. 10 d, e) in males and narrowly and evenly rounded (Fig. 10b, c) or medially divided (Fig. 10a) in females. The parts of the ninth and tenth abdominal segments are usually defined as the genitalia.
Fig. 10 a-e. Abdomen in Coccinellidae: a, b. general appearance; c. terminal segments, female; d-e. terminal segments, male
The first visible sternite is usually the largest and has a pair of postcoxal lines (also known as postcoxal plates or femoral lines), which are characteristic of the family (besides the first abdominal segment, the metasternum also has postcoxal plates as mentioned earlier). Their shape, extent and nature of punctations in the area enclosed by them are important taxonomic characters. Based on their completeness, they are referred to as Pullus type (complete) (Figs. 11a,b), Scymnus, Nephus or Diomus type (all incomplete) (Figs. 11e-h). In some groups, an additional, lateral oblique line dividing the postcoxal line (Figs. 11c,d) is present. The postcoxal line is completely absent in some groups (e.g., Coleomegilla Timberlake and some species of Hippodamia). There are five pairs of functional abdominal spiracles.
Figs.
11a-h. Postcoxal plate in Coccinellidae: a-b. Complete: a. Scymnus (Pullus);
b. Rodolia; c-d.
Incomplete, with an
associate line: c. Protoplotina; d. Oenopia; e-h. Incomplete: e. Pseudoscymnus;
f. Sticholotis; g. Nephus; h. Psyllobora.
Male genitalia
The male genitalia (Figs. 12b,c) consist of a tegmen and a sipho. The components of tegmen are a basal piece, a distinct median projection or the basal lobe (also termed frequently and incorrectly as the median lobe), a pair of lateral arms or parameres and a median basal strut or trabes (Fig. 12b). The tegmen is collectively also referred to as aedeagus in some papers. The median lobe is symmetrical (Fig. 12b) or asymmetrical (e.g., tribe Serangiini). The parameres are usually setose at their apices and / or outer margins. The sipho (Fig. 12c) is usually elongate, tubular and curved with a basal siphonal capsule and is variously modified at the apex. The sipho is the true penis or the intromittent organ. The structure of the male genitalia is species-specific and is the most important diagnostic character, in the absence of other reliable external diagnostic characters.
Female genitalia
The female genitalia consist of a pair of genital plates (Fig.12a), a spermatheca (receptaculum seminis), a sperm duct and an accessory gland. A typical spermatheca is differentiated into a nodulus and ramus in the basal part, to which the sperm duct and accessory gland are connected, respectively, and a distal curved arm called cornu. Sometimes, the nodulus and ramus are continuous and not clearly demarcated. The infundibulum is usually elongate cylindrical; it is highly sclerotized and diagnostically shaped in some groups, but lacking in others. The spermatheca itself is membranous and not visible in some groups (e.g., some genera of Sticholotidini such as Jauravia, Sticholotis and Pharoscymnus).
The shape and structure of the genital plates (also known as coxites or hemisternites, together forming the ninth sternite) are of taxonomic importance at the higher level. In some groups, these are elongate triangular structures and apparently function as an ovipositor. The structure of the spermatheca and coxites usually remain more or less constant within a genus and not of much importance in species diagnosis, except in some groups (e.g., some species of Epilachna Mulsant).
Figs.12a-c. Genitalia in Coccinellidae: a. Female genitalia; b-c. Male genitalia: b. tegmen; c. sipho
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Hodek, I. 1973. Biology
of Coccinellidae. W. Junk, The Hague. 260 pp.
Kovář, I. 1996. Morphology and anatomy, pp. 1-18. In: Ecology of Coccinellidae (Eds. I. Hodek & A. Honěk), Kluwer Academic, Dordrecht. 464 pp.
Kuznetsov, V.N. 1997. Lady Beetles of the Russian Far East. Memoir No. 1, Center for Systematic Entomology, 248 pp.
Sasaji, H. 1968.
Phylogeny of the family Coccinellidae (Coleoptera). Etizenia,
35: 1-37.
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Japan. 340 pp.
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