FNZ 11 - Pseudococcidae (Insecta: Hemiptera) - Morphology of Adult Females
Cox, JM 1987. Pseudococcidae (Insecta: Hemiptera). Fauna of New Zealand 11, 232 pages.
( ISSN 0111-5383 (print), ; no. 11. ISBN 0-477-06791-3 (print), ). Published 07 Apr 1987
Morphology of Adult Females
BODY FORM (Figure 2). Individual adult females may vary in size according to the environmental conditions under which they developed, and all undergo enlargement during egg production after they reach maturity. However, some species are characteristically very much smaller than others. For instance, all three species of Asaphococcus and both species of Maskellococcus, which live under the bracts of Nothofagus, are very small. Body shape appears to be related to habitat, and is characteristic of species rather than genera. Futhermore, adult females tend to become more rotund as their eggs develop. Species living in the leaf sheaths of grasses are generally elongate, those living underground tend to be rotund, and those living under the bracts of Nothofagus are turbinate in outline. On either side of the anal ring the body usually projects slightly to form the anal lobes, on which the ultimate pair of cerarii are borne. In some species this projection is very marked, and in a verv few species all the cerarii are borne on the ends of sclerotised, finger-like protuberances. The numbering of the abdominal segments has the vulva between segments VII and VIII (see Figure 6).
ANTENNAE. Most mealybugs have eight-segmented antennae in the proportions shown in Figures 2 and 4. Some genera, such as Phenacoccus, typically have nine-segmented antennae; and some genera, and species within other genera, have fewer segments in the antennae, often accompanied by a general reduction in the form of the whole antennae, as in Renicaula (Figure 5).
LEGS. A typical mealybug leg is shown in Figure 6. Denticles are present on the tarsal claws of many species around the world, but in New Zealand only two species - Phenacoccus graminicola and Spilococcus leucopogi, both introduced - have these denticles. Translucent pores are usually present on the hind legs, and the segments on which they occur are characteristic of species and sometimes also of genera. The proportions of the legs vary. Some species, such as Rastrococcus asteliae, have distinctly elongate legs, whereas those species that have reduced antennal segments often also have proportionately small, stout, and somewhat distorted hind legs. In these species the translucent pores may extend out on to the surrounding integument, as in Figure 7. In some species not known from New Zealand the legs may drop off at maturity.
SPIRACLES. Mealybugs typically have lightly sclerotised spiracles without pores inside the atria. In some species, such as those in the genus Renicaula, each spiracle is heavily sclerotised and has several pores within this sclerotisation.
CIRCULI. Circuli are structures on the midline of the abdominal venter that help the female mealybug adhere to its substrate. Mealybugs may lack circuli, or have any number from one to five, but the most commonly encountered condition is a single circulus situated on the intersegmental line between abdominal segments III and IV. This circulus occurs in a variety of shapes and sizes, often characteristic of the species, and varying from small and round, undivided by the intersegmental fold, to large and hourglass-shaped, with a clear horizontal fold.
OSTIOLES. When a mealybug is disturbed these lip-like structures on the dorsum (see Figure 2) exude a fast-drying substance that is believed to be a defence against predators. Ostioles are characteristic of mealybugs, and occur as an anterior and a posterior pair, although the anterior pair, and sometimes also the posterior pair, may be absent. In order to preveni the exudate from sticking to the mealybug itself, the lips of the ostioles are usually well provided with wax-producing pores.
CERARII. These are characteristic of mealybugs, and consist of groups of large setae, usually conical, on the lateral margins of the body (see Figure 2). Cerarian setae usually have trilocular pores aggregated around their bases, and are often situated on sclerotised areas of the integument. The conical setae have been shown to produce long rods of stiff wax on which the filamentous wax secreted by the trilocular pores is supported, so producing the characteristic lateral wax filaments of mealybugs (Cox & Pearce 1983). The primitive number of cerarii appears to be seventeen or eighteen pairs, although some species may have more, and many have less than this number. If there are few cerarii, these are generally situated on the posterior abdominal segments with the setae becoming less stout and more flagellate, and with fewer associated trilocular pores around the bases of those cerarii towards the anterior of the body. The most commonly encountered number of conical setae in a cerarius is two, although any number up to about twenty may be found. Most species additionally have flagellate auxiliary setae in the anal lobe cerarii, and some, such as those in the genus Psetidococcus, have a few flagellate auxiliary setae in most of the cerarii.
ANAL LOBE BARS. These are lines of sclerotisation on the ventral surface extending forward from the anal lobe setae (see Figure 2). Groups of similar-appearing species tend to have these bars in common, and Ezzat & McConnell (1956) went as far as to place all the genera with anal lobe bars together in a tribe, the Planococcini. Several groups of New Zealand species have these bars, including the species placed in the genera Crisicoccus, Paracoccus, Planococcus, and Sarococcus. It is not known whether these bars are a primitive or a derived character, so it is difficult to know how much emphasis to place on them in generic classification. Even if their presence is a derived condition, they may be expected to have been secondarily lost in some species.
ANAL RING. Mealybug anal rings typically have six setae and a double row of cells, as shown in Figure 8. Sometimes unusual forms are encountered, such as the kidney-shaped anal rings of Renicaiila (Figure 9), and anal rings with reduced numbers of cells, as in Rhizoecus (Figure 10).
PORES. Four different types of wax-producing pore are found in mealybugs. Multilocular disc pores usually have ten loculi and produce short, white wax filaments with a 'C'-shaped cross-section. They are found in most species of mealybug, usually around the vulva, where they contribute to the production of the ovisac, but they may also be found on any part of the dorsal and ventral surfaces. Quinquelocular pores are less widespread among mealybug species, and their presence is often used to characterise genera. In New Zealand only two species have them. Phenacoccus graminicola and Rastrococcus asteliae. Trilocular pores are found over both surfaces of the body in most species of mealybug, and are characteristic of the family. In some species they may be absent, as in some of the species of Balanococcus known from New Zealand. Trilocular pores produce the long, spiralled filaments of wax, coarser than the filaments produced by the multilocular disc pores or quinquelocular pores, that make up the bulk of the wax covering over the insect. This wax is usually white, but may be yellow, tan, or buff in some species. Simple pores, sometimes known as discoidal pores, are usually smaller than the trilocular pores and, if present, are scattered over both body surfaces. Their function is not known.
TUBULAR DUCTS. Tubular ducts produce long, hollow filaments of white wax that are a major constituent of the ovisac. They are found in a variety of forms, the most commonly encountered of which is known as an oral collar tubular duct. These ducts may be entirely simple in form when viewed under the light microscope (Figure 11), or have a distinct sclerotised collar at the end nearest the aperture, and in some species the collars may be distinctly flange-shaped (Figure 12). Oral collar tubular ducts are usually found on the venter of the posterior abdominal segments, but they may be absent, or present anywhere on the ventral and dorsal surfaces. Another form commonly encountered is the oral rim tubular duct. These ducts are similar tc oral collar tubular ducts, but have a raised rim of integument around the aperture. In some species, such as those in the genus Pseudococcus, these ducts are large and have very distinctive rims. In other species, however, such as some of the New Zealand species here placed in Paracoccus, these ducts are no larger than oral collar tubular ducts and the rims are frequently obscure or not apparent, so that the distinction between the two supposed forms of duct becomes questionable. Large, tubular ducts with well defined oral rims are usually relatively less numerous than oral collar tubular ducts, and are commonly situated singly or in small groups on the dorsal margins of the body segments. Some other unusual and distinctive forms of tubular duct are found, and their presence is often used to help define genera, as in Acrochordontus and Paraferrisia.
SETAE. Many different types of seta are encountered. Cerarian setae are usually conical (Figure 13), and sometimes on enlarged setal bases (Figure 14). Dorsal body setae may be conical, flagellate (Figure 15), lanceolate (Figure 16), or spine-like (Figure 17). Most ventral body setae are flagellate, and are generally longer than those on the dorsum. Some unusual setal forms occur in mealybugs. and are usually characteristic ot species or genera.