Most male scale insects (Hemiptera: Coccoidea) only feed in their first and second instars and then pass through non-feeding prepupal and pupal instars before emerging as an adult that can be either wingless or alate. During development of what are now usually termed the archaeococcoid scale insects (Gullan and Cook 2007), the prepupa of alate species may be similar in morphology to the previous feeding stage except that they have no functional mouthparts, and the legs are sometimes reduced in size. Other archaeococcoids that are alate may have a prepupa with developing wing pads and legs. The prepupae and pupae of the morphologically more derived families, the neococcoids, show some signs of legs and the alate species possess developing wing pads. For examples of the life cycles of some families see Danzig (1980) and Gill (1993). Before its moult to a prepupa, the second-instar male usually secretes a covering for the developing prepupa and pupa. It may be a fairly loose covering of wax, an intricate shelter of felted wax, a cocoon-like structure as in the Eriococcidae, or a pupal cell formed of translucent wax as in the Coccidae (Gill 1988). Adult males always emerge backwards from whatever covering protected the prepupal and pupal stages.

Because most male prepupae and pupae develop beneath this waxy cover, the legs are usually non-functional with the claw either showing no signs of development or reduced to a mere point. However, among male mealybugs (Pseudococcidae), there are some taxa in which the prepupa and pupa have relatively well-developed legs, including claws and digitules, that would appear to allow mobility of these insects (Figs 1–3).

Digitules in scale insects are modified setae. The term is usually used for a pair of setae at the base of the claw and a pair at the outer distal end of the tibia of all female instars and the male feeding stages of most taxa. Although sometimes these digitules are setose, many are so-called knobbed or actually spoon-shaped. The adult females of Steingelia Nasonov (Steingeliidae) have 12 such digitules on the claw (Morrison 1928), but this is not usual. The claw digitules are often longer than the claw and the tarsal digitules are usually longer than the claw digitules. As far as we know, digitules are present in all first-instar nymphs or crawlers, the main dispersal stage. It has been shown that first-instar nymphs of some armoured scale insects (Diaspididae) attach themselves to their phoretic hosts (Diptera and Coleoptera) by the digitules (Magsig-Castillo et al. 2010). These authors suggest that the swollen ends of each digitule can cling by suction. Regardless of the means by which digitules adhere to surfaces, they must be released rapidly as the nymphs walk. In most illustrations of scale insects that possess legs, the claw is a shown as curved inwards because it is in this position on slide-mounted specimens. In life, however, the claws point outwards so that the plantar surface and the digitules are in contact with a surface.

Digitules reach their fullest development in mealybugs of the tribe Allomyrmococcini (Pseudococcidae) as they are much larger than the claw and are widely expanded distally, sometimes wider than the width of the claw (Williams 1978; Dill et al. 2002). These well-developed digitules are used to climb onto herdsmen ants of the genus Dolichoderus when the colony is transported or even onto each other when the ants scoop up a few of the mealybugs when the colony is disturbed. Additional knobbed setae, similar to knobbed digitules, are present also on the lateral surface of the tibiae and tarsi of the adult females of the ant-attended mealybugs Malaicoccus clavulatus Williams, Malaicoccus pilulosus Williams and Malaicoccus sumatranus Williams, and, in addition to these setae, there are knobbed setae on the tibiae and tarsi and body margin in Thaimyrmococcus daviesi Williams (Dill et al. 2002; Williams 2004).

Allomyrmococcine mealybugs associated with herdsmen ants are either in the ant trails or in the ants’ nests. It has been shown by Dill et al. (2002) that only about 30% of the mealybugs from an ant-mealybug association is carried in the trail and the remainder are in the nest. Although some gravid females are in the trails, most are present in the ant nests. It was only at the end of the study of the mealybug Promyrmococcus dilli Williams by Dill et al. (2002) that adult males, prepupae and pupae were found and these were in nests that had been dropped whole into ethanol. There was no sign of any wax covering on the prepupae or pupae but all stages had well-developed claws and knobbed tarsal digitules (Figs 1, 2). It would be an advantage for prepupae and pupae of mealybugs associated with herdsmen ants to move in the nests and even attach themselves to ants if the nest was moved to another location and the inference is that they are mobile.

Female mealybugs of the genus Leptococcus Reyne and Macrocepicoccus Morrison have unusually long legs and long slender claws. These mealybugs live on leaf surfaces and are probably parenchyma feeders (Miller and Denno 1977; Williams 2004; Kondo and Gullan 2008). Adult females and nymphs are very active when disturbed. Claws in all of these stages are long and slender. The prepupa and pupa of Macrocepicoccus loranthi Morrison and the prepupa of Leptococcus metroxyli Reyne possess well-developed tarsal digitules although the claw digitules are short (Miller and Denno 1977). Macrocepicoccusloranthi was described from Guyana on Loranthus sp. by Morrison (1919) and has been recorded from Colombia (also on Loranthus sp.) by Kondo et al. (2008). Recent observations of Macrocepicoccus loranthi on Oryctanthus amplexicatus (Loranthaceae) show that aggregations of the mealybugs on the leaves are very active when disturbed (Takumasa Kondo, personal communication). This activity is not only confined to the feeding stages but also applies to the prepupae and pupae, which move rapidly. These prepupae and pupae are without any covering or cocoon-like structures and have little wax.

Among the group of root mealybugs based on the genus Rhizoecus Künckel d’Herculais, elevated recently to family level, the Rhizoecidae (Hodgson 2012), there are two subfamilies, the Rhizoecinae and the Xenococcinae. Prepupae and pupae of the Xenococcinae have legs without tarsal or claw digitules, and the claws are very poorly developed (Williams 1998). Within the Rhizoecinae, despite the large numbers of species, little is known of their life histories. Mukhopadhyay and Ghose (1996) report that prepupae and pupae of Rhizoecus amorphophalli Betrem are without any covering. Adult males of Rhizoecidae are either wingless, brachypterous or alate (Hodgson 2012). Prepupae and pupae of Ripersiella malschae (Williams) possess legs with well-developed claws and, although the claw digitules and tarsal digitules are short and setose (Fig. 3), they are similar to those of mobile female stages, as shown in Williams (2004). This species lives in close association with ants of the genus Pseudolasius (Malsch et al. 2001; their mealybug #21). The adult male is wingless. It would be an advantage for the prepupae and pupae living in ants’ nests to move and the well-developed claws would help in this process.

It is clear that prepupae and pupae of some Pseudococcidae and probably of the Rhizoecidae can show mobility. Observations on other species of mealybugs and root mealybugs in which the prepupae and pupae have claw and tarsal digitules also may show that these stages can move.

We are taking the opportunity to describe and illustrate the prepupa and pupa of Promyrmococcus dilli and the prepupa of Ripersiella malschae.