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Ground or hypogaeic mealybugs
Adult females are small, elongate, with geniculate antennae visible using hand lense; body white covered by white almost blue powdery secretion that covers the body. Some species produce an ovisac that covers body; without marginal filaments. Strictly subterranean, occurring on roots and rootlets of host.
Look for the following combination of characters; none are present in all species. Tri- or bitubular ducts present; ostioles usually present, rarely absent; cerarii absent; antennae usually geniculate, never with more than 6 segments; circuli present or absent; swirled-type trilocular pores present; without translucent pores on hind legs; without basal denticle on claw. Other characters are: trochanter pores parallel to front edge of femur, not oriented transversely; 3 labial segments; usually 3 pairs of anal-ring setae; more than 4 setae on tibia.
This family was recently separated from the Pseudococcidae based on analysis of information derived from the adult males (Hodgson 2012), molecular sequences (Downie & Gullan 2004, Hardy et al. 2008 and two other unpublished analyses), and endosymbionts (Gruwell et al. 2010). Rhizoecidae Williams was first used as a family by Hodgson (2012).
Rhizoecids occur in all zoogeographical regions of the world. Find a list of species from the Australasian region, Afrotropical region, Nearctic region, Neotropical region, Oriental region, and Palaearctic region. They are most speciose in the Neotropical region, and least numerous in the Afrotropical region.
Based on an analysis of the host information in ScaleNet (2012), the ground mealybugs occur on about 100 families of host plants. The most common host family is Poaceae with 73 species. The Asteraceae is a distant second with 36 species. The top ten most common host families are: Rubiaceae 32; Fabaceae 17; Rosaceae 14; Cyperaceae 13; Euphorbiaceae 12; Arecaceae 12; Cactaceae 11; Musaceae 10. This pattern of host preference is very similar to the mealybugs.
Ground mealybugs have 4 instars in the female and 5 instars in the male. The third-instar females in the subfamily Rhizoecinae are a normal feeding stage, but in the subfamily Xenococcinae the third-instar female is a non-feeding pupal stage. All members of the family occur on the roots of their hosts and sometimes become abundant enough to cause host damage (McKenzie 1967). Xenococcine species are obligately associated with Acropyga ants which apparently are dependent upon the honeydew produced by the mealybugs. Acropyga queens carry a xenococcine mealybug in their mandibles when they establish a new colony so that their offspring have a source of food (Schneider & LaPolla 2011).
Hambleton 1976; Hodgson 2012; Kozár & Konczné Benedicty 2007; Schneider & LaPolla 2011; Williams 1998; Williams 2004a.
Click here for a check list of all rhizoecid genera and species.