Over 300 scale insects and about 200 mealybug species have been recorded from California. Considering just the scales, roughly half of our species belong to the family Diaspididae, the armored scales, though there are many smaller families represented in the state. Some families have very narrow host ranges, such as the cochineal scales which are restricted to Cactaceae, or the Matsucoccidae which are restricted to pine. Still other families are very polyphagous, especially non-native species. Many scale families are not represented in California, so it may be useful to list here the families that are, along with their diversity in the state and any host restrictions. While IDing scales to species level may be impossible without an expert in front of a microscope, many of these families and even genera are distinctive and should be identifiable to those levels. Images of representative members of the majority of these families may be found online for comparison.
This is a rudimentary list, I'd like to explore each of these families in depth later.
Aclerdidae (flat grass scales)
3 spp. (2 native, 1 introduced,in one genus, Aclerda) restricted to Poaceae.
Asterolecaniidae (pit scales)
11 spp. in 7 genera
Cerococcidae (oak wax scale)
1 sp., Cerococcus quercus, native, restricted to Quercus; distinct
Coccidae (soft scales)
50 spp. in 16 genera
Conchaspididae (orchid scale)
1 introduced polyphagous sp., Conchaspis angraeci
Dactylopiidae (cochineal scales)
4 spp. in one genus, Dactylopius, restricted to Cactaceae
Diaspididae (armored scales)
156 spp. in many genera
Eriococcidae (felt scales)
39 spp. in 9 genera
Kermesidae (gall-like scales)
13 spp. in 3 genera, mostly restricted to Quercus and Chrysolepis but Eriokermes gillettei occurs on juniper
Kerridae (lac scales)
2 spp. in 1 genus, Tachardiella (native)
Kuwaniidae (kuwana oak scale)
1 spp., Kuwania raygilli, native, on Quercus
Lecanodiaspididae (false pit scales)
3 spp. in 1 genus, Lecanodiaspis
Margarodidae (ground pearls)
2 spp. in 2 genera, subterranean
Matsucoccidae (pine vast scales)
7 spp. in 1 genus, Matsucoccus, restricted to pine
Monophlebidae (giant scales)
3 spp. in 2 genera, 2 native and 1 introduced
Ortheziidae (ensign scales)
9 spp. in 5 genera
Phoenicococcidae (palm scales)
1 sp., Phoenicococcus marlatti (date palm scale), restricted to palms
Pseudococcidae (mealybugs)
166 spp. in many genera
Putoidae (giant mealybugs)
16 spp. in one genus, Puto
Rhizoecidae (ground mealybugs)
17 spp. in 3 genera, all subterranean root-feeders
Steingeliidae (sycamore scale)
1 spp., Stomacoccus platani, restricted to sycamore
Xylococcidae (no common name)
3 spp. in one genus, Xylococculus
Comments
You may have already known this, but the scale insect preparation video on the Systematic Entomology Lab USDA site is pretty good ( https://www.ars.usda.gov/northeast-area/beltsville-md/beltsville-agricultural-research-center/systematic-entomology-laboratory/docs/sels-slide-mounting-tutorial-videos/ ).
It seems to give the steps needed for preparing scales for identification. Going from that to an identification still seems like a challenge but it looks much more manageable after going through the videos. I have two obscure scale species in NaOH at the moment, hopefully I can manage to get good enough photographs to make them identifiable.
Very useful resource - thanks for sharing! With prepared specimens, this website with interactive keys and fact sheets may be useful to aid identification: http://idtools.org/id/scales/index.php
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