The Red Gum Lerp Psyllid in California
Glycaspis brimblecombei was described by Moore (1964) from specimens collected in Queensland on Eucalyptus globulus (blue gum). This psyllid, however, is primarily on red gums and this is where it has been observed as a pest (Moore, 1970; Morgan, 1984; CPPDR, 1998). We have observed adults on blue gum in California as well and thus a possible explanation for the type specimens used by Moore (1964).
Glycaspis is a diverse Genus and contains 127 species that occur throughout Australia and beyond to the Philippine Islands. Most of the species are associated with Eucalyptus spp. but there are12 associated with Melaleuca spp. (Moore, 1970). The lerps (scales) differ for most species of psyllids even those in the same genus. However, the least useful in this regard are the lerps of Glycaspis (Morgan, 1984)
The most intensive studies of psyllid ecology in Australia have been on a lerp-forming psyllid, Cardiaspina albtextura Taylor, which causes leaf necrosis on its host plants. Monitoring of outbreaks of several species of psyllids including C. densitextura Taylor and G. brimblecombei has been done in South Australia since 1959 ( Morgan, 1984). It is not clear if this has continued past 1984. Detailed studies of the biology of a closely related species, G. baileyei Moore, have been done by Moore (1961) in New South Wales. Stone (1996) has done some interesting work on the ecological relationships of this species. Both G. baileyi and G. brimblecombei are multivoltine and G. baileyi may have as many as seven generations per year (Morgan, 1984). While G. baileyi may debilitate and kill its host plant, G. brimblecombei at most induces copious growth of sooty mold due to the production of large amounts of honeydew over the surfaces of infested leaves according to Morgan (1984). In California, all stages of the psyllid have been observed in every month since its discovery in June of 1998 so it is certainly multivoltine here. Many of the heavily infested red gums at Stanford and at Ardenwood Park lost their foliage in 1998, however the trees refoliated in 1999 and are now being defoliated a second time. There is concern that these trees may die due to the psyllid or be susceptible to attack by the Eucalyptus long horn beetle.
There are some data from the work of Moore (1961) with G. baileyi to indicate that climate may be fairly important with this species as well as with other species of psyllids. There is a relationship between outbreak cycles of psyllids and periods of high rainfall and higher than normal temperatures were found to cause drastic reductions in populations.
Moore (1961) found parasitism of up to 72% due to nothing more specific than chalcidoid wasps in his studies with G. baileyi and states that the parasites are not effective when the lerps are moist due to rain or high humidity. He reports that the nymphs were attacked by complex of chalcidoid species during all months of the year but that first instar nymphs were not attacked. He found parasitism to be much higher during drier periods. Although the parasites and hyperparasites or secondary parasites were not identified he gives descriptive material in the text along with drawings of antennae for some of the species. These species are identified by letter and are available at the Forestry Commission. Moore does mention several predators that may be of importance as follows: Syrphus viridiceps Macq. (Syrphidae), Drepanacra sp. (Hemerobiidae), Notochrysa ramburi Schneider (Chrysopidae), Rhizobius evansi Mulsant and Leis conformis (Biosd.) (Coccinellidae). He also said that spiders were numerous and were predatory on the psyllids. Spiders covered the lerps with webs and trapped the adult psyllids as they emerged. Species were identified as Theridion pyramidale L.Koch, Deliochus zelivera (Keyserling), and Areys clavatus Keys. Morgan (1984) shows a late instar G. brimblecombei that is parasitzed but doesn’t give an identification. It is very likely that an encyrtid wasp in the genus Psyllaphagous will be one of the important parasites.
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