February 2012. A query from Cambodia: what are these on the Jatropha stems?
These are soft scales insects (Hemiptera: Sternorrhyncha: family Coccidae: tribe Pulvinariini)
It was thought likely that the photods were a species of Megapulvinaria, but to be sure high magnification od slide-mounted spoecimens is required. See:
The writer also said the following:
"Species of Megapulvinaria become quite large at maturity; a large adult female can measure 1.5-2 cm in length or conceivably a little more, depending on the species. She lives many months and gradually produces a long, white waxy ovisac (full of eggs) behind her that eventually becomes much longer than her own body.
"I don't know how common Megapulvinaria are - I have never seen an infestation myself. I have rarely had any sent to me for identification, so I'm guessing that maybe they aren't all that common or damaging. It's not as though you would not notice and infestation!"
A grower of Jatropha in Cambodia suggested that the infested branches are pruned and the cuttings burnt. Mangement using cultural practices and monitoring were given.
Another members suggested that the scale was in the genus Lichtensia, but that was unlikely because the record is from southern Asia, and Lichtensia is known only from the Palaeartic, Afro-tropical and Neotropical regions.
Furthermore, a search for "Scales on a Host" on the ScaleNet website (http://www.sel.barc.usda.gov/SCALENET/query.htm) for the family Coccidae on "Host" Jatropha (www.sel.barc.usda.gov/scalecgi/scaleson.exe), there and 3 records of Megapulvinaria maxima in the list of Jatropha. The ScaleNet entry on M. maxima is at www.sel.barc.usda.gov/catalogs/coccidae/Megapulvinariamaxima.htm.
The species seems to be fairly widespread in southern Asia including Thailand and Vietnam, but there is no published record of it from Cambodia. This circumstantial evidence suggests that the Cambodian scale on Jatropha is probably M. maxima, but for an authoritative identification, examination of slide-mounted material by an expert would be necessary.
As a follow up, a member from CABI-Malaysia said they had also recorded this pest Pulvinaria sp. on Jatropha curcas and it is especially severe during dry periods compounding the effect of leaf fall. We also observed incidence under shaded conditions when we grew Jatropha under coconut. Perhaps abiotic stress related factors could be implicated. We have not done any host spectrum search, but experience suggest a narrow range just like the leafminer Stomaphastis sp. which seems interestingly specific to Jatropha curcas.